The preparation of [closo-1-CB9H8-1-COOH-10-(4-C3H7C5H9S)] as intermediate to polar liquid crystals

The preparation of iodo acid [closo-1-CB9H8-1-COOH-10-I](-) (1) is optimized and scaled from 1 to 40 g of B10H14. The improved preparation of the [arachno-6-CB9H13-6-COOH](-) (5) uses four times smaller volume and can be run conveniently in up to 40 g scale in a 3-L vessel. The optimized oxidation of 5 to [closo-2-CB9H9-2-COOH](-) (4) requires less oxidant, 12 times smaller volume, and significantly shorter reaction time. The overall yields of the iodo acid 1 as the [NMe4](+) salt are typically 8-10% (10-12 g) for 40 g of B10H14. The iodo acid 1 was transformed to amino acid 8, then to dinitrogen acid 10, and finally to sulfonium acid 2[3] in overall yield of about 13%. The search for a more efficient phosphine ligand for the Pd-catalyzed amination process was not fruitful. Three routes to the sulfonium acid 2[n] were investigated, and the best yield of about 47% was obtained for Cs2CO3-assisted cycloalkylation. Liquid crystalline ester of acid 2[3] and 4-butoxyphenol was prepared and investigated. (C) 2011 Elsevier Ltd. All rights reserved.