- Solvent, counterion, and secondary deuterium kinetic isotope effects in the anionic oxy-Cope rearrangement
-
The potassium and sodium alkoxides of 3-methyl-1,5-hexadien-3-ol follow first-order kinetics in the process of undergoing the anionic oxy-Cope rearrangement in tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO). The first-order rate constant for the rearrangement of the potassium alkoxide in DMSO is ca. 1000 times faster than that in THF, as is the first-order rate constant in THF in the presence of 1 equiv or excess 18-crown-6. The rate constants in THF are independent of initial alkoxide concentration; in contrast, the first-order rate constants in DMSO are inversely proportional to the initial alkoxide concentration, and addition of potassium salts to the DMSO solution results in a retardation of rearrangement rate. Addition of 1/4 and 1/2 equiv of 18-crown-6 in THF gave first-order behavior only over the first 25% of reaction with an initial rate constant linearly related to that with 1 equiv of crown ether. Secondary deuterium kinetic isotope effects have been determined at the bond-breaking and bond-making sites in the Cope rearrangement of the potassium alkoxide in THF, in THF in the presence of 18-crown-6, and in DMSO. The isotope effects indicate a highly dissociative transition state with substantial bond breaking of the C3-C4 bond and little bond making between the allylic termini (C1 and C6). The effects of aggregation and ionic dissociation are discussed in the context of mechanistic pathways proposed for the rearrangement in THF and in DMSO.
- Gajewski, Joseph J.,Gee, Kyle R.
-
-
Read Online
- Chemiluminescence-promoted oxidation of alkyl enol ethers by NHPI under mild conditions and in the dark
-
The hydroperoxidation of alkyl enol ethers using N-hydroxyphthalimide and molecular oxygen occurred in the absence of catalyst, initiator, or light. The reaction proceeds through a radical mechanism that is initiated by N-hydroxyphthalimide-promoted autoxidation of the enol ether substrate. The resulting dioxetane products decompose in a chemiluminescent reaction that allows for photochemical activation of N-hydroxyphthalimide in the absence of other light sources.
- Anderson,Andia, Alexander A.,Woerpel
-
supporting information
(2021/02/03)
-
- Iron-Catalyzed Synthesis of α-Dienyl Five- and Six-Membered N-Heterocycles
-
The iron-catalyzed synthesis of α-dienyl N-heterocycles is reported. The method is cost-effective, atom-economic, and led to a range of substituted α-dienyl heterocycles in moderate to good yields and diastereoselectivities. The α-dienyl piperidines are key synthetic intermediates as demonstrated by the preparation of a panel of α-polyenyl N-heterocycles.
- Gonnard, Laurine,Guérinot, Amandine,Cossy, Janine
-
supporting information
p. 6160 - 6167
(2017/11/15)
-
- Synthesis of 3D-Rich Heterocycles: Hexahydropyrazolo[1,5-A]pyridin-2(1H)-ones and Octahydro-2H-2a,2a1-diazacyclopenta[cd]inden-2-ones
-
Two cyclic azomethine imines, 7-methyl- and 7-phenyl-2-oxo-Δ7-hexahydropyrazolo[1,5-A]pyridin-8-ium-1-ide, were prepared in seven steps from the respective commercially available δ-keto acids. The addition of Grignard reagents followed by N-Alkylation at position 1 afforded the 1,7,7-trisubstituted hexahydropyrazolo[1,5-A]pyridin-2(1H)-ones, whereas 1,3-dipolar cycloadditions of these dipoles to typical acetylenic and olefinic dipolarophiles gave 4a-substituted 2a,2a1-diazacyclopenta[cd]indene derivatives as the first representatives of a novel heterocyclic system. Regio- and stereoselectivity as well as the mechanism of these [3 + 2]-cycloadditions were evaluated using computational and experimental methods. The data obtained were in agreement with the polar concerted cycloaddition mechanism via the energetically favorable syn/endo-transition states.
- Pu?avec Kirar, Eva,Drev, Miha,Mirnik, Jona,Gro?elj, Uro?,Golobi?, Amalija,Dahmann, Georg,Po?gan, Franc,?tefane, Bogdan,Svete, Jurij
-
p. 8920 - 8933
(2016/10/14)
-
- Visible Light Photocatalysis of Carbon-Carbon σ-Bond Anaerobic Oxidation of Ketones with Water by Cobalt(II) Porphyrins
-
CoII(por) (por = porphyrinato dianion) reacted selectively with isopropyl ketones at the carbon (CO)-carbon (α) bond at room temperature to give high yields of CoIII(por) acyls and the corresponding oxidized carbonyl compounds in up
- Lee, Siu Yin,Fung, Hong Sang,Feng, Shiyu,Chan, Kin Shing
-
supporting information
p. 2480 - 2487
(2016/08/16)
-
- Is H Atom Abstraction Important in the Reaction of Cl with 1-Alkenes?
-
The relative yields of products of the reaction of Cl atoms with 1-alkenes (C4-C9) were determined to see whether H atom abstraction is an important channel and if it is to identify the preferred position of abstraction. The presence of all the possible positional isomers of long chain alkenones and alkenols among the products, along with chloroketones and chloroalcohols, confirms the occurrence of H atom abstraction. A consistent pattern of distribution of abstraction products is observed with oxidation at C4 (next to allyl) being the lowest and that at CH2 groups away from the double bond being the highest. This contradicts with the higher stability of allyl (C3) radical. For a better understanding of the relative reactivity, ab initio calculations at MP2/6-311+G (d,p) level of theory are carried out in the case of 1-heptene. The total rate coefficient, calculated using conventional transition state theory, was found to be in good agreement with the experimental value at room temperature. The preferred position of Cl atom addition is predicted to be the terminal carbon atom, which matches with the experimental observation, whereas the rate coefficients calculated for individual channels of H atom abstraction do not explain the observed pattern of products. The distribution of abstraction products except at C4 is found to be better explained by reported structure activity relationship, developed from experimental rate coefficient data. This implies the reactions to be kinetically dictated and emphasizes the importance of secondary reactions.
- Walavalkar,Vijayakumar,Sharma,Rajakumar,Dhanya
-
p. 4096 - 4107
(2016/07/06)
-
- Transaminase Triggered Aza-Michael Approach for the Enantioselective Synthesis of Piperidine Scaffolds
-
The expanding “toolbox” of biocatalysts opens new opportunities to redesign synthetic strategies to target molecules by incorporating a key enzymatic step into the synthesis. Herein, we describe a general biocatalytic approach for the enantioselective preparation of 2,6-disubstituted piperidines starting from easily accessible pro-chiral ketoenones. The strategy represents a new biocatalytic disconnection, which relies on an ω-TA-mediated aza-Michael reaction. Significantly, we show that the reversible enzymatic process can power the shuttling of amine functionality across a molecular framework, providing access to the desired aza-Michael products.
- Ryan, James,?iau?iulis, Mindaugas,Gomm, Andrew,Maciá, Beatriz,O’Reilly, Elaine,Caprio, Vittorio
-
supporting information
p. 15798 - 15800
(2016/12/22)
-
- Catalytic asymmetric total synthesis of (S)-(-)-zearalenone, a novel lipoxygenase inhibitor
-
A catalytic asymmetric synthesis of (S)-(-)-zearalenone is reported using asymmetric allylic alkylation for the introduction of the stereocenter. (S)-(-)-Zearalenone turned out to be a novel lipoxygenase inhibitor.
- Baggelaar, Marc P.,Huang, Yange,Feringa, Ben L.,Dekker, Frank J.,Minnaard, Adriaan J.
-
p. 5271 - 5274
(2013/09/02)
-
- Synthesis and reactivity of unsymmetrical azomethine imines formed using alkene aminocarbonylation
-
Complex cyclic azomethine imines possessing a β-aminocarbonyl motif can be accessed readily from simple alkenes and hydrazones. This alkene aminocarbonylation approach allows formation of ketone-derived azomethine imines of unprecedented complexity. Since unsymmetrical hydrazones are used, two stereoisomers are formed: the reactivity of chiral derivatives is explored in both intra- and intermolecular systems.
- Gan, Wei,Moon, Patrick J.,Clavette, Christian,Das Neves, Nicolas,Markiewicz, Thomas,Toderian, Amy B.,Beauchemin, Andre M.
-
supporting information
p. 1890 - 1893
(2013/06/05)
-
- FeCl3-catalyzed highly diastereoselective synthesis of substituted piperidines and tetrahydropyrans
-
The eco-friendly and highly diastereoselective synthesis of substituted cis-2,6-piperidines and cis-2,6-tetrahydropyrans is described. The key step of this method is the iron-catalyzed thermodynamic equilibration of 2-alkenyl 6-substituted piperidines and 2-alkenyl 6-substituted tetrahydropyrans allowing the isolation of enriched mixtures of the most stable cis-isomers.
- Guerinot, Amandine,Serra-Muns, Anna,Gnamm, Christian,Bensoussan, Charlelie,Reymond, Sebastien,Cossy, Janine
-
supporting information; experimental part
p. 1808 - 1811
(2010/10/03)
-
- Combination of RCM and the Pauson-Khand reaction: One-step synthesis of tricyclic structures
-
The combination of ring-closing metathesis (RCM) followed by an intramolecular Pauson-Khand reaction gives direct entry to tricyclic compounds. The RCM was carried out on a hexacarbonylcobalt-complexed alkyne, this complex acting as a protecting group against enyne metathesis. The procedure was studied for dienynes containing heteroatoms and allows the building of [6,5,5] and [7,5,5] tricyclic systems. The feasibility of the process depends strongly on the nature of the substrate. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Rosillo, Marta,Arnaiz, Eduardo,Abdi, Delbrin,Blanco-Urgoiti, Jaime,Dominguez, Gema,Perez-Castells, Javier
-
experimental part
p. 3917 - 3927
(2009/04/07)
-
- Practical synthesis of (E)-α,β-unsaturated carboxylic acids using a one-pot hydroformylation/decarboxylative Knoevenagel reaction sequence
-
Combining the regioselective room temperature/ambient pressure hydroformylation and a modification of the Doebner-Knoevenagel reaction allowed for the development of an efficient, one-pot procedure for the synthesis of (E)-α,β-unsaturated carboxylic acids. The reaction proceeds under mild conditions, tolerates a variety of functional groups and gives (E)-α,β-unsaturated carboxylic acids in good yields and with excellent regio-and stereocontrol. The practicability of this process has been demonstrated by a short protecting group-free synthesis of the queen honeybee pheromones 9-ODA[( E)-9-oxodec-2-enoic acid] and 9-HDA[( E)-9-hydroxydec-2-enoic acid].
- Kemme, Susanne T.,?mejkal, Tomá?,Breita, Bernhard
-
scheme or table
p. 989 - 994
(2009/05/27)
-
- Diazo chemistry controlling the selectivity of olefin ketonisation by nitrous oxide
-
The thermal reaction of olefins with nitrous oxide was recently put forward as a promising synthetic ketone source. The 1,3-dipolar cycloaddition of N 2O to the C=C double bond, forming a 4,5-dihydro-[1,2,3]oxadiazole intermediate, was predicted to be the first elementary reaction step. This oxadiazole can subsequently decompose to the desired carbonyl product and N 2 via a hydrogen shift. In this contribution, Potential Energy Surfaces are constructed at the reliable G2M level of theory and used to evaluate thermal rate constants by Transition State Theory. Compelling theoretical and experimental evidence is presented that an oxadiazole intermediate not only can undergo a hydrogen shift, but eventually also a methyl- or even an alkyl-shift. Special emphasis is also given on a hitherto neglected decomposition of the oxadiazole via a concerted C-C and N-O cleavage. For some substrates, such as internal olefins, this diazo route is negligibly slow, compared to the ketone path, leaving no marks on the selectivity. For cyclopentene the diazo cleavage was however found to be nearly as fast as the desired ketone route. However, the diazo compound, viz. 5-diazopentanal, reconstitutes the oxadiazole much faster upon ring-closure than it is converted to side-products. Therefore, a pre-equilibrium between the diazoalkanal and the oxadiazole is established, explaining the high ketone yield. On the other hand, for primary alkenes, such a concerted C-C and N-O cleavage to diazomethane is identified as an important side reaction, producing aldehydes with the loss of one C-atom. For these substrates, the bimolecular back-reaction of the C n-1 aldehyde and diazomethane is too slow to sustain an equilibrium with the oxadiazole; diazomethane rather reacts with the substrate to form cyclopropane derivatives. The overall selectivity is thus determined by a combination of H-, methyl- or alkyl-shift, and the eventual impact of a diazo cleavage in the oxadiazole intermediate. the Owner Societies.
- Hermans, Ive,Moens, Bart,Peeters, Jozef,Jacobs, Pierre,Sels, Bert
-
p. 4269 - 4274
(2008/09/19)
-
- A cross-metathesis route to functionalized α-methyl α-substituted amino acids
-
A chemoenzymatic approach to the synthesis of functionalized α-methyl α-substituted amino acids is detailed. This involves amidasemediated enzymatic resolution of α-methyl α-substituted side-chain ω-unsaturated amino acids followed by functionalization via cross-metathesis.
- Storcken, Roy P. M.,Panella, Lavinia,Van Delft, Floris L.,Kaptein, Bernard,Broxterman, Quirinus B.,Schoemaker, Hans E.,Rutjes, Floris P. J. T.
-
p. 161 - 164
(2008/02/03)
-
- 3,3′-Bis(trisarylsilyl)-substituted binaphtholate rare earth metal catalysts for asymmetric hydroamination
-
Chiral 3,3′-bis(trisarylsilyl)-substituted binaphtholate rare earth metal complexes (R)-[Ln{Binol-SiAr3}(o-C6H 4CH2NMe2)(Me2NCH2Ph)] (Ln = Sc, Lu, Y; Binol-SiAr3 = 3,3′-bis(trisarylsilyl)-2,2′- dihydroxy-1,1′-binaphthyl; Ar = Ph (2-Ln), 3,5-xylyl (3-Ln)) and (R)-[La{Binol-Si(3,5-xylyl)3}{E(SiMe3)2}(THF) 2] (E = CH (4a), N (4b)) are accessible via facile arene, alkane, and amine elimination. They are efficient catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, giving TOF of up to 840 h -1 at 25 °C for 2,2-diphenyl-pent-4-enylamine (5c) using (R)-2-Y. Enantioselectivities of up to 95% ee were achieved in the cyclization of 5c with (R)-2-Sc. The reactions show apparently zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, but rates depend on total amine concentrations. Activation parameters for the cyclization of pent-4-enylamine using (R)-2-Y (ΔH(S)? = 57.4-(0.8) kJ mol-1 and ΔS(S)? = -102(3) J K-1 mol-1; ΔH(R)? = 61.5(0.7) kJ mol-1 and ΔS(R)? = -103(3) J K-1 mol -1) indicate a highly organized transition state. The binaphtholate catalysts were also applied to the kinetic resolution of chiral α-substituted aminoalkenes with resolution factors f of up to 19. The 2,5-disubstituted aminopentenes were formed in 7:1 to ≥50:1 trans diastereoselectivity, depending on the size of the α-substituent of the aminoalkene. Rate studies with (S)-1-phenyl-pent-4-enylamine ((S)-15e) gave the activation parameters for the matching (ΔH? = 52.2(2.8) kJ mol -1, ΔS? = -127(8) J K-1 mol-1 using (S)-2-Y) and mismatching (ΔH? = 57.7(1.3) kJ mol -1, ΔS? = -126(4) J K-1 mol-1 using (R)-2-Y) substrate/catalyst combination. The absolute configuration of the Mosher amide of (2S)-2-methyl-4,4-diphenyl-pyrrolidine and (2R)-methyl-(5S)- phenyl-pyrrolidinium chloride, prepared from (S)-15e, were determined by crystallographic analysis. Catalyst (R)-4a showed activity in the anti-Markovnikov addition of n-propylamine to styrene.
- Gribkov, Denis V.,Hultzsch, Kai C.,Hampel, Frank
-
p. 3748 - 3759
(2007/10/03)
-
- Syn- and anti-selective prins cyclizations of δ,ε-unsaturated ketones to 1,3-halohydrins with Lewis acids
-
Ten acyclic and monocyclic δ,ε-unsaturated ketones, with and without methyl substituents on the double bond, underwent halide-terminated Prins (halo-Prins) cyclizations under anhydrous conditions in the presence of Lewis acids. TiCl4, TiBr4, BCl3, and BBr 3 promoted syn-selective cyclizations to sterically congested chloro- and bromohydrins, while SnCl4, SnBr4, InCl3, ZrCl4, and several other Lewis acids effected highly anti-selective reactions to furnish the corresponding trans halohydrins. The stronger Lewis acids (TiX4 and BX3) favor the syn process that involves axial delivery of a halide ligand. Competition experiments showed that substitution at the δ carbon (methallyl enones) led to increased rates (40-50-fold), while substitution at the ε position (cis and trans crotyl enones) retarded the rate and eroded the selectivity of the cyclizations. The trends in syn vs anti selectivity, reactivity, and effects of different Lewis acidic metal halides are rationalized by competitive reaction pathways proceeding through syn carbocation-halide ion pairs and a higher order transition state that leads to inversion of configuration and formation of trans halohydrins, along with cyclic olefins arising from proton elimination.
- Miles, R. Brandon,Davis, Chad E.,Coates, Robert M.
-
p. 1493 - 1501
(2007/10/03)
-
- Liquid phase oxidation of alkenes with nitrous oxide to carbonyl compounds
-
A variety of substrates including linear, cyclic, heterocyclic alkenes and their derivatives were tested in the liquid phase non-catalytic oxidation with nitrous oxide (N2O). The structure and composition of the alkenes have a significant effect on the reaction selectivity. With many alkenes, N 2O oxidation provides a selective way for the preparation of carbonyl compounds. The generation of carbene (or diazomethane) species is a remarkable feature of the oxidation of terminal alkenes.
- Starokon,Dubkov,Babushkin,Parmon,Panov
-
p. 268 - 274
(2007/10/03)
-
- New ketone homoenolate anion equivalents derived from (alkenyl)pentamethyl phosphoric triamides
-
Lithiated ambident anions derived from (1-alkyl-2-propenyl)- or (1-phenyl-2-propenyl)-pentamethyl phosphoric triamides undergo regioselectively γ-reaction with various alkylating reagents and isobutyraldehyde. Further hydrolysis of adducts releases the ketone under acid conditions. Number of synthetic applications clearly show the ketone homoenolate behaviour of these new carbanions.
- Grison, Claude,Thomas, Antoine,Coutrot, Frédéric,Coutrot, Philippe
-
p. 2101 - 2123
(2007/10/03)
-
- Efficient Addition of Allylsilanes to α,β-Enones Using Catalytic Indium and Trimethylsilyl Chloride
-
α,β-Enones undergo an efficient Hosomi-Sakurai reaction with allyltrimethylsilane, in which a catalytic amount of indium is used in the presence of trimethylsilyl chloride as an activator under mild conditions to produce the conjugate addition products in good yields.
- Lee, Phil Ho,Seomoon, Dong,Kim, Sundae,Nagaiah,Damle,Lee, Kooyeon
-
p. 2189 - 2193
(2007/10/03)
-
- Highly efficient amphiphilic cleavage of γ-iodo carbonyl substrates with aluminum tris(2,6-diphenylphenoxide)/t-BuLi system
-
A conceptually new amphiphilic cleavage of the αβ C-C bonds of γ-iodo carbonyl substrates has been realized by the effective use of a combined Lewis acid/base system consisting of aluminum tris(2,6-diphenylphenoxide) (ATPH)/t-BuLi. This new amphiphilic bond cleavage reaction can be applied to a wide variety of γ-iodo carbonyl substrates and therefore serves as a highly efficient and general route to both cyclic and acyclic unsaturated carbonyl compounds.
- Kondo, Yuichiro,Kon-i, Kana,Ooi, Takashi,Maruoka, Keiji
-
p. 9041 - 9044
(2007/10/03)
-
- Flexible molecules with defined shape. Part 3.1 Conformational analysis of bis(tetrahydropyran-2-yl)methanes
-
(R,R)-Bis(tetrahydropyran-2-yl)methane 4 along with its racemate have been synthesized. MM3 calculations suggest that the conformer 4a should be populated to ca. 85% in the conformer equilibrium. Analysis of the 1H NMR coupling constants show that one conformer predominates by about 9:1. That this is the conformer 4a is shown by various NMR techniques, as well as by comparison of calculated with measured CD spectroscopic data. The study is extended to the methyl-substituted bis(tetrahydropyranyl)methanes 21 and 23 which show, as predicted from MM3 calculations, essentially mono-conformational behaviour.
- Hoffmann, Reinhard W.,Colin Kahrs,Schiffer, Jan,Fleischhauer, Joerg
-
p. 2407 - 2414
(2007/10/03)
-
- Radical formation in the oxidation of 2,2′-azo-2-methyl-6-heptene by thianthrene cation radical
-
Reaction of 2,2′-azo-2-methyl-6-heptene (1) with thianthrene cation radical perchlorate (Th?+ClO4-) in CH2Cl2 solution containing 2,6-di-tert-butyl-4-methylpyridine (DTBMP) gave a mixture of nine C8 hydrocarbons, namely, 1,1,2-trimethylcyclopentane (4, 2.2%), 6-methyl-1-heptene (5, 2.2%), 2-methyl-1,6-heptadiene (6, 9.8%), 2,2-dimethyl-1-methylenecyclopentane (7, 2.9%), 6-methyl-1,5-heptadiene (8, 39%), 3,3-dimethyl- (9, 7.6%), 4,4-dimethyl- (10, 11%), 1,2-dimethyl- (11, 5.4%), and 1,6-dimethylcyclohexene (12, 1.5%). The amounts of acyclic dienes (6, 8) fell and of cyclohexenes (9, 10) rose when DTBMP was omitted from or diminished in the solution. The results provide firm evidence (products 4, 5, and 7) for the formation of the 2-methyl-6-hepten-2-yl radical (2), although the major fate of 2 is its oxidation to the corresponding cation 13, the origin of the bulk of the other products.
- Chen, Tonghua,Shine, Henry J.
-
p. 4716 - 4719
(2007/10/03)
-
- Clemmensen Reduction. XI. Fragmentation Reactions of Some 3-Acetylcycloalkanones
-
Clemmensen reduction of a series of 3-acetylcycloalkanones yields, as the major product, an acyclic unsaturated ketone, the product of fragmentation.Some normal carbonyl-methylene reduction also occurs.A mechanistic rationale for the fragmentation is advanced.
- Bailey, Karen E.,Davis, Brian R.
-
p. 1827 - 1834
(2007/10/03)
-
- SYNTHESIS VIA ULTRASOUND: A CONVENIENT SYNTHESIS OF 6-(4-TOLYL)HEPT-1-ENE AND 6-(2-OXO-4-METHYLCYCLOHEX-3-EN-1-YL)HEPT-1-ENE
-
6-(4-Tolyl)hept-1-ene (I) and 6-(2-oxo-4-methylcyclohex-3-en-1-yl)hept-1-ene (II), monocyclic norsesquiterpenes from aerial parts of South Africa Senecio digitalifolium, have been synthesized using ultrasonic waves and tandem phenylation reduction.
- Trehan, Inder R.,Singh, Jasvinder,Arora, Ajay K.,Kaur, Jasamrit,Kad, Goverdhan L.
-
p. 1889 - 1891
(2007/10/02)
-
- ω-Alkenyl α-Nitroalkyl Radicals. Part 3. Radical Chain Reactions of ω-Alkenyl α-Halogenonitroalkanes
-
SRN1 reactions between 5-bromo-5-nitrohex-1-ene and the nitronate anions of 2-nitropropane and 5-nitrohex-1-ene failed to give cyclisation of the intermediate α-nitroalkyl radical onto the alkene.Reaction between exo-5-bromo-endo-5-nitro-exo-6-phenylbicyclohept-2-ene 1 and the anion of 2-nitropropane did not undergo an SRN1 reaction and Br+ abstraction gave 2-bromo-2-nitropropane and 5-endo-nitro-exo-6-phenylbicyclohept-2-ene.BNAH reduction of exo-5-bromo-endo-5-nitro-exo-6-phenylbicyclohept-2-ene 1, 6-bromo-6-nitrohept-1-ene, and 1-bromo-1-nitro-2-(prop-2-enyl)cyclohexane gave the corresponding nitroalkanes without any cyclosation of the intermediate α-nitroalkyl radicals.Initial results indicate that an iodine atom transfer methodology provides a possible general method for the cylisation of ω-alkenyl α-nitroalkyl radicals.Cyclisation of intermediate α-nitroalkyl radicals, generated by photolysis of 1-(bicyclohept-5-en-endo-2-yl)-2-iodo-2-nitropropane 5a, gave a good yield of two diastereomeric tricyclic iodonitro compounds 6a and 7a.Photolysis of 1-(bicyclohept-5-en-endo-2-yl)-2-iodo-2-nitroethane 5b and 2-(but-3-enyl)-1-iodo-1-nitrocyclohexane 11 also gave the expected products from 5-exo cyclisation of the intermediate α-nitroalkyl radicals.The tricyclic iodonitro compound 6a was synthesised from the corresponding endo-methanesulfonate 15, the structure of which was determined by X-ray crystallography.
- Bowman, W. Russell,Brown, David S.,Burns, Catherine A.,Crosby, David
-
p. 2083 - 2090
(2007/10/02)
-
- Enantioselective synthesis of the 6,8-dioxabicyclo-[3.2.1]octane skeleton by asymmetric dihydroxylation
-
Sharpless asymmetric dihydroxylation (AD) of 6-hepten-2-one with AD-mix-α followed by acidification gives (1S,5R)-5-methyl-6,8-dioxabicyclo[3.2.1]octane in moderate ee. This methodology defines a two-pot enantioselective construction of the (-)-frontalin and brevicomin skeleton from the corresponding 2-alkyl-1,3-dithiane and 5-bromo-1-hexene derivatives.
- Turpin,Weigel
-
p. 6563 - 6564
(2007/10/02)
-
- Reduction of Substituted Nitro Compounds with Tri-n-butyltin Hydride
-
α-Substituted nitro compounds have been reduced with tri-n-butyltin hydride to give replacement of the α-substituent by hydrogen (2-bromo, 2-chloro- and 2-nitro-2-phenylsulphonylpropane to 2-nitropropane; p-nitrobenzyl chloride, bromide, iodide and thiocyanate to p-nitrotoluene; 5-nitrofurfuryl nitrate to 2-methyl-5-nitrofuran and 2-hydroxymethyl-5-nitrofuran; 2-(bromomethyl)-1-methyl-5-nitroimidazole to 1,2-dimethylimidazole). 2-Bromo-2-nitrohept-6-ene and 1-bromo-1-nitrohex-5-ene were reduced to 2-nitrohept-6-ene and 1-nitrohex-5-ene,5-bromo- and 5-phenylsulphonyl-5-nitro-6-phenyl-norborn-6-ene to 5-nitro-6-phenylnorborn-6-ene and 2-iodo-2-nitro-3-(endo-norborn-2-en-5-yl)propane to 2-nitro-3-(endo-norborn-2-en-5-yl)propane without cyclisation of the intermediate alkenyl α-nitroalkyl radicals. 2-Bromo-2-nitrohex-5-ene and 1-bromo-1-nitropent-4-ene were reduced to the respective nitroalkenes at high but at lower cyclisation to 1-methyl-1-nitrocyclopentane and 1-nitrocyclopentane took place.Inhibition studies of the reductions of 2-bromo-2-nitrohex-5-ene and p-nitrobenzyl bromide showed a radical chain mechanism.In some of the reductions at low , radical rearrangement of the intermediate α-nitroalkyl radicals gave the respective ketones.Mechanisms involving (a) addition/elimination and (b) dissociation of intermediate radical anions, are proposed.
- Bowman, W. Russell,Crosby, David,Westlake, Paul J.
-
-
- ENZYMATIC KINETIC RESOLUTION OF CYANOHYDRIN ACETATES AND ITS APPLICATION TO THE SYNTHESIS OF (S)-(-)-FRONTALIN
-
Kinetic resolution of racemic 1-cyano-1-methylalkyl and alkenyl acetates has been achieved on incubation with Pichia miso IAM 4682, which hydrolyzed selectively the (R)-enantiomer, leving behind the (S)-enantiomer intact.The chiral 1-cyano-1-methyl-5-hexenyl acetate thus obtained was converted to (S)-frontalin via unsaturated diol.
- Ohta, Hiromichi,Kimura, Yoichi,Sugano, Yasushi,Sugai, Takeshi
-
p. 5469 - 5476
(2007/10/02)
-
- Investigation of 1,4-elimination reactions of γ-trimethylsilyl alcohols via ionic and radical processes
-
Oxidative fragmentation of γ-trimethylsilyl alcohols with cerium ammonium nitrate occurs rapidly via a radical processes to provide keto olefins.Attempts to obtain the same products via an ionic type 1,4-elimination with the trimethylsilyl group as the directing moiety proved unsuccesful, even under a variety of harsh experimental conditions.Instead, dehydration products were produced in certain cases.
- Hwu, Jih Ru,Gilbert, Bryant A.
-
-
- CONVENIENT SYNTHETIC ROUTE TO (+/-) -FRONTALIN
-
(+/-)-Frontalin was synthesized in a few steps sequence starting from ethyl acetoacetate involving intramolecular cyclization using palladium chloride as catalyst
- Kongkathip, Boonsong,Sokkho, Rongsan,Kongkathip, Ngampong
-
p. 1849 - 1850
(2007/10/02)
-
- FREE RADICAL REARRANGEMENTS OF ORGANOCOBALOXIMES: ALKYNYL TO CYCLOALKYLIDENE AND HEXENYL TO CYCLOPENTYLMETHYL
-
Under irradiation by tungsten light in pyridine solution, several substituted alkylcobaloximes undergo rearrangement to more stable substituted alkyl- or alkenyl-cobaloximes.When the same reactions are carried out in the presence of carbon tetrachloride or chloroform, no rearranged organobaloximes are obtained, but a variety of organic products are obtained derived from the interception of transient organic radicals by the halogenated solvent.The rearrangements are rationalised in terms of a reversible homolysis of the carbon-cobalt bond, rearrangement of the organic radical and recapture by the cobalt(II) fragment to give complexes that are more stable to irradiation than their precursors.
- Bougeard, Peter,Cooksey, Christopher J.,Johnson, Michael D.,Lewin, Melanie J.,Mitchell, Stewart,Owens, Paul A.
-
p. 349 - 358
(2007/10/02)
-
- Organic Photochemistry with 6.7-ev Photons: γ,δ-Unsaturated Ketones
-
The photochemistry of a series of acyclic, aliphatic γ,δ-unsaturated ketones in pentane solution with 185-nm light has been investigated.The variety of products formed can be rationalized as arising from discrete reactions of the individually excited chromophores.Neither intramolecular energy transfer nor internal conversion leading to population of the lowest (n,?*) singlet state are competitive with product formation at 185 nm.The mechanism of alkyne formation in the solution-phase photolysis of these and terminal alkenes at 185 nm is elucidated by using a deuterated derivative, and the reaction is postulated to proceed from the olefinic ?,?* singlet state.
- Leigh, William J.,Srinivasan, R.
-
p. 4424 - 4429
(2007/10/02)
-
- Reaction Of Allylic Boron and Aluminium "Ate" Complexes with Organic Halides and Carbonyl Compounds. Trialkylboranes as Regio-, Stereo-, and Chemoselective Control Elements
-
Lithium allylic boron ate complexes, prepared by the addition of trilakylboranes to an ether solution of allylic lithium compounds, regioselectively react with allylic halides to produce head-to-tail 1,5-dienes (eq 1).The ate complexes are also prepared from the reaction of allylic boranes with alkyllithium derivatives.Magnesium or copper allylic boron ate complexes are less effective.Lithium crotyl boron ate complexes undergo a rapid reaction with aldehydes with good threoselectivity (eq 2).The selectivity is affected by the steric hindrance of trialkylboranes, as explained by the steric parameters of the 6-membered transition state.The ate complexes react with α,β-unsaturated ketones in a competitive manner of 1,2 and 1,4 addition, while they add to cinnamaldehyde exclusively in a 1,2 manner.The chemoselective aspects are only investigated. 1H and 13 C NMR spectra of lithium allylic boron ate complexes clearly indicate (i) the prevention of allylic rearrangement, (ii) the predominant trans geometry of the crotyl unit in comparison with the corresponding trivalent crotylboron, and (iii) the relative importance of ?-? conjugation between the double bond and the carbon-boron bond (eq 3).
- Yamamoto, Yoshinori,Yatagai, Hidetaka,Maruyama, Kazuhiro
-
p. 1969 - 1975
(2007/10/02)
-
- RADICAL REACTIONS OF CARBONYL COMPOUNDS INITIATED BY METAL SALTS AND OXIDES. XIV. RADICAL OXIDATIVE TELOMERIZATION OF ETHYLENE WITH ACETONE
-
The radical telomerization of ethylene with acetone was investigated.The telomeric radicals CH3COCH2(CH2CH2)n-1C.H2CH2 (n=1-5) are oxidized by the metal ions with the formation of unsaturated and acetoxy-substituted ketones.The effect of the nature of metal ion and the solvent (acetic acid, ethyl acetate, ethanol, acetonitrile) on the direction of oxidation of the radicals was studied.It was shown that oxidative telomerization takes place most selectively in the presence of divalent copper ions; here the main products are γ-acetopropyl and γ-acetopropenyl acetates or ω-unsaturated ketones, depending on the reaction conditions.
- Vinogradov, M. G.,Petrenko, O. N.,Verenchikov, S. P.,Nikishin, G. I.
-
p. 626 - 631
(2007/10/02)
-
- A NOVEL SYNTHESIS OF TERMINAL OLEFINS BY ANODIC OXIDATION OF CARBOXYLIC ACIDS HAVING A TRIMETHYLSILYL GROUP ON THE β-POSITION
-
Anodic oxidation of carboxylic acids having a trimethylsilyl group on the β-position gave exclusively terminal olefins in reasonable yields.
- Shono, Tatsuya,Ohmizu, Hiroshi,Kise, Naoki
-
p. 1517 - 1520
(2007/10/02)
-