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,-d 4 gives rise to the deuterium incorporation into the benzylic carbon of diphenylmethane. Worthy of note is that 1,3-propanediol acts as the hydride source. Herein, diphenylmethyl 3-hydroxypropyl ether is assumed to be the most likely intermediate. In this reaction, Sc(OTf)3 catalyst effectively promotes initial acetal formation, electrophilic aromatic substitution, and successive intramolecular hydride transfer.

No abstract

Scandium(III) Triflate-Catalyzed Friedel-Crafts Alkylation Reactions.-The Sc(OTf) 3 -catalyzed Friedel-Crafts alkylation of aromatics (II) with an alcohol, arenecarboxaldehyde or its acetal as the alkylating agents affords diarylmethanes or allylbenzenes in high selectivity, whereby Sc(OTf) 3 is recycled. -(TSUCHIMOTO, T.; TOBITA, K.; HIYAMA, T.; FUKUZAWA, S.; J. Org. Chem. 62 (1997) 20, 6997-7005; Dep. Appl. Chem., Fac. Sci. Eng., Chuo Univ., Bunkyo, Tokyo 112, Japan; EN)

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.