Chemo- and Regioselective 1,3-Dipolar Cycloaddition of Nitrile Imines to 5-Arylmethylene-2-methylthiohydantoins

The 1,3-dipolar cycloaddition of nitrile imines to 11-aryl-4-(arylmethylidene)-1,2,3,4,11,11a-hexahydrodibenzo[b,e][1,4]thiazepines possessing exocyclic C=C and endocyclic C=N bonds as dipolarophilic sites showed site selectivity, depending on the type of C-substituent in the nitrile imine. 1,3-Dipolar cycloaddition of C-aryl nitrile imines occurred selectively to the exocyclic C=C bond, whereas the endocyclic C=N bond was involved in the cycloaddition with C-ethoxycarbonyl nitrile imines. A combination of total energy and molecular orbital plots for the highest occupied and lowest unoccupied molecular orbitals was used to verify the proposed reaction mechanisms and stereoselectivity. Some of the isolated products exhibited moderate to good antitumor activity. The results of POM analysis of the relative cytotoxicity of these new derivatives in comparison to Doxorubicin are also reported.

A strategy for constructing trifluoromethylated spiroisoxazolones has been developed. This approach relies on the 1,3-dipolar cycloaddition of CF3-substituted nitrile imines, generated in situ from trifluoroacetyl hydrazonoyl bromides and K2CO3, with the exocyclic double bond of 4-benzylidene-3-methylisoxazol-5(4H)-ones. The reaction provides a series of trifluoromethylated spiro(isoxazolone-pyrazoline) derivatives in moderate to high yields (up to 93%). The protocol exhibits broad substrate compatibility with respect to aromatic substituents on both reaction partners. To the best of our knowledge, the introduction of a trifluoromethyl group at the 3-position of the pyrazoline ring via nitrile imine cycloaddition chemistry has not been previously reported. The resulting products incorporate a valuable CF3-substituted pyrazoline pharmacophore spiro-fused to an isoxazolone core and may be of interest for medicinal chemistry programs.

A DFT study of the role of Lewis acid catalysts in the mechanism of the 1,3-dipolar cycloaddition of nitrile imines towards electron-deficient acryloyl derivatives

The first case of asymmetric induction in intramolecular nitrile imine cycloadditions: synthesis of enantiopure 3-substituted 6-oxo-2,3,3a,5-tetrahydro-4-carbomethoxy-furo[3,4- c]pyrazoles

Nitrile imines and nitrile oxides are capable of undergoing (3+2)-cycloaddition reactions at double and triple carbon-carbon, carbon-heteroatom, or heteroatom-heteroatom bonds of various dipolarophiles, forming five-membered heterocyclic compounds. When cyclic dipolarophiles bearing an exocyclic carbon-nitrogen double bond (exo-C=N) are introduced into the reaction with these dipoles, spiro-fused 1,2,4-triazoline or 1,2,4-oxadiazoline cycles are formed. Such reactions can provide efficient synthetic approaches to spiro-heterocyclic compounds with enhanced biological activity. This review comprehensively summarizes the literature data on the 1,3-dipolar cycloaddition of nitrile imines and nitrile oxides to exo-C=N bonds for spiro compound synthesis. The research area covers reactions of both saturated and unsaturated dipolarophiles, monocyclic and polycyclic molecules, as well as compounds containing one to three heteroatoms, with special emphasis on systems containing biologically significant heterocyclic pharmacophores. Recent advances in reaction techniques, such as microwave and ultrasonic activation, as well as one-pot and diffusion protocols, are also mentioned.

New stable [6,6]-closed cycloadducts, fulleropyrazolines containing aryl, hetaryl, trifluoromethyl, and other substituents in the five-membered ring, have been obtained by the 1,3-dipolar cycloaddition of nitrile imines to C60. Two methods of generating nitrile imines in situ have been used, the dehydrohalogenation of the corresponding hydrazonoyl halides by the action of triethylamine and the thermal decomposition of 2,5-diaryltetrazoles.

Treatment of 1‐chlorohydrazones (IIa‐c) with triethylamine gave fused ring 1,2,4‐triazoles arising from an intramolecular cycloaddition of the intermediate nitrile imines (IIIa‐c). This reaction was not observed in the case of one compound (IId) bearing an unactivated nitrile group.

Stereoconvergent and stepwise 1,3-dipolar cycloadditions of nitrile oxides and nitrile imines

An efficient [3 + 2] cycloaddition of in situ generated nitrile imines with enamides has been established. A wide range of functionalized pyrazoline derivatives (53 examples) were obtained in moderate to good yields (up to 96%) under very mild conditions. This protocol features broad substrate scope, good functional group tolerance, and operational simplicity. Practical transformation of the products into useful pyrazoles via a one-pot process and the scalability of this protocol highlight the utility of this synthetic methodology.

A novel one-pot two-step process for the preparation of 1,3,4-triarylpyrazoles is disclosed. This process involves a 1,3-dipolar cycloaddition reaction of alkenyl isoxazoles with nitrile imines generated in situ, followed by SnCl2-promoted aromatization/elimination reaction to give a range of 1,3,4-triarylpyrazoles in a fully regioselective manner. This protocol features mild reaction conditions, easily available raw materials, and excellent regioselectivity.

For Abstract see ChemInform Abstract in Full Text.

An approach for the construction of 5‐trifluoromethyl‐1,4‐dihydro‐1,2,4‐triazines has been developed via base‐mediated [3+3] cycloaddition of in‐situ generated nitrile imines and CF3‐substituted imidoyl sulfoxonium ylides. The metal‐free protocol is characterized by readily available starting materials, mild conditions, a broad substrate scope, high efficiency, good synthetic prospect, and scalability.magnified image

We have developed a versatile strategy to access dihydropyrazoles in highly enantioenriched form. Dipolar cycloaddition of electron-deficient acceptors and in situ-generated nitrile imines proceeds with high regio- and enantioselectivity using 10 mol % chiral Lewis acid catalyst. A variety of dihydropyrazoles that incorporate functionality for further manipulation have been prepared.

A wide range of substituted spiro‐pyrazoline derivatives containing the pyrrolidinone core have been prepared by alkalic treatment of 3‐benzylidene succinimides and nitrile imines. All reactions proceeded under mild conditions and the products were isolated by column chromatography in good yields with high diastereoselectivity. Furthermore, this method featured several advantages such as good functional group tolerance and simple scalability.

After the feasibility of the 1,3-dipolar cycloaddition reaction between nitrile imines and exfoliated graphene by density functional theory calculations was proved, very few-layer graphene was effectively functionalized using this procedure. Hydrazones with different electronic properties were used as precursors for the 1,3-dipoles, and microwave irradiation as an energy source enabled the reaction to be performed in a few minutes. The anchoring of organic addends on the graphene surface was confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis. Ultraviolet photoelectron spectroscopy (UPS) was used to measure the work function and band gap of these new hybrids. Our results demonstrate that it is possible to modulate these important electronic valence band parameters by tailoring the electron richness of the organic addends and/or the degree of functionalization.