Regio- and Diastereoselective C—C Coupling of a-OIefins and Styrenes to 3-Hydroxy-2-oxindoIes by Ru-Catalyzed Hydrohydroxyalkylation

摘要

α-Olefins are abundant petrochemical feedstocks used in the manufacture of diverse chemical products. Despite their commercial significance, intermolecular catalytic reductive C—C couplings of α-olefins to carbonyl compounds are unknown, withstanding the special case of hydroformylation Motivated in part by the prospect of addressing this deficiency, our research group embarked upon a systematic exploration of hydrogen-mediated reductive couplings beyond hydroformylation. These efforts led to a broad family of catalytic C—C couplings wherein two or more πunsaturated reactants are hydrogenated to form a single, more complex product. Such transformations typically proceed through pathways involving metallacycle formation and hydrogenolysis (Scheme 1 a, top). Based on these studies, related C—C bond-forming transfer hydrogenations were developed, in which hydrogen transfer from alcohols to πunsaturated reactants through hydrometallation triggers generation of organometal-carbonyl pairs that combine to form products of addition (Scheme 1 a, bottom). In a more recent advance, a third pathway involving alcohol-mediated transfer hydrogenolysis of metallacycles was uncovered, as illustrated in couplings of α-hydroxy esters to isoprene or myrcene to form products of prenylation or geranylation, respectively, and related couplings of dienes to 3-hydroxy-2oxindoles (Scheme 1 b). The availability of this novel mechanistic pathway prompted a reinvestigation of the coupling of a-olefins. Herein, we report that the ruthenium(O) catalyst generated from [Ru3(CO)_(12)] and tricyclohexylphosphine, PCy3, promotes direct C—C coupling of a-olefins and styrenes to 3-hydroxy-2-oxindoles to form branched products of hydrohydroxyalkylation as single diastereomers. To our knowledge, this work represents the first example of the metal-catalyzed hydrohydroxyalkylation of unactivated olefins.