Tunable Zinc-Mediated Reductive Cyclization of Diastereomeric 3-Nitro-4-phenacyl-2-(trihalomethyl)chromanes to Fused Pyrroline -Oxides, Pyrrolines, and Pyrrolidines.

Reductive cyclization of trans,trans- and trans,cis-isomers of the 2-CF-substituted 3-nitro-4-phenacylchromanes with Zn-based reductive systems, depending on the conditions, affords 4-CF-substituted 1,3a,4,9b-tetrahydrochromeno[3,4-]pyrrole 3-oxides, 1,3a,4,9b-tetrahydrochromeno[3,4-]pyrroles, or 1,2,3,3a,4,9b-hexahydrochromeno[3,4-]pyrroles in good yields without changing the relative configuration of the pyran ring. A similar process involving the 2-CCl-substituted 3-nitro-4-phenacylchromanes is accompanied by reductive dehalogenation to form the corresponding 4-dichloromethyl-substituted fused chromanes along with the 3-(2-hydroxyaryl)-2-(2,2-dichlorovinyl)-5-phenyl-2-pyrroline 1-oxides as pyran ring opening products. The structure and relative configuration of the obtained products was reliably confirmed by X-ray diffraction analysis and 2D NMR spectroscopy.

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.

Green and Efficient Construction of Chromeno[3,4-]pyrrole Core via Barton-Zard Reaction from 3-Nitro-2-chromenes and Ethyl Isocyanoacetate.

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

Catalyst-free Tandem 1,3-Dipolar Cycloaddition/Aldol Condensation: Diastereoselective Construction of the Azatetraquinane Skeleton.

The one-pot regioselective and diastereoselective method for the synthesis of 5-(het)aroyl-7-(het)arylhexahydrobenzo[4,5]pentaleno[1,6-](thia)pyrrolizine-6,12-diones from accessible 1,5-di(het)arylpent-4-ene-1,3-diones or curcuminoids in 38-98% yield was developed. This reaction proceeds as a sequence of 1,3-dipolar cycloaddition of azomethine ylide generated from ninhydrin and (thia)proline at the C═C bond of corresponding enedione, followed by spontaneous intramolecular aldol condensation and leads to the formation of an azatetraquinane scaffold.

Reaction of polyhaloalkyl-substituted chromones, pyrones, and furanones with salicylaldehydes as a direct route to fused 2H-chromenes.

Polyhaloalkyl-substituted chromones, gamma-pyrones, and beta-furanones react with salicylaldehydes in the presence of piperidine to give a wide variety of fused 2H-chromenes in good yields. This novel annulation reaction presumably proceeds by a tandem intermolecular oxa-Michael addition and subsequent intramolecular Mannich condensation.