Stereoselective synthesis of separable amide rotamers using π-allyl-Pd catalyst and their thermodynamic behavior
作者:Nobutaka Ototake、Takeo Taguchi、Osamu Kitagawa
DOI:10.1016/j.tetlet.2008.07.017
日期:2008.9
Separableamiderotamers were prepared with moderate to excellent Z-selectivities by N-allylation of 2,4,6-tri-tert-butyl-NH-anilides using a π-allyl-Pd catalyst. The present allylation proceeded through a unique mechanism involving O-allylation and the subsequent O,N-allylic rearrangement. The prepared amiderotamers of Z-major changed to equilibrium mixtures of E-major when heated in toluene.
Going separate ways: By using π‐allyl–palladium chemistry (path A) and PdII‐catalyzed Claisen chemistry (path B), a highlyselectivestereodivergentsynthesis of separableamiderotamers was achieved (see scheme).
Interconversion between the separable2,4,6-tri-tert-butylaniliderotamers was found to easily occur through formation of the lithium enolate. Protonation of the anilideenolate gave the aniliderotamer mixture of E-major. On the other hand, reactions of lithium enolate prepared from 2,4,6-tri-tert-butylpropionanilide with alkyl bromides preferentially afforded a Z-rotamer of alkylated products.