A Likely Intermediate during the CO2-Induced Activation of 2-Alkylindoles toward Electrophilic Substitution: Structure of a Unique Tetramer Formed by Joining Two Boat-Shaped (LiOCO)2 Rings

Abstract

Reaction of 2,3-dimethylindole in thf with nBuLi and CO2 gives a lithium carbamate complex (2·thf)n, which has a unique tetrameric solid-state structure (n = 4) containing two boat-shaped (−LiOCOLiOCO−) rings joined by four inter-ring Li−O connections. The two-coordinate O atoms of these rings are near to the 2-Me groups of the indolyl residues, suggesting an explanation for second lithiation (and subsequent electrophilic substitution) of 2-alkylindoles and related heterocyclics occurring specifically at the 2-alkyl position.