The stereochemistry of organometallic compounds. Part IX. Sodium borohydride reduction of oxymercury compounds

Reduction of either 3-acetoxynorborn-5-en-2-ylmercury(II) chloride (1) or 5-acetoxy-3-nortricyclylmercury(II) chloride (2) with sodium borohydride in tetrahydrofuran gives three acetates: 2-exo-acetoxynorborn-5-ene (3), 7-anti-acetoxynorborn-2-ene (4), and 3-acetoxynortricyclene (5) in the ratio 8: 35: 57 (±3). Reduction of (1) with sodium borodeuteride led to stereospecific formation of 5-exo-deuterio-substituted (4) but non-stereospecific incorporation of deuterim into the 5-position of compound (5). These results are discussed in terms of the proposed radical mechanism for the reduction of mercurials with borohydride. Reduction of the acetoxymercurial from 7-propionoxynorbornadiene (9; R = COEt) gives a mixture of the acetoxypropionoxynorbornenes (11 and 12; R = COEt) together with some substituted nortricyclene (13), indicating that a similar rearrangement has occurred.