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
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Anastasia, L
[1
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Xu, C
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Purdue Univ, Herbert C Brown Labs, W Lafayette, IN 47907 USAPurdue Univ, Herbert C Brown Labs, W Lafayette, IN 47907 USA
Xu, C
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Negishi, E
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Purdue Univ, Herbert C Brown Labs, W Lafayette, IN 47907 USAPurdue Univ, Herbert C Brown Labs, W Lafayette, IN 47907 USA
Negishi, E
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]
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[1] Purdue Univ, Herbert C Brown Labs, W Lafayette, IN 47907 USA
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.