Boron, Trichloride as a Selective Demethylating Agent for Hindered Ethers: a Synthesis of the Phytoalexins α- and Β-Pyrufuran, a Synthesis of Tri- O -methylleprolomin and its Demethylation

Boron trichloride has been found to be an efficient reagent for the selective cleavage of sterically hindered methoxy groups in methoxyarenes . The scope and utility of this reaction are explored with examples drawn from derivatives of benzene, naphthalene, 9,10- dihydrophenanthrene and dibenzofuran. The method is applied to the synthesis of the phytoalexins a-(56) and ß- pyrufuran (58) (1,3,4- trimethoxydibenzofuran-2-ol and 1,2,4-trimethoxydibenzofuran-3-ol). A synthesis of tri-O- methylleprolomin (61), a derivative of the unusual lichen metabolite leprolomin (60), is described and its demethylation with boron trichloride is studied.