5-Substituted-1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylic acids of the formula ##STR1## wherein: X is hydrogen or lower alkyl; Ar is a moiety selected from the group consisting of ##STR2## in which: Y is oxygen or sulfur;R is hydrogen, methyl, chloro, or bromo, the R substitution being at the 3, 4 or 5 position of the ring;R.sup.1 is hydrogen, lower alkyl, lower alkoxyl, lower alkoxycarbonyl, lower alkylcarbonyl, fluoro, chloro or bromo, the R.sup.1 substitution being at any available position in the ring;R.sup.2 is hydrogen or lower alkyl;are prepared by .beta.-decarboxylation of the corresponding dialkyl-1,1-dicarboxylates. Certain substituted pyrroles are useful as intermediates for preparing the compounds of formula I.