Chiral 1,2-diamines are privileged structural motifs in organocatalysis, whereas efficient 1,3-diamine-derived organocatalysts are very rare. A highly efficient camphor-1,3-diamine-derived squaramide organocatalyst is reported. Its catalytic activity in Michael additions of 1,3-dicarbonyl nucleophiles to trans-b-nitrostyrene derivatives provides excellent enantioselectivities (up to )99% ee).
A correlation between the absolute configuration and chiroptical properties of nonracemic 2,3-dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles was studied. A series of 16 novel representatives were prepared by Cu-catalyzed [3 + 2] cycloadditions of azomethine imines to ynones and their structures were determined by NMR, VCD, ECD, and X-ray diffraction. A clear correlation between the sign of specific rotation and configuration at position C(1) allows for easy determination of the absolute configuration of 2,3-dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles by ECD and NMR.
A series of 16 copper metal-catalyzed CuAIAC reactions between four pyrazolidinone-1-azomethine imines and four terminal ynones gave the corresponding fluorescent cycloadducts as bimane analogues in very high yields. Applicability of CuAIAC was demonstrated by fluorescent labelling of functionalized polystyrene and by using Cu–C and Cu–Fe as catalysts. Experimental evidence is in agreement with homotopic catalytic system with catalytic CuI-acetylide formed from copper metal by 'in situ' oxidation. Availability of azomethine imines, mild reaction conditions, simple workup, and scalability make CuAIAC a viable supplement to CuAAC reaction in 'click' chemistry.
Title compounds were prepared in five steps from 2-nitrobenzoic acid. Reduction of the nitro group followed by derivatization of the so formed anilines gave the N-alkyl, N-acyl, and N-vinyl derivatives. NMR spectra of (S)-alanine and (S)-proline derived compounds exhibited two sets of signals corresponding to pairs of conformational diastereomers. The free energy barriers of rotation, ΔG‡298 = 82–86 kJ mol–1, were determined by 1H NMR and evaluated by DFT calculations.
Two cyclic azomethine imines, 7-methyl- and 7-phenyl-2-oxo-Δ7-hexahydropyrazolo[1,5-a]pyridin-8-ium-1-ide were prepared in seven steps from the respective commercially available δ-keto acids. The addition of Grignard reagents followed by N-alkylation at position 1 afforded the 1,7,7-trisubstituted hexahydropyrazolo[1,5-a]pyridin-2(1H)-ones, whereas 1,3-dipolar cycloadditions of these dipoles to typical acetylenic and olefinic dipolarophiles gave 4a-substituted 2a,2a1-diazacyclopenta[cd]indene derivatives, as the first representatives of a novel heterocyclic system. Regio- and stereoselectivity as well as the mechanism of these [3+2]-cycloadditions were evaluated using computational and experimental methods. The data obtained were in agreement with the polar concerted cycloaddition mechanism via the energetically favorable syn/endo-transition states.