A practical synthesis of isomerically pure 1,10-difunctionalized derivatives of the [closo-1-CB9H10] anion

The isomer-free [closo-1-CB(9)H(8)-1-COOH-10-I](-) anion (4) was prepared in four steps and 10% overall yield from B(10)H(14). The key step is the skeletal isomerization of the [closo-2-CB(9)H(8)-2-COOH-7-I](-) anion (3) to a mixture of the 10- and 6-iodo derivatives of [closo-1-CB(9)H(9)-1-COOH](-) formed in up to a 3:1 ratio. The carboxylic acid 4 was converted to the amine [closo-1-CB(9)H(8)-1-NH(2)-10-I](-) (1) using the Curtius reaction. The relative thermodynamic stability of each product was calculated at the DFT and MP2 levels of theory. The regioselectivity of electrophilic substitution in [closo-CB(9)H(10)](-) derivatives was briefly investigated using the NBO population analysis of the MP2 wave function.