PYRROLE CHEMISTRY: V. FRIEDEL–CRAFTS ISOPROPYLATIONS OF SOME PYRROLE DERIVATIVES

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Abstract
The Friedel–Crafts isopropylations of methyl 2-pyrrolecarboxylate, 2-pyrrolecarboxaldehyde, and 2-pyrryl methyl ketone have been investigated under a variety of conditions. Products have been isolated and identified. The effects of different Lewis acid catalysts, solvents, and reaction times upon conversion and product isomer distribution have been determined. These results support the sequence of mechanistic steps suggested in an earlier publication. Further experiments have involved attempted rearrangements and disproportionations under alkylation conditions. The evidence indicates that Lewis acid complexing of the carbonyl oxygen deactivates position 4 in electrophilic substitution less than it does positions 3 and 5. The extent of deactivation of the different positions varies from 2-ester to 2-ketone to 2-aldehyde. Some proton nuclear magnetic resonance investigations of the Lewis acid complexes of these 2-carbonyl pyrroles are also reported.

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