4-Phenylspiro[2.2]pentane-1,1-dicarboxylate: synthesis and reactions with EtAlCl2 and 4,5-diazaspiro[2.4]hept-4-ene derivative

Cyclopropanation of 1-methylidene-2-phenylcyclopropane with dimethyl diazomalonate affords new dimethyl 4-phenyl-spiro[2.2]pentane-1,1-dicarboxylate. On contact with EtAlCl2, this compound undergoes opening of both cyclopropane rings to give dimethyl (2-chloromethyl-3-phenylallyl)malonate. Its EtAlCl2-assisted reaction with methyl 5′-methylspiro[cyclo-propane-1,3′-pyrazoline]-5′-carboxylate proceeds as the 1,3:1′,5′-addition to afford mainly 3-(2-chloroethyl)-1-cyclo-propylmethyl-1H-pyrazoline derivative.