The preparation and properties of some pyrrole aldehydes

Abstract

The anomalous physical and chemical properties of 2-pyrrolecarbaldehyde are discussed. The preparation of 3-pyrrolecarbaldehyde was carried out on an increased scale, and the properties of this compound were investigated, especially in comparison to 2-pyrrolecarbaldehyde. The chemical properties of the two compounds were similar. 1-Methyl-3-pyrrolecarbaldehyde was prepared; in some reactions it resembled 3-pyrrolecarbaldehyde. The Wolff-Kishner reductions of the aldehydes gave good yields of the corresponding methyl compounds. Reactions were attempted using a protecting acetal group on some aldehydes, but these failed as the acetals were unstable. -- The ultraviolet spectra of 2- and 3-pyrrolecarbaldehydes obeyed the Beer-Lambert law and there was no evidence of association. The nuclear magnetic spectra, contrary to expectations, did not show long-range spin coupling to the aldehydic proton. The mass spectra of some new compounds are recorded. A suggested fragmentation pattern is given for 2-pyrrolecarbaldehyde, 3-pyrrolecarbaldehyde, l-methylpyrrole-2-carbaldehyde and 1-methylpyrrole-3-carbaldehyde.