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Two dispiro[cyclopropane-1,3’-bicyclo[3.3.1]nonane-7′,1″-cyclopropanes] were treated with various oxidative systems. The conditions providing mono- or dioxidation of the CH2 groups neighbouring to spiro-annulated cyclopropane moieties to afford the corresponding mono- or diketones were found.

New 8-arylidene-4-cyanotetrahydroquinazoline N-oxides were obtained via the condensation of readily available 4-cyanotetrahydroquinazoline N-oxides with aromatic aldehydes. Some of the synthesized compounds revealed fluorescent properties and moderate cytotoxic activity.

4-Azido-2-methyltetrahydroquinazoline N-oxide cleanly undergoes the copper( i )-catalyzed azide–alkyne cycloaddition (CuAAC) reaction with alkynes to give new conjugates with pyrimidine N-oxide and triazole moieties. Its deoxygenated analogue, 4-azido-2-methyltetrahydroquinazoline, is inert in CuACC process due to the shift of imidoyl azide–tetrazole equilibrium towards the tetrazole tautomer.

5-Aminoisoxazoles bearing 3-positioned electron-withdrawing group react chemoselectively with trifluoroacetyl nitrate (generated from ammonium nitrate and trifluoroacetic anhydride) to give the corresponding 4-nitro derivatives in yields up to 80%. The results were rationalized by computation studies. Several 5-amino-4-nitroisoxazole-3-carboxilic acid derivatives revealed moderate antibacterial activity.

Pyrimidine N-oxide moiety for the first time was used as a heterocyclic core for the construction of π-conjugated molecules with fluorescent properties. For the synthesis of the title compounds a simple two-step protocol starting from readily available 4-fluoro-2-methylpyrimidine N-oxides was elaborated. A series of 17 novel pyrimidine N-oxide derivatives containing various functional substituents and π-conjugated systems of different length were obtained. The title compounds revealed fluorescent properties in visible region, possessing emission maximum up to 575 nm. Deoxygenation of the N-oxide group led to the loss of visible fluorescence. The chemosensor properties towards TFA and a number of metal cations were demonstrated for 3a, the first representative of the title series. Cytotoxic activity against breast adenocarcinoma cell line was found for three pyrimidine N-oxide derivatives 3b,i,n. Pyrimidine N-oxide 3a was shown to possess excellent biocompatibility and capability to enter cells, that makes it a promising structure for development of bioimaging fluorescent probes.

The heterocyclization of gem-dichlorocyclopropanes upon treatment with nitronium triflate in organic nitriles was studied and the influence of the medium on the reaction pathway was shown. While in anhydrous solvent 5-chloroisoxazole was the only product, the admixture with water promoted a three-component heterocyclization affording 4-chloropyrimidine N-oxides. This phenomenon was rationalized using DFT calculations.

Novel N-(1-oxidopyrimidin-4-yl)- and N,N′-bis(1-oxidopyrimidin-4-yl)diamines were prepared from 4-fluoropyrimidine N-oxides and diamines basing on SNAr reaction. One compound from this series possessed antiviral activity against tick-borne encephalitis virus (TBEV).

A convenient approach to novel symmetric bispyrimidine diamines comprises SNAr reactions of 4-fluoropyrimidine N-oxide with alkane-α,ω-diamines with subsequent reduction of N-oxide function. The obtained substances were tested in patch-clamp experiments for the influence on the kainateinduced currents in Purkinje neurons and showed negative modulating effect.

A number of nitrosonium and nitronium salts were probed as reagents for the heterocyclization of 1-bromo-1-fluorocyclopropanes in the presence of organic nitriles to give pyrimidine N -oxides. Nitronium triflate, either preformed or generated in situ from nitric and triflic acids, was shown to be the most efficient reagent for this reaction, affording a mild and convenient procedure for the synthesis of 4-halogenopyrimidine derivatives. X-ray crystallography was used to confirm the ionic structure of nitronium triflate (NO 2 + )(CF 3 SO 3 − ).

An unusual condensation reaction of 2-methyltetrahydroquinazoline N-oxides with aromatic aldehydes was found. The reaction of 4-cyano substituted heterocycles as well as the use of microwave irradiation for 4-morpholinyl substituted heterocycles resulted in the condensation engaging the methylene group of the tetrahydroquinazoline fragment with simultaneous deoxygenation of the N-oxide. A preparative approach towards previously unknown pyrimidine-containing conjugated molecules was developed based on this process.

A skeletal carbenoid rearrangement of the gem-bromochlorospiropentanes in the presence of methyllithium has been studied. The synthetic and mechanistic aspects of this rearrangement as well as the influence of the halogen atom nature on the reaction pathway are discussed.

A series of novel gem-bromofluorospiropentanes were synthesized and investigated in the reaction with methyllithium. Either substitution of the fluorine atom for a methyl group or rearrangement into methylated cyclobutene derivatives occurred under these conditions.

A skeletal rearrangement of dihalogenospiropentanes in the presence of alkyllithium reagents has been systematically studied using a number of gem-dibromospiropentanes. The scope and limitations of this carbenoid rearrangement are outlined and its mechanism is discussed.

A series of 4-fluoropyrimidine 1-oxides, obtained via three-component heterocyclization, was studied under various reduction conditions. An effective preparative method for the synthesis of 4-fluoropyrimidines from readily available starting materials was elaborated. 4-Fluoro-substituted tetrahydroquinazolines and tetrahydroquinazoline N-oxides were demonstrated to be highly reactive in aromatic nucleophilic substitution.