63(P1-11) 新規環拡大反応と(-)ムスコン合成への応用(ポスター発表の部)  [in Japanese] 63(P1-11) A NOVEL RING EXPANSION REACTION AND ITS APPLICATION TO THE SYNTHESIS OF (-)-MUSCONE  [in Japanese]

A one-pot three carbon ring expansion reaction involving intramolecular aldol condensation and subsequent retro-aldol cleavage is induced by treatment of β-keto esters with potassium tert-butoxide in dimethyl sulfoxide to afford functionalized 8-, 9-, 10-, and 15-membered rings, respectively. The stereochemistry of intermediate 7 was clarified to be cis-fused carbocyclic ring system with the methyl ketone in the cis-position by chemical conversion. A novel mechanistic consideration for this successful three carbon ring expansion was made by taking the dual function of electron withdrawing group (EWG) in I. This facile ring expansion was also applied to the synthesis of (-)-muscone. Treatment of compound 31 with t-BuOK led to unusual rearrangement product 33 without the formation of two carbon ring expansion product. We suggest the mechanism for this new reaction as depicted in Scheme 12. It involves a reverse intramolecular [3.3]sigmatropic rearrangement and subsequent [3.3]sigmatropic rearrangement.