Photoactivation of amino-substituted 1,4-benzoquinones for release of carboxylate and phenolate leaving groups using visible light
Photoactivation of amino-substituted 1,4-benzoquinones for release of carboxylate and phenolate leaving groups using visible light
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DOI：
10.1021/jo060790g
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发表时间：
2006-08-04
影响因子：
3.6
通讯作者：
Steinmetz, Mark G.
中科院分区：
文献类型：
--
作者：
Chen, Yugang;Steinmetz, Mark G.
在可见光下，2-吡咯烷基取代的3，6-二甲基-1，4-苯醌类化合物光环合得到苯并恶唑类化合物，在CH2Cl2中的量子产率为0.07-0.10，在CH3CN中的量子产率为0.02-0.04，在30%的AQ-CH3CN中为<；0.01。随着羧酸盐或酚类离开基团通过偶联到苯二酮的5-羟甲基而结合，光环化反应得到苯并恶唑并在暗反应中消除离开基团。当Y=H、CF3和CN时，在Cd3CN(Pd7)中30%磷酸盐缓冲液中消除4-YC6H4OH的寿命分别为13.1h、0.54h和0.13h，线性方程logk(h(-1))=0.998(-pk(A))+8.80.在AQ CH3CN中，当苯二酚光解时，羧酸盐离开基团被迅速消除，以产生邻苯二酚甲基中间体，该中间体通过与未反应的起始原料或与添加的3-(dimethylamino)-5，5-dimethyl-2-cyclohexen-1-one.的4+2环加成来捕获用常规吸收光谱在339 nm和455 nm处观察到邻苯二酚甲醚，在20℃，30%磷酸盐缓冲溶液中，邻苯二酚甲醚的衰减动力学符合拟一级动力学方程，tau(1/2)=34.9min。
Upon exposure to visible light, 2-pyrrolidino-substituted 3,6-dimethyl-1,4-benzoquinones photocyclize to give benzoxazolines with quantum yields of 0.07-0.10 in CH2Cl2, 0.02-0.04 in CH3CN, and < 0.01 in 30% aq CH3CN. With carboxylate or phenolate leaving groups incorporated via coupling to a 5-hydroxymethyl group of the quinones, the photocyclizations give benzoxazolines that eliminate the leaving groups in a dark reaction. Lifetimes for elimination of 4-YC6H4OH in 30% phosphate buffer in CD3CN (pD 7) at 17 degrees C are 13.1, 0.54, and 0.13 h for Y = H, CF3, and CN, respectively, and the linear equation log k (h(-1)) = 0.998(-pK(a)) + 8.80 gives a best fit to the data. Carboxylate leaving groups are rapidly eliminated upon photolysis of the quinones in aq CH3CN to produce an o-quinone methide intermediate that is trapped by 4 + 2 cycloaddition with unreacted starting material or with added 3-(dimethylamino)-5,5-dimethyl-2-cyclohexen-1-one. The ortho-quinone methide is observed at 339 and 455 nm by conventional absorption spectroscopy and gives a pseudo-first-order fit of the decay kinetics with tau(1/2) = 34.9 min in 30% phosphate buffer in CH3CN at 20 degrees C.