The preparation of [ closo-1-CB 9H 8-1-COOH-10-(4-C 3H 7C 5H 9S)] as intermediate to polar liquid crystals

Abstract

The preparation of iodo acid [ closo-1-CB 9H 8-1-COOH-10-I] − ( 1) is optimized and scaled from 1 to 40 g of B 10H 14. The improved preparation of the [ arachno-6-CB 9H 13-6-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-CB 9H 9-2-COOH] − ( 4) requires less oxidant, 12 times smaller volume, and significantly shorter reaction time. The overall yields of the iodo acid 1 as the [NMe 4] + salt are typically 8–10% (10–12 g) for 40 g of B 10H 14. 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 Cs 2CO 3-assisted cycloalkylation. Liquid crystalline ester of acid 2[ 3] and 4-butoxyphenol was prepared and investigated.