A novel and highly efficient two-carbon ring expansion

[reaction: see text]. Dynamic gas-phase thermoisomerization (DGPTI) of medium- and large-ring 3-vinylcycloalkanones at 600-630 degrees C produces isomeric gamma,delta-unsaturated cycloalkanones expanded by two carbon atoms. A reaction mechanism involving an open-chain diradical intermediate, followed by intramolecular recombination under insertion of the vinyl group is proposed. Substituents on the vinyl moiety are transferred locospecifically to the ring-expanded ketones as corresponding beta- and gamma-substituents, respectively. The preparation of extraordinary cyclic allenes can be accomplished by DGPTI (540 degrees C) of 3-ethinylcyclododecanone.     

A novel base-induced ring expansion of quaternized heterocycles

The synthesis of some 6-, 7- and 8-membered heterocycles through a base induced ring expansion of quaternized thiazolium, oxazolium and selenazolium salts is described.     

Bridged ring systems—VIII A novel ring expansion reaction

Acid treatment of 2-(β-Benzoylethyl)-cyclopentanone (III) leads directly to a phenylcycloheptene carboxylic acid (VII) and the related lactone (XI), via a bicyclic intermediate.     

Ionic liquid-promoted regiospecific Friedlander annulation: novel synthesis of quinolines and fused polycyclic quinolines

Several room-temperature ionic liquids (ILs) based on 1-butylimidazolium salts with varying anions were synthesized and evaluated for the preparation of biologically active substituted quinolines and fused polycyclic quinolines using the Friedlander heteroannulation reaction. On screening, 1-butylimidazolium tetrafluoroborate [Hbim]BF4 was found to be the best ionic liquid for the heteroannulation reaction, and the reasons to this effect are well explained. The reactions proceed very well under relatively mild conditions without any added catalyst. The IL acts as a promoter for this regiospecific synthesis and can be recycled. By this green approach, various quinolines were prepared in excellent yields and purity and well-characterized.     

First example of carbohydrate-based Prins cyclization: a novel class of sugar-annulated tetrahydropyrans

The secondary homoallylic alcohol derived from d-glucose undergoes smooth coupling with aldehydes in the presence of molecular iodine under mild reaction conditions to produce 7-iodofurano[3,2-b]pyrans in good yields. This method is highly stereoselective, affording cis-tetrahydropyrans exclusively.     

First synthesis of biquinoliziniun salts: novel example of a chiral azonia dication

[Structure: see text] The 1,1'-, 2,2'-, and 3,3'-biquinolizinium dications are described for the first time and were prepared using palladium-catalyzed homocoupling reactions of the corresponding isomeric bromoquinolizinium bromides. Theoretical calculations show 1,1'- and 4,4'-biquinolizinium dications to be chiral molecules, the latter of which has a high energy of formation, a factor that probably precludes its formation.     

Synthesis of isoquinolines and naphthyridines by electrophilic ring closure of iminoalkynes

Substituted isoquinolines and naphthyridines have been prepared in good to excellent yields by the reaction of iminoalkynes with a variety of electrophiles under mild reaction conditions. Reaction: see text.     

Regiospecific hydrogenation of quinolines and indoles in the heterocyclic ring

Quinolines, indoles, acridine, and carbazole were hydrogenated using a large variety of heterogeneous catalysts in hydrocarbon solvents in an effort to achieve selective hydrogenation of the heterocyclic ring. When quinolines were hydrogenated using supported platinum, palladium, rhodium, ruthenium, or nickel metal catalysts in the presence of hydrogen sulfide, carbon disulfide, or carbon monoxide, there was exclusive hydrogenation of the heterocyclic ring to give only 1,2,3,4-tetrahydroquinolines. Use of iridium, rhenium, molybdenum(VI) oxide, tungsten(VI) oxide, chromium(III) oxide, iron(III) oxide, cobalt(II) oxide-molybdenum(VI) oxide, or copper chromite catalysts also caused exclusive hydrogenation of the heterocyclic ring even without addition of sulfur Compounds or carbon monoxide. Hydrogenation of indoles using platinum, rhenium, or, in some cases, nickel catalysts (with or without sulfur Compounds) occurred exclusively in the heterocyclic ring to give indolines, but conversions were affected by indole-indoline equilibria.     

Synthesis of some novel polyoxygenated quinolines

Polyfunctional quinolines were obtained via thermal cyclization of phenylaminocrotonates and malonanilides and characterized by uv, ir, and ¹H and ¹³C nmr spectra. Dehydration of a derivative of 5-hydroxymethyl-4(1H)-quinolone yielded a derivative of 5H-furo[2,3,4-de]quinoline, representing a novel tricyclic system.     

Cross-coupling of 2-methylquinolines and in-situ activated isoquinolines: Construction of 1,2-disubstituted isoquinolinones

In this study, a method was developed to form C(sp³)–C(sp²) bonds via copper catalyst-promoted cross coupling of 2-methylquinoline and in-situ-activated 3-haloisoquinoline under mild conditions. The multi-component tandem reaction was used to construct new C–N, C=O and C–C bonds in one pot via sequential functionalization of the N1, C3 and C1 positions of 3-haloisoquinoline. This method can be used to efficiently access 1,2-disubstituted isoquinolinones by the three-component reaction of 3-halogen isoquinoline, alkyl halide, and 2-methylquinoline.     

A furan ring expansion approach to the synthesis of novel pyridazino-psoralen derivatives

A convenient preparation of the parent tetrahydrobenzodifuran 2 was developed from resorcinol. The oxidation of one or both furan rings of this key intermediate was accomplished with DDQ and the resulting benzodifuran was subsequently reacted with 3,6-dimethoxycarbonyl-1,2,4,5-tetrazine to afford the expected pyridazino-psoralen derivative in good yield. This simple method allowed the efficient preparation of a pyridazino-psoralen derivative with a formyl group at C-7, which was introduced by directed ortho-lithiation in the intermediate 2. An aminoalkyl side-chain was also introduced to the tetracyclic skeleton through the aldehyde functionality in a reductive amination process, which was accompanied by an unprecedented reduction of the pyridazine ring.     

Thermolytic ring opening of acyloxybenzocyclobutenes: an efficient route to 3-substituted isoquinolines

Upon flash vacuum pyrolysis acyloxybenzocyclobutenes 4 rearrange through an intramolecular 1,5-acyl shift to 2-formylbenzyl ketones 6 which can be converted to 3-substituted isoquinolines 7.     

A novel, one-pot ring expansion of cyclobutanones. Syntheses of carbovir and aristeromycin

A novel, one-pot ring-expansion procedure was developed using Me3S(O)I, NaH, and Sc(OTf)3. The scope and limitations were briefly examined, and a tentative mechanism was proposed. Application of the methodology to known cyclobutanone 1 provided the corresponding cyclopentanone, which was successfully advanced to (+)-carbovir and (+)-aristeromycin.     

Nickel-catalyzed reactions of silacyclobutanes with aldehydes: ring opening and ring expansion reaction

[reaction: see text]. The nickel-catalyzed ring opening reaction of silacyclobutanes with aldehydes affords the corresponding alkoxyallylsilanes. In contrast, the ring expansion reaction of benzosilacyclobutene with aldehydes occurs under nickel catalysis to give oxasilacyclohexenes.     

2-Quinolyl- and 1-isoquinolylnitrenes: ring expansion and ring opening in heteroarylnitrenes

Argon matrix photolysis of tetrazolo[1,5-a]quinoline 8 and tetrazolo[5,1-a]isoquinoline 7 causes nitrogen elimination and ring expansion to 1,3-diazabenzo[d]cyclohepta-1,2,4,6-tetraene 13. The photolysis of tetrazolo[5,1-a]isoquinoline 7 also causes ring opening to o-cyanophenylketenimine 22. Mechanisms of ring opening of heteroarylnitrenes are discussed.     

Stereoselective ring expansion via bicyclooxonium ion. A novel approach to oxocanes

[reaction: see text] The stereoselective 1,4-rearrangement-ring expansion of tetrahydrofurans via bicyclo[3.3.0]oxonium ions was developed to synthesize oxocanes. On the basis of this rearrangement, the stereoselective synthesis of 2,8-syn-2,8-dimethyloxocane was accomplished.