The hydantoin moiety is an important structural scaffold found in a number of biologically active compounds.

Rh2(esp)2 has been identified as a highly efficient catalyst for O–H insertion of carboxylic acids into acceptor/acceptor diazo compounds. The insertion reaction proceeds in CH2Cl2 within minutes at room temperature in excellent yields and accommodates carboxylic acids having varying functionalities including amino acids, free alcoholic and phenolic O–H, indole N–H, alkenes, alkynes, and substituted aromatics. In addition, the reaction tolerates a broad range of stable diazo compounds carrying diverse functional groups.

A novel diazo-cascade approach has been developed for the synthesis of nine-membered oxacycles utilizing readily accessible β-hydroxy vinyl ketones and vinyl diazo esters. The Rh(II)-catalyzed cascade reaction begins with carbene O-H insertion followed by an intramolecular aldol cyclization to provide a substituted tetrahydrofuran intermediate that undergoes an oxy-Cope rearrangement to provide functionalized nine-membered oxacycles with complete stereoselectivity.

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A serendipitous five-step cascade of rhodium vinylcarbenoids with aminochalcones enables a unique synthetic approach to highly functionalized tri- and tetra-cyclic quinolines. The cascade reaction begins with the insertion of aminochalcone nitrogen into rhodium vinylcarbenoids followed by intramolecular aldol cyclization to provide a substituted indoline intermediate that undergoes an oxy-Cope rearrangement to provide a 9-membered azacycle, which then rearranges to the functionalized quinoline through an intramolecular aldol/dehydration sequence. With a catalyst loading as low as 0.1 mol%, the cascade reaction has proven to be general with a range of aminochalcones and vinylcarbenoids.