Reactions of cobalt-complexed acetylenic aldehydes with chiral (γ -alkoxyallyl)boranes: enantioselective synthesis of 3,4-dioxy 1,5-enynes and stereoselective entry to polyfunctional building blocks

摘要

Toward the goal of developing enantioselective routes to polyfunctional bulding blocks using Co- based technology, the reactions of(Z)- and (E)-(γ-alkoxyallyl)diisopinocampheylboranes (8,13) with acetylenic aldehydes and their -Co_2(CO)_6 complexes (10a-c) have been investigated. Whereas phenylpropynal reacts with (Z)-8 with poor efficiency (<10/100 yield) and moderate enantioselectivity, the corresponding Co derivatives 10 undergo high-yielding (65-76/100), diastereoselective (88->95/100 de), and enantioselective (>96/100 ee) reactions, producing syn-(3,4-dioxy 1,5-enyne)Co_2(CO)_6 11a-f.