Bromenium-Catalysed Tandem Ring Opening/Cyclisation of Vinylcyclopropanes and Vinylcyclobutanes: A Metal-Free [3+2+1]/[4+2+1] Cascade for the Synthesis of Chiral Amidines and Computational Investigation
作者:Venkataraman Ganesh、Devarajulu Sureshkumar、Debasree Chanda、Srinivasan Chandrasekaran
DOI:10.1002/chem.201103556
日期:2012.9.24
reaction has been further extended to vinylcyclobutane systems and involves a [4+2+1] cascade cyclisation with the same reagents. The versatility of the methodology has been demonstrated by careful choice of VCPs and VCBs to yield bicyclo[4.3.0]‐, ‐[4.3.1]‐ and ‐[4.4.0]amidines in enantiomerically pure form. On the basis of the experimental observations and DFT calculations, a reasonable mechanism has
我们提出通过bromenium物种催化vinylcyclopropanes(VCP)的[3 + 2 + 1]级联环化的详细研究(BR δ + X δ - )原位产生的,其结果在手性二环脒在合成串联一锅操作。脒的形成涉及VCP厂商与溴开环X,然后与氯胺T进行Ritter型反应,并进行串联环化反应。该反应已进一步扩展至乙烯基环丁烷体系,并涉及使用相同试剂进行的[4 + 2 + 1]级联环化。通过仔细选择VCP和VCB可以产生对映体纯形式的双环[4.3.0]-,-[4.3.1]-和-[4.4.0] idine,证明了该方法的多功能性。在实验观察和DFT计算的基础上,提出了一种合理的机制来解释产物的形成和观察到的立体选择性。我们提出在环丙烷碳上存在π稳定的均碳正离子化是高立体选择性的原因。X)。从使用可极化连续体模型(PCM)溶剂化模型的固溶相(乙腈)计算中可以清楚地看出这一点,从中发现V