Definitizable extensions of positive symmetric operators in a Krein space

The Friedrichs extension and the Krein extension of a positive operator in a Krein space are characterized in terms of their spectral functions in a Krein space.     

A simple stereoselective one-pot synthesis of C-nucleosides by 1,3-dipolar cycloaddition of chiral azomethine imines prepared in situ

The NH,NH-dihydrocycloadduct 1 (6-chloro-9,9-dimethyl-7,8-dihydro-9H-pyrazolo[4,3-d]tetrazolo[1,5-b]-pyridazine) obtained by the cycloaddition of 2-diazopropane to 6-chlorotetrazolo[1,5-b]pyridazine, is transformed with protected or unprotected carbohydrates 2, 5, 7,9, 11, 13 and 15 in the presence of methyl acrylate ( 3 ) into the corresponding C-nucleosides 4,6,8,10,12,14 and 16 . In this one-pot synthesis two new chiral centers are formed stereoselectively, dependent on the chirality at C-atom next to aldehydo group in the carbohydrate.     

Synthesis and antimycobacterial activity of alkyl 1‐heteroaryl‐1H‐1,2,3‐triazole‐4‐carboxylates

A series of alkyl l‐heteroaryl‐1H‐1,2,3‐triazole‐4‐carboxylates 6a‐u were synthesised in four steps from methyl (Z)‐2‐benzyloxycarbonylarmino‐3‐(dimethylamino)prop‐2‐enoate ( 1 ) and heterocyclic amines 2a‐s. Triazoles 6a‐o were tested against antimycobacterial activity. For the most active compound, n‐pentyl 1‐(6‐phenylpyridazin‐3‐yl)‐1H‐1,2,3‐triazole‐4‐carboxylate ( 6n ), minimum inhibitory concentration 3.13 μg/ml was determined.     

Heterocyclic diazo compounds as starting materials in organic synthesis (review)

Data on the structures and reactions of heterocyclic diazo compounds that lead to the formation of new heterocyclic systems as a result of intra- or intermolecular cyclization and rearrangements are systematized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 579–603, May, 1980.     

Parallel solution-phase synthesis of (Z)-3-(arylamino)-2,3-dehydroalanine derivatives and solid-phase synthesis of fused pyrimidones

N-Protected (Z)-3-(arylamino)-2,3-dehydroalanine esters 5 and 10 were prepared in one step from methyl (Z)-2-acylamino-3-(dimethylamino)prop-2-enoates 3 and 9 and anilines 4 employing a parallel solution-phase synthetic approach. In most cases, analytically pure products 5 and 10 were obtained. On the other hand, a three-step parallel solid-phase synthesis of 2-acetylamino-4H-azino[1,2-x]pyrimidin-4-ones 15 via the polymer-bound methyl (Z)-2-acetylamino-3-(dimethylamino)prop-2-enoate (12) was also developed.     

A new approach for the synthesis of fused pyrroles. The synthesis of acyl substituted pyrrolo[1,2-x]azines

N-Acetonyl- and N-phenacyl quaternary salts of α-methyl substituted heterocycles 16, 17, 21, 23 and 26 were converted with DMFDMA into the corresponding 3-acylpyrrolo[1,2-a]pyridine 18 , 7-benzoylpyrrolo-[1,2-c]pyrimidine 22 , and 6-benzoylpyrrolo[1,2-a]pyrazine derivatives 24 and 27 . A concurrent reaction produced methyl and phenyl substituted pyrrolo[1,2-x]azines 19, 20, 25 and 28 .     

Photoelectron spectroscopy of heterocycles. Azaindenes and azaindolizines

The HeI photoelectron (PE) spectra of indole ( 1 ), benzimidazole ( 2 ), indazole ( 3 ), 3-chloro-indazole ( 4 ), imidazo[1,2-b]pyridazine ( 5 ), 6-chloroimidazo[1,2-b]pyridazine ( 6 ), 2-phenyl-imidazo[1,2-b]pyridazine ( 7 ), 2-phenyl-6-chloroimidazo[1,2-b]pyridazine ( 8 ), tetrazolo[1,2-a]-pyridine ( 9 ) and 8-cyanotetrazolo[1,5-a]pyridine ( 10 ) have been recorded. The spectra of 2–10 are of special interest for studying lone pair interactions. The assignment of the PE spectra submitted here, conjointly with the electronic structure of the studied compounds is discussed on the basis of molecular orbital calculations.     

Pyridazines. LXV. Reactions of some I-phenacylazolopyridazinium halides with 2,3-diphenylcyclopropenone, -thione,or hydrazine

I-Phenacylazolopyridazinium bromides reacted with 2,3-diphenylcyclopropenone or -thione in the presence of triethylaminc to give 3,4,6-triphenyl-2-pyrone or -2-thiopyrone and the corresponding azolopyridazine. Quaternized azolopyridazines reacted with hydrazine to give either 3,6-diphenylpyridazine and the corresponding azoloazine or hy ring opening of the azine part to give 1-methyl-2-(pyrazolyl-5′)imidazole.     

Allenes and transition metals: a diverging approach to heterocycles

[reaction: see text] An alkynyl allene has been converted to heterocycles possessing an alpha-alkylidene cyclopentenone, a 4-alkylidene cyclopentenone, or a cross-conjugated triene. Thus, a common intermediate has been converted to three structurally unique compounds by changing only the reaction conditions and, therefore, controlling various reaction pathways.