NBS-mediated cyclization of trans-cinnamic alcohols

An efficient and straightforward three-step synthetic route toward 2,4-disubstituted-3-bromooxetanes 5 with the trans–trans contiguous stereogenic centers is developed from functionalized chalcones 3 via NaBH4-mediated reduction of chalcones 3, followed by NBS-mediated electrophilic cyclization of the resulting trans-cinnamic alcohols 4 in good yield. Skeleton 3 is prepared by Claisen–Schmidt condensation of substituted arylaldehydes 1 and aryl methyl ketones or tert-butyl methyl ketones 2. The synthetic route obtained high yields, and the total reaction procedure took only one day. The substituent effect of skeleton 3, various reaction conditions, and plausible mechanism were well-investigated.