A One-pot Access to Diastereoselective Benzo[5,6]oxepino[2,3-c]pyrroles via Formal (5+2)-Annulation of Donor-/Acceptor-Type Aryl Vinyl diazosuccinimide with Ketones Under Silver Catalysis

A silver triflimide catalyzed one-pot protocol for the diastereoselective synthesis of dihydrobenzoxepines has been developed. Silver triflimide found to be an efficient catalyst for the formal (5+2)-cycloaddition to access dihydrobenzoxepines as a single diastereomer using vinyl diazo compounds as 5-C-synthons and ketones. An unmet challenge of utilizing the donor-/acceptor-type vinyl diazosuccinimides as 5-C-synthons under silver-catalysis is presented. This protocol found to be highly regio-, chemo- and diastereoselective, and works well with aliphatic as well as aromatic methyl ketones bearing electron deactivating as well as donating groups to afford dihydrobenzo[5,6]oxepino[2,3-c]pyrroles with a broad substrates scope. The control experiments and time dependent NMR studies revealed the plausible mechanism of this transformation. The protocol also proved to be scalable on the gram scale synthesis.