Organic Letters 2008-03-20

Efficient enantioselective hetero-Diels-Alder reaction of Brassard's diene with aliphatic aldehydes: a one-step synthesis of (R)-(+)-kavain and (S)-(+)-dihydrokavain.

Lili Lin, Zhenling Chen, Xu Yang, Xiaohua Liu, Xiaoming Feng

Index: Org. Lett. 10(6) , 1311-4, (2008)

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Abstract

An efficient catalytic asymmetric hetero-Diels-Alder reaction of Brassard's diene with aliphatic aldehydes was reported. The catalyst, which was generated from (R)-BINOL, Ti(i-PrO)4, and 4-picolyl chloride hydrochloride, promoted the reaction smoothly to afford the corresponding alpha,beta-unsaturated delta-lactone derivatives in moderate-to-good yields (46-79%) with high enantioselectivities (up to 88% ee). Natural products (R)-(+)-kavain (70% ee, >99% ee after single recrystallization) and (S)-(+)-dihydrokavain (84% ee) were also prepared in one step by using this methodology.