Thermal rearrangements of .alpha.-(acyloxy)silanes: formation of chiral precursors and migratory preference of silicon-based groups
作者:John D. Buynak、J. Byron Strickland、Grady W. Lamb、Dipti Khasnis、Seema Modi、Delena Williams、Hongming Zhang
DOI:10.1021/jo00025a024
日期:1991.12
The asymmetric reduction of acylsilanes to chiral alpha-hydroxysilanes and the thermal rearrangement of the corresponding chiral alpha-acetoxysilanes was explored. IpcBCl reduces many acylsilanes in > 95% ee. The rate of the thermal rearrangement of the alpha-acetoxysilanes was dependent upon the substituents at both silicon and carbon. Evidence is presented to indicate there is electron deficiency at the alpha-carbon in the transition state. Migratory aptitudes follow those expected on the basis of the migrating group assuming an apical migratory group at a pentacoordinate silicon. A previously unreported hydrolytic transformation of a proposed acylsilyl hydride to a stable 1-sila-1,2-diol was observed.
α-β Unsaturated Acylsilanes as Surrogates of Acrolein for Morita-Baylis-Hillman Reactions
A short approach toward new acrolein‐type derivatives, functionalized in position 2 is described. It involves, as the key step, a smooth transformation of acylsilanes into aldehydes by irradiation in water‐organic solvent mixtures. The functionalized enals obtained by this newroute appear as versatile building blocks for the preparation of natural products and/or bioactive compounds.