Preparation of vinylogous 2-sulfonylindolines by the palladium-catalyzed heteroannulation of o-iodoanilines with dienyl sulfones and their further transformation to indoles and carbazoles

The palladium-catalyzed heteroannulation of o-iodoanilines with dienyl sulf ones provides a convenient route to vinylogous 2-sulfonylindolines 3. The r eaction proceeds in DMF/water in the presence of potassium carbonate and ca talytic palladium(II) acetate and is compatible with both electron-donating and -withdrawing substituents in the para position of the aniline, and wit h an alkyl substituent at C-2 of the dienyl sulfone. The indolines underwen t oxidation with DDQ to afford the corresponding indoles 4. The latter were then employed as dienes in Diels-Alder reactions with dimethyl acetylenedi carboxylate (DMAD), methyl propiolate, or methyl acrylate. In the case of t he latter two dienophiles, the cycloadditions were highly regioselective, a ffording the corresponding 1,3-products (with respect to the relative posit ions of the sulfone and ester groups), exclusively. The cycloadducts from a cetylenic dienophiles were converted to the corresponding carbazoles by eli mination of the sulfone moiety with DBU, and that from methyl acrylate was subjected to reductive desulfonylation and oxidation to the corresponding c arbazole with DDQ. The method thus provides access to carbazoles with vario us substituents at the 3-, 4-, and 6-positions.