An approach to 2,3-dihydropyrroles and β-iodopyrroles based on 5-endo-dig cyclisations
A representative series of homopropargylic sulfonamides 19 and 22b have been found to undergo smooth 5-endo-dig cyclisation upon exposure to excess iodine in acetonitrile containing potassium carbonate. The resulting 4-iodo-2,3-dihydropyrroles 23 readily react with two equivalents of DBU in DMF at 20°C to give the corresponding β-iodopyrroles 24 and 26 in excellent yields by the elimination of toluene-p-sulfinic acid. Use of less than two equivalents of base results in some loss of iodine. The iodo-2,3-dihydropyrroles 23 can be used in palladium-catalysed coupling reactions as shown by the efficient formation of the Sonogashira product 29 under mild conditions.
Knight, David W.,Redfern, Adele L.,Gilmore, Jeremy
p. 622 - 628
(2007/10/03)
5-Endo-dig cyclisations of homopropargylic sulfonamides: A new route to 2,3-dihydropyrroles and β-iodopyrroles
5-endo-dig Iodocyclisations of the homopropargylic sulfonamides 12a-c and 13 give excellent yields of the iododihydropyrroles 14a-d and thence the β-iodopyrroles 15a-d, following base-catalysed elimination of sulfinic acid.
Knight, David W.,Redfern, Adele L.,Gilmore, Jeremy
p. 2207 - 2208
(2007/10/03)
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