Sergei F. Vasilevsky

Dissecting alkynes: full cleavage of polarized C≡C moiety via sequential bis-Michael addition/retro-Mannich cascade.

The reaction of diaryl ketoalkynes with 1,2-diamino ethane leads to the full scission of the triple bond with the formation of acetophenone and imidazoline fragments. In this transformation, one of the alkyne carbons undergoes formal reduction with the formation of three C-H bonds, whereas the other carbon undergoes formal oxidation via the formation of three C-N bonds (one π and two σ). Computational analysis confirmed that the key fragmentation step proceeds via a six-membered TS in a concerted manner. Both amines are involved in the fragmentation: the N-H moiety of one amine transfers a proton to the developing negative charge at the enolate oxygen, while the other amine provides direct stereoelectronic assistance to the C-C bond cleavage via a hyperconjugative n(N) → σ*(C-C) interaction.

An Unexpected Rearrangement That Disassembles Alkyne Moiety Through Formal Nitrogen Atom Insertion between Two Acetylenic Carbons and Related Cascade Transformations: New Approach to Sampangine Derivatives and Polycyclic Aromatic Amides

This work analyzes multiple new reaction pathways which originate from intramolecular reactions of activated alkynes with the appropriately positioned multifunctional hemiaminal moiety. Combination of experimental substituent effects with Natural Bond Orbital (NBO) analysis revealed that alkyne polarization controls partitioning between these cascades. A particularly remarkable transformation leads to the formation of six new bonds at the two alkyne carbons due to complete disassembly of the alkyne moiety and formal insertion of a nitrogen atom between the two acetylenic carbons of the reactant. This reaction offers a new synthetic approach for the preparation of polycyclic aromatic amides with a number of possible applications in molecular electronics. Another of the newly discovered cascades opens access to substituted analogues of Sampangine alkaloids which are known for their antifungal and antimycobacterial activity against AIDS-related opportunistic infection pathogens.

Synthesis and Properties of Acetylenic Derivatives of Pyrazoles

Publisher Summary This chapter discusses the compounds that have two important functionalities in the same molecule: acetylene (69MI2; 78MI3) and pyrazole (67MI1; 84MI2; 96MI1). It demonstrates the versatile and frequently unexpected nature of acetylene, and pyrazole reactions. The chapter discusses the synthesis of acetylenylpyrazoles, chemical and biological properties of acetylenylpyrazoles, structure, and spectra. Acetylenyl pyrazoles are highly valuable intermediates because a triple bond is susceptible to nucleophilic, electrophilic, radical, and cycloaddition reactions, and because the terminal acetylenes display an unusually high CH acidity that can be used for both functionalizing and building up C–C bonds. Acetylenes occupy a central place in the synthetic organic chemistry because of their availability and the great versatility of their transformations. Because of their stability, acid–base equilibria, coordination behavior, pharmaceutical properties, and easy preparation pyrazoles are among the most used heterocycles.

Copper(II) thenoyltrifluoroacetonate as acceptor matrix in design of heterospin complexes

Abstract Coordination compounds of Cu(II) thenoyltrifluoroacetonate with stable 2-imidazoline nitroxides were synthesized; their structure and magnetic properties were investigated. The complex with a pyrazole nitroxide was isolated as two polymorphous modifications. For both polymorphs, the structure is comprised of Cu(tta)2(NITPz1,3Me) molecules shaped as nearly regular pyramids with four O atoms of the two tta ligands lying at the base. The solid polymorphs are constructed from formal binuclear fragments appearing when the pyramid bases of two neighboring molecules approach each other forming rather short contacts Cu–S (3.848 and 3.596 A), due to which the polymorphs differ considerably in magnetic properties. In the modification with longer Cu–S distances, there are no exchange interactions between the paramagnetic centers of the neighboring Cu(tta)2(NITPz1,3Me) molecules whereas in the polymorph with shorter Cu–S distances the interactions are significant and analogous to those in real dimer molecules based on the Cu(AcO)2 matrix with a nitroxide.

Urea as an organic solvent and reagent for the addition/cyclization/fragmentation cascades leading to 2-R-7H-dibenzo[de,h]quinolin-7-one analogues of Aporphinoid alkaloids

Molten urea serves both as a solvent and a reagent for the one-pot addition/cyclizations/fragmentation cascade which converts peri-alkynyl-9,10-anthraquinones into 2-R-7H-dibenzo[de,h]quinolin-7-ones – substituted analogues of Aporphinoid alkaloids.

A one-pot synthesis of 1-arylalka-1,3-diynes by sequential acetylene zipper and Sonogashira reactions

1,3-Diynes, formed in situ by base-induced acetylene zipper reactions, following anion quenching with water, undergo smooth Sonogashira-type couplings with functionalized aryl iodides, to give good overall yields of 1-arylalka-1,3-diynes.

Heterocyclization of vic-Substituted Hydroxamic Acid Salts of Acetylenylpyrazoles: A New Procedure for the Preparation of Pyrazolo[3,4-c]pyridin-7-ones

Procedures for the preparation of 5-substituted pyrazolo[3,4-c]pyridin-7-ones and 5-substituted 6-hydroxypyrazolo[3,4-c]pyridin-7-ones have been developed based on heterocyclization of vic-acetylenylpyrazolylhydroxamic acids under the influence of copper(I) salts in dimethylformamide or with organic bases in butanol or methanol.

Acetylenic compounds as intermediates in heterocyclic synthesis: Reaction of 1-acetylenylanthraquinones with hydrazine

Abstract Reaction of 1-acetylenic derivatives of anthraquinone with hydrazine affording substituted 4 H -anthra [9, 1-cd] -1,2-diazepin-8-ones and 7H-dibenzo [de, h] quinolin-7-ones is reported.

On the diverse outcomes of base-induced cyclisations of 2-alkynylphenylhydroxamic acids

Base-induced cyclisations of 2-alkynylphenylhydroxamic acids occur by attack of nitrogen onto the alkyne group in either exo or endo fashions to give the corresponding isoindol-1(2H)-ones or 1(2H)-isoquinolinones depending upon the alkyne substituent.

Conformational Flexibility of Fused Tetracenedione Propellers Obtained from One-Pot Reductive Dimerization of Acetylenic Quinones

Reductive dimerization of acetylenic anthraquinones provides synthetic access to flexible nonplanar polyaromatics with a tetracenedione core. In solution, these nonplanar, contorted polycycles exist as equilibrating mixtures of two symmetric conformers. The fused tetracenediones are easily reduced and exhibit rich electrochemical behavior.