Synthesis of pyrrolo[3,2-b]benzofurans and pyrrolo[3,2-b]naphthofurans via addition of a silyloxypyrrole to activated quinones

The uncatalyzed reaction of N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole with 1,4-quinones bearing an electron withdrawing group at C-2 has been studied. Use of 1,4-quinones , bearing an ester group at C-2 provided an efficient synthesis of the respective pyrrolidinobenzofuran adduct or pyrrolidinonaphthofuran adduct whereas use of 1,4-quinones , and bearing an acetyl group at C-2 afforded silyloxypyrroles , and resulting from direct electrophilic substitution of the silyloxypyrrole by the electrophilic quinone. Addition of Eu(fod)3 to the reaction of 2-acetyl-1,4-naphthoquinone and 3-acetyl-5-methoxy-1,4-naphthoquinone with N-(tert-butoxycarbonyl)-2-tert-butyldimethylsilyloxypyrrole provided a method for obtaining the pyrrolidinonaphthofuran adducts and together with silyloxypyrroles and . Oxidative rearrangement of pyrrolidinonaphthofuran adduct to pyrrolidino pyranonaphthoquinone using ceric ammonium nitrate in acetonitrile provided a novel approach for the synthesis of an aza-analogue of the pyranonaphthoquinone antibiotic kalafungin.