PHOTOSENSITIZED ELECTRON-TRANSFER FROM AZOALKANES - GENERATION, FRAGMENTATION, AND REARRANGEMENT OF RADICAL CATIONS STRUCTURALLY RELATED TO DICYCLOPENTADIENE
PHOTOSENSITIZED ELECTRON-TRANSFER FROM AZOALKANES - GENERATION, FRAGMENTATION, AND REARRANGEMENT OF RADICAL CATIONS STRUCTURALLY RELATED TO DICYCLOPENTADIENE
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DOI：
10.1021/jo00072a008
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发表时间：
1993-09-24
影响因子：
3.6
通讯作者：
SENDELBACH, J
中科院分区：
文献类型：
--
作者：
ADAM, W;SENDELBACH, J
偶氮烷烃1a-c在光敏化电子转移（PET）时挤出氮以产生1，3-自由基阳离子中间体2.+，经历了有趣的转变。电子反向转移（BET）得到未重排的housane 2，但在BET之前发生显著的重排为二环戊二烯衍生物3。在某些情况下，观察到环戊二烯4的断裂，在1，3-径向阳离子阶段而不是通过相应的1，3-双自由基中间体发生的环逆转。二苯基取代的偶氮烷烃Ia提供高产率的对称环戊二烯4a，而烷基取代的Ib仅产生少量的重排的环戊二烯4 'b。外壳2a、B也被PET氧化，但更不愿意重排。必须利用强电子受体如三苯基吡喃四氟硼酸盐（TPT）或与联苯（Ph 2）共敏化来诱导重排为3a，B并断裂为4和4 '。
The azoalkanes 1a-c extrude nitrogen upon photosensitized electron transfer (PET) to yield 1,3-radical cation intermediates 2.+, which undergo interesting transformations. Electron back transfer (BET) affords the unrearranged housanes 2, but significant rearrangement to dicyclopentadiene derivatives 3 occurs prior to BET. In some cases, fragmentation to cyclopentadienes 4 is observed, a cycloreversion that occurs at the 1,3-radial cation stage rather than through the corresponding 1,3-biradical intermediates. The diphenyl-substituted azoalkane la affords high yields of the symmetric cyclopentadiene 4a, while the alkyl-substituted lb produces only small amounts of a rearranged cyclopentadiene 4'b. The housanes 2a,b are also oxidized by PET, but are more reluctant to rearrange. Strong electron acceptors such as triphenylpyrylium tetrafluoroborate (TPT) or cosensitization with biphenyl (Ph2) must be utilized to induce rearrangement to 3a,b and fragmentation to 4 and 4'.