Organic Syntheses on an Icosahedral Borane Surface: Closomer Structures with Twelvefold Functionality

The syntheses of a series of novel ester-linked derivatives of the icosahedral [closo-B12(OH)12]2-
boron cluster (closomer esters) are described using several synthetic methods. The reaction of bis(tetrabutylammonium)-closo-dodecahydroxy-dodecaborate, [NBu4]21, with carboxylic acid chlorides and
anhydrides, vinyl esters with a Y5(OiPr)13O catalyst and 1,1‘-carbonyldiimidazole-activated carboxylic acids
yields the corresponding dianionic dodeca-ester closomers. The method using 1,1‘-carbonyldiimidazole-activated carboxylic acids may be employed as a general synthetic strategy. The use of elevated reaction
temperatures, achievable under pressure, to expedite syntheses is described. An attractive methodology
using immobilized scavenger reagents for the expeditious purification of the closomer esters was employed.
The developed methodology is compatible with a variety of peripheral functional groups attached to the
termini of densely packed, carboxylate ester-linked radial arms bonded to the icosahedral borane surface.
A closomer ester having twelve terminal amino groups was prepared, and without isolation, fully acetylated
in good yield.

本文报道了一系列基于二十面体闭合式十二羟基十二硼酸盐二阴离子（closo-B12(OH)12]2-）的新型酯键连接衍生物（closomer酯，closomer esters）的多种合成路径。以双（四丁基铵）-闭合式十二羟基十二硼酸盐[NBu4]21分别与酰氯、酸酐，以Y5(OiPr)13O为催化剂的乙烯基酯，以及经1,1'-羰基二咪唑（1,1'-carbonyldiimidazole）活化的羧酸反应，均可得到对应的双阴离子型十二酯基closomer。其中，以1,1'-羰基二咪唑活化羧酸的合成方法可作为通用策略。本文同时报道了通过加压实现升高反应温度以加速合成的实验手段。此外，我们采用了一种极具应用价值的方法：使用固定化清除试剂对closomer酯进行快速纯化。所开发的合成体系可兼容多种连接于二十面体硼烷表面的、由羧酸酯键连接的紧密排列径向臂末端的外围官能团。本文还制备了一种带有十二个末端氨基的closomer酯，且无需分离即可将其以良好收率完成完全乙酰化。