FURANNULATION STRATEGY FOR SYNTHESIS OF THE NATURALLY-OCCURRING FUSED 3-METHYLFURANS - EFFICIENT SYNTHESIS OF EVODONE AND MENTHOFURAN AND REGIOSELECTIVE SYNTHESIS OF MATURONE VIA A LEWIS-ACID CATALYZED DIELS-ALDER REACTION - SOME COMMENTS FOR ITS MECHANISTIC ASPECTS

Fused 3-methylfurans are readily obtained by the reaction of allenic sulfonium salt 1 and the enolate anions of cyclic 1,3-dicarbonyl compounds in two steps. Using these fused 3-methylfuran compounds as intermediates, furanoterpenoids such as menthofuran (8) and evodone (4b) are synthesized efficiently. Moreover, maturone (15) is also obtained regioselectivity by Lewis acid CatalYzed Diels-Alder reaction of benzofuranquinone (12) with piperylene. In the context with the regioselectivity observed in the Diels-Alder reaction of 12, semiempirical molecular orbital calculations are applied to gain its theoretical interpretation based upon frontier molecular orbital theory and transition state analysis.