Birch Reduction of Hexaphenyl- and Pentaphenylbenzene and an X-ray Crystallography and NMR Spectroscopy Study ofcis- andepi-1,2,3,4,5,6-Hexaphenylcyclohexane and of 2,3,5,6-Tetraphenyl-1,1′-bicyclohexylidene: Cannizzaro's Conundrum Revisited
作者:John P. Grealis、Helge Müller-Bunz、Yannick Ortin、Mark Condell、Michael Casey、Michael J. McGlinchey
DOI:10.1002/chem.200701306
日期:2008.2.8
same face of the C(6)Ph(6) precursor. A variable-temperature NMR study of the all-cis isomer 1 yielded a chair-to-chair inversion barrier of approximately 19 kcal mol(-1), which is somewhat higher than the previously reported values for all-cis-1,2,3,4,5,6-C(6)H(6)R(6) in which R=Me or CO(2)Me. The possible relevance to Cannizzaro's 1854 report of a product with the formula (C(7)H(6))(n) is discussed
六苯基苯的桦木还原得到1,2,3,4,5,6-六苯基环己烷的两种异构体。全顺式异构体1的X射线晶体结构表明,相对于常规椅子结构中的位置,这三个芳基取代基的显着张开可以缓解三个轴向苯基之间的严重空间拥挤。晶体学上和通过NMR光谱法鉴定的第二种产物2为六苯基环己烷的1,3-二轴-2,4,5,6-四赤道(epi)异构体,其中六个另外的氢原子中只有五个位于C(6)Ph(6)前体的同一面。全顺式异构体1的变温NMR研究得出大约19 kcal mol(-1)的椅子到椅子倒置势垒,它比以前报道的全顺式1,2,3值要高一些, 3,4,5,6-C(6)H(6)R(6)其中R = Me或CO(2)Me。讨论了可能与Cannizzaro 1854年报告的具有式(C(7)H(6))(n)的产品有关的问题。相反,桦木还原五苯苯导致形成2,3,5,6-四苯基-1,1'-双环己叉基。