Undergo Ring Contraction Research Articles

ChemInform Abstract: Sodium Dichloroisocyanurate Oxidation of a Sterically Hindered Tetrahydro‐9(10H)‐acridinone.

AbstractThe tetrahydroacridinone (I) is oxidized with the isocyanurate mentioned in the title to give the cis‐diol (II).

Sodium dichloroisocyanurate oxidation of a sterically hindered tetrahydro-9(10H)-acridinone

Treatment of 1,2,3,4-tetrahydro-9-(10H)-acridinone (1a) with sodium dichloroisocyanurate (2) yields cis-1,2-diol 3a or azepino[1,2-a]indole 4a. Here we present further developments which lead us to propose that a more plausible pathway to 4a form 3a involves a N-chloro 1,2-diol intermediate which undergoes ring contraction to the product

ChemInform Abstract: Photoreductive Cyclization: Application to the Total Synthesis of (.+‐.)‐Actinidine.

AbstractThe 2‐diazocyclohexane‐1,3‐dione (III) is irradiated in the presence of diallylamine (IV) to undergo ring contraction, yielding the cyclopentanonecarboxamide (V).

ChemInform Abstract: A Novel Ring Transformation of 5‐Acylaminouracils and 5‐Acylaminopyrimidin‐4(3H)‐ones into Imidazoles.

AbstractThe 5‐acylaminouracils (III) and the 5‐acylaminopyrimidin‐4(3H)‐ones (VI), prepared by acylation of the amino derivatives (I) or (V), undergo ring contraction upon treatment with sodium hydroxide in aqueous ethanol to give the imidazolecarboxamides (IV) or (VII).

ChemInform Abstract: Reactions with Heterocyclic Enaminonitriles: Synthesis of Pyrrolo‐(2,3‐b)pyridine, Pyrrolo(2,3‐d)pyrimidine, and Pyrrole Derivatives.

AbstractCyclocondensation reaction of ethyl 3‐(dicyanomethylene)butyrate (I) with the diazonium salts (II) yields the dihydropyridazines (III) which undergo ring contraction on treatment with zinc/acetic acid, forming the pyrroles (IV).

The disaccharide composition of heparins and heparan sulfates

Heparin and heparan sulfate can be cleaved selectively at their N-sulfated glucosamine residues by direct treatment with nitrous acid at pH 1.5. These polymers can also be cleaved selectively at their N-acetylated glucosamine residues by first N-deacetylating with hydrazine and then treating the products with nitrous acid at pH 4. These procedures have been combined and optimized for the conversion of these glycosaminoglycan chains into their disaccharide units. A modified hydrazinolysis procedure in which the glycosaminoglycans were heated with hydrazine:water (70:30) containing 1% hydrazine sulfate gave rapid rates of N-deacetylation and minimal conversion of the uronic acid residues to their hydrazide derivatives. Under these conditions, N-deacetylation was complete in 4 h and the β-eliminative cleavage of the polymer chains that occurs during hydrazinolysis ( P. N. Shaklee and H. E. Conrad (1984) Biochem. J. 217, 187–197 ) was eliminated. Treatment of the N-deacetylated polymer with nitrous acid at pH 3 for 15 h at 25°C then gave simulataneous cleavage at the N-unsubstituted glucosamine residues and the N-sulfated glucosamine residues. These deamination conditions minimized, but did not eliminate, the side reaction in which nitrous acidreactive glucosamine residues undergo ring contraction without glucosaminide bond cleavage. Thus, the disaccharides were obtained in a yield of 90% of those originally present in the glycosaminoglycan chains. Since the ring contraction side reaction occurs randomly at the diazotized glucosamine residues, the disaccharides formed in the pH 3 nitrous acid reaction were recovered in proportions equal to those in the original glycosaminoglycan chain. Anion-exchange high-pressure liquid chromatography analysis of the disaccharides ( M. J. Bienkowski and H. E. Conrad (1985) J. Biol. Chem. 260, 356–365 ) then gave quantitative analyses of the amounts of each disaccharide type in the heparinoid chains.

ChemInform Abstract: Chemistry of O,N‐ and S,N‐Containing Heterocycles. Part 6. Investigations on the Behavior of Activated 1,5‐Benzoxazepines Under Basic Conditions.

AbstractThe benzoxazepine derivatives (I), (IV) and (V) undergo ring contraction under basic conditions to give the benzoxazoles (III) and (VI)‐(VIII).

ChemInform Abstract: A Novel Synthesis of cis‐1‐((6‐Chloro‐3‐((2‐chloro‐3‐thienyl)methoxy)‐2,3‐dihydrobenzo(b)thien‐2‐yl)methyl)‐1H‐imidazole: A New Class of Azole Antifungal Agents.

AbstractThe thiiranium cation, initially formed from the thiopyran (II), undergoes ring contraction in the presence of imidazole (III) to give the cis compound (IV) as major product (X‐ray analysis of the solvent‐free alcohol: space group P21/c; Z=4).

ChemInform Abstract: Lactone Formation in Superacidic Media.

AbstractWhereas (I) forms the lactone (II) (isolable by quenching) (III) does not.

ChemInform Abstract: Alloisolongifolene. Part 4. Some Novel Transformations of an Alloisolongifolene‐Derived 4‐Substituted 3,6‐Dihydro‐2H‐pyran.

AbstractThe epoxide (I), readily available from the unsaturated compound, undergoes ring contraction in the presence of BF3‐etherate to give the aldehyde (IIa).

ChemInform Abstract: 3,12‐Cycloiceane (Pentacyclo(6.3.1.02,4.05,10.07,8)dodecane).

AbstractThe pentacyclotridecene (I) is transformed into the diazo ketone (III) which undergoes ring contraction on irradiation, producing the ester (IV).

Lactone formation in superacidic media

The reaction of substituted 1-hydroxycyclohexanecarboxylic acids in fluorosulphuric acid has been studied. Cyclisation takes place around 0 °C, accompanied by rearrangement in appropriate cases, yielding the thermodynamically stable lactone or mixture of lactones. An unexpected feature of these reactions is that the carboxy-substituted cyclohexyl carbocation does not undergo ring contraction, unlike the unsubstituted cyclohexyl carbocation, although the cycloheptyl system contracts to cyclohexyl. We suggest that the cyclohexyl carbocation is strongly stabilised by carboxyl substitution, as a result of throug-space interaction between the carboxyl oxygen atom and the carbocation centre.

ChemInform Abstract: Cyclization of N‐Substituted 2,2‐Diarylglycolohydroxamic Acids to 1,2‐Oxazetidin‐3‐ones.

AbstractThe hydroxamic acids (Ia)‐(Ii) react directly with CDI (II) to give the oxazetidines (IVa)‐(IVi) while the acids (Ij)‐(Il) yield the dioxazinanes (IIIj)‐(IIII) which undergo ring contraction in the presence of molecular sieves to give (IVj)‐(IVl).

Cyclisierung von N‐substituierten 2,2‐Diarylglycolohydroxamsäuren zu 1,2‐Oxazetidin‐3‐onen

Cyclization of N‐Substituted 2,2‐Diarylglycolohydroxamic Acids to 1,2‐Oxazetidin‐3‐onesUnder mild conditions the reaction of N‐substituted 2,2‐diarylglycolohydroxamic acids 1 with 1,1′‐carbonyldiimidazole (CDI) gives either directly 1,2‐oxazetidin‐3‐ones 3 or 1,5,2‐dioxazinane‐3,6‐diones 2 which undergo ring contraction to give 3 in boiling toluene or at ambient temperature in the presence of molecular sieves. The rate of benzylaminolysis of 3 into 2‐aminooxy‐N‐benzylacetamides 4 is substantially affected by the size of the ring substituents.

Electron-deficient heteroaromatic ammonioamidates. Part 27. Quinazolinioamidates. Part 14. N-Amination of some quinazoline derivatives and some reactions of the resulting quinazolinioamides

Treatment of the quinazolines (4d) and (4e) bearing no substituents at position 4 with O- mesitylenesulphonylhydroxylamine leads to amination of N-3 and formation of the mesitylene- sulphonates of the corresponding (quinazolin-3-io)amides (5a) and (5b). Upon alkaline treatment these mesitylenesulphonates yield the free (quinazolin-3-io)amides (5a) and (5b) which exist predominantly in the form of the dimers (6a) and (6b), respectively. O-Mesitylenesulphonyl hydroxylamine aminates the 4-substituted quinazolines (4f)–(4h) at N-1, affording the mesitylenesulphonates (7b–d) of the corresponding (quinazolin-1-io)amides. The salts (7b) and (7c) undergo ring contraction to indazole derivatives of type (10) on alkaline treatment. All attempts to acylate the (quinazolin-3-io)amide (5a), its dimer, or its mesitylenesulphonate failed, whereas the mesitylenesulphonate of the (quinazolin- 1-io)amide (7b) could be both benzoylated and ethoxycarbonylated. Irradiation studies of the (quinazolin-3-io)amides (5a) and (5b), respectively, of their dimers (6a) and (6b), and of the N-(quinazolin-1-io)amidate (8c) are also reported.

Synthesis of styrylcycloheptatriene derivatives via the electrophilic addition of tropylium ions to [Fe(CO)3(η4-C8H8)]: X-ray crystal structure of tricarbonyl(1–4-η-7-styrylcyclohepta-1,3,5-triene)iron

The reaction between [Fe(CO)3(η4-cot)](cot = cyclo-octatetraene) and tropylium tetrafluoroborate yields [Fe(CO)3(η4-C7H7CHCHPh)](1), X-ray studies on which have revealed the formation of a co-ordinated styrylcycloheptatriene ligand. The C7 ring adopts an envelope conformation (interplanar angle 138°) to which the Fe(CO)3 fragment is η4 bonded on the convex face. The atoms of the styryl substituent are all coplanar, and this plane lies approximately orthogonal to the mean plane of the C7 ring. Crystals of [Fe(CO)3(η4-C7H7CHCHPh)] are monoclinic, with space group C2/c, and the structure has been refined to R 0.063 for 1 977 reflections to 2θ= 55°(Mo-Kα) at 293 K. The reaction between [C7H7]+ and [Fe(CO)3(η4-C8H7Me)], giving [Fe(CO)3{η4-C7H6(Me)CHCHPh}] in which the methyl group is located on the cycloheptatriene ring, shows that both the cot and tropylium groups undergo ring contraction during the generation of the exocyclic alkene bond of (1). Complex (1) reacts with HBF4, giving the cycloheptadienyl complex [Fe(CO)3(η5-C7H8CHCHPh)][BF4], and with tetracyanoethylene to give the 1,3-cyclo-adduct, 9-σ: 2–4-η-7,7,8,8-tetracyano-5-styrylbicyclo[4.2.1]nonenediyliron.

Electrochemical oxidation of 7,9-dimethyluric acid in acid solution

The electrochemical oxidation of 7,9-dimethyluric acid between pH 3 and pH 5 has been studied using a pyrolytic graphite electrode. Two voltammetric oxidation peaks (I a and II a) are observed. Peak I a is a 2 e-1 H + reaction yielding a very reactive quinonoid cation that, in a reaction catalyzed by H 2PO 4 −, is hydrated to an UV-absorbing tertiary alcohol intermediate. This intermediate can undergo ring contraction to give 1-carbohydroxy-2,4-dimethyl-2,4,6,8-tetraaza-3,7-dioxo-5-ene-bicyclo[3.3.0]octane (IV) or react with H 2PO 4 − and 7,9-dimethyluric acid to give a relatively long-lived complex. Compound IV is hydrated and decomposes to 1,3-dimethylallantoin. The tertiary alcohol-H 2PO 4 −-7,9-dimethyluric acid complex very slowly decomposes regenerating 7,9-dimethyluric acid and, ultimately, 1,3-dimethyl-5-hydroxyhydantoin-5-carboxamide. Peak IIa is a minor process and is due to 2 e oxidation of the anion of IV in a Kolbe-type reaction giving 1-hydroxy-2,4-dimethyl-2,4,6,8-tetraaza-3,7-dioxo-5-ene-bicyclo[3.3.0]octane.

Ring contraction in an arylcopper(I) compound promoted by a sulphur donor ligand : penta[mesitylcopper(I)] forms a tetra[mesitylcopper(I)] compound

Mesitylcopper(I)(CuMes)n was shown by an X-ray analysis to be a cyclic pentameric arylcopper(I) complex (CuMes)5 in the solid state, which undergoes ring contraction with tetrahydrothiophene to the corresponding tetrameric species [Cu4Mes4(C4H8S)2], the structure of which has been found by X-ray crystallography.

ChemInform Abstract: SYNTHESIS OF PENEMS BY RING CONTRACTION OF A 2‐THIACEPHEM

AbstractDie Azetidinone (I) reagieren mit Schwefelwasserstoff zu den Polysulfiden (II), die bei der Behandlung mit Natriumhydrogensulfid oder Kaliumthioacetat in Tetrahydrofuran bei 0°C zu den Thiacephemen (III) führen.

Ring contractions of thiochroman-4-ones and thiochromen-4-ones

3-Bromothiochroman-4-one and its S-oxide undergo ring contraction on heating, especially in the presence of sodium acetate, to give mixtures which include thioindigo (9) and the ethanediylidenethioindigo (10). Brominated 2,2-dimethylthiochroman-4-one reacts on silica gel to form thioindigo, thioindirubin, and the bis(benzothieno)pyran (17).Bromination of thiochromanone gives a number of products, including 2,3-dibromothiochromen-4-one S-oxide which, on heating with sodium acetate in acetic acid, is converted efficiently into thioindigo. The mechanism of this reaction is investigated.