Cycloaddition Chemistry of 1,3- and 2,3-Bis(phenylsulfonyl) 1,3-Dienes with Enamines and Ynamines

Article abstract of DOI:10.1021/jo00039a008

1,3- and 2,3-bis(phenylsulfonyl)dienes were found to react smoothly with a variety of enamines 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 cycloaddducts 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(pheylsulfonyl)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>-cycloadduct.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.