Unsaturated Oxo−Nitriles: Stereoselective, Chelation-Controlled Conjugate Additions
1999; American Chemical Society; Volume: 64; Issue: 23 Linguagem: Inglês
10.1021/jo9909709
ISSN1520-6904
AutoresFraser F. Fleming, Jianping Guo, Qunzhao Wang, Douglas Weaver,
Tópico(s)Synthetic Organic Chemistry Methods
ResumoAddition of Grignard reagents to the unsaturated oxo−nitrile 10 (4-hydroxy-4-methyl-6-oxocyclohex-1-enecarbonitrile) provides conjugate addition products with virtually complete stereocontrol. Mechanistic evidence supports a chelation-controlled conjugate addition via alkylmagnesium alkoxide intermediates. Diverse Grignard reagents having sp3-, sp2-, and sp-hybridized carbons react with comparable efficiency, with even sterically demanding nucleophiles adding with complete stereocontrol. Unsaturated oxo−nitriles that are incapable of chelation afford diastereomeric conjugate addition products through an unusual boatlike transition state. Collectively, these reactions illustrate the complementary stereoselectivity of chelation-controlled conjugate additions to hydroxylated, unsaturated oxo−nitriles and stereoelectronically controlled conjugate additions to enones.
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