Diastereoselective synthesis of 3,6-disubstituted 3,6-dihydropyridin-2-ones

In a short sequence, 5-vinyloxazolidin-2-ones were converted into the 3,6-disubstituted 3,6-dihydropyridin-2-ones via Pd-catalysed carbonylation and enolate alkylation with high diastereoselectivity. Alkylation of 6-substituted N-methylpyridin-2-ones gives stereoselectively the 3,6-anti diastereoisomer with MeI, BuI and i-PrI. Alkylation of the corresponding N-BOC pyridinones gives the 3,6-syn diastereoisomer with high selectivity.     

Preparation and fungitoxicity of 3,6-dichloro-and 3,6-dibromo-8-quinolinols

Summary 3,6-Dichloro- and 3,6-dibromo-8-quinolinols were prepared by direct halogenation of 8-nitroquinoline by N-halosuccinimide in acetic acid or by halogenation of the corresponding 6-halo-8-nitroquinoline prepared via aSkraup reaction. The nitro group was reduced to amino and the amine was hydrolyzed to the phenol in 70% sulfuric acid at 220°C. The fungitoxicity of 3,6-dichloro- and 3,6-dibromo-8-quinolinols, as well as intermediates in their preparation, againstAspergillus niger, Aspergillus oryzae, Myrothecium verrucaria, Trichoderma viride, andMucor cirinelloides was determined. 3,6-dichloro-8-quinolinol is the most fungitoxic analogue of this class of compounds observed to date.

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Herstellung und Fungitoxizität von 3,6-Dichlor- und 3,6-Dibrom-8-chinolinen

Zusammenfassung 3,6-Dichlor- und 3,6-Dibrom-8-chinoline wurden durch direkte Halogenierung von 8-Nitrochinolin mit N-Halogensuccinimid in Essigsäure oder durch Halogenierung der entsprechenden nachSkraup synthetisierten 6-Halogen-8-nitrochinoline hergestellt. Die Nitrogruppe wurde zum Amin reduziert und die Aminofunktion in 70% iger Schwefelsäure bei 220°C zum Phenol hydrolysiert. Die Fungitoxizität der 3,6-Dichlor- und 3,6-Dibrom-8-chinoline und jene der bei ihrer Herstellung auftretenden Zwischenstufen gegenAspergillus niger, Aspergillus oryzae, Myrothecium verrucaria, Trichoderma viride undMucor cirinelloides wurde bestimmt. 3,6-Dichlor-8-chinolin ist der derzeit stärkste bekannte fungitoxische Vertreter dieser Substanzklasse.

     

Ring-rearrangement metathesis of 3,6-dialkoxy-3,6-dihydro-2H-pyrans

The first RCM-ROM-RCM sequence using a non-strained heterocycle as relay moiety is described. The course of the reaction strongly depends on the nature and relative configuration of the substituents in the starting trienic system. In addition, for a productive reaction to be observed, the site of initiation of the metathesis cascade is crucial. The compounds thus obtained may be useful for the synthesis of unusual polydeoxydisaccharides.     

The reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide

Reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide in aprotic solvents leads to the generation of semiquinone (SQ^.H), alkylperoxy (ROO^.), and alkyloxy radicals. The reaction of SQ^.H and ROO^. produces 2,5-di-tert-butyl-6-hydroxy-1,4-benzoquinone, 3,6-di-tert-butyl-1-oxacyclohepta-3,5-diene-2,7-dione, and 2,5-di-tert-butyl-3,6-dihydroxy-1,4-benzoquinone. The radical generated from solvent attacks SQ^.H at position 4 with C−C bond formation. 4-Benzyl-2,5-di-tert-butyl-6-hydroxycyclohexa-2,5-diene-1-dione produced in this way is transformed into 4-benzyl-3,6-di-tert-butyl-1,2-benzoquinone under the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 943–946, May, 1999.     

Fluorinated 3,6-di-tert-butyl-o-benzoquinones

New fluorine- containing 3,6-di-tert-butyl-o-benzoquinones have been synthesized. In the EPR spectra the¹⁹F hyper fine coupling constant of the corresponding semiquinones was shown to be highly dependent on the metal, its surrounding ligand, and the solvent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1098–1101, May, 1990.     

Synthesis of 3,6-diazahomoadamantane

Condensation of 1-phenylsulfanylpropan-2-one with 1,3,6,8-tetraazatricyclo[4.4.1.1^3,8]dodecane gave 1-phenylsulfanyl-3,6-diazahomoadamantan-9-one which was reduced to 1-phenylsulfanyl-3,6-diazahomoadamantane, and the latter was subjected to desulfurization over Raney nickel to obtain previously unknown 3,6-diazahomoadamantane. Heating of 9-phenyl-3,6-diazahomoadamantan-9-ols with Raney nickel resulted in reduction of the hydroxy group with formation of 9-phenyl-3,6-diazahomoadamantanes.     

Photooxygenolysis of 3,6-di-tert-butyl-o-benzoquinone

The photolysis of 3,6-and 3,5-di-tert-butyl-o-benzoquinones in benzene (λ > 380 nm, inert atmosphere) involves decarbonylation of the compounds to furnish respectively 2,5-and 2,4-di-tert-butylcyclopentadienones. The 2,5-isomer is stable, and the 2,4-di-tert-butylcyclopentadienone suffers a conversion into a Diels-Alder adduct. The participation of oxygen inhibited the decarbonylation and changed the direction of the photolysis: Here the products of the 3,5-di-tert-butyl-o-benzoquinones conversion were a di-tert-butylmuconic anhydride and dipivalylethylene. It was concluded that a singlet oxygen was involved in the process which formed by a triplet-triplet annihilation at the interaction of ³O₂ with a triplet-excited initial quinone.     

Darstellung und Konformationsuntersuchungen von cis- und trans-Isomeren des 1,2,4,5-Tetramethyl-3,6-diphenoxy-3,6-dithioxo-1,2,4,5-tetraaza-3,6-diphosphacyclohexans

Synthesis and Conformational Analysis of Cis- and Trans-Isomers of 1,2,4,5-Tetramethyl-3,6-diphenoxy-3,6-dithioxo-1,2,4,5-tetraaza-3,6-diphosphacyclohexane A mixture of isomers of the title compound could be prepared in much better yields (up to ca. 25%) by the reaction of bis(1,2-dimethylhydrazido) thiophosphoric acid O-phenylester with phenoxythiophosphoryl dichloride in the presence of triethylamine and aluminum chloride as catalyst. Separation of cis- and trans-isomers was achieved by sorting of crystals or in low yields by fractional crystallization. ³¹P- and mainly ¹H-NMR investigations at different temperatures show, that in both isomers the saturated sixmembered ring has a twist-conformation in which sulfur and phenoxy substituents located cis or trans respectively adopt the isoclinal positions. The isomers reveal remarkably different barriers of activation for the interconversion of two enantiomeric twist forms (cis ΔG^# = 63 ± 1 kJ/mol; trans 47 ± 1 kJ/mol).     

Self-association of trimethylsilyl-3,6-di-tert-butyl-o-semiquinone

The reaction of sodium 3,6-di-tert-butyl-o-semiquinolate with Me₃SiCl in THF leads to the formation of 2-(2-trimethylsiloxy-3,6-di-tert-butylphenoxy)-2-trimethylsiloxy-3,6-di-tert-butylcyclohexadien-3,5-one 1. On the basis of IR and UV spectroscopy and analysis of the reaction products, it has been determined that the cyclohexadiene structure 1 is preserved on heating to moderate temperatures or on reaction with water or HCl, but photolysis leads to its decomposition, and so does reaction with metallic sodium or alkali. A scheme of the process is propounded.Institute of Organometallic Chemistry, Russian Academy of Sciences, 603600 Nizhnii Novgorod. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2385–2389, October, 1992.     

Photosensitized oxidation of 3,6-dimethyloctane

In this paper an interesting mechanism involving a Barton reaction which leads to a propagation of photooxidation processes between γ positioned tertiary carbons is described.