Synthesis and Stability of o-Carborane-Fused Phospholes.

Herein, we report that ArLi, formed in situ through the Li/Br exchange between aryl bromide and n-butyllithium, can undergo rapid intramolecular Li/H(Ccage-H) exchange to functionalize o-carboranes. Based on this observation, a dual C-H lithiation reaction of 2- or 3-o-carboryl benzothiophenes was developed, and a series of o-carborane-fused phospholes were synthesized by the reaction of dilithio compounds with chlorophosphine. This reaction is simple with high chemical selectivity and medium to high yields. It is also be applied to the furan derivative. Stability studies demonstrated that these o-carborane-fused phosphole derivatives are stable in both trivalent and coordination states for phosphorus. In contrast, their oxides are sensitive to moisture in air and are susceptible to attack by nucleophiles, leading to the breakage of the Ccage-P bond. Computational results indicate that the newly generated phosphole rings have weak aromaticity.