An experimental study on the mechanism and stereochemistry of a photochemical [1,3]-oh shift. A non-woodward and hoffmann reaction path for photochemic
作者:W.J.G.M. Peijnenburg、H.M. Buck
DOI:10.1016/s0040-4020(01)86186-x
日期:1988.1
place. The stereochemical outcome of the resulting [1,3]-OH shift agrees well with the one expected in case of a planar shift. Further evidence In favour of the occurrence of a non-Woodward and Hoffmann reaction path is obtained from the Irradiation of 5a,b; despite a favourable ground-state conformation for a suprafacial shift to occur, this shift does not take place. Instead a 90°-twisted intermediate
提出了对4-甲基,4-乙基二取代的3-亚烷基-2-萘酚衍生物1a,b和5a,b的光化学的实验研究。已表明[1,3] -OH位移的发生仅取决于基底的基态构象。该构象又由C 2和C 4的手性固定。对于化合物1a,b,羟基位于环外双键的平面内。激发该有利构象导致环外双键旋转90°。由于取代基之间在C 4和C 9之间的相互作用优先形成一种扭曲的几何形状。产生的[1,3] -OH位移的立体化学结果与在平面位移的情况下预期的结果非常吻合。进一步的证据是通过5a,b的辐照获得了非伍德沃德和霍夫曼反应路径的发生的证据。尽管发生了有利的基态构象,但发生了超分子转移,但这种转移并未发生。取而代之的是形成一个90°扭曲的中间体,从中可以观察到仅无辐射的过渡到基态。借助于低温NOE测量来建立所形成的光产物的立体结构。