Protonation of the 1:1 intermediate produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates by pyrrole-2-carbaldehyde leads to a vinylphosphonium salt, which undergoes intramolecular Wittig reaction to produce the title compounds in good yields.
References
1.
FlitshW., in Comprehensive Heterocyclic Chemistry, eds. KatritzkyA. R. and ReesC. W., Pergamon, London, 1984, vol. 3, pp. 443–470; SwinbourneJ. F., HuntH. J. and KlinkertG., Adv. Heterocycl. Chem., 1987, 23, 103; TislerM., Pure Appl. Chem., 1980, 52, 1611.
2.
SchulzS., Eur. J. Org. Chem., 1998, 13; MosbyW. L., Heterocyclic Compounds, Interscience, New York, 1961, vol. 15, ch. III.
SchweizerE. E. and LightK. K., J. Org. Chem., 1966, 31, 870; BrandangeS. and LundinC., Acta Chem. Scand, 1971, 25, 2447; McIntoshJ. M. and SielerR. A., J. Org. Chem., 1978, 43, 4431; KloseW., NikischK. and BohlmannF., Chem. Ber., 1980, 113, 2694; MuchowskiJ. M. and NelsonP. H., Tetrahedron Lett., 1980, 21, 4585; MinamiT., SuganumaH. and AgawaT., Chem. Lett., 1978, 285.
