Terminal alkenes are readily available functional groups that appear in α-olefins produced by chemical industry, and they appear in the products of many contemporary synthetic reactions. While the organic transformations that apply to such alkenes are amongst the most studied reactions in all of chemical synthesis, the number of reactions that apply to nonactivated terminal alkenes in a catalytic enantioselective fashion is small in number. This Review highlights the cases where stereocontrol in catalytic reactions of 1-alkenes is high enough to be useful for asymmetric synthesis.
A highly stereoselective boron-Wittig reaction between stable and readily accessible 1,1-bis(pinacolboronates) and aldehydes furnishes a variety of synthetically useful di- and trisubstituted vinyl boronate esters.
The catalytic enantioselective diboration of vinyl boronate esters furnishes chiral tris(boronates) in a selective fashion. Subsequent deborylative alkylation occurs in a diastereoselective fashion, both for intermolecular and intermolecular processes.
The palladium-catalyzed coupling of aryl and heteroaryl chlorides with primary amides under mild homogeneous reaction conditions is reported. Successful C−N coupling is enabled by the use of a unique "dual-base" system consisting of DBU and NaTFA, which serve as proton acceptor and halide scavenger, respectively, using low catalyst loadings (0.5 mol %) with readily available, air-stable palladium precatalysts. The DBU/NaTFA system also enables the room-temperature coupling of primary aryl amines with aryl chlorides and is tolerant of a variety of base-sensitive functional groups.
The Pt-catalyzed enantioselective diboration of terminal alkenes can be accomplished in an enantioselective fashion in the presence of chiral phosphonite ligands. Optimal procedures and the substrate scope of this transformation are fully investigated. Reaction progress kinetic analysis and natural abundance isotope effects suggest that the stereodefining step in the catalytic cycle is olefin migratory insertion into a Pt-B bond. DFT analysis, combined with other experimental data, suggest that the insertion reaction positions platinum at the internal carbon of the substrate. A stereochemical model for this reaction is advanced that is in line both with these features and with the crystal structure of a Pt-ligand complex.
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