Dilongifolylborane: A New Effective Chiral Hydroborating Agent with Intermediate Steric Requirements

Article abstract of DOI:10.1021/jo00327a036

Dilongifolylborane, (Lgf)2BH, a new effective chiral hydroborating agent, is readily synthesized from (+)-longifolene.Thus, treatment of (+)-longifolene with borane-methyl sulfide (BH3*SMe2) in ethyl ether rapidly precipitates snow-white crystalline (Lgf)2BH: mp 160-161 deg C; dimer; IR 1565 cm^-1.The new chiral dialkylborane achieves the successful asymmetric hydroboration of cis, trisubstituted acyclic, and trisubstituted cyclic prochiral olefins to provide alcohols, after oxidation of the intermediate organoboranes, with optical purities in the range of 60-78percent ee.In the cases studied, the new asymmetric center at the alcohol position is predominantly the R enantiomer.