Substitution Reactions of α-Alkyl 4- and 5-Nitropyrrol-2-ylmethyl Derivatives

Abstract

The α-t-butyl 4- and 5-nitropyrrol-2-yl chlorides (5b) and (6b) react with azide, thiocyanate and p- toluenethiolate ions in dimethylformamide through cationic species in an SN 1-type process, rather than by the S_RNl or S_N(AEAE) processes, by which their analogues in the benzene, furan or thiophen systems react. These reactions are so facile that they take place in the aqueous dimethylformamide solutions produced during the workup of reaction mixtures. Solvolysis of (5b) or (6b) in methanol produces high yields of the corresponding methyl ethers (5f) and (6f) The chloride (6b) reacts with methoxide ion to produce the diene (33), which reacts reversibly with excess methoxide to give polymethoxylated derivatives. The mesitoic ester (3d) and the acetic ester (3c) are sufficiently unreactive by the cationic pathway, unlike the highly reactive chlorides (3b) and (4c), to allow reaction with the lithium salt (16) and the tetrabutylammonium salt (17) of 2-nitropropane to occur by an S_RNl mechanism to give the C- alkylate (3e).