Brønsted Acid Catalyzed Oxocarbenium-Olefin Metathesis/Rearrangements of 1<i>H</i>-Isochromene Acetals with Vinyl Diazo Compounds
Haifeng Zheng, Kan Wang, Luca De Angelis, Hadi D. Arman, Michael P. Doyle
Abstract
-isochromene acetals with vinyl diazo compounds. Formally a carbonyl-alkene [2 + 2]-cyclization between isobenzopyrylium ions and the vinyl group of vinyl diazoesters, the retro-[2 + 2] cycloaddition produces a tethered alkene and a vinyl diazonium ion that, upon loss of dinitrogen, undergoes a highly selective carbocationic cascade rearrangements to diverse products whose formation is controlled by reactant substituents. Polysubstituted benzobicyclo[3.3.1]oxocines, benzobicyclo[3.2.2]oxepines, benzobicyclopropane, and naphthalenes are obtained in good to excellent yields and selectivities. Furthermore, isotopic tracer and control experiments shed light on the oxocarbenium-olefin metathesis/rearrangement process as well as on the origin of the interesting substituent-dependent selectivity.