Hydroboration. 94. Rates of hydroboration of 2-organylapopinesnes with 9-borabicyclo[3.3.1]nonane, providing B-(2-organylapoisopinocampheyl)-9-borabicyclo[3.3.1]nonanes, Potentially valuable for the asymmetric reduction of prochiral ketones

摘要

Five representative enantiomerically pure, hindered terpenes, derived from α-pinene, namely 2-organylapopinenes (2-R-apopinenes, R=Et, Pr, I-Bu, Ph, and I-Pr) have been treted with 9-borabicyclo[3.3.1]nonane (9-BBN) in a 1:1 molar ratio in THF at 24 deg C and the rate of hydroboration followed. Increasing the bulk of the 2-R group from the 2-methyl of α-pinen (Ipc, 2-methylapopinene) to 2-ethyl-(Eap), to 2-propyl- (Prap), to 2-isobutyl- (I-Bap), to 2-phenyl- (Pap), and to 2-isopropyl- (I-Prap) significantly lowers the rate of hydroboration with 9-BBN.