Stereoselective Lewis Acid-Catalyzed α-Acylvinyl Additions
摘要:
Silyloxyallenes derived from alpha-hydroxypropargylsilanes undergo efficient addition to aldehydes with catalytic amounts of Lewis acids. The allenes are accessed from the corresponding propargylsilanes in a base-catalyzed 1,2-Brook rearrangement/SE2' process. Enantioenriched propargylsilanes are synthesized by a new zinc-promoted addition of alkynes to acylsilanes in up to 74% ee. This work demonstrates that conversion to the silyloxyallenes occurs with minimal erosion in optical activity. The use of a chiral chromium(III) Lewis acid effects the catalytic asymmetric addition of racemic silyloxyallenes to aromatic aldehydes in up to 92% ee. The overall reaction is broad in scope and accommodates a wide variety of aromatic and aliphatic substituents on both the propargylsilane and aldehyde.
Highly Selective α-Acylvinyl Anion Additions to Imines
作者:Troy E. Reynolds、Michael S. Binkley、Karl A. Scheidt
DOI:10.1021/ol802227t
日期:2008.11.20
alpha-Hydroxypropargylsilanes undergo rearrangement to form reactive lithium allenolates. The resulting alpha-acylvinyl anion equivalents undergo highly selective additions to N-tert-butanesulfinyl imines generating beta-substituted aza-MBH-type products. High yields are achieved for a wide range of alpha-hydroxypropargylsilanes as well as for a diverse selection of imines. The reactions proceed with good