Concise [4+3] cycloaddition reaction of pyrroles leading to tropinone derivatives

A concise [4+3] cycloaddition reaction of pyrroles with 2-(silyloxy)allyl cations has been developed. The oxyallyl cations stabilized with a methylthio group or geminal methyl groups were generated from the corresponding allylic alcohols under the influence of a Brönsted acid (Tf2NH), respectively. The use of N-nosyl-protected pyrroles as the four-carbon unit was found to give tropinone derivatives in high yield.