Cascade triple-aldehyde addition of 1,2,3,4-tetrakis(pinacolatoboryl)but-2-ene: Stereoselective synthesis of 2,3-bis(alkylidene)alkane-1,5-diols

摘要

Treatment of (Z)-l,2,3,4-tetrakis(pinacolatoboryl)but-2-ene, prepared from 2,3-bis(pinacolatoboryl)buta-1,3-diene and bis(pinacolato)diboron, with three molar equivalents of aldehyde in toluene at 100 degrees C gave the 2,3-bis(alkylidene)alkane-1,5-anti-diol as a single stereoisomer. The reaction is applicable to both aromatic and alpha-unbranched aliphatic aldehydes. The 1,5-anti-diols were also synthesized by the one-pot preparation/triple-aldehyde addition of the tetraborylated butene. Experimental results for the stepwise treatment of the butene with two types of aldehydes suggest that the rate-determining step of the triple-aldehyde addition is the third allylation.