期刊
TETRAHEDRON
卷 60, 期 45, 页码 10311-10320出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2004.08.068
关键词
Baylis-Hillman; isoxazolecarbaldehyde; hydrogenation; Raney-Ni; Pd-C; enaminones; furanone
Results of the catalytic hydrogenation of Baylis-Hillman adducts obtained from substituted 3, 4- and 5-isoxazolecarboxaldehydes and their corresponding acetates in the presence of Raney-Ni and Pd-C are presented. The hydrogenation of Baylis-Hillman adducts of substituted 5-isoxazolecarbaldehydes and 3-isoxazolecarbaldehydes in the presence of Raney-Ni furnishes diastereoselectively syn enaminones over anti and in the presence of boric acid as an additive further enhancement of diastereoselectivity in favor of syn isomer is observed. The Pd-C-promoted hydrogenation of these substrates is also diastereoselective in favor of syn isomer but occurs without the hydrogenolysis of isoxazole-ring. The presence of boric acid as an additive in this hydrogenation exhibits no pronounced effect on diastereoselectivity. The Raney-Ni-mediated hydrogenation of Baylis-Hillman adducts of substituted 4-isoxazolecarbaldehydes yield pyridone derivatives and Pd-C-promoted hydrogenation of the same substrate is diastereoselective to afford the anti isomer of the resulting products. The enaminones derived from Baylis-Hillman adducts of 3- and 5-isoxazolecarbaldehydes serve as versatile precursors for alpha'-hydroxy-1,3-diketones, which undergo acid-catalyzed ring-closure reaction to afford the furanone derivatives in excellent yields. (C) 2004 Elsevier Ltd. All rights reserved.
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