- Iodine-mediated Z-selective oxidation of ketones to α,β- unsaturated esters: Synthesis and mechanistic studies
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The Z-selective oxidation of simple acyclic ketones to Z-2,3-trisubstituted α,β-unsaturated esters is described. Enolates generated under the reaction conditions undergo double iodination followed by a Favorskii-related rearrangement to the unsaturated ester. This reaction represents the first stereoselective one-step transformation of ketones to α,β-unsaturated esters. Mechanistic studies suggest that an electrocyclic reaction governs the Favorskii-related rearrangement.
- Zacuto, Michael J.,Cai, Dongwei
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- Asymmetric Aza-Wacker-Type Cyclization of N-Ts Hydrazine-Tethered Tetrasubstituted Olefins: Synthesis of Pyrazolines Bearing One Quaternary or Two Vicinal Stereocenters
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We have developed an asymmetric aza-Wacker-type cyclization of N-Ts hydrazine-tethered tetrasubstituted olefins, affording optically active pyrazolines bearing chiral tetrasubstituted carbon stereocenters. This reaction is tolerant to a broad range of substrates under mild reaction conditions, giving the desired chiral products with high enantioselectivities. Generation of two vicinal stereocenters on the C=C double bonds was also achieved with high selectivities, a process which has been rarely studied for Wacker-type reactions. A mechanistic study revealed that this aza-Wacker-type cyclization undergoes a syn-aminopalladation process. It was also found that for substrates bearing two linear alkyl substituents on the outer carbon atom of the olefin, both of which are larger than a methyl group, the alkyl substituent that is cis to the intranucleophilic group participates more readily in β-hydride elimination. When one of the two alkyl substituents on the outer carbon atom of the olefin is a methyl group, β-hydride elimination proceeds selectively at the methylene side, thus both diastereomers can be prepared via switching the configuration of the olefin. Furthermore, the product can be converted to a pharmaceutical compound in high yields over three steps.
- Kou, Xuezhen,Shao, Qihang,Ye, Chenghao,Yang, Guoqiang,Zhang, Wanbin
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supporting information
p. 7587 - 7597
(2018/06/04)
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- Synthesis of α,α-dialkoxy imines and α-keto acetals
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A convenient synthesis of monoacetals of α-diones, i.e. α-keto acetals, was developed by silver ion induced alcoholysis of regiospecifically formed α-bromo-α-chloro ketones. Similarly, the corresponding α,α-dialkoxy ketimines were synthesized from silver ion induced alcoholysis of α-bromo-α-chloro ketimines. Both methods provide an easy access to protected forms of α-diones, useful as building blocks in organic chemistry.
- De Kimpe,Stanoeva,Boeykens
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p. 427 - 431
(2007/10/02)
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