Chiral acetals derived from aldehydes and (-)-(2R,4R)-2,4-pentanediol are cleaved selectively by organoaluminumreagents. The reaction proceeds via the retentive-alkylation process with >95% selectivities in most cases. Trialkylaluminum reagent is utilized for higher alkyl transfers, but for smaller alkyl transfers, a newreagent system, combining trialkylaluminum and the halophenols such as pentafluorophenol
A highly chemo- and stereo-selective cleavage of acetals derived from (−)(2R,4R)-2,4-pentanediol with organoaluminum and organotitanium reagents has been demonstrated. The reactions proceed under mild conditions with excellent yields and high chemoselectivities to give, after removal of the auxiliary, chiral alcohols of high enantiomeric purities.
Some chiralacetals are cleaved by organoaluminum reagents. The products are formed diastereoselectively, and the removal of the chiral auxiliary affords optically active alcohols.
Asymmetric cleavage of chiral acetals by R2CuLi,BF3 reagents
作者:A. Ghribi、A. Alexakis、J.F. Normant
DOI:10.1016/0040-4039(84)80013-1
日期:——
The title reagents cleave diastereoselectively the acetals derived from various aldehydes and chiral 2–3 butane diol (or higher homologs). This reaction affords an asymetric synthesis of secondary alcohols from an aldehyde and a trivial organolithium reagent.