Victor A. Korolev

A New Type of Donor–Acceptor Cyclopropane Reactivity: The Generation of Formal 1,2‐ and 1,4‐Dipoles

A new type of donor-acceptor cyclopropane reactivity has been discovered. On treatment with anhydrous GaCl3 , they react as sources of even-numbered 1,2- and 1,4-dipoles instead of the classical odd-numbered 1,3-dipoles due to migration of positive charge from the benzyl center. This type of reactivity has been demonstrated for new reactions, namely, cyclodimerizations of donor-acceptor cyclopropanes that occur as [2+2]-, [3+2]-, [4+2]-, [5+2], [4+3]-, and [5+4]-annulations. The [4+2]-annulation of 2-arylcyclopropane-1,1-dicarboxylates to give polysubstituted 2-aryltetralins has been developed in a preparative version that provides exceedingly high regio- and diastereoselectivity and high yields. The strategy for selective hetero-combination of donor-acceptor cyclopropanes was also been developed. The mechanisms of the discovered reactions involving the formation of a comparatively stable 1,2-ylide intermediate have been studied.

Donor–Acceptor Cyclopropanes as 1,2-Dipoles in GaCl3-Mediated [4 + 2]-Annulation with Alkenes: Easy Access to the Tetralin Skeleton

A new process for (4 + 2)-annulation of donor-acceptor cyclopropanes (DACs) with unsaturated compounds in the presence of anhydrous GaCl3 has been developed. In this process, DACs act as sources of formal 1,2- and 1,4-dipoles to give polysubstituted tetralins in high yields and with high regio- and diastereoselectivity. Alkenes with both aryl and alkyl substituents at the double bond undergo this reaction equally readily. A most likely mechanism of the reaction has been proposed. It involves preliminary generation of a key 1,2-dipolar gallium complex and its subsequent participation in annulation with an alkene.

[4 + 2] Annulation of Donor–Acceptor Cyclopropanes with Acetylenes Using 1,2-Zwitterionic Reactivity

A new process for the [4 + 2] annulation of donor-acceptor cyclopropanes with acetylenes under the effect of anhydrous GaCl3 using 1,2-zwitterion reactivity was elaborated. The reaction opens access to substituted dihydronaphthalenes, naphthalenes, and other fused carbocycles. The direction of the reaction can be efficiently controlled by temperature.

Pot, atom and step-economic (PASE) synthesis of medicinally relevant spiro[oxindole-3,4′-pyrano[4,3-b]pyran] scaffold

Abstract Fast (3 min) pot, atom and step economics (PASE) potassium fluoride catalyzed multicomponent reaction of isatins, malononitrile and 4-hydroxy-6-methyl-2H-pyran-2-one results in efficient formation of substituted spirooxindole-3,4′-pyrano[4,3-b]pyrans in 92–96% yields. The developed ‘on-solvent’ approach to the substituted spirooxindole-3,4′-pyrano[4,3-b]pyrans – the pharmacologically perspective substances with known antiviral, antileishmanial, anticonvulsant and anti-HIV activities – is beneficial from the viewpoint of diversity-oriented large-scale processes and represents fast and environmentally benign synthetic concept for the multicomponent reactions strategy.

Cascade Cleavage of Three-Membered Rings in the Reaction of D–A Cyclopropanes with 4,5-Diazaspiro[2.4]hept-4-enes: A Route to Highly Functionalized Pyrazolines

A new cascade process for reactions of donor-acceptor cyclopropanes (DACs) with spiro[cyclopropanepyrazolines] in the presence of EtAlCl2 or Ga halides is reported. The action of a Lewis acid results in DAC activation and addition of the carbocationic intermediate to the azocyclopropane system of the pyrazoline with opening of the second three-membered ring and addition of a halide anion from the Lewis acid. A specific feature of this process is that one activated cyclopropane ring activates another one, and depending on the component ratio, the process can involve two DAC molecules and one pyrazoline molecule or one DAC molecule and two pyrazoline molecules. The process is tolerant to various functional groups and occurs with a wide range of substrates to give polyfunctionalized structures based on a 2-pyrazoline moiety.

Cascade assembling of pyrazolin-5-ones and benzylidenemalononitriles: the facile and efficient approach to medicinally relevant spirocyclopropylpyrazolone scaffold

Abstract A new cascade reaction provides a direct transformation of pyrazolin-5-ones and benzylidene-malononitriles by the action of bromine into substituted spirocyclopropylpyrazolones in 60–88% yields. This process can be realized in two variants, namely, (1) by treatment with bromine in the presence of base and (2) by treatment with bromine only with heating. These facile and efficient one-step cascade processes lead to the spirocyclopropylpyrazolone framework, which is present in a perspective class of compounds with prominent pharmacological and physiological activity.