Lewis acid mediated [3+2] and [3+3] annulations of azomethine imine with donor-acceptor cyclopropanes

The [3+2] and [3+3] regioselective cycloaddition reactions of azomethine imines with activated cyclopropanes have been developed using two different Lewis acids. Scandium (III) triflate serves as a catalyst for the [3+2] cycloaddition reactions of azomethine imines with cyclopropanes to form tetrahydropyrazolone derivatives and tricyclic tetrahydrofuran derivatives in moderate yields. In complementary to this, novel [3+3] cycloaddition reactions of azomethine imine with activated cyclopropanes have been developed using EtAlCl2 as a Lewis acid to form hexahydropyridazinone derivatives in high regioselectivity.

Synthesis of spiro pyrazolone-oxindole and bicyclic pyrazolone derivatives via solvent dependent regioselective aza-1,4/1,6-Michael and intramolecular cycloaddition under catalyst-free conditions

A solvent dependent and highly regioselective [3+2]-cycloaddition reaction of isoxazole-styrenes and azomethine imines is reported under catalyst-free conditions furnishing a library of pyrazolone-spirooxindole hybrids. Regioselectivity for the isomeric structures were achieved in good yields by the reaction of isoxazole-styrene (1) and azomethine imine (2) in different solvents and temperature. The developed method was extended for the synthesis of tri-substituted dinitrogen-fused pyrazolones for the using 1,6-Michael addition reaction. Further, the isoxazole moiety was converted into carboxylic acid as a model study via ring opening

Synthesis of 6,7-Dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles by Azomethine Imine-Alkyne Cycloadditions Using Immobilized Cu(II)-Catalysts

A series of 12 silica gel-bound enaminones and their Cu(II) complexes were prepared and tested for their suitability as heterogeneous catalysts in azomethine imine-alkyne cycloadditions (CuAIAC). Immobilized Cu(II)–enaminone complexes showed promising catalytic activity in the CuAIAC reaction, but these new catalysts suffered from poor reusability. This was not due to the decoordination of copper ions, as the use of enaminone ligands with additional complexation sites resulted in negligible improvement. On the other hand, reusability was improved by the use of 4-aminobenzoic acid linker, attached to 3-aminopropyl silica gel via an amide bond to the enaminone over the more hydrolytically stable N-arylenamine C-N bond. The study showed that silica gel-bound Cu(II)–enaminone complexes are readily available and suitable heterogeneous catalysts for the synthesis of 6,7-dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles.

Rapid umpolung Michael addition of isatin N,N'-cyclic azomethine imine 1,3-dipoles with chalcones

An umpolung Michael addition of isatin N,N'-cyclic azomethine imine 1,3-dipoles with chalcones is reported. The reaction could be finished within very short time (0.3-2 min), with the 3,3-disubustited oxoindole derivatives...

Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

The first example of the cycloaddition of in situ-generated azomethine imine under microwave conditions is described. The reaction of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones proceeds regio- and stereoselectively giving mostly good yields of the corresponding perhydropyrazolopyrazoles. The products of the reaction undergo cycloreversion under the reaction conditions.