Bielefeld University, Faculty of Chemistry, Universitätsstr. 25, D-33615 Bielefeld, Germany.
Beilstein J Org Chem. 2010 Jun 1;6:57. doi: 10.3762/bjoc.6.57.
One important access to monodisperse (functionalized) oligoPPEs is based on the orthogonality of the alkyne protecting groups triisopropylsilyl and hydroxymethyl (HOM) and on the polar tagging with the hydroxymethyl moiety for an easy chromatographic separation of the products. This paper provides an update of this synthetic route. For the deprotection of HOM protected alkynes, γ-MnO₂ proved to be better than (highly) activated MnO₂. The use of HOM as an alkyne protecting group is accompanied by carbometalation as a side reaction in the alkynyl-aryl coupling. The extent of carbometalation can be distinctly reduced through substitution of HOM for 1-hydroxyethyl. The strategy of polar tagging is extended by embedding ether linkages within the solubilising side chains. With building blocks such as 1,4-diiodo-2,5-bis(6-methoxyhexyl) less steps are needed to assemble oligoPPEs with functional end groups and the isolation of pure compounds becomes simple. For the preparation of 1,4-dialkyl-2,5-diiodobenzene a better procedure is presented together with the finding that 1,4-dialkyl-2,3-diiodobenzene, a constitutional isomer of 1,4-dialkyl-2,5-diiodobenzene, is one of the byproducts.
一种获得单分散（功能化）寡聚 PPE 的重要途径是基于炔烃保护基三异丙基硅基和羟甲基（HOM）的正交性，以及通过羟甲基部分进行极性标记，以便于产品的色谱分离。本文提供了该合成路线的更新。对于 HOM 保护的炔烃的脱保护，γ-MnO₂ 被证明优于（高）活性 MnO₂。在炔基-芳基偶联中，HOM 作为炔烃保护基的使用伴随着碳金属化作为副反应。通过将 HOM 取代为 1-羟乙基，可以明显降低碳金属化的程度。通过在增溶侧链中嵌入醚键，极性标记策略得到了扩展。使用 1,4-二碘-2,5-双（6-甲氧基己基）等砌块，组装具有功能端基的寡聚 PPE 需要的步骤更少，并且纯化合物的分离变得简单。对于 1,4-二烷基-2,5-二碘苯的制备，提出了一种更好的方法，并发现 1,4-二烷基-2,3-二碘苯是 1,4-二烷基-2,5-二碘苯的结构异构体之一，是副产物之一。
