Rhodium-Catalyzed Formal Hydrocarbamoylation toward an α,β-Unsaturated Carbonyl Compound Using Aryl Isocyanate and Hydrosilane

The “hydrocarbamoylation”, which introduces a hydrogen and N-substituted carbamoyl group to the olefinic part of an α,β-unsaturated carbonyl compound ( 2 ), has been accomplished by three-component coupling of an isocyanate ( 1 ), 2, and a hydrosilane ( 3 ) in the presence of the cationic rhodium complex. The regiochemistry of the addition is strictly regulated so that the carbamoyl group links to the α-position of 2 . Many types of aryl isocyanates are suitable for this coupling to form α-carbamoyl esters regardless of the substituent on the phenyl ring, though an alkyl isocyanate shows less reactivity. Isocyanates bearing an electron-withdrawing group are also applicable to this transformation to give α-carbamoyl esters in high yields. This type of three-component coupling can be elucidated by assuming intervention of the rhodium-enolate complex, which becomes a trigger of a nucleophilic attack to an isocyanate.