Abstract
The reaction of alkyl 3-hydroxypyrrole-2-carboxylates (1) with some electrophiles was investigated. The alkylation of 1c occurred at the O and C-2 position as in the case of usual β-keto esters. An N-substituted 3-hydroxypyrrole-2-carboxylate (1e) reacted at the 2-position upon the Michael reaction. In addition to the C-2 adduct (9), an unexpected 2, 2-bis-adduct (10) was concurrently obtained possibly via the ketonic cleavage of the mono-adduct (9) followed by the second addition of acrylate. The N-unsubstituted one (1b) gave a mono-adduct at C-2 (12) and a bis-adduct at C-2 and N (13). Upon bromination, 1c reacted at the 4-and 5-position, not at the 2-position ; namely 1c reacted with bromine as an enamine or a pyrrole, and not as a β-keto ester. The Mannich reaction occurred rapidly and selectively at the 4-position, and the 4-bromo derivative (15) reacted preferentially at the 5-position. In the cyanation of the quarternary salts of the Mannich bases, a dimer (23), a trimer (24) and a dicyano compound (26) were obtained in addition to the expected cyanides (22, 25).
