Stereoselective titanium-mediated aldol reactions of (S)-2-tert-butyldimethylsilyloxy-3-pentanone
摘要:
Titanium-mediated aldol reactions based on (S)-2-tert-butyldimethylsilyloxy-3-pentanone, a lactate-derived chiral ketone, provide the corresponding 2,4-syn-4,5-syn adducts in high yields and diastereomeric ratios with a wide array of achiral and chiral aldehydes. Furthermore, spectroscopic studies of intermediates involved in the process have permitted to propose a mechanism that accounts for the experimental results. (c) 2006 Elsevier Ltd. All rights reserved.
Highly Diastereoselective Aldol Additions of a Chiral Ethyl Ketone Enolate under Lewis Base Catalysis
作者:Scott E. Denmark、Son M. Pham
DOI:10.1021/ol0160497
日期:2001.7.1
[reaction: see text] The aldol addition of a chiral ethyl ketone enolate bearing an oxygen substituent (OTBS) at the alpha-position proceeds with high internal and relative diastereoselectivities with various achiral aldehydes in good yields. The profound influence of the resident stereogenic center allows for the use of an achiral catalyst, such as HMPA, with minor attenuation in internal stereoselectivity
Aldol-like reactions of titanium enolates derived from α-OH, α-OBn, and α-OTBS ketones with a series of aldehydes have been studied. In sharp contrast to the O-benzyl derivatives, the TBS-protected ketones lead to excellent yields and selectivities ( ratios from 30:1 to >95:1) even for the lactate-derived substrate (2-tert-butyldimethylsilyloxy-3-pentanone).