Scandium(III) Triflate-Catalyzed Friedel−Crafts Alkylation Reactions

TLDR: The Sc(OTf)3-catalyzed Friedel−Crafts alkylation reaction with an alcohol, an arenecarbaldehyde and 1,3-propanediol or their acetal as the alkylating agent affords diarylmethane or an allylbenzene derivative highly selectively as mentioned in this paper.

Abstract: The Sc(OTf)3-catalyzed Friedel−Crafts alkylation reaction with an alcohol, an arenecarbaldehyde or an arenecarbaldehyde acetal as the alkylating agent affords a diarylmethane or an allylbenzene derivative highly selectively. The salient feature of this reaction is that only a catalytic amount of Sc(OTf)3 can effect the reaction. Furthermore, Sc(OTf)3 is recoverable and reusable after the synthetic reaction. The Sc(OTf)3-catalyzed benzylation using an arenecarbaldehyde and 1,3-propanediol or their acetal affords diarylmethane as a sole product in excellent yields in sharp contrast to the original Friedel−Crafts reaction. Since no reaction occurs in the absence of 1,3-propanediol, the reaction is considered to proceed through a redox process including a hydride shift. The hydride shift mechanism is strongly supported by the experimental evidence. The reaction of benzaldehyde with benzene in the presence of 1,3-propanediol-1,1,3,3,-d4 gives rise to the deuterium incorporation into the benzylic carbon of diph...