Vasiliy G. Shtamburg

Chiral ureas with two electronegative substituents at 1-N: An unusual case of coexisting pyramidal and almost planar 1-N atoms in the same crystal†

XRD studies of structure of N-acetoxy-N-methoxyurea and N,N-bis(methoxycarbonyl)-N-methoxyimide have revealed that in N-methoxy-N-X-ureas (X = OAc, Cl, OMe, N(+)C(5)H(5)) the additional shortening of N-OMe bond took place, which arising from an n(O(Me))-sigma*(N-X) anomeric orbital interaction. XRD studies of N-chloro-N-ethoxyurea crystal have revealed the presence of two kinds of anomeric nitrogen configuration in the O-N-Cl group in the form of a pyramidal configuration and a planar configuration for same 1-N nitrogen atom. XRD studies of N-4-chlorobenzoyloxy-N-ethoxyurea have revealed that the degree of pyramidality of the 1-N nitrogen in N-aroyloxy-N-alkoxyureas is tuned by orientation of benzoyl group with respect to the N-O bond, which in turn depends of size of N-alkoxy group.

Single-stage synthesis of 3-hydroxy- and 3-alkoxy-5-arylimidazolidine-2,4-diones by reaction of arylglyoxal hydrates with N -hydroxy- and N -alkoxyureas

Arylglyoxal hydrates interact with N-alkoxyureas and N-hydroxyurea in acetic acid with selective formation of 3-alkoxy-5-arylimidazolidine-2,4-diones and 5-aryl-3-hydroxyimidazolidine-2,4-diones, respectively. The structures of 3-methoxy-5-phenylimidazolidine-2,4-dione, 3-ethoxy-5-phenylimidazolidine-2,4-dione, and 3-butoxy-5-(4-chlorophenyl)imidazolidine-2,4-dione were studied by X-ray structural analysis.

A new synthesis of N-alkoxyaminopyridinium salts

It was found, that methyl N-alkoxy-N-chlorocarbamates interaction with 4-dimethylaminopyridine was overall manner of synthesis of 1-N-alkoxyaminopyridinium chlorides. New1-N-n-octyloxyamino-4-dimethylaminopyridinium and 1-Nbenzyloxyamino-4-dimethylaminopyridinium chlorides have been synthesized by the methyl N-chloro-N-n-octyloxycarbamate and methyl N-benzyloxy-N-chlorocarbamate interaction with 4-dimethylaminopyridine in acetonitrile solution, respectively. The novel synthesis of 1-N-alkoxyaminopyridinium chlorides by reaction of N-алкоксимочевин alkoxy-N-(1pyridinium)ureas chlorides ammonolysis has been proposed. 1-N-Methoxyamino-4-dimethylaminopyridinium chloride and 1N-n-butyloxyamino-4-dimethylaminopyridinium chloride have been synthesized by reaction of N-1-4-dimethylaminopyridiniumN-methoxyurea chloride and N-n-butyloxy-N-(1-4-dimethylaminopyridinium)urea chloride, respectively, with excess of ammonia in ethanol solution at room temperature during few minutes. Evidently, the carbamoyl proton elimination by ammonia causes further formation 1-N-alkoxy-4-dimethylaminopyridinium chlorides and HNCO. It is new example of decarbamoylation of N-alkoxy-N-(1-pyridinium)ureas salts. 1-N-Metoxyamino-4-dimethylaminopyridinium fluoride has been synthesized by N-1-(4-dimethylamino)pyridinium-N-methoxyurea chloride reaction with potassium fluoride in acetonitrile. Probably, in this reaction N-1-(4-dimethylamino)pyridinium-N-methoxyurea caution decarbamoylation occurs after the chloride anion exchange on fluoride anion. 1-N-Alkoxyaminopyridinium salts structures have been confirmed by data of NMR 1H spectra, NMR 13C spectra and mass-spectra.

Synthesis and Structure of New N-Alkoxy-N-(1-pyridinium)urea Chlorides

New N-[1-(4-amino)pyridinium]-N-methoxyurea chloride, N-[1-(2-amino)pyridinium]-N-methoxyurea chloride and their analogs were synthesized by N-alkoxy-N-chloroureas reaction with the proper pyridines in acetonitrile or ether solution by improved procedure. XRD study of N-[1-(4-amino)pyridinium]-N-methoxyurea and N-[1-(2-amino)pyridinium]-N-methoxyurea revealed the elongation of N-N + bonds and some shortening of MeO-N bonds, qunonoid deformation of pyridine rings compare to it unsubstituted analog. The substantial pyramidality of central nitrogen atom in O-N-N + moiety and N-C carbamoyl bonds difference were established too. The structure summary of N-alkoxy-N-(1-pyridinium)ureas salts and other derivatives of 1-(N-alkoxyamino)pyridinium salts has been done.

UNUSUAL SPONTANEOUS α→β ISOMERIZATION OF UNSYMMETRICAL BENZOINS. PRODUCTS AND THEIR STRUCTURE

The article describes reactions of a series of arylglyoxals with 2-methylfuran and furfural N,N -dimethylhydrazone. These interactions lead selectively to unsymmetrical benzoins. It was found that some of the benzoins underwent spontaneous thermal α→β benzoin isomerization in situ . The rearrangement took place in the absence of bases, which could be explained by two structural factors: (a) the presence of a halogen atom in the para -position of the aryl moiety, and (b) the presence of the Me 2 NN=CH-substituent in the 5-position of the furan ring. The proposed mechanism of the thermal rearrangement starts with an intramolecular protonation of the carbonyl oxygen by the hydroxyl. This leads to the 1,2-hydride shift onto the carbonyl group, finally yielding β-benzoins. The S -isomer of 2-hydroxy-2-(4’’-chlorophenyl)-1-(5’- N,N -dimethylhydrazonylfuryl-2’)-ethanone-1 was isolated by crystallization, and its structure was confirmed by the X-ray crystallography.