Unusual Preference for Ketone and Reversal of Chemoselectivity in Lewis Acid-Catalyzed Aldol Reaction of Ketene Silyl Acetal
摘要:
Ketene silyl acetals undergo facile reaction with ketones in the presence of a Lewis acid such as (C6F5)(2)SnBr2, TMSOTf, or Sc(OTf)(3). This unique reactivity allows ketones to react in preference to aldehydes or acetals in competitive aldol-type reactions. Upon treatment with keto aldehydes or keto acetals, ketene silyl acetals provide single products derived from the exclusive reaction with the ketonic function. Particularly noteworthy is the discrimination of ketones from aldehydes in naked forms. It has been proved that such bias results from the differentiated recognition of ketone and aldehyde carbonyls. The ternary system consisting of ketene silyl acetal, carbonyl, and an appropriate Lewis acid is crucial for achieving the effective differentiation.
Preparation of Cyclic .ALPHA.-Hydroxy Ketones from .DELTA.- and .EPSILON.-Keto Acids Induced by the Generation of a Novel Acyl Anion Equivalent from the Carboxyl Group.
Parallel recognition by virtue of differentiation between ketone and aldehyde
作者:Jian-xie Chen、Junzo Otera
DOI:10.1016/s0040-4039(98)00039-2
日期:1998.3
The concept of parallelrecognition has been applied to differentiate between ketone and aldehyde: (C6F5)2SnBr2-catalyzed Mukaiyama-aldol reaction of a mixture of these two carbonyl substrates with a mixture of enol silyl ethers derived from esters and ketones results in exclusive formation of ketone/ester and aldehyde/ketone aldol adducts, respectively.
平行识别的概念已用于区分酮和醛:(C 6 F 5)2 SnBr 2催化的这两种羰基底物的混合物与衍生自酯和酮的烯醇甲硅烷基醚的混合物的Mukaiyama- aldol反应分别导致酮/酯和醛/酮羟醛加合物的排他性形成。
Parallel recognition by virtue of differentiation between carbonyls, acetals and enones
are performed simultaneously on separate reaction sites, has been advanced. Ketones/α,β-enones and aldehydes/acetals are able to react selectively with different silyl nucleophiles in parallel. The subtle differentiation between the substrates possessing similar reactivities has recourse to the strong preference of ketene silyl acetal for ketones/α,β-enones.