Stereoselective Catalytic Synthesis of Tetrasubstituted Olefins from the Intermolecular Conjugate Addition of Simple Alkenes to α,β-Unsaturated Carbonyl Compounds
Angewandte Chemie International Edition
Recent efforts in designing expeditious catalytic synthesis of tetrasubstituted olefins have in part been stimulated by growing needs for developing generally applicable methods for tamoxifen analogs (anti-breast cancer drug) as well as for photo-responsive organic materials and molecular devices. A number of different catalytic methods have been developed to synthesize tetrasubstituted olefins, including: Suzuki-type Pd-catalyzed coupling reactions, Ni- and Rhcatalyzed exocyclization methods, Ni- and Pd-catalyzed nucleophilic coupling reactions of alkynes and of alkyne-to-arylboronic acids, Ti-catalyzed tandem alkyne-epoxide-ethyl acetate coupling, and the ring-closing olefin metathesis by using Grubbs catalyst. Though catalytic conjugate addition of alkenes has been recognized as a potentially powerful synthetic methodology in forming tetrasubstituted olefins, generally applicable conjugate addition of simple olefins to α,β-unsaturated carbonyl compounds has been hampered by lack of reactivity of the olefin substrates and due to the formation of homocoupling and other byproducts. Chelate-assisted C–H insertion and cross coupling methods are among the most notable advances in catalytic coupling reaction of enones with simple alkenes. Ni-catalyzed conjugate addition and allylic substitution reactions of simple alkenes have also been reported recently. We recently discovered that the cationic complex [(C6H6)(CO)(PCy3)RuH]+BF4 − (1) is a highly effective catalyst precursor for the coupling reactions of arylketones and alkenes involving C–H activation. Herein we report a novel catalytic synthesis of tetrasubstituted olefins from the intermolecular conjugate addition reaction of simple olefins to α,β-unsaturated carbonyl compounds.