Valerij A. Nikolaev

Chemistry of diazocarbonyl compounds: XXV. Comparative photochemistry of diazo compounds and sulfur ylides of the 1,3-dioxane-4,6-dione series

Photochemical decomposition of 2,2-dialkyl-5-diazo-1,3-dioxane-4,6-diones in the presence of pyridine, methanol, or dimethyl sulfide as carbene traps involves mainly the Wolff rearrangement which is likely to follow a concerted pattern, while the yield of the “carbene” products does not exceed 27–28%. No carbene intermediates are formed in the photolysis of the corresponding dioxo sulfonium ylides under analogous conditions, and the main photochemical process is 1,2-methyl shift (Stevens rearrangement), followed by photochemical transformations of the primary products according to the Norrish type II pattern.

Chemistry of diazocarbonyl compounds: XXX. Development of a synthetic approach to pyridazine structure via wittig reaction of fluoroalkyl-containing diazo keto esters

Abstract3,4,6-Trisubstituted pyridazines were synthesized from fluoroalkyl-containing diazo keto esters in three steps along two different reaction sequences: (1) Wittig, Staudinger, and diaza-Wittig and (2) Staudinger, Wittig, and diaza-Wittig. According to the first of these with the initial Wittig reaction, the yield of the target 4-fluoroalkyl-substituted pyridazines is almost twice as large as in the reaction sequence involving the corresponding N-phosphanylidene derivatives as intermediates. In both sequences, the final steps (synthesis of vinylphosphazenes and the subsequent diaza-Wittig reaction) occurred as a tandem process, and intermediate vinylphosphazenes could not be isolated. Non-fluorinated diazo keto esters and the respective phosphazenes failed to react with alkoxycarbonylmethylidene(triphenyl)phosphoranes under the same conditions.

Influence of an Internal Trifluoromethyl Group on the Rhodium(II)-Catalyzed Reactions of Vinyldiazocarbonyl Compounds

Incorporation of a trifluoromethyl group into the structure of 4-(alkoxycarbonyl)vinyldiazocarbonyl compounds greatly decreases the tendency of the carbenoid intermediates formed during Rh(II)-catalyzed reactions to undergo intermolecular processes. Instead, they are prone to experience intramolecular [1,5]- and [1,3]-electrocyclizations to produce reactive cyclopropenes and furans, and these are capable of further transformations.

Chemistry of Diazocarbonyl Compounds: XX. Chemoselective O-Alkylation of 3(2H)-Oxoisothiazole-1,1-dioxides

Catalytic decomposition of diazoacetylacetone, ethyl diazoacetate, and diethyl diazomalonate effected by dirhodium tetraacetate in the presence of 3(2H)-oxoisothiazole-1,1-dioxides resulted in O-alkylation of amide carbonyl of the heterocycle affording the corresponding enol ethers in preparative yield. The reaction occurred chemoselectively. The 1,3-dicarbonyl derivatives of 3-hydroxyisothiazole-1,1-dioxides obtained in contrast to analogous N-alkylated products are not enolized in solutions and in crystals.

Less reactive dipoles of diazodicarbonyl compounds in reaction with cycloaliphatic thioketones - First evidence for the 1,3-oxathiole-thiocarbonyl ylide interconversion

Summary Acyclic diazodicarbonyl compounds react at room temperature with cycloaliphatic thioketones, e.g. 2,2,4,4-tetramethyl-3-thioxocyclobutanе-1-one and adamantanethione, via a cascade process in which the key step is a 1,5-electrocyclization of the intermediate thiocarbonyl ylide leading to tetrasubstituted spirocyclic 1,3-oxathioles. The most reactive diazodicarbonyl compound was diazoacetylacetone. In the case of dimethyl diazomalonate competitive 1,3-electrocyclization yielded the corresponding thiirane at elevated temperature, which after spontaneous desulfurization produced a tetrasubstituted alkene. To explain the observed temperature dependence of the main reaction product type obtained from dimethyl diazomalonate and 2,2,4,4-tetramethyl-3-thioxocyclobutanе-1-one as well as to verify reversibility of the thiocarbonyl ylide and 1,3-oxathiole interconversion, the calculations of the energy profile for the transformation of 1,3-oxathiole to alkene were performed at the DFT PBE1PBE/6-31G(d) level.

Chemistry of diazocarbonyl compounds: XXVII. Thermolysis and photolysis of diazirines, derivatives of 1,3-dioxane-4,6-dione

Photolysis of diazirines, 1,3-dioxane-4,6-dione derivatives, occurs in the presence of methanol or dimethyl sulfide as carbene traps without a formation of carbene intermediates. It was established for the first time that the thermolysis and photolysis of diazirines from the 1,3-dioxane-4,6-dione series led mainly to Wolff rearrangement with a subsequent formation of 5-oxo-1,3-dioxolane-4-carboxylic acids or their derivatives. The data obtained show that the α-oxodiazirines are the key intermediates in the photolysis and Wolff rearrangement of α-diazocarbonyl compounds.

Stereochemical aspect of the intramolecular diaza-wittig reaction

Reactions of fluoroalkyl-substituted vinyl diazo carbonyl compounds with triphenylphosphine are accompanied by spontaneous intramolecular cyclization of the initially formed phosphazene, and pyridazines are formed as a result of tandem process [1–3]. However, no analogous transformations occur with fluorine-free vinyl diazo carbonyl compounds. Taking into account that fluoroalkyl-containing vinyl diazo carbonyl compounds are usually characterized by cis configuration* of the double bond [1, 4] and that their fluorine-free analogs are trans isomers [5, 6], the most probable reason for their different reactivities is different arrangement of functional groups (CO2Alk, CN2) at the double C=C bond. The goal of the present work was to compare chemical transformations of diastereoisomeric fluoroalkyl-containing and fluorinefree phosphazenes derived from vinyl diazo carbonyl compounds.

Decomposition of 2-diazo-1,3-diketones: Stereocontrol of the mechanism.

Abstract Complete “inversion” of alkyl to aryl migratory tendency in Wolff rearrangement of diazodiketones with Z,Z-conformation was revealed by comparing decomposition behavior of the planar diazo tetralindione with its twisted acyclic analogues. Dramatic change in regioselectivity of this process was accompanied by the appearance of X-H insertion products in the reaction mixture. These data suggest that on the way from planar cyclic to highly skewed acyclic aroylacyldiazomethanes concerted Wolff rearrangement turns into a carbenic process.

Diazo Strategy for the Synthesis of Pyridazines: Pivotal Impact of the Configuration of the Diazo Precursor on the Process

Phosphazenes of vinyldiazocarbonyl compounds having cis stereochemistry of the functional groups on the vinyl bond readily produce pyridazines by a diaza-Wittig process, whereas their counterparts with trans configuration remain intact under similar reaction conditions. Upon UV irradiation trans-phosphazenes furnish pyridazines through a tandem trans-to-cis isomerization followed by intramolecular cyclization. At elevated temperatures trans-(triphenyl)phosphazenes dissociate to give the initial vinyldiazo compounds, which produce pyrazoles in high yields. The first theoretical study on the mechanism of the diaza-Wittig process by DFT calculations at the M06-2X/6-31G(d) level of theory suggest that for the cis-phosphazenes a rapid tandem [2+2] cycloaddition/cycloelimination process with low energy barriers is preferred over trans isomers.

Modern Trends of Organic Chemistry in Russian Universities

This review is devoted to the scientific achievements of the departments of organic chemistry in higher schools of Russia within the past decade.