CYCLOADDITION CHEMISTRY OF 1,3-BIS(PHENYLSULFONYL) AND 2,3-BIS(PHENYLSULFONYL) 1,3-DIENES WITH ENAMINES AND YNAMINES

1,3- and 2,3-bis(phenylsulfonyl) dienes were found to react smoothly with a variety of enamimes and enamine equivalents to give [4 + 2]-cycloadducts in excellent yields. The cycloaddition proceeds with high regioselectivity affording carbocycles as well as heterocycles. The reactivity of the 1,3-isomer was found to be much greater than the 2,3-isomer and is a consequence of both conformational and electronic factors. Formation of rearranged cycloadducts occurs when unactivated enamines are used with the 2,3-substituted diene. This reaction occurs by an initial rearrangement of the 2,3-diene to the 1,3-isomer followed by cycloaddition with the enamine. Cycloaddition of several 4-substituted 1,3-bis(phenylsulfonyl)butadienes with amidines and thioformamide gave dihydropyridines and thiopyrans, respectively. Indole reacts with both the 1,3- and 2,3-dienes to give the same product distribution of epimeric carbazoles. An entirely different reaction occurred when 1-indolylmagnesium iodide was used. The 2,3-diene reacts with 1-(diethylamino)-1-propyne at low temperatures to give a [2 + 2]-cyloadduct. Reaction of the isomeric 1,3-diene with the same ynamine gave [4 + 2]-cycloadducts as did several 4-substituted 1,3-bis(phenylsulfonyl)butadienes.