Chiral Synthesis via Organoboranes. 17. Preparation of α-Chiral α'-Alkynyl Ketones of High Enantiomeric Excess from Optically Pure Organyl(1-alkynyl)borinic Esters

Article abstract of DOI:10.1021/jo00242a009

Optically pure alkynylborinic esters R*BC<*>CR''(OR') are cleanly obtained from optically pure boronic esters R*B(OR')2 and a lithium acetylide followed by treatment of the "ate" complex LiR*BC<*>CR''(OR')2 with ethereal hydrogen chloride.These borinic esters react with α,α-dichloromethyl methyl ether, DCME, in the presence of a hindered base to yield, after hydrogen peroxide oxidation, α-chiral α'-alkynyl ketones R*COC<*>CR'' which exhibit the same high enantio- and stereoselectivity of the chiral boronic esters. β-Heterosubstituted (1-alkynyl)borinic esters, such as , despite their sensitivity to elimination reactions, can be similarly converted into the corresponding ketones in excellent yields.This development considerably expands the range of applicability of the "DCME" reaction.