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.