A new strategy for the synthesis of substituted dihydropyrones and tetrahydropyrones via palladium-catalyzed coupling of thioesters

In this paper, we describe a new strategy for the synthesis of substituted dihydropyrones and tetrahydropyrones. By exploiting palladium-catalyzed coupling of thioesters with terminal alkynes or alkenylboronic acids, a variety of beta-hydroxy ynones or enones, respectively, could be prepared in an efficient manner under mild conditions. AgOTf-promoted intramolecular oxa-conjugate cyclization of beta-hydroxy ynones provided 2,6-substituted dihydropyrones in excellent yields. On the other hand, acid-catalyzed cyclization of beta-hydroxy enones caused racemization of the product 2,6-substituted tetrahydropyrones due to its reversible nature. Eventually, stereoselective hydrogenation of substituted dihydropyrones was found to be a solid and efficient approach for the synthesis of 2,6-cis-substituted tetrahydropyrone derivatives. (C) 2011 Elsevier Ltd. All rights reserved.