Terpenoids : Part CIX. Application of β-ketosulphoxides. Syntheses of ( ± )-Dihydrocarvone, lsopulegone and p-Menthofuran

Department of Chemistry, Panjab University, Chandigarh-160014

Manuscript received 10 April 1975; revised 4 August 1975; accepted 21 August 1975

Use has been made of β-ketosulphoxide as an important Intermediate to achieve a new synthesis of dibydrocarvone, isopulegone and p-menthofuran. 4-Methyl-3,3-ethylenedioxy-1-carbethoxy-cyelohexane was treated with methylsulphinyl carbanlon to give β-ketosulphoxide which on desulphurisation with aluminium amalgam in aqueous tetrahydrofuran afforded 4-methyl-3,3-ethylenedioxy-1-acetyl-cyclohexane. This ketal ketode when submitted to Wittig reaction with methylenetriphenylphosphorane, followed by deketalisation, gave ( ± )· dihydrocarvone. Starting with 4-methyl-2,2-ethylenedioxy-1-carbethoxy-eyelohexane and following similar reaction sequence, isopulegone was obtained. For achieving the synthesis of p-menthofuran, 4-methyl-2,2- ethylenedioxy-1-acetyl-cyclohexane, obtained through the cleavage of β-ketosulphoxide formed by the reaction of 4-methyl-2, 2-ethylenedioxy-1-earbethoxy-cyclohexane, was submitted to Wittig reaction with methoxymethyl-enetriphenylphesphorane and the product was cyclised with 90 per cent sulphuric acid to get p-menthofuran.