Aspects of the Reduction of Double Bonds Using Cob (I)alamin as Catalys

The olefinic system in 3β‐methoxy‐4‐cholesten‐6 a ‐ol ( 2 ) is reduced using cob (I)alamin ( 1 ( I ); see Scheme 1 ) as catalyst, aqueous acetic acid as solvent and metallic zinc as electron source ( cf. Schemes 2 and 3 ). Experimental evidence for an attack of 1 ( I ) on both faces of the double bond is presented. By the same catalyst (1 R )‐10, 10‐dimethyl‐2‐pinene‐ 10‐carbonitrile ( 9 ) is first transformed to the menthene derivative 11 (see Schemes 4 and 5 ). The ring opening is then followed by a fast saturation of the disubstituted olefinic system in 11 , and ultimately the remaining double bond is reduced in a slow reaction. The cis‐configurated saturated menthane derivative 16 is the main final product ( 16 / 17 ≈ 10:1).