Efficient enantioselective hetero-diels-alder reaction of brassard's diene with aliphatic aldehydes: A one-step synthesis of (R)-(+)-kavain and (S)-(+)-dihydrokavain
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 α, β-unsaturated λ-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 re crystallization) and (S)-(+)-dihydrokavain (84% ee) were also prepared in one step by using this methodology.