Claisen rearrangements of enantiomerically pure C3-(acyloxy)-(E)-vinylsilanes
摘要:
The Ireland ester Claisen rearrangement of chiral (R)- and (S)-C3-(acyloxy)-(E)-vinylsilanes gives access to a wide range of alpha-chiral-beta-silyl-(E)-hexenoic acids with useful levels of diastereoselectivity for both the 2,3-syn and 2,3-anti diastereomers as illustrated in eqs 1 and 2. The vicinal diastereoselectivities for simple propionate esters rac-1b, (S)-1e, and (R)-1g can be varied from 1:12 to 16:1 (syn:anti) depending on reaction conditions. The employment of appropriately protected glycolate esters yields Claisen products with diastereoselectivities ranging from 23:1 (syn:anti), resulting from chelation control of enolate geometry, to 1:3.6 (syn:anti) via the use of a nonchelating, silicon-protecting group. The reaction of alpha-azido acetate (R)-1i is the first example of a Claisen rearrangement involving an alpha-azido ester and results in a new approach toward the asymmetric synthesis of alpha-amino acids. The assignment of relative stereochemistry based on the vicinal coupling constant data has been well documented.
Lipase mediated resolution of chiral (E)-vinylsilanes: an improved procedure for the production of (R)- and (S)-(E)-1-trialkylsilyl-1-buten-3-ol derivatives
作者:Michelle A. Sparks、James S. Panek
DOI:10.1016/s0040-4039(00)79869-8
日期:1991.8
A crude enzymic extract of Pseudomonas AK in pentane catalyzes the transesterification of chiral (E)-vinylsilanes 1, resulting in the production of highly enantiomerically enriched (R)- and (S)-(E)-1-trialkylsilyl-1-buten-3-ol derivatives (S)-2 and (R)-3. A series of related vinylsilanes and two-different lipases have been screened to identify optimal reaction conditions.