在手性配体存在下,对钯催化的不饱和酰胺的分子内烯丙基烷基化反应生成γ-和δ-内酰胺进行了研究。配体(R)-3,5- t Bu-MeOBIPHEP(MeOBIPHEP = 6,6'-二甲氧基联苯-2-2,2-二基)双(二苯基膦))提供了最佳结果,并使环化反应可在多达94个条件下进行:6对映体比率。制备了钯-烯丙基复合物模型,并通过NMR光谱分析进行了研究,该分析提供了对观察到的对映体比率负责的过程的见解。DFT研究用于表征非对映异构反应途径。计算出的能量差与实验观察到的对映体比率非常吻合。
A new molecular queuing process has been achieved, in which a single Pd-based catalytic system promotes two unrelated, sequential catalytic cycles in chronologically distinct order. This study demonstrates also that allylic alkylations can be catalyzed by the Herrmann's phosphapalladacycle, a result that further supports the involvement of a Pd(0) species in its mechanism of action. (C) 2001 Elsevier Science Ltd. All rights reserved.
Palladium-catalyzed intramolecular allylic alkylations of unsaturated EWG-activated amides can take place under phase-transfer conditions or in the presence of a crown ether. These new reaction conditions are milder and higher yielding than those previously reported. A rationalization for such an unexpected result is put forth and validated by DFT-B3LYP calculations. The results suggest cyclization via a counterion-free (E)-enolate TS.