Efficient construction of 1,2-dihydroquinoline and 1,2,3,4-tetrahydroquinoline rings using tandem Michael-aldol reaction

1,2-Dihydroquinolines and a 1,2,3,4-tetrahydroquinoline were efficiently constructed using tandem Michael-aldol reaction starting from N-protected o-aminobenzaldehydes and α,β-unsaturated carbonyl compounds in good yield.     

Synthesis and stereochemistry of 1-acyl-2-alkyl-1,2,3,4-tetrahydroquinoline-3,4-epoxides

Summary Analogous to the recently described synthesis of Reissert epoxides the treatment of 1-acyl-2-alkyl-1,2-dihydroquinolines withm-chloroperoxybenzoic acid gave diasteromeric pure epoxides which are stable in crystalline state, but reactive in solution versus nucleophiles. Acting as useful intermediates to stereocontrolled functionalized 1,2,3,4-tetrahydroquinolines an X-ray analysis was performed to confirm the relative stereochemistry of the epoxides.

---

Synthese und Stereochemie von 1-Acyl-2-alkyl-1,2,3,4-tetrahydrochinolin-3,4-epoxiden

Zusammenfassung Analog zu der kürzlich beschriebenen Synthese von Reissert-Epoxiden liefern 1-Acyl-2-alkyl-1,2-dihydrochinoline bei Behandlung mitm-Chlorperbenzoesäure diastereomerenreine Epoxide, die sich als Festsubstanzen außerordentlich stabil, in Lösung aber reaktiv gegenüber Nucleophilen erweisen. Da sie wertvolle Ausgangsverbindungen zu 1,2,3,4-substituierten Tetrahydrochinolinen mit definierter relativer Konfiguration darstellen, wurde die Stereochemie der Epoxide mittels Röntgenstrukturanalyse abgesichert.

     

A novel convenient synthesis of 5-acyl-1,2-dihydropyrimidin-2-ones via 4-trichloromethyl-1,2,3,4-tetrahydropyrimidin-2-ones

A novel four-step methodology for the synthesis of 5-acyl-1,2-dihydropyrimidin-2-ones has been developed. The reaction of readily available N-[(1-acetoxy-2,2,2-trichloro)ethyl]ureas with Na-enolates of 1,3-diketones or β-oxoesters followed by heterocyclization-dehydration of the oxoalkylureas formed gave 5-acyl-4-trichloromethyl-1,2,3,4-tetrahydropyrimidin-2-ones. The latter, in the presence of NaH, eliminate CHCl₃ to give the target compounds.     

Über die Oxo‐cyclotetraphosphane (PBut)4O1–4

Contributions to the Chemistry of Phosphorus. 243 On the Oxocyclotetraphosphanes (PBu^t)₄O_1–4 Under suitable conditions, the reaction of tetra‐tert‐butylcyclotetraphosphane, (PBu^t)₄, with dry atmospheric oxygen gives rise to the corresponding monoxide (PBu^t)₄O ( 1 ) which has been isolated by column chromatography. The reaction with hydrogen peroxide furnishes a mixture of oxocyclotetraphosphanes (PBu^t)₄O_1–4 consisting of two constitutionally isomeric dioxides (PBu^t)₄O₂ ( 2 a , 2 b ), the trioxide (PBu^t)₄O₃ ( 3 ), and the tetraoxide (PBu^t)₄O₄ ( 4 ), in addition to 1 . According to the ³¹P NMR parameters the oxygen atoms are exclusively exocyclically bonded to the phosphorus four‐membered ring. Which of the P atoms are present as λ⁵‐phosphorus follows from the different low‐field shifts of the individual P nuclei compared with the starting compound. Accordingly, 1 is 1,2,3,4‐Tetra‐tert‐butyl‐1‐oxocyclotetraphosphane, 2 a and 2 b are 1,2,3,4‐Tetra‐tert‐butyl‐1,2‐dioxo‐ and ‐1,3‐dioxocyclotetraphosphane, respectively, 3 is 1,2,3,4‐Tetra‐tert‐butyl‐1,2,3‐trioxocyclotetraphosphane, and 4 is 1,2,3,4‐Tetra‐tert‐butyl‐1,2,3,4‐tetraoxocyclotetraphosphane. When the oxidation reaction proceeds a fission of the P₄ ring takes place.     

Synthesis of 1,2,3,4-tetrachlorohexafluorobutane

The condensation of 1-iodo-1,2,2-trifluoro-1,2-dichloroethane induced by granulated Zn in the presence of catalytic amounts of AcOEt without a solvent results in 1,2,3,4-tetrachlorohexafluorobutane in high yield.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2236–2238, October, 2004.     

New approach to 5-arylsulfonyl-substituted 1,2-dihydropyrimidin-2-ones via base-induced chloroform elimination from 4-trichloromethyl-1,2,3,4-tetrahydropyrimidin-2-ones

A four-step method for the synthesis of 5-arylsulfonyl-substituted 1,2-dihydropyrimidin-2-ones has been developed. The reaction of readily available N-[(1-acetoxy-2,2,2-trichloro)ethyl]ureas with sodium enolates of α-arylsulfonylketones followed by heterocyclization-dehydration of the oxoalkylureas formed gave 5-arylsulfonyl-4-trichloromethyl-1,2,3,4-tetrahydropyrimidin-2-ones. The latter, in the presence of strong bases, eliminate CHCl₃ to give the target compounds.     

Ring-opening of 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane in the presence of transition metal catalysts

Ring opening of 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane in the presence of various transition metal catalysts has been studied. Pd and Pt compounds are most active. Compounds with bulky ligands [e.g., Pd(PPh₃)₄] lead to the formation of “dimeric” cyclooctasilanes. Compounds with less bulky groups convert monomer to dimers and mixture of oligomers and polymers. Reactions with the all-trans monomer, tttt-(MePhSi)₄, result in the formation of stereoregular dimer, presumably all-trans, tttttttt-(MePhSi)₈, in high yields. Reactions in the presence of oxygen lead to the formation of polymers with inserted oxygen atoms in the main chain. © 1996 John Wiley & Sons, Inc.     

Approaches to the preparation of (Z)-1,2-difluorostilbenes

Methodology directed at the preparation of (Z)-1,2-difluorostilbenes has been evaluated. For symmetrical (Z)-1,2-difluorostilbenes, photochemical isomerization of the isomeric (E)-1,2-difluorostilbenes, and HPLC separation of the mixture of stilbene isomers is a reasonable route to a particular (Z)-stilbene. An alternative approach to both symmetrical and/or unsymmetrical (Z)-1,2-difluorostilbenes has been developed via stereospecific Pd(0) coupling of (E)-1,2-difluoro-aryl-ethenyltributylstannanes under Stille-Liebiskind conditions with aryl idodies. The requisite arylstannanes can be obtained via the reported route developed by Davis or via (E)-1,2-difluorovinyltributylstannane - a new route described in this work. The methodology tolerates almost any functionality in the aryl ring, is easily carried out, is stereospecific and provides the first general route to (Z)-1,2-difluorostilbenes.     

Ring-Chain Tautomerism of 1,2,3,4-Tetrahydroquinazolines. The Products of Reaction of 1,3-Dicarbonyl Compounds with 2-Aminomethylaniline

The reaction of 2-aminomethylaniline with 1,3-dicarbonyl compounds gives a series of 1,2,3,4-tetrahydroquinazoline derivatives. A ring-chain tautomeric equilibrium of the type enamine-1,2,3,4-tetrahydroquinazoline is observed in solutions of these compounds and its position depends of the structure of the starting dicarbonyl component and the solvent polarity.     

Mild and Efficient Syntheses of 1-Aryl-3,4-dihydroisoquinolines and 1-Aryl-3,4-dihydro-β-carbolines via Regiospecific β-Eliminations of the Corresponding N-Tosyl-1,2,3,4-tetrahydroisoquinolines and N-Tosyl-1,2,3,4-tetrahydro-β-carbolines

Treatment of N-tosyl-1-aryl-1,2,3,4-tetrahydro-isoquinolines or N-tosyl-1-aryl-1,2,3,4-tetrahydro-β-carbolines with a strong base such as NaOH or KOH at 70 °C in dimethylsulfoxide (DMSO) produced 1-aryl-3,4-dihydroisoquinolines or 1-aryl-3,4-dihydro-β-carbolines in good yields via mild and regiospecific β-eliminations. A dramatic solvent effect was observed, DMSO was crucial for the reactions. The temperature is also crucial for the reactions and should be kept between 60 and 80 °C.     

N-Cyanomethyl-β-chloroamines: a convenient source of aziridinium ions

N-Cyanomethyl-β-chloroamines smoothly react with a range of alcohols or amines to give regio- and stereoselectively 1,2-aminoethers or 1,2-diamines. The reaction proceeds through the formation of an intermediate aziridinium ion. The N-cyanomethyl group can then be cleaved easily.     

Practical synthesis of a functionalized 1-oxo-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid

The synthesis of a functionalized 1-oxo-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid has been performed in 10 steps from the readily available dimedone. Only three purifications by flash chromatography are required through the whole sequence. The key step is the reaction between a dimedone derivative and a chlorotetrolic ester, that gives a tetrasubstituted benzene ring (through a Diels-Alder/retro- Diels-Alder process) bearing the substituents in the suitable positions for further functionalization.     

Syntheses,separation of enantiomers and barriers to racemization of some sterically hindered N-aryl-1,2,3,4-tetrahydro-3,3-dimethyl-2,4-quinolinediones and their thio analogues

Summary The novel N-aryl-1,2,3,4-tetrahydro-3,3-dimethyl-2,4-quinolinediones1,4 and8 were thiated with Lawesson reagent and P₄S₁₀ to yield the monothio derivatives2 and5 and the dithio compounds3, 6 and9. Their enantiomers were separated by liquid chromatography on triacetyl- or tribenzoylcellulose. Rotation barriers for1–4 and8 were determined by thermal racemization and discussed in terms of steric effects.

---

Synthese, Enantiomerentrennung und Barrieren zur Racemisierung einiger sterisch gehinderter N-Aryl-1,2,3,4-tetrahydro-3,3-dimethyl-2,4-chinolindione und ihrer Thio-Analogen

Zusammenfassung Die neuen N-Aryl-1,2,3,4-tetrahydro-3,3-dimethyl-2,4-chinolindione1, 4 und8 wurden mit Lawesson-Reagens und P₄S₁₀ zu den Monothioderivate2 und5 und den Dithioverbindungen3, 6 und9 thioniert. Ihre Enantiomeren wurden mittels Flüssigchromatographie an Triacetyloder Tribenzoylcellulose getrennt. Die Rotationsbarrieren für1–4 und8 wurden mittels thermischer Racemisierung bestimmt und aufgrund der sterischen Gegebenheiten diskutiert.

     

Fluoroalkene chemistry: Part 2. Reactions of thiols with some toxic 1,2-dichlorinated polyfluorocycloalkenes

1,2-Dichlorotetrafluorocyclobutene, 1,2-dichlorohexafluorocyclopentene and 1,2-dichlorooctafluorocyclohexene were treated with an equimolar amount of benzenethiol, 2-methoxybenzenethiol, 3-methoxybenzenethiol and 4-methoxybenzenethiol in acetonitrile with potassium carbonate. Each combination of fluoroalkene and thiol gave a mixture of mono and bis vinyl substitution products whose proportions depended on the ring size of the fluorocycloalkene and the size and electronic characteristics of the thiol. Treatment of 1,2-dichlorotetrafluorocyclobutene with one or two molar equivalents of N-acetylcysteine isopropyl ester in acetonitrile with potassium carbonate produced the mono and bis vinyl substitution products accordingly. The results support the contention that the high inhalation toxicity of the fluorocycloalkenes is due to reaction with two molar equivalents of biological thiols in the lung.     

Die CuCl-katalysierte Reaktion von Trimethylsilyl(t-butyl)chlorphosphan mit Dimethylzirconocen: Ein Beispiel der Tandem-Katalyse

The CuCl-catalyzed Reaction of Trimethylsilyl(t-butyl)chlorophosphane with Dimethylzirconocene: An Example for Tandem Catalysis t-BuP(SiMe₃)Cl was prepared from t-BuP(SiMe₃)₂ and hexachloroethane and reacted in situ with Cp₂ZrMe₂ in the presence of catalytic amounts of copper(I) chloride yielding t-Bu(Me)P? P(Cl)t-Bu ( 1 ) (2 : 1 reaction) or t-Bu(Me)P? P · (Me)t-Bu ( 2 ) (1 : 1 reaction) and Cp₂ZrCl(Me). To understand the course of reaction, the reaction of dimethylzirconocene with CuCl and the decomposition of t-BuP(SiMe₃)Cl in the presence of CuCl and tetrachloroethene were studied. The results suggest that CuCl reacts with t-BuP(SiMe₃)Cl in the presence of C₂Cl₄ to give t-Bu(Cl)P? P(Cl)t-Bu ( 3 ); simultaneously, CuCl reacts with Cp₂ZrMe₂ with formation of methylcopper, which reacts with 3 to give 1 or 2 , respectively.     

Molecular structure and conformation flexibility of 2-oxo- and 2-thioxo-1,2,3,4-tetrahydropyrimidines and their derivatives

The conformational flexibility and effects of the substituents in 2-oxo- and 2-thioxo-1,2,3,4-tetrahydropyrimidines were studied by the semiempirical quantum-chemical AM1 method. The substituents at the double bond have no appreciable effect on the conformational characteristics of the heterocycle. The introduction of substituents to the saturated carbon atom results in the conversion of the tetrahydrocycle to a half-chair conformation and in a substantial decrease in the ring flexibility. The results of calculations are confirmed by the X-ray study of both compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya No. 11, pp. 1941–1946, November, 1997.     

Highly Efficient Solvent-Free Synthesis of Dihydropyrimidinones Catalyzed by Zinc Oxide

A simple, efficient and practical procedure for the Biginelli reaction using zinc oxid (ZnO) as a novel and reusable catalyst is described under solvent-free conditions in high yields. The use of this agent is characterized by remarkable reactivity, moderate costs, low toxicity and simple work up procedures.