Electrochemical reactions. Part XVI. Stereochemistry of two known diketonic hydrodimers from reduction of carvone

Abstract

Electrochemical reduction of (+)-carvone (p-mentha-6,8-dien-2-one) is known to give two crystalline diketonic hydrodimers, along with oily dimeric products. Each crystalline dimer on treatment with sulphuric acid gives a different enantiomer of 2,2′-bi-p-meth-4-ene-6,6′-dione. On the basis of this and the n.m.r. spectra (solutions in CDCl₃ and C₆D₆) the hydrodimers are identified as (–)-(1S,2S,4S)-2,2′-bi-p-menth-8-ene-6,6′-dione (α-dicarvelone), m.p. 150–151°, [α]_D ²⁰–85·8°(CHCl₃) and (+)-(1R,2R,4S)-2,2′-bi-p-menth-8-ene-6,6′-dione, m.p. 149–150°, [α]_D ²⁰+41.0°(CHCl₃). Both cyclohexane rings in a given dimer have the same absolute stereochemistry. The stereochemistry of the related 2,2′-bi-p-menth-4-ene-6,6′-dione (γ-dicarvelone) and 4,4′-bicarane-2,2′-dione (β-dicarvelone) is also discussed.