Synthesis and Reaction of Tetramethyleneethane Derivatives Induced by Photosensitized Electron Transfer

We have studied photoinduced electron-transfer reactions of the following four compounds，A precursor of the 1，1-diaryl-or1，4-diaryl-substituted tetramethyleneethane(TME)cation radicals and diradicals.1-diaryl-substituted TME system·2，3-bis(2-phenylvinyl)-5，5-dimethylcyclopenta-1，3-diene(1)·1，4-diphenyl-5，6-dimethylene-2，3-diazabicyclo[2.2.2]9，10-dicyanoanthracene(DCA)-photoinduced electron-transfer reaction of 1in the presence of N-methylmaleimide(NMI)as a diylophile gave the adducts with NMI(5)in good yields，suggesting generation of a1，1-diaryl-substituted TME diradical(6)。This was most likely generated by back electron transfer from sensitizer anion radical to the corresponding1，1-diaryl-substituted TME cation radical(6I D1·+I D1)。Further supports were obtained by laser flash photolyses of 1.Similar photoinduced electron-transfer reactions of 2 underwent deazetation to give3，4-dimethylene-2，5-diphenyl-1，5-hexadiene(7)quantitatively.Trapping experiment with NMI gave two adducts(8and9)，suggesting generation of the corresponding1，1-diaryl-substituted TME diradical(10).In contrast，compounds(3)and(4)did not gave any products through1，4-diaryl-substituted TME intermediates but underwent novel reactions under photoinduced electron-transfer conditions.Surprisingly，3gave1，3-dimethylene-2，2-bis(4-methoxyphenyl)cyclobutane(11)under the DCA-sensitized photoconditions。Similar photoreactions of 4underwent formal[4+4]cyloadditions to give two kinds of dimer(syn-12，anti-12)and an adduct(13)of4with DCA.

We have studied photoinduced electron-transfer reactions of the following four compounds, a precursor of the 1,1-diaryl- or 1,4-diaryl-substituted tetramethyleneethane (TME) cation radicals and diradicals.1.1-diaryl-substituted TME system・ 2,3-bis(2-phenylvinyl)-5,5-dimethylcyclopenta-1,3-diene (1)・ 1,4-diphenyl-5,6-dimethylene-2,3-diazabicyclo[2.2.2]oct-2-ene (2)1.4-diaryl-substituted TME system・ 1-methylene-3,3-bis(4-methoxyphenyl)spiropentane (3)・ 3,3-diphenyl-2-methylene-1-(methylethylidence)cyclobutane (4)As a result, 9,10-dicyanoanthracene (DCA)-photoinduced electron-transfer reaction of 1 in the presence of N-methylmaleimide (NMI) as a diylophile gave the adducts with NMI (5) in good yields, suggesting generation of a 1,1-diaryl-substituted TME diradical (6). This was most likely generated by back electron transfer from sensitizer anion radical to the corresponding 1,1-diaryl-substituted TME cation radical (6ィイD1・+ィエD1). Further supports were obtained by laser flash photolyses of 1. Similar photoinduced electron-transfer reactions of 2 underwent deazetation to give 3,4-dimethylene-2,5-diphenyl-1,5-hexadiene (7) quantitatively. Trapping experiment with NMI gave two adducts (8 and 9), suggesting generation of the corresponding 1,1-diaryl-substituted TME diradical (10).In contrast, compounds (3) and (4) did not gave any products through 1,4-diaryl-substituted TME intermediates but underwent novel reactions under photoinduced electron-transfer conditions. Surprisingly, 3 gave 1,3-dimethylene-2,2-bis(4-methoxyphenyl)cyclobutane (11) under the DCA-sensitized photoconditions. Similar photoreactions of 4 underwent formal [4+4] cyloadditions to give two kinds of dimer (syn-12, anti-12) and an adduct (13) of 4 with DCA.