Novel isomerically pure tetrasubstituted allylboronates: stereocontrolled synthesis of alpha-exomethylene gamma-lactones as aldol-like adducts with a stereogenic quaternary carbon center.
In spite of their inherent isomerization tendency and low reactivity, 1-alkoxycarbonyl vinylcopper(I) intermediates from the conjugate addition of organocuprates onto acetylenic esters were trapped with very high cis-addition selectivity with iodomethylboronic esters in the presence of HMPA. The resulting isomerically pure 3,3-disubstituted allylboronates react with aldehydes in a highly diastereo- and enantioselective manner, providing alpha-exomethylene gamma-lactones with a stereogenic quaternary beta-carbon center.
Kennedy
Jason W J
JW
Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada.
Hall
Dennis G
DG