Cyclization reactions of methylthioacetanilides

The cyclization reactions of methylthioacetanilides mediated by manganese(III) acetate and/or copper(II) acetate are described. Indolinones and indolinediones can be produced effectively via a 5-membered ring cyclization of methylthioacetanilides. The product distributions are highly dependent on the reaction conditions. In most cases, the electronic effect of the substituents on the aryl ring was found to significantly affect the yields of cyclization products. This cyclization reaction proceeded faster with manganese(III) acetate/copper(II) acetate.     

Cyclization reactions in confined space

Cyclization of chain substrates into ring products is an important reaction in organic synthesis. The ease of this process is measured by the Effective Molarity, which indicates that some rings (5, 6 and 7-membered ones) are especially facile to close, while others (>8 membered) are far more challenging. Confinement of the cyclization inside the nanometric cavity of capsules, coordination cages or porous materials can greatly facilitate the reaction via preorganization of the reagents and stabilization of the transition states, also offering the chance to alter the innate selectivity of the reaction. Moreover, the use of chiral cavities enables control over cyclization stereoselectivity. Eventually, pre-organization of the substrate chain inside the cavity can facilitate the closure of medium and large rings, a longstanding goal in organic synthesis. This review analyzes examples of the use of nanoconfinement to improve cyclization reactions, control their selectivity and close challenging rings.     

Cyclization reactions of quaternary salts of azaaromatics

Cyclization reactions of quaternary salts of azaaromatics including inter- and intramolecular condensation as well as radical processes are described.Institute of Chemistry, Pedagogical University, Czestochowa, Poland. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 23–40, January, 1997.     

Acetylenes and nitriles as unconventional reactants for aza-Wittig reactions

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Cyclization reactions of nitriles. 26. Synthesis,structure, and properties of 2-amino-4-methylthio-5-cyano-6(1H)-pyrimidinethione

2-Amino-4-methylthio-5-cyano-6(1H)-pyrimidinethione has been prepared via treatment of N-cyanodimethyldithioimidate or 1,1-di(methylthio)-2-thiocar-bamoyl-2-cyanoethylene with cyanothioacetamide or cyanamide. The structure of the complex formed between 2-amino-4-methylthio-5-cyano-6(1H)-pyrimidinethione and urea has been studied by x-ray structural analysis. Thieno[2,3-d]pyrimidines and thiazolo[3,2-c]pyrimidinium salts have been synthesized based on the 6(1H)-pyrimidinethione.For Communication 25, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1377–1384, October, 1987.     

Cyclization reactions involving palladium-catalyzed carbene insertion into aryl halides

Palladium is shown to catalyze the insertion of trimethylsilylmethylene into aryl halides, leading to benzylpalladium intermediates that cyclize to give indenylsilanes through carbopalladation of pendant alkenes or allenes. Allylsilanes generated through these processes are susceptible to protodesilylation in situ.     

Cyclization reactions of nitriles. 28. Synthesis and reactions of 3β-acetoxy-2′-methyl-5′-cyanoandrost-5-eno[17,16-c]pyridine-6′ (1′H)-thione

3-Acetoxy-2-methyl-5-cyanoandrost-5-eno[17,16-c]pyridine-6(1H)-thione was obtained by thiylation of 16-dicyanomethyl-3-hydroxypregn-5-en-20-one acetate, and its alkylation by chloroacetonitrile and phenacyl bromide was studied. The same thione was also synthesized by treating the corresponding 6-bromo-2-methyl-5-cyanoandrost-5-eno[17,16-c]pyridine with urea.Communication 27, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 943–946, July, 1988.     

Activation of nitriles by trifluoroacetic acid in exchange reactions of functional groups

A strong catalytic effect of trifluoroacetic acid in reactions of nitriles with carboxylic acids and their amides has been found. The formation of stable intermediates in reactions with aliphatic carboxylic acids has been studied. Kinetic data permit to suggest that nitriles in TFA solutions form stable n-complexes.

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Kinetics of exchange reactions between substituted benzoic acid amides and aliphatic nitriles

The functional group exchange between benzamides and various nitriles in trifluoroacetic acid solution has been studied to obtain kinetic and thermodynamic reaction parameters. The reactions are suggested to follow a synchronous mechanism.

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Regio- and stereodirectivity in the reactions of isoquinolinium ylides with unsaturated nitriles

Reactions of isoquinolinium ylides with arylmethylenemalonitriles involve 1,3-dipolar cycloaddition, with the highly regio- and stereoselective formation of 2-aryl-3-benzoyl(or carbamoyl)1,1-dicyano-2,3-trans-1,2,3,10b-tetrahydropyrrolo[2, 1-a]isoquinolines. In contrast, N-phenacylisoquinolinium ylide reacts with aryl-methylenecyanothioacetamides differently, proceeding regio- and stereoselectively to give 4-aryl-2-hydroxy-3-(1-isoquinolinio)-2-phenyl-3-cyano-3,4-trans-1,2,3,4-tetrahydropyridine-6-thiolates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2593–2599, November, 1990.     

Cyclization/acylation reactions by nickel-catalyzed reactions of 1,6-ynal and 1,6-enyne derivatives with acylzirconocene chloride

NiCl₂(PPh₃)₂-catalyzed reactions of 1,6-ynal or 1,6-enyne compounds with n-nonanoylzirconocene chloride afforded stereoselectively cyclopentane derivatives or bicyclo[3.1.0] compounds by catalytic cyclization/acylation reactions, which would involve (i) the primary formation of a metallacycle followed by (ii) the transfer of an acyl group from the acylzirconocene complex (transmetalation).     

Cyclization reactions in the chemical ionization spectra of bifunctional alkyl phenyl ethers

Evidence is presented for the formation of cyclic onium ions from bifunctional alkyl phenyl ethers under chemical ionization conditions.     

Cyclization reactions of long-lived 10,10-dimethyl-9-phenylethynyl-9,10-dihydrophenanthren-9-yl cation

According to the NMR data, long-lived 10,10-dimethyl-9-phenylethynyl-9,10-dihydrophenanthren-9-ylium in acid medium undergoes cyclization whose direction is determined by the acidity of the medium. The cyclization in HSO₃F-SbF₅ superacid involves the aromatic ring in the phenanthrene core as nucleophilic component and yields 5a,6-dimethyl-4-phenyl-4,5,5a,6-tetrahydroacephenantrylene-4,6-bis(ylium). In trifluoroacetic acid the nucleophilic component is the side-chain phenyl group, and the cyclization product is neutral 8b,14b-dimethyl-8b,14b-dihydrobenzo[g]chrysen-10-yl trifluoroacetate. Both cyclization directions are observed in moderate-strength trifluoromethanesulfonic acid.     

Synthesis,formation constants and reactions of cationic rhodium(I) complexes of nitriles

Reactions of Rh(ClO₄)(CO)(PPh₃)₂ with nitriles produce new cationic rhodium(I) complexes, [RhL(CO)(PPh₃)₂]ClO₄ [L = CH₃CN (1), CH₃CH₂CH₂CN (2) or C₆H₅CN (3)], whose spectral data suggest that the nitriles are coordinated through the nitrogen atom. Formation constants for the reaction Rh(ClO₄)(CO)(PPh₃)₂ + L ⇋ [RhL(CO)(PPh₃)₂]ClO₄, have been measured to be 1.01 × 10⁵ M⁻¹ (CH₃CN), 1.07 × 10⁵ M⁻¹ (CH₃CH₂CH₂CN) and 2.59 × 10⁴ M⁻¹ (C₆H₅CN) at 25°C in monochlorobenzene. The differences in the formation constants for the different nitriles seem to be predominantly due to differences in ΔH (not to differences in ΔS). The nitriles in 1–3 are readily replaced with nitrogen base ligands (unsaturated nitriles and pyridine) and PPh₃.     

Mechanistic aspects of the formation of aldehydes and nitriles in photosensitized reactions of aldoxime ethers

The photooxidation of a series of aldoxime ethers was studied by laser flash photolysis and steady-state (product studies) methods. Nanosecond laser flash photolysis studies have shown that chloranil (CA)-sensitized reactions of the O-methyl (1), O-ethyl (2), O-benzyl (3), and O-tert-butyl (4) benzaldehyde oximes result in the formation of the corresponding radical cations. In polar non-nucleophilic solvents such as acetonitrile, there are several follow-up pathways available depending on the structure of the aldoxime ether and the energetics of the reaction pathway. When the free energy of electron transfer (DeltaGET) becomes endothermic, syn-anti isomerization is the dominant pathway. This isomerization pathway is a result of triplet energy transfer from CA to the aldoxime ether. For substrates with alpha-protons (aldoxime ethers 1-3), the follow-up reactions involve deprotonation at the alpha-position followed by beta-scission to form the benziminyl radical (and an aldehyde). The benziminyl radical reacts to give benzaldehyde, the major product under these conditions. A small amount of benzonitrile is also observed. In the absence of alpha-hydrogens (aldoxime ether 4), the major product is benzonitrile, which is thought to occur via reaction of the excited (triplet) sensitizer with the aldoxime ether. Abstraction of the iminyl hydrogen yields an imidoyl radical, which undergoes a beta-scission to yield benzonitrile. An alternative pathway involving electron transfer followed by removal of the iminyl proton was not deemed viable based on charge densities obtained from DFT (B3LYP/6-31G*) calculations. Similarly, a rearrangement pathway involving an intramolecular hydrogen atom transfer process was ruled out through experiments with a deuterium-labeled benzaldehyde oxime ether. Studies involving nucleophilic solvents have shown that all aldoxime ethers reacted with MeOH by clean second-order kinetics with rate constants of 0.7 to 1.2 x 10(7) M(-1) s(-1), which suggests that there is only a small steric effect in these reactions. The steady-state experiments demonstrated that under these conditions no nitrile is formed. This is explained by a mechanistic scheme involving nucleophilic attack on the nitrogen of the aldoxime ether radical cation, followed by solvent-assisted [1,3]-proton transfer and elimination of an alcohol, similar to the results obtained for a series of acetophenone oxime ethers.     

Cyclization and rearrangement reactions of a(n) fragment ions of protonated peptides

a(n) ions are frequently formed in collision-induced dissociation (CID) of protonated peptides in tandem mass spectrometry (MS/MS) based sequencing experiments. These ions have generally been assumed to exist as immonium derivatives (-HN(+)═CHR). Using a quadrupole ion trap mass spectrometer, MS/MS experiments have been performed and the structure of a(n) ions formed from oligoglycines was probed by infrared spectroscopy. The structure and isomerization reactions of the same ions were studied using density functional theory. Overall, theory and infrared spectroscopy provide compelling evidence that a(n) ions undergo cyclization and/or rearrangement reactions, and the resulting structure(s) observed under our experimental conditions depends on the size (n). The a(2) ion (GG sequence) undergoes cyclization to form a 5-membered ring isomer. The a(3) ion (GGG sequence) undergoes cyclization initiated by nucleophilic attack of the carbonyl oxygen of the N-terminal glycine residue on the carbon center of the C-terminal immonium group forming a 7-membered ring isomer. The barrier to this reaction is comparatively low at 10.5 kcal mol(-1), and the resulting cyclic isomer (-5.4 kcal mol(-1)) is more energetically favorable than the linear form. The a(4) ion with the GGGG sequence undergoes head-to-tail cyclization via nucleophilic attack of the N-terminal amino group on the carbon center of the C-terminal immonium ion, forming an 11-membered macroring which contains a secondary amine and three trans amide bonds. Then an intermolecular proton transfer isomerizes the initially formed secondary amine moiety (-CH(2)-NH(2)(+)-CH(2)-NH-CO-) to form a new -CH(2)-NH-CH(2)-NH(2)(+)-CO- form. This structure is readily cleaved at the -CH(2)-NH(2)(+)- bond, leading to opening of the macrocycle and formation of a rearranged linear isomer with the H(2)C═NH(+)-CH(2)- moiety at the N terminus and the -CO-NH(2) amide bond at the C terminus. This rearranged linear structure is much more energetically favorable (-14.0 kcal mol(-1)) than the initially formed imine-protonated linear a(4) ion structure. Furthermore, the barriers to these cyclization and ring-opening reactions are low (8-11 kcal mol(-1)), allowing facile formation of the rearranged linear species in the mass spectrometer. This finding is not limited to 'simple' glycine-containing systems, as evidenced by the IRMPD spectrum of the a(4) ion generated from protonated AAAAA, which shows a stronger tendency toward formation of the energetically favorable (-12.3 kcal mol(-1)) rearranged linear structure with the MeHC═NH(+)-CHMe- moiety at the N terminus and the -CO-NH(2) amide bond at the C terminus. Our results indicate that one needs to consider a complex variety of cyclization and rearrangement reactions in order to decipher the structure and fragmentation pathways of peptide a(n) ions. The implications this potentially has for peptide sequencing are also discussed.     

Cyclization of nitriles 41. Reaction of arylmethylenemalononitriles with malononitrile; crystal structure of 1-amino-3.5-diphenyl-2,4,4,6,6-pentacyano-1-Cyclohexene

1-Amino-3,5-diaryl-2,4,4,6,6-pentacyano-1-cyclohexenes are prepared by reaction of arylmethylenemalononitriles with malononitrile. The cyclohexene ring of (IVa) has a distorted N₂-C¹=C²-C⁷=N¹ fragment. Steric effects in (IVa) cause a substantial increase in C⁶-C¹ and C³-C⁴ bond length to 1.546(4) and 1.570(4) Å, respectively.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2771–2775, December, 1989.     

Acetals of lactams and acid amides. 42. Cyclization of dienamino esters,dienamino nitriles,and acylamidines to pyridine derivatives

The reaction of derivatives of alkylidene (cycloalkylidene) cyanoacetic ester, -malo-nodinitrile, and -cyanoacetamide with dimethylformamide diethylacetal with subsequent cyclization of the resulting enamine systems gives derivatives of pyridine, 2-pyridine, and isoquinoline. 2-Amino-3-cyano-4-methylpyridine, which was synthesized by this method, was converted to a pyrido[1,2-a]pyrimidine derivative.See [1] for communication 41.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 799–802, June, 1984.