Synthesis of Strained Systems via Vinyl Carbocation Intermediates

Vinyl carbocations are a class of dicoordinated carbocations. Due to their challenging generation, they have been less studied compared to tricoordinated carbocations. This thesis reports multiple novel reactivities involving vinyl carbocation intermediates. The first chapter reviews methods for generating vinyl carbocations and past reports of vinyl carbocation C–H insertion. It then introduces a field guide to assist researchers in using vinyl carbocation C–H insertion in their synthesis, providing detailed information and optimal reaction conditions developed in our laboratory. The second chapter describes a catalytic method for forming medium-sized rings via intramolecular Friedel-Crafts reactions of vinyl carbocation intermediates. These reactive species are catalytically generated through the ionization of vinyl toluenesulfonates by a Lewis acidic lithium cation/weakly coordinating anion salt. The third chapter details selective [2+2] cycloadditions between vinyl carbocations and terminal alkenes, using a LiHMDS-mediated approach. This method allows for the efficient synthesis of strained cyclobutene-containing bicycles under mild conditions, demonstrating the versatile application of vinyl carbocations in constructing complex strained organic structures.