Conformational effects in compounds with six-membered rings—V : Reduction of unsaturated ketones by dissolving metals Δ 1(9)-2-octalones

Abstract

Cis-2-decalones have been detected for the first time in the reduction of Δ 1(9)-2-octalones by metals and alcohols in liquid ammonia. The effects of alkyl substituents on the ratio of cis- to trans-ring fused products and the high stereoselectivity are not consistent with product determining transition states in which the β-carbon atom (i.e. C9), is nearly tetrahedral, as has been previously supposed. The product ratios may be accounted for qualitatively if in accordance with Hammond's postulate the transition states are similar to the conformations of the highly basic intermediate anion (IV), in which the C9-carbon atom is trigonal, rather than to the products in which the C9-carbon atom is tetrahedral. A considerable improvement in the yield and purity of the products from metal in liquid ammonia reductions of unsaturated ketones results when the reaction time is minimized by rapid mixing of the reagents.