Lewis Acid-Catalyzed Diastereoselective C-C Bond Insertion of Diazo Esters into Secondary Benzylic Halides for the Synthesis of α,β-Diaryl-β-haloesters.

We report a formal carbon-carbon (C-C) bond insertion via the reaction of secondary benzylic halides (fluorides, chlorides, and bromides) with α-diazo esters catalyzed by Lewis acid catalysts. Secondary benzylic halides underwent elongation to afford α,β-diaryl-β-haloesters diastereoselectively. Density functional theory calculation revealed that the present formal C-C bond insertion was the result of Lewis acid-promoted cleavage and the re-formation of a carbon-halogen bond and that the aryl-migration step determined the diastereoselectivity. Various diarylmethyl halides and α-diazo esters were applicable to this reaction system. In addition, ring expansion in cyclic benzylic chlorides was accomplished.