CATION-RADICAL CYCLO-ADDITION AND POLYMERIZATION REACTIONS OF N-VINYLCARBAZOLE WITH ELECTROPHILIC ETHYLENES

The uncatalyzed reactions of Nvinylearbazole with electrophilic olefins have been studied. The products included both small molecules and polymers. N-Vinylcarbazole reacted with tricarbomethoxyethylene in inert solvents such as benzene at 110°C to form trimethyl l-carbazol-9-ylbut-l-ene-3,4,4-tricarboxylate. Donor solvents such as acetone or acetonitrile gave trimethyl-l-carbazol-9-ylcyclobutane-2,2,3-tricarboxylate. A variety of additives in the inert solvents also diverted the product from the 3,4,4-tricarboxylate to the 2,2,3-tricarboxylate. These included oxygen, several silver salts, metallic mercury, diphenylpicrylhydrazyl, and tributyltinhydride. Polymers also formed in low yields in many of these reactions. Either homopolyvinylcarbazole or the alternating copolymer of N-vinylcarba-zole with tricarbomethoxyethylene formed, depending on the solvent. Pyridine prevented the formation of the former, and tert-butylhydroquinone the latter; thus their formation is ascribed to cationic and free radical processes, respectively. N-Vinylcarbazole reacted with tetracarbomethoxyethylene at 155° C in either inert or donor solvents to produce tetramethyl 1-carbazol-9-ylbut~l-ene-3,3,4,4-tetracarboxylate. In the presence of DPPH, tetraraethyl l-carbazol-9-ylcyclobutane-2,2,3,3-tetracarboxylate was the product. N-Vinylcarbazole reacted with dimethyl cyano-fumarate at 28° C in inert solvents with air present to give dimethyl 4-cyano-l-carbazol-9-ylbut-l-ene-3,4-dicarboxylate, while donor solvents with air present gave dimethyl 2-cyano-l-carbazol-9-ylcyclobutane-2,3-dicarboxylate. N-Vinylcarbazole reacted with 1,2-disubstituted ethylenes at 155 °C to give only copolymers. The above results are interpreted as proceeding by electron transfer from N-vinylcarbazole to the electrophilic olefin. In inert solvents the N-vinylcarbazole cation-radical transfers a proton to the anionradical and couples to form the 1-butene derivative. In donor solvents or in presence of additives which scavenge or stabilize the anionradical, the N-vinylcarbazole cation-radical reacts instead with the electrophilic ethylene monomer. The resulting butane radical-cation cyclizes and leads to the cyclobutane derivatives. This new cyclobutane synthesis extends the cyclodimerization mechanism of Tada, Shirota, and Mikawa and of Ledwith for electron-rich olefins to the cycloaddition of electron-rich olefins to electron-poor olefins. © 1979, Taylor & Francis Group, LLC. All rights reserved.