Enynones in Organic Synthesis. 7. Substituent Effects on the .alpha.-Tocopherol-Catalyzed Cyclization of Enynones to Methylenecyclopentenones. Convenient Syntheses of Members of the Methylenomycin Class of Antibiotics
作者:Peter A. Jacobi、Harry L. Brielmann、Reginald O. Cann
DOI:10.1021/jo00097a036
日期:1994.9
Substituent effects on the a-tocopherol (vitamin E, 3b) catalyzed cyclization of a wide variety of enynones 1a-z to methylenecyclopentenones 7a-z have been examined, with particular emphasis given to electron-withdrawing and -donating groups at positions 2-4 and 6. In general, electron-withdrawing groups at positions 4 and 6 dramatically accelerate the cyclization process, while strong electron-donating groups at positions 3 and 4 completely inhibit reaction. Relatively little effect is exerted by groups at C-2, except for the methyl ester derivative 1i, which is totally unreactive. This methodology was employed in the syntheses of the methylenecyclopentenone antibiotics methylenomycin B (7a) and desepoxy-4,5-didehydromethylenomycin A (7z) and in formal syntheses of methylenomycin A (8) and xanthocidin (9).
Die Gasphasen-Flussthermolyse von 1-Isobutenyl- und 2-Methylphenyl-alkinyl-ketonen. Eine Synthese von Methylenomycin B
作者:Manuel Koller、Martin Karpf、Andr� S. Dreiding
DOI:10.1002/hlca.19860690306
日期:1986.5.7
The Gas-Flow Thermolysis of 1-Isobutenyl Alkynyl and 2-Methylphenyl Alkynyl Ketones. Synthesis of Methylenomycin B