作者:Pawel Rempala、Robert S. Sheridan
DOI:10.1039/a905042f
日期:——
We have for the first time characterized the 1- and 2-naphthylchlorocarbenes by IR and UV/vis spectroscopy in N2 matrices at 10 K. Although evidence suggests the presence of predominantly only one geometric isomer in the case of the 1-naphthylchlorocarbene, the IR and UV/vis spectra of the 2-naphthylchlorocarbene indicate two distinct conformations. With selective irradiation, the longer-wavelength absorbing s-Z-isomer of 2-naphthylchlorocarbene can be photochemically driven to the alternate s-E conformation. Irradiation of the 1- and 2-naphthylchlorocarbenes induces cyclization to 7-chloro-4,5-benzobicyclo[4.1.0]hepta-2,4,6-triene and 7-chloro-2,3-benzobicyclo[4.1.0]hepta-2,4,6-triene, respectively. The cyclization can be reversed by irradiation at shorter wavelengths.Our results on the singlet naphthylchlorocarbenes photochemical ring-closures parallel observations of Chapman, McMahon, and co-workers on the parent triplet 1- and 2-naphthylcarbenes (P. R. West, A. M. Mooring, R. J. McMahon and O. L. Chapman, J. Org. Chem., 1986, 51, 1316; S. W. Albrecht and R. J. McMahon, J. Am. Chem. Soc., 1993, 115, 855). In particular, under matrix isolation conditions, the naphthylcarbenes appear to photochemically only cyclize to the corresponding cyclopropenes, which in turn only photochemically ring-open back to the carbenes. Ring-expansion in these systems to benzocycloheptatetraenes is not detected.
尽管有证据表明 1-萘基-1-氯代碳主要只存在一种几何异构体,但 2-萘基-1-氯代碳的红外和紫外/可见光谱却显示出两种不同的构象。在选择性辐照下,2-萘基二氯甲烷吸收波长较长的 s-Z 异构体可通过光化学作用转变为另一种 s-E 构象。辐照 1-萘基和 2-萘基氯化羰烯可分别诱导环化成 7-氯-4,5-苯并双环[4.1.0]庚-2,4,6-三烯和 7-氯-2,3-苯并双环[4.1.0]庚-2,4,6-三烯。我们对单色萘基氯化萘光化学环闭的研究结果与 Chapman、McMahon 及合作者对母体三色 1-和 2-萘基萘的观察结果相同(P. R. West、A. M. Mooring、R. J. McMahon 和 O. L. Chapman,J. Org.Chem.,1986,51,1316;S. W. Albrecht 和 R. J. McMahon,J. Am.Chem.Soc.,1993,115,855)。特别是,在基质分离条件下,萘羧似乎只能光化学环化成相应的环丙烯,而环丙烯又只能光化学环开回到萘。在这些体系中,没有检测到环向苯并环庚四烯的扩展。