Three-step synthetic pathway to fused bicyclic hydantoins involving a selenocyclization step

Abstract

Sequential 5-alkenyl hydantoin and pyrrolidine ring-forming reactions have been applied in the synthesis of conformationally constrained fused bicyclic scaffold. They are assembled by a three-step reaction sequence from two variable building blocks (readily available β-ketoesters and alkenyl halides) by combining a Bucherer–Bergs reaction with a final selenium-promoted intramolecular cyclization as a key step. The chemoselectivity of this bicyclic hydantoin formation is strongly influenced by experimental factors such as the solvent and the use of additives. The reaction is regiospecific giving only five-membered fused bicyclic hydantoins in good to excellent yields stemming from the nucleophilic attack of the nitrogen atom to a cyclic seleniranium ion intermediate during the cyclization step. A separable diastereomeric mixture is obtained; the products with bridgehead substituents and phenylseleno groups in cis relationships were formed predominantly. The reaction tolerates a variety of substitution at the double bond, furthermore, the presence of substituents at C(5) and N(3) position opens up the capability of generating a broad structural diversity.