Enantioselective Bromolactonization of Conjugated (Z)-Enynes

A catalytic enantioselective syn-1,4-bromolactonization of conjugated (Z)-enynes was reported. Diastereomeric ratios >20:1 and up to 99% enantiomeric excesses were observed. Di-, tri-, and tetra-substituted bromoallenes were prepared together with lactone heterocycles efficiently and stereoselectively, Preliminary investigations Suggest that the chiral catalyst may serve as a bifunctional reagent by interacting with both a carboxylic acid nucleophile and NBS electrophile.