Electron impact mass spectra of enamine esters,ketones and nitriles

The behaviour of some enamine-esters, -ketones and -nitriles under electron impact has been investigated by means of low-resolution mass Spectrometry.     

Synthesis of new bi- and tricyclic azamacrocycles using cyclene

A method was developed for preparing bi- and tricyclic tetra- and hexaazamacrocycles using the reaction of 1, 4, 7,10-tetraazacyclododecane with various alkylating ditosylates.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 255–258, February, 1996.     

Synthesis and fluorescent properties of bi- and tricyclic 4-N-carbamoyldeoxycytidine derivatives

New bi- and tricyclic deoxycytidine derivatives (dChpd, dCmpp, dCtpp, dCppp) were synthesized as analogues of a fluorescent nucleoside, dChpp, previously reported. The carbamoyl group of dChpd and the 5-position of the cytosine ring are bridged via an ethylene linker so that the modified group forms a nonplanar structure with the cytosine ring. The fluorescent study of dChpd indicated that the coplanar structure between the carbamoyl group and the cytosine ring is of importance. N-Methylation of the carbamoyl group (dCmpp) weakened the intensity of the fluorescence of dChpp, and the derivative (dCtpp), which had a thiocarbamoyl group, lost its fluorescent property. Moreover, addition of a pyrrolo-ring (dCppp) to dChpp enhanced the intensity of fluorescence, and an emission light was observed with a marked Stokes shift of 120 nm.     

Synthesis of bi- and tricyclic acrylates in the presence of boron trifluoride etherate

The addition of acrylic acid to bicyclo[2.2.1]heptene hydrocarbons and tricyclo[5.2.1.0^2,6]deca-3,8-diene catalyzed with BF₃·O(C₂H₅)₂ was studied and bi- and tricyclic esters of acrylic acid were synthesized that were reactive monomers for preparation of macromolecular compounds.     

Synthesis and chemistry of α-iodoperfluoroacid esters

The title compounds have been synthesized by irradiation of acetonitrile solutions of perfluoroacid esters and diesters containing tetrabutylammonium iodide. They are versatile synthetic intermediates from which ketenes, Reformatsky adducts, α,β-unsaturated esters and α-hydroesters can be prepared.     

Polymerization of cyclic monomers, 4. Synthesis and radical polymerization of bi- and trifunctional 2-vinylcyclopropanes

Multifunctional 2-vinylcyclopropanes were synthesized by esterification of the 1-methoxycarbonyl-2-vinylcyclopropane-1-carboxylic acid with ethylene glycol, 1,1,1-trimethylolpropane or 1,4-cyclohexanediol in the presence of 1,3-dicyclohexylcarbodiimide (DCC). The structure of the new vinylcyclopropanes was confirmed by elemental analysis, IR, ¹H NMR and ¹³C NMR spectroscopy. The radical polymerization of the 2-vinylcyclopropanes in bulk with 2,2′-azoisobutyronitrile (AIBN) results in transparent crosslinked polymers. The polymerization of the liquid monomers is accompanied by a low shrinkage in volume.     

Reactions of cyclic enaminoketones with benzylidenemalononitriles. Synthesis of new fused heterocyclic systems containing the 1,4-dihydropyridine fragment

The reactions of cyclic enaminoketones with benzylidenemalononitriles were examined and a new procedure was developed for the synthesis of fused heterocyclic systems containing the 1,4-dihydropyridine ring, viz., thienopyrimidoquinolines and furopyrimidoquinolines. The characteristic features of the reactions and the structures of the resulting compounds were investigated.     

Synthesis and enzymatic kinetic resolution of alpha,alpha-disubstituted cyclic hydroxy nitriles

Herein, we describe the diastereoselective synthesis of five- and six-membered alpha,alpha-disubstituted cyclic beta-hydroxy nitriles and their resolution via enzymatic transesterification. By this method, all possible stereoisomers were obtained in enantiopure form and high yield.     

Synthesis of bi- and tricyclic arylboronates via Cp*RuCl-catalyzed cycloaddition of alpha,omega-diynes with ethynylboronate

In the presence of 5-10 mol% Cp*RuCl(cod), 1,6- and 1,7-diynes were allowed to react with an ethynylboronate at ambient temperature to give rise to bi- and tricyclic arylboronates in 64-93% isolated yields.     

Synthesis of cyclic beta-amino acid esters from methionine, allylglycine, and serine

Here we report a versatile ring-closing metathesis-based approach to 5-, 6-, and 7-membered cyclic beta-amino esters starting with simple and readily available building blocks-methionine, allylglycine, and serine-where the nature of the amino acid determines the size of the carbocyclic ring.     

The chemistry of acylals. 3. Cyanohydrin esters from acylals with cyanide reagents

[reaction: see text] When treated with KCN in DMSO at room temperature, acylals from aliphatic aldehydes gave the corresponding cyanohydrin esters in good to excellent yields. Acylals from aromatic aldehydes were less reactive and gave several byproducts in addition to fair yields of cyanohydrin under the same conditions. Trimethylsilyl cyanide mixed with titanium(IV) chloride afforded cyanohydrin esters in good to excellent yields from both aliphatic and aromatic aldehydes.     

Michael-Stork addition of cyclopentyl enamine to allenyl ketones and esters

[Chemical reaction: see text] We report the first examples of a Michael-Stork enamine addition to allenyl esters and ketones. Studies reveal that 2 equivalents of enamine are required for optimal yields. In the case of an allenyl methyl ketone, cyclopentyl enamine addition led to 8-oxobicyclo[3.2.1]octane formation, providing evidence for the in situ formation of an enamine intermediate following the initial Michael-Stork reaction.     

Heterocyclic β-Enamino esters. 28. The reaction of heterocyclic β-Enamino esters and nitriles with cyclic amidines. A simple route to azolopyrimidines

Whereas 2-amino-3-ethoxycarbonyl-4,5-dihydrofurans Ia-c condense with 5-membered amidine derivatives, via elimination of ethanol to afford the azolopyrimidines IIIa,b, XI, and XIVa,b, the 2-amino-3-cyano-4,5-dihydrofurans Id,e give with the same reagents, under elimination of ammonia, the novel ring systems of furo-azolopyrimidines XVIII and XXa,b. 2-Amino-3-ethoxycarbonyl-5,6-dihydro-4H-thiopyrane (XXI) reacts with 5-amino-1,2,4-triazole (II) to yield the triazolo[1,5-a]pyrimidine XXII, and with 2-aminobenzimidazole to XXIII. The mechanism of these reactions is discussed. XIVb and VIIb are cyclized in a secondary step to give the novel furo[2,3-d]benzimidazo[1,2-a]pyrimidine XXVI, and furo[2,3-d]-1,2,4-triazolo[1,5-a]pyrimidine XXVIII respectively, besides the acetoxy derivatives XVII and XXIX.     

Heteroatom chemistry of cyclic benzopolychalcogenides: Synthesis and characterization

Many benzopolychalcogenides, for example benzotrithioles, benzotetrathiins, and benzopentathiepins were synthesized from corresponding 1,2‐benzenedichalcogenols as starting compounds. The stability of the pentathiepin ring toward functional groups was confirmed by use of amino and sulfide groups as substituents in the molecule of benzopentathiepin. Furthermore, the intramolecular interaction between two polysulfide rings was also studied by synthesis of bisbenzotrithiole, 7,7′‐diethyl‐4,4′‐ethylenedioxybis (benzo[1,2‐d][1,2,3]trithiole). © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:419–423, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10069     

The relative stabilities of 6-membered cyclic allylamine/enamine systems

Evidence on the relative stabilities of acyclic allylamine/enamine systems and methods for the isomerisation of the former into the latter are reviewed. Previous evidence on the related question of the thermodynamic stabilities of 3-piperideines/2-piperideines is presented. The view that 6-membered cyclic allylamines are thermodynamically preferred over their enamine isomers is refuted by demonstrating the base-catalysed equilibrative isomerisations of several 1-alkyl-4-acyl-1,2,5,6-tetrahydropyridines into their 1-alkyl-4-acyl-1,4,5,6-tetrahydropyridine isomers. It is shown that the conjugated CO group in these examples is unnecessary to effect isomerisation: for example even in the simplest possible situation, 1-methyl-1,2,5,6-tetrahydropyridine can be isomerised into 1-methyl-1,4,5,6-tetrahydropyridine, though a stronger base is necessary.     

Synthesis of cyclic oligomers from histidine-derived building blocks using dynamic combinatorial chemistry

Histidine-derived hydrazide acetal monomers (3-dimethoxymethylbenzoyl)-L-histidine methyl ester 1 and (3-dimethoxymethylbenzoyl)-tau-benzyl-L-histidine methyl ester 2 were prepared from a histidine methyl ester and a tau-benzyl-histidine methyl ester by N-acylation with 3-(dimethoxymethyl)benzoic acid (3) followed by hydrazinolysis. Acid-promoted hydrolysis of each acetal hydrazide initially produced a library of cyclic oligomers that eventually converted to a cyclic dimer. The cyclic dimers 12 and 22 were spectroscopically characterized and found to direct their imidazole-bearing sidechains outward (exo). No evidence for templating the cyclic oligomers was observed using various metal ions and anionic substrates. The average of pKa1 and pKa2 of dimer 12 was determined by potentiometric titration to be 6.6. Dimer 12 was found to catalyze the hydrolysis of p-nitrophenylacetate 10 times faster than 4-methyl imidazole.