Regioselective Synthesis of β-Aryl- and β-Amino-Substituted Aliphatic Esters by Rhodium-Catalyzed Tandem Double-Bond Migration/Conjugate Addition

Rhodium–phosphite catalysts were found to effectively mediate double‐bond migrations within unsaturated esters. Once the double‐bond is in conjugation with the carboxylate group, they also catalyze the Michael addition of carbon and nitrogen nucleophiles. In the presence of these catalysts, unsaturated carboxylates enter a dynamic equilibrium of positional and geometrical double‐bond isomers. The conjugated species are continuously removed through 1,4‐additions with formation of β‐amino esters or β‐arylated products, depending on the nucleophile employed. The applicability of both protocols to a range of substrates, such as fatty esters of different chain lengths and double‐bond positions, and several nucleophiles including arylborates and primary and secondary amines, is demonstrated. Rhodium–phosphite catalysts effectively mediate double‐bond migration within unsaturated esters (see scheme; acac=acetylacetonate; cod=cyclo‐1,5‐octadiene). In this method, they enter a constantly renewed equilibrium of double‐bond isomers. From this mixture, the α,β‐unsaturated isomers are continuously removed through 1,4‐addition reactions with aryl or amino nucleophiles allowing selective syntheses of β‐amino and β‐aryl esters.