Different Behavior of 2-Substituted 3-Nitro-2-chromenes in the Reaction with Stabilized Azomethine Ylides Generated from α-Iminoesters.

The AgOAc-catalysed reaction of 3-nitro-2-phenyl-2-chromenes with stabilized azomethine ylides generated from the imines based on methyl glycinate and arylaldehydes leads to a mixture of and ' isomers of the corresponding chromeno[3,4-]pyrrolidines in a ratio of 2.0-2.3:1 in 85-93% total yields as a result of a Michael addition/Mannich reaction sequence. In a similar reaction involving 2-trifluoromethyl-3-nitro-2-chromenes, only chromeno[3,4-]pyrrolidines are formed in 85-94% yields. 3-Nitro-2-(trichloromethyl)-2-chromenes under the same conditions react with these azomethine ylides to give the corresponding Michael adducts as individual -isomers with the ,-configuration of the chromane ring in 40-67% yields. Some 4-CF-substituted chromano[3,4-]pyrrolidines exhibited high cytotoxic activity against HeLa human cervical carcinoma cells.