Nikolay E. Shevchenko

Stereoelectronic umpolung: converting a p-donor into a σ-acceptor via electron injection and a conformational change.

The para-OMe functional group, usually regarded as a conjugative p-donor, acts as an efficient hyperconjugative σ-acceptor in reductive cycloaromatization reactions. This apparent reversal of electronic properties is associated with a conformational change that aligns the σ*(O-C) orbital with the adjacent aromatic system and provides stabilization to the developing negative charge in the TS of the dianionic cyclization of enediynes. The chameleonic character of the OMe group illustrates the important role of negative hyperconjugation in anionic processes.

Synthesis of methylthiosubstituted heterocycles using the complex of trifluoromethanesulfonic anhydride with dimethyl sulfide

A new method was developed for the electrophilic introduction of methylthio group into a series of aromatic heterocyclic compounds through the hetaryl(dimethyl)sulfonium salts formed in the course of the reaction of the respective heterocycles with the complex of dimethyl sulfide and trifluoromethanesulfonic anhydride. By demethylation with triethylamine it was possible to obtain the methylthio-substituted heterocycles.

Synthetic potentialities of sulfonylsulfonium salts: A new approach to the preparation of disulfonium dications

A new efficient method for the generation of disulfonium dications whose subsequent hydrolysis selectively affords monosulfoxides was developed based on the oxidation of bissulfides by trifluoromethanesulfonic anhydride.

Electronic structure and reactivity of S—S dications

The electronic structure and reactivity of some S—S dications were studied at the MP2/6-31G* level of theory. The results obtained indicate a stepwise electrophilic addition of disulfonium dication moiety to the double C=C bond to be the preferable mechanism.

Stereochemistry of addition of disulfonium dications to alkenes

Stereochemistry of the addition of a cyclic disulfonium dication generated from 1,4-dithiane to alkenes was studied. The reaction is nonstereospecific, which can be attributed to a stepwise mechanism.

Synthesis and structural study of 3-phenyl-6,7,8,9-tetrahydrocyclopenta[ a ]naphthalene-containing ansa -complexes of zirconium

The zirconium rac- and meso-complexes of the ansa-type that contain a 3-phenyl-6,7,8,9-tetrahydrocyclopenta[a]naphthalene fragment and a dimethylsilylene bridge are synthesized. The compounds obtained are characterized by NMR spectroscopy; the structure of rac-complex is studied by X-ray diffraction, which maked it possible to evaluate the steric availability of the zirconium center in the corresponding catalysts for the olefin polymerization.

CHAPTER 7.2:Organochalcogen Multication Species

1,2-dications – unique compounds with two cationic centers located at two directly connected atoms have unusual structure and reactivity. Despite the extremely strong electrostatic repulsion of the two positive charges, these compounds often possess remarkable kinetic stability.1 The rapid developme...