Solvent-free, microwave-assisted synthesis of thiophene oligomers via Suzuki coupling
Solvent-free, microwave-assisted synthesis of thiophene oligomers via Suzuki coupling
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DOI：
10.1021/jo026269d
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发表时间：
2002-12-13
影响因子：
3.6
通讯作者：
Sotgiu, G
中科院分区：
文献类型：
--
作者：
Melucci, M;Barbarella, G;Sotgiu, G
本研究的目的是获得一种快速，高效，环境友好的方法来合成高纯度的噻吩低聚物。无溶剂，微波辅助下的噻吩基硼酸和噻吩基溴化物的偶联，使用氧化铝作为固体载体，使我们能够快速检查反应的变化时间，温度，催化剂和碱的趋势，并容易地优化实验条件，以获得相当数量的目标产物。该方法为制备可溶性噻吩低聚物提供了一种新的、通用的、非常快速的途径。因此，例如，通过2-溴-2，2 ′-联噻吩与双（频哪醇合）二硼反应在6分钟内获得四噻吩（分离产率65%），而通过二溴三噻吩与噻吩基硼酸反应在11分钟内获得喹噻吩（分离产率74%）。报道了新的手性2，2 ′-联噻吩的合成。对某些反应副产物的详细分析使我们能够阐明反应机理的几个方面。虽然微波的使用被证明对于常规噻吩基部分之间的偶联是非常方便的，但是对于噻吩基环与噻吩基-S，S-二氧化物部分的偶联不是如此。实际上，在这种情况下，由于提供多种缩合产物的竞争性加速的狄尔斯-阿尔德反应，以低收率获得目标产物。
The purpose of this study was to obtain a rapid, efficient, and environmentally friendly methodology for the synthesis of highly pure thiophene oligomers. The solvent-free, microwave-assisted coupling of thienyl boronic acids and esters with thienyl bromides, using aluminum oxide as the solid support, allowed us to rapidly check the reaction trends on changing times, temperature, catalyst, and base and easily optimize the experimental conditions to obtain the targeted product in fair amounts. This procedure offers a novel, general, and very rapid route to the preparation of soluble thiophene oligomers. Thus, for example, quaterthiophene was obtained in 6 min by reaction of 2-bromo-2,2'bithiophene with bis(pinacolato)diboron (isolated yield 65%), whereas quinquethiophene was obtained in 11 min by reaction of dibromoterthiophene with thienylboronic acid (isolated yield 74%). The synthesis of new chiral 2,2'-bithiophenes is reported. The detailed analysis of the byproducts of some reactions allowed us to elucidate a few aspects of reaction mechanisms. While the use of microwaves proved to be very convenient for the coupling between conventional thienyl moieties, the same was not true for the coupling of thienyl rings to thienyl-S,S-dioxide moieties. Indeed, in this case, the targeted product was obtained in low yields because of the competitive, accelerated, Diels-Alder reaction that affords a variety of condensation products.