Al-isopropoxydiisobutylalane: a study of the effect of solvent on the rate and stereoselectivity of cyclic ketone reduction.

The effect of solvent on the rate and stereoselectivity of cyclic ketone reduction by Al-isopropoxydiisobutylalane (DIBA(i)OPr) has been investigated. In dichloromethane, DIBA(i)OPr behaves as a bulky reducing agent, approaching the carbonyl group along an equatorial trajectory to produce the axial alcohol with >10:1 stereoselectivity. In sharp contrast, reduction in toluene gives the complementary outcome, affording the thermodynamically more stable isomer with >99:1 stereoselectivity.