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The AgOAc-catalysed reaction of 3-nitro-2-phenyl-2H-chromenes with stabilized azomethine ylides generated from the imines based on methyl glycinate and arylaldehydes leads to a mixture of endo and endo’ isomers of the corresponding chromeno[3,4-c]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-2H-chromenes, only endo chromeno[3,4-c]pyrrolidines are formed in 85–94% yields. 3-Nitro-2-(trichloromethyl)-2H-chromenes under the same conditions react with these azomethine ylides to give the corresponding Michael adducts as individual anti-isomers with the cis,trans-configuration of the chromane ring in 40–67% yields. Some 4-CF3-substituted chromano[3,4-c]pyrrolidines exhibited high cytotoxic activity against HeLa human cervical carcinoma cells.

A regioselective one-pot method for the synthesis of 1-ethyl 2,4-dihydrochromene[3,4-c]pyrroles in 63–94% yields from available 2-phenyl-, 2-trifluoro(trichloro)methyl- or 2-phenyl-2-(trifluoromethyl)-3-nitro-2H-chromenes and ethyl isocyanoacetate through the Barton–Zard reaction in ethanol at reflux for 0.5 h, using K2CO3 as a base, has been developed.

Reactions of 3-nitro-2-trifluoro(trichloro)methyl-2H-chromenes, including 2-unsubstituted derivatives, with N-alkyl-α-amino acids (sarcosine, proline) and paraformaldehyde proceed diastereoselectively to give 1-benzopyrano[3,4-c]pyrrolidines in good yields as a result of a 1,3-dipolar cycloaddition of the intermediate nonstabilized azomethine ylide at the Δ3-bond of the chromene system. © 2013 Elsevier Ltd. All rights reserved.

Reactions of 3-nitro-2H-chromenes with aminoenones derived from acetylacetone and cyclic amines proceed diastereoselectively to give functionalized 2,3,4-trisubstituted chromanes as a result of nucleophilic addition of the vinylogous β-methyl group at the C-4 atom of the chromene system. From these compounds, under acidic conditions, 5-(trifluoromethyl)-5H- chromeno[3,4-b]pyridines and 4-acetoacetonyl-3-nitro-2-(trichloromethyl/phenyl) chromanes, depending on the substituent at the 2-position, were obtained in moderate to good yields. © 2013 Elsevier Ltd. All rights reserved.

A novel methodology has been developed to obtain enantiopure 2-C-glycosyl-3-nitrochromenes. First, (Z)-1-bromo-1-nitroalkenes were prepared from the corresponding sugar aldehydes through a sodium iodide-catalyzed Henry reaction with bromonitromethane followed by elimination of the resulting 1-bromo-1-nitroalkan-2-ols. In the next step, reaction of the sugar-derived (Z)-1-bromo-1-nitroalkenes with o-hydroxybenzaldehydes afforded enantiopure (2S,3S,4S)-3-bromo-3,4-dihydro-4-hydroxy-3-nitro-2H-1-benzopyrans, which, upon SmI2-promoted beta-elimination, yielded chiral enantiopure 2-C-glycosyl-3-nitrochromenes.