Catalytic and selective conversion of (Z)-2-en-4-ynoic acids to either 2H-pyran-2-ones in the presence of ZnBr2 or (Z)-5-alkylidenefuran-2(5H)-ones in the presence of Ag2CO3

Treatment of (Z)-5-alkyl-2-en-4-ynoic acids (1), prepared by the Pd-catalyzed alkynylzinc-beta-haloacrylic acid coupling, with 5 10 mol% of ZnBr2 can produce 6-alkyl-2H-pyran-2-ones (2) along with minor amounts of (Z)-5-alkylidenefuran-2(5H)ones (3) in >90% combined yields, with often very high (approximate to95/5) pyranone/furanone ratios. On the other hand, lactonization of 1 catalyzed by Ag2CO3 provides a selective synthesis of (Z)-5-alkylidenefuran-2(5H)-ones (3) in >90% yields along with minor amounts (less than or equal to5%) of 2. (C) 2002 Published by Elsevier Science Ltd.