Enantio- and diastereoselectivity in the reduction of spiro[4.5]decane-1,4-dione derivatives with baker's yeast

Reductions mediated by baker's yeast were carried out on five spiro[4,5]decane 1,4-dione derivatives 4, 9, 12, 15, and 18. Enantioselectivity was always very high, but this did not correlate with the facial diastereoselectivity, which ranged from very high to zero. In some instances, the facial selectivity of the yeast-mediated reduction was lower than that of NaBH4. The reduction product of 4 was transformed in a few steps to the enatiomerically enriched form of a bicylic intermediate 5 for the synthesis of the angular triquinane pentalenene 1. The yeast-mediated reduction of spirodiketone 21 demonstrated that reduction of the equatorial carbonyl aas very much the preferred mode of reaction. Copyright (C) 1996 Elsevier Science Ltd