Chiral Synthesis via Organoboranes. 47. Efficient Synthesis of Unsymmetrical Ketones and Enantiomerically Pure Spiroketals Using (+/-)-Isopinocampheyldichloroborane.
Readily prepared and stable (+/-)-isopinocampheyldichloroborane [(+/-)-IpcBCl(2)] was conveniently used for the stepwise hydroboration of two different alkenes using the in situ reduction-hydroboration protocol to give mixed trialkylboranes, IpcBR(1)R(2). Convenient elimination of alpha-pinene from these trialkylboranes by treatment with an aldehyde, RCHO, provided the borinate ester, R(1)R(2)BOCH(2)R. This intermediate was readily converted into the unsymmetrical ketones, R(1)COR(2), in high yields and purity, by an established method. This methodology was successfully applied to the synthesis of enantiomerically pure spiroketals using optically pure TBS ether protected homoallylic alcohols as the alkenes for stepwise hydroboration.
Brown
Herbert C.
HC
H. C. Brown and R. B. Wetherill Laboratories of Chemistry, 1393 Brown Building, Purdue University, West Lafayette, Indiana 47907.
Kulkarni
Shekhar V.
SV
Racherla
Uday S.
US
Dhokte
Ulhas P.
UP