The Clemmensen reduction of 1,4-diketones and diterpenoid transformations

Abstract

The Clemmensen reduction of 1,4-diketones can lead to normal saturation, carbon-carbon cleavage, and alcohol formation, the nature of the products depending on the structure of the substrate. Compounds in which the ketone groups have an anti-periplanar conformation readily undergo carbon-carbon cleavage to give both diketones and unsaturated ketones. Acetone, hexane-2, 5-dions (53) and hex-5-en-2-one (129) were found amongst the products from cyclohexane-1,4-dione (49) whilst the products from 6 ,7-dimethyloctalin-1, 4-dione (169) included 1,2-diacetyl-4, 5-dimethylcyclohex-4-ene (175), 5,6-dimethyldecacis5, 9-dien-2-one (174) , 4,5-dimethylcyclodec-cis4-en-1-one (181) and 6, 7-dimethyl-4, 5, 8-tetrahydro-1-(2H)-azulenone (182), the latter three presumably arising from the initial formation of 7, 8-dimethylcyclodec-7-ene-1, 4-dione (176).