Stereoselective Synthesis of Lactones From Conjugated Enynes

Significance

Reported is the DABCO-catalyzed, highly regio- and diastereoselective 1,4-bromolactonization of conjugated enynes 1 and 3 to give bromoallenes 2 and 4, respectively. Both (E)- and (Z)-enynes undergo highly selective syn-addition to give the products with complementary stereo-chemistries. The reaction is amenable to the synthesis of both five- and six-membered lactones containing all-carbon or heteroatom based linkers. Although excellent yields were obtained in almost all cases, low yields were observed for tetrasubstituted allenes 5 and 6, due to the formation of products from competing 1,2-addition.