NOVEL MICHAEL ADDITIONS TO PHENOLS PROMOTED BY OSMIUM(II) - CONVENIENT STEREOSELECTIVE SYNTHESES OF 2,4-CYCLOHEXADIENONE AND 2,5-CYCLOHEXADIENONE

Citation
Me. Kopach et Wd. Harman, NOVEL MICHAEL ADDITIONS TO PHENOLS PROMOTED BY OSMIUM(II) - CONVENIENT STEREOSELECTIVE SYNTHESES OF 2,4-CYCLOHEXADIENONE AND 2,5-CYCLOHEXADIENONE, Journal of the American Chemical Society, 116(15), 1994, pp. 6581-6592
Citations number
29
Categorie Soggetti
Chemistry
ISSN journal
00027863
Volume
116
Issue
15
Year of publication
1994
Pages
6581 - 6592
Database
ISI
SICI code
0002-7863(1994)116:15<6581:NMATPP>2.0.ZU;2-L
Abstract
A series of alkylated phenols (phenol,p- and o-cresol, 4-methoxy- and 3,4-dimethoxyphenol, 5,6,7,8-tetrahydro-2-naphthol, and beta-estradiol ) are complexed with pentaammineosmium(II) and treated with a variety of Michael accepters (e.g., MVK, methyl acrylate, acrylonitrile, N-met hylmaleimide, and 3-butyn-2-one). Under both acidic and basic reaction conditions, a single conjugate addition takes place either ortho or p ara to the hydroxy group to generate stable 2,4- or 2,5-cyclohexadien- 1-one complexes, respectively. For phenol the conjugate addition occur s exclusively at C(4) for all Michael accepters investigated. For case s where C(4) is substituted, the regioselectivity depends on reaction conditions and the nature of the electrophile, but examples of selecti ve addition at both C(4) and C(6) are reported. When the sp(3) carbon of the resulting cyclohexadienone is a methine, the ligand may be rear omatized and removed from the metal by moderate heating (70-80 degrees C). When the sp(3) carbon is quaternary, stable dienone products may be obtained by oxidative removal of the metal with Ce(IV) or DDQ, and a number of substituted arene and dienone products are synthesized by this methodology in good overall yield (54-83%).