Search results for "SELECTIVITY"

Synthesis of ?-fucosyl glycosides and disaccharides using 4-methoxybenzyl (Mpm) protected fucosyl donors

1992

The 4-methoxybenzyl (Mpm) group removable by selective oxidation was applied as a nonneighbouring-group-active protection of fucose hydroxy functions in the stereoselective synthesis of α-fucosides of acceptors containing double bonds sensitive to hydrogenation. With this aim, the synthesis of the α-fucosyl chloride (4) carrying the acidsensitive Mpm protection was elaborated.

Polyenolates of Unsaturated Carboxylic Acids in Synthesis. Synthesis of Unsaturated α-Amino Acids and β-Hydrazing Acids

1991

Abstract Regioselective reaction of lithium diene-and triene-diolates 1 and 2 with O-diphenylphosphinyl hydroxylamine affords unsaturated α-amino acids 3 and 4. Addition to DEAD leads selectively to γ-hydrazino unsaturated acids 5 and 6.

Einführung einer Dreifachbindung in das Bicyclo[6.1.0]nonan-Gerüst

1987

Ausgehend von den auf verschiedenen Wegen zuganglichen Ketonen 1a–c wird die Einfuhrung einer Dreifachbindung in das Bicyclo[6.1.0]nonan-Gerust mit Hilfe der Selenadiazol-Methode untersucht. Dabei Konnen die hochgespannten Bicyclo-[6.1.0]nonine 2a und 2b in reiner Form isoliert werden. Masgeblich fur die Position der Dreifachbindung ist die Regioselektivitat der Ringschlusreaktion bei der Selenadiazolbildung. Introduction of a Triple Bond into the Bicyclo[6.1.0]nonane Skeleton The introduction of a triple bond into the bicyclo[6.1.0]nonane skeleton is investigated by applying the selenadiazole method to the ketones 1a–c, accessible on different pathways. The highly strained bicyclo[6.1.0]no…

Synthese von Benzo[b]thioxanthenen

1995

Synthesis of Benzo[b]thioxanthenes Benzo[b]thioxanthenes, heterocyclic compounds related to tetracenes and tetracyclines can be obtained by the reaction of 2H-benzo[b]thiete (1) and 1,4-naphthoquinones (3a–g). The primary cycloadducts 4a–g undergo an autoxidation process leading to the quinones 6a–g. The dihydroxy compound 4e shows an additional isomerization by a tetrafold H transfer (4e 5e′). Another preparative route to benzo[b]thioxanthenes makes use of the cycloadditon reaction of 1 and 1,4-epoxynaphthalenes (7a–d). The primary adducts can be transformed to the title compounds by catalytic dehydration processes (8a–d 9a-d). An alternate regioselective opening of the oxygen bridge can b…

A tetramethoxybenzophenone as efficient triplet photocatalyst for the transformation of diazo compounds.

2007

The aromatic ketone 2,2',4,4'-tetramethoxybenzophenone has a strong absorption band between 300 and 375 nm, and its pi,pi* triplet excited-state is selectively populated in methanol. Both facts make this aromatic ketone a versatile and efficient triplet photocatalyst for the transformation of alpha-diazo carbonyl compounds into mainly the cyclopropanation product.

WEITERE SELEKTIVITÄTSSTUDIEN AM BEISPIEL EINES ARYLSULFONYLACETYLENS

1984

Abstract With 1-(phenylsulfonyl)propyne-(1) 1 as a model compound, we have investigated the competition reactions with RSH, RNH2 and ROH (R=n-Bu). With RSH and RNH2, the cis-trans-isomeric olefins 2 to 5 are formed. ROH does not react under these conditions. The compounds 6 and 7 are obtained only with ROH as the alcoholate. The reactivity of 1 with nucleophiles is increased in comparison to phenylvinyl sulfone; the selectivity of 1 is, however, decreased. The difference in reactivity of 1 and phenylvinyl sulfone corresponds to ca. 10:1. Mit 1-(Phenylsulfonyl)-propin-(1) 1 als Modellverbindung haben wir die konkurrierenden Umsetzungen mit RSH, RNH2 und ROH (R=n-Bu) studiert. Mit RSH und RNH…

Experimental and Theoretical MEDT Study of the Thermal [3+2] Cycloaddition Reactions of Aryl Azides with Alkyne Derivatives

2018

Fluoreszierende und nicht fluoreszierende (Aryl)(vinyl)sulfone — Reagenzien zum Schutz und Nachweis von Thiolfunktionen

1985

Konkurrenzversuche und kinetisch verfolgte Umsetzungen geben Aufschlus uber die Geschwindigkeit der Addition von primaren, sekundaren und tertiaren Thiolen an die (Aryl)- bzw. (Alkyl)-(vinyl)sulfone 1 und 4 – 7. Die gebildeten saurestabilen 2-(Alkyl-/arylthio)ethylsulfone werden durch Basen in einer der Bildung analogen Geschwindigkeitsabstufung wieder in die Thiole und Vinylsulfone zerlegt. Eine kinetisch gesteuerte, selektive Einfuhrung und selektive Ablosung unterschiedlicher Arylsulfonylethyl-Schutzgruppen in dem gleichen Molekul ist damit moglich. – Die Verwendung fluoreszierender Vinylsulfone (5, 10 und 11) eroffnet der Analyse und Synthese neue Einsatzfelder. Die SH-selektiven Vinyls…

Oxidative halogenation of substituted pyrroles with Cu(II). PartIV.Bromination of 2-(2′-hydroxybenzoyl)pyrrole. A new synthesis of bioactive analogs …

1994

The selective bromination with copper(II) bromide of the pyrrole ring in 2-(2'-hydroxybenzoyl)pyrrole (II) in the heterogeneous phase is des- cribed giving in almost quantitative yield the 4,5-dibromo derivative (VI). The subsequent introduction of halogen into the phenol moiety was observed when the reaction was perfomed in the homogeneous phase with an excess of halogenating agent. The pentabromo derivative (IX), a com- pound very active against Staphylococcus aureus (mic=17 nmoles per dm -3 ), was obtained by exhaustive bromination of the title compound. Poor yields of chloro derivatives of (II) were obtained by reaction of the parent compound with copper(II) chloride

Reaction of 3-Methylamino-1,2-diols with Dihalomethanes. Synthesis of Chiral 4-Substituted 3-Methyltetrahydro-1,3-oxazin-5-ols

2000

Abstract Enantiomerically pure 4,5-disubstituted 3-methyltetrahydro-1,3-oxazines have been obtained by reaction of 3-methylamino-1,2-diols with dichloromethane by regioselective differentiation of hydroxyl groups.