- BENZINDENE AND ITS KATZ REACTION
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A novel and very short synthesis of the useful title hydrocarbon 2 is presented.Its key step is based on a Diels-Alder reaction of isobenzofuran 4.The lithium salt of 2 gives a remarkably stable valence isomer of anthracene 1 in a reaction analogous to the indene -> benzobenzvalene transformation.
- Burger, Ulrich,Thorel, Pierre-Jean,Schaller, Jean-Pierre
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p. 3155 - 3156
(2007/10/02)
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- Isobenzofuran-Aryne Cycloadducts: Formation and Regioselective Conversion to Anthrones and Substituted Polycyclic Aromatics
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Several substituted anthracenes, benzanthracenes, dibenzanthracene, and more complex ring system derivatives are formed by the cycloaddition of 1,3-bis(trimethylsilyl)isobenzofuran (2) with arynes generated by LTMP-induced dehydrohalogenation of readily accessible haloaromatics.The cycloadducts undergo a novel acid-induced conversion to anthracenones.For several substrates this reaction is highly regioselective, allowing position specific introduction of another substituent at this stage.Reduction/dehydration of the anthrones provides an expeditious route to various polycyclic aromatic hydrocarbons.
- Netka, Jill,Crump, Stephen L.,Rickborn, Bruce
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p. 1189 - 1199
(2007/10/02)
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- The Chemistry of Phthalide-3-carboxylic Acid. II. Decarboxylation of Salts in the Presence of Aldehydes
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Salts of phthalide-3-carboxylic acid decarboxylate in the presence of aromatic aldehydes to give mixtures of the 3-(arylhydroxymethyl)phthalide (2) and the 2-aryl-3-hydroxyindenone (3).The former may be obtained exclusively in the presence of the weak proton donor, triethyl(2-phenylethyl)ammonium chloride, and the latter in the presence of crown ethers or after longer reaction times.A study of the effect of different cations allows a mechanism to be deduced.
- Dibbens, Justin A.,Prager, Rolf H.,Schiesser, Carl H.,Wells, Andrew J.
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p. 913 - 920
(2007/10/02)
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- Preparation of Isobenzofuran-Aryne Cycloadducts
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A one-pot procedure is described for carrying out the sequence 1,4-elimination of acetal 1 to form isobenzofuran; the formation of 1,3-dilithioisobenzofuran; the conversion to 1,3-bis(trimethylsilyl)isobenzofuran (5); the generation of arynes and cycloaddition to 5.This method allows the use of lithium tetramethylpiperidide induced dehydrohalogenation of haloaromatics to generate the arynes, a procedure which fails with unsilylated isobenzofuran due to the acidity of the 1,3-protons.The protiodesilylation of the cycloadducts occurs with surprising ease, upon treatmentwith either tetraalkylammonium fluoride/THF or base (potassium tert-butoxide or KOH) in Me2SO, to furnish the novel unsubstituted isobenzofuran-aryne adducts.Three examples are given, utilizing benzyne, 1-naphthalyne, and 3-pyridine.Procedures for subsequent deoxygenation of the cycloadducts to anthracene, benzanthracene, and benzisoquinoline, respectively, are described.The cycloadduct precursor of benzanthracene is shown to undergo highly regioselective reduction on treatment with lithium tri-tert-butoxyaluminohydride/triethylborane, with preferential attack occurring at the more accessible 7-position.
- Crump, Stephen L.,Netka, Jill,Rickborn, Bruce
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p. 2746 - 2750
(2007/10/02)
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- 1-Lithio- and 1,3-Dilithioisobenzofuran: Formation and Reactions with Electrophiles
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The acetal 1 reacts with 1 equiv of alkyllithium in the presence of catalytic diisopropylamine to form isobenzofuran (2), which with an additional equivalent of alkyllithium gives 1-lithioisobenzofuran (3).Solutions of 3 have been treated with various electrophiles and the resulting products characterized by NMR and as cycloadducts formed on addition of dienophiles.Lithiation of 2 occurs cleanly at C-1, as shown by quenching with D2O.Both the metalation and subsequent alkylation reactions are more rapid in THF than in ether.Reaction of 3 with CH3I gives 1-methylisobenzofuran (6) as the major product, accompanied by some 1,3-dialkylated material.Further treatment of 6 with alkyllithium results in specific lithiation at C-3 to give 14, as demonstrated by deuteration and analysis of cycloadducts by 2H NMR.Ethylation of 14 gives 1-ethyl-3-methylisobenzofuran, illustrating the feasibility of a one-pot procedure for preparing unsymmetrically disubstituted isobenzofurans.Dilithiation of 2 occurs when excess base is employed in THF, and this allows the direct formation of some symmetrical 1,3-disubstituted isobenzofurans.The 1-alkyl- and 1,3-dialkylisobenzofurans are moderately stable in neutral or mildly basic solution, resembling the parent 2 in this respect.Exchange reactions demonstrate that isobenzofuran is more acidic than both furan and diisopropylamine.
- Crump, Stephen L.,Rickborn, Bruce
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p. 304 - 310
(2007/10/02)
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