Selective benzylic cross-dehydrogenative arylation and α,β-dehydrogenation under mild conditions

Abstract

Site-selective benzylic C(sp³)–H/C(sp²)–H arylation with an unpreactivated arene under mild conditions is realized through a novel remote activating strategy-enabled (RASE) dealcoholative Friedel–Crafts alkylation with in situ-generated benzylic ether, which represents the first Brønsted acid-catalyzed intermolecular Friedel–Crafts alkylation with noncyclic dialkyl ether as the alkyl donor. Site- and stereoselective α,β-dehydrogenation of alkyl benzene is also achieved through intramolecular dealcoholization of the same in situ-generated benzylic ether. A probable mechanism for the two crucial RASE dealcoholative conversions involved in these benzylic C(sp³)–H functionalizations is proposed based on the results of control experiments and DFT calculations, which demonstrate that the remote activating strategy (RAS) plays an indispensable role during C(sp³)–O activation in these dealcoholative conversions.