N-Vinylpyridinium tetrafluoroborate salts as reagents for the stereoselective and regioselective synthesis of symmetrical (2E,4E)-1,6-dioxo-2,4-dienes
作者:Ge Gao、Neil Brown、Machiko Minatoya、Keith R. Buszek
DOI:10.1016/j.tetlet.2008.08.076
日期:2008.11
in Pd(0)-catalyzed Suzuki cross-couplingreactions with aryl and vinyl boronic acids. We now report that these crystalline, air-stable, and non-hygroscopic salts are also useful reagents for the synthesis of symmetrical (2E,4E)-1,6-dioxo-2,4-dienes (diene diones), which in turn are valuable starting materials for the synthesis of various five-membered heterocycles. The optimization of reaction conditions
properly activated by electron-withdrawing groups on both ends, are shown to be suitable substrates for phosphine-promoted organocatalytic processes. Their reactions with imines, under phosphine catalysis, afford a new and efficient synthetic approach to functionalized 3-pyrrolines.
The dimerization of vinyl ketones RC(O)CHCH2, I (R = Me, tBu, Ph, p-MeC6H4, cyclopropyl, 2-(5-methylfuryl)) at 80°C in the presence of the catalytic system [RhCl(C2H4)2]2MCl2 leads preferably to either α, β-unsaturated 1,6-diketones RC(O)CHCHCH2CH2C(O)R, II when M = Ge or to diene 1,6-diketones RC(O)CHCHCHCHC(O)R, III when M = Sn. The yields of II and III are 20–85% to converted I, the conversion