E. V. Babaev

Application of simulated annealing approach for structure solution of molecular crystals from X-ray laboratory powder data

Abstract Simulated annealing approach was successfully applied to solve three unknown molecular structures from X-ray laboratory powder data using a priory known structural fragments. Some possible developments of the method are discussed.

Novel route to b-fused thiazoles starting from a 2-chloro-1-phenacylpyridinium salt and KSCN. Crystal structures of thiazolo- and oxazolo[3,2-a]pyridinium thiocyanates

Abstract Reaction of 2-chloro-1-phenacylpyridinium bromide 1a with KSCN led to 2-amino-thiazolo[3,2-a]pyridinium salts 4a,b thus opening a novel route to fused thiazoles. In reaction with KSCN oxazolo[3,2-a]pyridinium perchlorate 2a was converted to thiocyanate 2b . Crystal structures of thiocyanates 2b and 4b were determined.

An Improved Synthesis of Some 5-Substituted Indolizines Using Regiospecific Lithiation

Various 2-substituted indolizines can be directly and selectively lithiated in the 5 position and subsequent reactions with different electrophiles lead to some novel classes of indolizines. In particular, previously unknown 5-formyl- and 5-iodoindolizine have been prepared by this way and the molecular structure of 5-formyl-2-phenylindolizine was confirmed by X-Ray analysis. The reactivity of the 5-CHO- and 5-COPh groups toward some nucleophiles has been examined, and some additional classes of derivatives (oximes and alcohols) have been obtained. The possibility of Suzuki cross-coupling of 5-iodoindolizines and boronic acids was proven.

Tris(1-phenacyl-2-pyridone) Hydroxonium Tetrafluoroborate, a Hydrogen-Bonded Complex

The hydrolytic cleavage of 2-phenyloxazolo[3,2-a]pyridinium tetrafluoroborate results in the formation of the title tris(l-phenacyl-2-pyridone) hydroxonium tetrafluoroborate complex, 3C13H11NO2.H3O+.BF4-. The structure is built up from hydrogen-bonded cations and disordered BF4~ anions. The strong hydrogen bonding causes considerable redistribution of electron density in the pyridone moiety.

Efficient synthesis of 5-substituted 2-aryl-6-cyanoindolizines via nucleophilic substitution reactions.

2-Aryl-6-cyano-7-methyl-5-indolizinones were successfully converted into 2-aryl-5-chloro-6-cyano-7-methylindolizines. The obtained 5-chloroindolizines readily underwent nucleophilic substitution at position 5 leading in high yields to novel 5-functionalised indolizines.

Heterocyclic Compounds with a Bridge Nitrogen Atom. 14. Cycloaddition of Acetylenedicarboxylic Acid Ester to 2-Chloro-N-phenacylpyridinium Ylide. Crystal Structure of Dimethyl Ester of 5-Chloro-3-(p-nitrobenzoyl)indolizine-1,2-dicarboxylic Acid

Derivative of 5-chloroindolizine is formed in the reaction of 2-chloro-1-(p-nitrophenacyl)pyridinium ylide with acetylenedicarboxylic acid dimethyl ester, the structure of which was demonstrated by X-ray diffraction analysis. According to data of 1H NMR and mass spectra indolizine obtained undergoes an unusual intramolecular cyclization with the formation of benz[e]cycl[3.3.2]azine nucleus.

New mesoionic systems of the azolopyridine series. 1. Synthesis and structures of thiazolo[3,2-a]pyridinium 2-thiolates

A procedure was developed for the synthesis of representatives of the previously unknown bicyclic mesoionic thiazolo[3,2-a]pyridinium 2-thiolate system by the reaction of 2-X-N-phenacylpyridinium salts (X = Cl, SMe) with CS2 in the presence of Et3N. The three-dimensional structure of 3-(p-nitrobenzoyl)thiazolo[3,2-a]pyridinium 2-thiolate was established by X-ray diffraction analysis.

NMR Spectra of indolizines and their σ complexes

New and previous data on the1H and13C NMR spectra of indolizines with electron-withdrawing groups at C(1), C(3), C(6), and C(8) obtained in our laboratory are reviewed. The chemical shifts in the13C NMR spectra were compared with the total atomic charge values calculated by the MNDO method. Feasibility was demonstrated for the use of PMR spectroscopy to identify isomers for pairs of 1(3)- and 6(8) -substituted indolizines and to establish the protonation site of such compounds. Evidence was obtained for the unexpected ipso protonation in 3-substituted indolizines. The spectral properties of cationic and anionic sigma complexes involving indolizines were discussed.

RING CLEAVAGE REACTIONS IN THE SERIES OF AZOLOAZINES WITH A BRIDGING NITROGEN ATOM (REVIEW)

Extensive data on the opening reactions of both the five- and the sir-membered fragments of the bicyclic structures of azoloazines with a bridging nitrogen atom (i.e., the aza, oxa, and thia heteroanalogs of indolizine), including the reactions leading to recyclization, are categorized systematically for the first time. A universal model is proposed for classification of the ring opening processes in azoloazines (according to the principle of endo or exo opening in heteroarenes), and an attempt is made to relate the direction of ring opening in heteroarenes to alternation (or loss of alternation) in the fragments of the heterocyclic ring.

Dakin-West Trick in the Design of Novel 2-Alkyl(aralkyl) Derivatives of Oxazolo[3,2-a]pyridines

A series of previously unavailable derivatives of 2-alkyl- and 2-benzylderivatives of oxazolo[3,2-a]pyridines III were obtained via tandem ring opening and ring closure from stable mesoionic 3-acyloxazolo[3,2-a]pyridinium-2-olates I. The key intermediates of this tandem transformation are N-(b-oxoethyl)pyridones-2 II obtained by Dakin-West acylation of (pyridone-2-yl-1)acetic acid. An example of further utilization of this strategy is illustrated by preparation of unknown 2-benzylimidazo[1,2-a]pyridine from the salt I and ammonia.