Phenyldimethylsilyllithium reacted with 5,5-dimethyl-3-(N,N-dimethylamino)cyclohex-2-enone (7), 3-(E)-N,N-dimethylaminopropenal (11), and 4-N,N-dimethylaminobut-3-en-2-one (13) to give the corresponding β-silyl-α,β-unsaturated carbonyl compounds 8, 12, and 14, in which the dimethylamino group has been displaced by the phenyldimethylsilyl group. Phenyldimethylsilyllithium reacted with ethyl β-N,N-dimethylaminopropenoate (15) by conjugate addition, but, in contrast to the ketones 7 and 13 and the aldehyde 11, the intermediate enolate 16 was C-protonated in the aqueous work-up to give ethyl 3-N,N-dimethylamino-3-dimethyl(phenyl)silylpropanoate (17). When the enolate 16 was instead given a mysteriously brief treatment with methyl iodide before work-up, the product was ethyl 3-(E)-dimethy(phenyl)silylpropenoate (18). Phenyllithium and methyllithium also added conjugatively to ethyl β-N,N-dimethylaminoacrylate (15) but, in contrast to the silyl case, the intermediate enolate 22 reacted unexceptionally with methyl iodide to give the products 25 and 26 of stereoselective C-methylation. This synthesis of the ester 18 was used to synthesize the Oppolzer sultam derivative 30.Key words: conjugate addition, elimination, substitution, silyllithium, silylenone.
苯基二甲基
硅基
锂与5,5-二甲基-3-(N,N-二甲基
氨基)环己-2-烯酮(7)、3-(E)-N,N-二甲基
氨基
丙烯醛(11)和4-N,N-二甲基
氨基丁-3-烯-2-酮(13)反应,得到相应的β-
硅基-α,β-不饱和羰基化合物8、12和14,其中二甲基
氨基团被苯基二甲基
硅基团取代。苯基二甲基
硅基
锂与乙基β-N,N-二甲基
氨基
丙烯酸酯(15)通过共轭加成发生反应,但与
酮类7和13以及醛11不同,中间体烯醇酸酯16在
水工作处理中被C-质子化,生成乙基3-N,N-二甲基
氨基-3-二甲基(苯基)
硅基
丙酸酯(17)。当烯醇酸酯16在工作处理前突然用
碘甲烷短暂处理时,产物为乙基3-(E)-二甲基(苯基)
硅基
丙烯酸酯(18)。
苯基锂和
甲基锂也与乙基β-N,N-二甲基
氨基
丙烯酸酯(15)发生共轭加成,但与
硅基情况不同,中间体烯醇酸酯22与
碘甲烷反应,产生立体选择性的C-甲基化产物25和26。这种合成酯18的方法被用来合成Oppolzer
磺胺衍
生物30。关键词:共轭加成,消除,取代,
硅基
锂,
硅烯酮。