20 ロジウムカルベノイドの分子内付加反応を利用する新規六員環形成反応とその天然物合成への応用(口頭発表の部)

抄録

Carbenes or carbenoids react with olefins to provide a powerful synthetic tool for the formation of new carbon-carbon bonds in organic synthesis. It has been well recognized that an intramolecular cyclization of a γ,δ-unsaturated diazoketone in the presence of an appropriate catalyst afforded the corresponding cyclopropane derivative, whereas the similar reaction with β,γ-unsaturated diazoketone led to the formation of the α,β-unsaturated enone system. We applied this procedure to the chiral γ,δ-unsaturated diazoketone, readily accessible from (-)-carvone and discovered an interesting and useful method of forming a new carbon-carbon bond. Decomposition of the diazoketone 6 leading to the cyclohexenone derivative 7, was carried out using various kinds of catalysts such as BF_3・OEt_2, Cu(OTf)_2, Cu(acac)_2, trifluoroacetic acid and Rh_2(OAc)_4 and found that rhodium acetate was the best catalyst for carbon-carbon bond formation. It should also be noted that the stereochemistry of the newly generated stereogenic center was entirely controlled in this reaction. The procedure developed above was successfully applied to the synthesis of 4-epi-isovalerenenol, (-)-neonepetalactone, and (-)-clavukerin A.