PREPARATION OF POLYFUNCTIONAL ALLENIC ALCOHOLS BY THE REGIOSELECTIVE ADDITION OF FUNCTIONALIZED PROPARGYLIC CHROMIUM(III) ORGANOMETALLICS TO CARBONYL-COMPOUNDS

The reaction of propargylic halides 1 (X = Cl, Br) with an aldehyde or ketone (0.67 equiv) in the presence of CrCl2 (2.0 equiv) and LiI (2 equiv, necessary if X = Cl) affords allenic alcohols 3 with excellent regioselectivities (3-6% of the regioisomeric acetylenic alcohol 4 is formed) and in good yields (68-90%). Interestingly, this method allows the generation of highly functionalized intermediate propargylic chromium organometallics contained an ester, cyano, or chloride functionality. The alpha-alkyl-substituted propargylic bromide 10 reacts with benzaldehyde yielding the acetylenic alcohol 11 as a diastereomeric mixture of only one regioisomer (90% yield).