On the mechanism of nucleophilic substitution of allenyl(aryl)iodine(III): Formation of propargyl cation and competition with sigmatropic rearrangement
作者:Masahito Ochiai、Michio Kida、Tadashi Okuyama
DOI:10.1016/s0040-4039(98)01276-3
日期:1998.8
The ratios of nucleophilicsubstitution versus [3,3] sigmatropic rearrangement for the collapse of allenyl(aryl)-iodine(III), generated from the reaction of aryliodanes with propargylsilanes in the presence of BF3Et2O in alcohols, were determined. A proposed mechanism involves generation of propargyl cations from the allenyliodine(III) via a unimolecular pathway.
reported that an acid‐activated form of phenyliodine diacetate, PhI(OAc)2, undergoes a reaction with propargyl‐silanes, germanes and stannanes to give the ortho‐propargyl iodobenzene. This formal C−H alkylation was proposed to take place through an unusual (even to date) iodonio‐based [3,3] rearrangement of an intermediate allenylsilane. Although this mechanistic principle has been invoked in related
iodinanes, which undergo [3,3]-sigmatropic rearrangement. The lack of crossover products argues for the intramolecularity of the rearrangement. When both ortho positions of aryliodinanes are occupied with alkyl substituents, the reductive iodonio-Claisen rearrangement affords meta substitution products. This is the first to show that meta-Claisen rearrangementoccurs preferentially even when a free para