Effect of a trifluoromethyl group on molecular structure: Competitive mono- and dilithiation of 1-[(trifluoromethyl)phenyl]pyrroles

Depending on the conditions used during the lithiation and subsequent carbo xylation of 1-[(trifluoromethyl)phenyl]pyrroles the mono- and the dicarboxy lated derivatives were selectively prepared. The regioselective formation o f the monocarboxylic acids could be rationalized in the light of the data c ollected from the literature. Explanation of the other phenomena, such as r egioselective dilithiation and the strong effect of the trifluoromethyl gro up on the structure and aromaticity of the pyrrole ring in the ortho positi on, has been elucidated by the aid of molecular modelling and single crysta l X-Ray measurements. (C) 1999 Elsevier Science Ltd. All rights reserved.