Synthesis of dendrimers containing 1,3,4-oxadiazoles.
Synthesis of dendrimers containing 1,3,4-oxadiazoles.
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DOI：
10.1021/jo005772s
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发表时间：
2001-06
期刊：
影响因子：
--
通讯作者：
B. Verheyde;W. Dehaen
中科院分区：
文献类型：
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作者：
B. Verheyde;W. Dehaen
Polymers1, 2 containing 1, 3, 4-oxadiazoles are accessible by several preparative methods and are known3-6 to be useful as electron transporting layers in organic light emitting diodes (LEDs). Charge transport through thin layers of these materials occurs via a so-called hopping mechanism. Because of their highly branched structures, dendritic molecules can be even more advantageous as the electrons have an enhanced probability to find an energetically favored pathway to hop from one to another. The usual way to prepare 2, 5-diaryl-1, 3, 4-oxadiazoles starts from an aroyl hydrazide 5. After the introduction of a second aroyl group, the resulting 1, 2-bis (aroyl)-hydrazide 6 can be cyclized, for instance with POCl3 or SOCl2, to form a 1, 3, 4-oxadiazole 4. This reaction sequence is rather difficult to apply to dendrimer synthesis since the polar intermediates are not easy to purify. A better way is the Huisgen route, 7 which involves the aroylation of 5-aryltetrazoles 2. These tetrazoles themselves are easily accessible starting from benzonitriles 1 (Scheme 1). However, even this reaction was not effective enough to go beyond the first-generation stage. 8-11 Therefore, we decided to prepare the 1, 3, 4-oxadiazole ring prior to the dendrimer propagation step and to use the nucleophilic aromatic substitution reaction (NAS) as the key step in the propagation of our dendrons. The well-known1 electron-withdrawing capacity of 1, 3, 4-oxadiazoles makes this reaction possible. We used a convergent strategy to build up higher generation dendrimers.
