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
Boron fluoride promoted cleavage of acetals by organocopper reagents application to asymmetric synthesis
作者:J.F. Normant、A. Alexakis、A. Ghribi、P. Mangeney
DOI:10.1016/0040-4020(89)80078-x
日期:1989.1
BF3. Et2O, organocopper and cuprate reagents promote the substitution of one alkoxy group of an acetal. Under the same conditions, alkoxy tetrahydropyrans react selectively, by ring cleavage. Chiral cyclic acetals, having a C2 axis of symmetry are diastereoselectively cleaved. The method serves to synthesize chiral secondary alcohols, after the removal of the chiral auxiliary.
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.