Efficient construction of organic molecular skeleton by using spiro-type catalysts

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We have developed a unique chiral ligand SPRIX (1), possessing isoxazoline coordination sites on a rigid spiro backbone. The good affinity of SPRIX towards Pd(II) and its high stability under acidic and oxidative conditions encouraged us to explore new asymmetric Pd catalysis.Herein, we have developed an enantioselective oxidative sequential reaction of alkynyl cyclohexadienones 2 catalyzed by Pd-SPRIX complex, which involves an unusual carboxylation of Pd enolate intermediate. The reaction of 2 in the presence of 10 mol % of Pd(OAc)2 and 15 mol % of (M,S,S)-i-Pr-SPRIX (1d) under an oxygen atmosphere (1 atm) in a 9:1 mixture of AcOH-toluene at 60 °C proceeded smoothly to give product 3 in good yields with up to 71% ee. We have also developed a novel enantioselective Pd(II)/Pd(IV) catalysis of alkenyl alcohols utilizing 1,1-diphenylbut-3-en-1-ol (4), leading to optically active 4-acetoxy-5,5-diphenyltetrahydrofuran (5) in 92% yield with 90% ee.