α-Chlor-nitrone I: Darstellung und Ag+-induzierte Reaktion mit Olefinen. Über synthetische Methoden, 5. (vorläufige) Mitteilung

Organic synthesis may be said to be in need of enophiles, i.e. reagents that would undergo cycloaddition reactions with any isolated olefinic double bond, in contrast to most of the classical Diels-Alder or 1,3-dipolar addition reagents which, as a rule, require activated olefins in order to participate smoothly in cycloaddition processes. This paper introduces α-chloronitrones as precursors of a new class of such reagents; they undergo an Ag⁺-induced reaction with unactivated olefins with great ease to give products considered to result from 1,4-cycloadditions of N-alkyl-N-vinyl-nitrosonium ions to the carbon-carbon double bond (see scheme 2). This process is believed to have a number of synthetic applications, two of them being illustrated in two subsequent communications.     

α-Chlor-nitrone IV: Zur Stereochemie der λ-Lacton-Synthese und eine Methode zum Aufbau von α-Methyliden-λ-lactonen aus Olefinen. Über synthetische Methoden, 8. (vorläufige) Mitteilung

The Ag⁺-induced reaction between N-cyclohexyl-α-chloro-propionaldonitrone and the two diastereomeric 2-butenes in liquid SO₂ is a stereospecific cis-addition. The use of N-cyclo-hexyl-α,β-dichloro-propionaldonitrone in this type of reaction provides a preparative route from olefines to α-methylidene-butyrolactones.     

α-Chlor-nitrone III: Ein Weg zur indirekten «carboxolytischen» Spaltung von Olefin-Doppelbindungen. Über synthetische Methoden, 7. (vorläufige) Mitteilung

The enaminoid derivatives formed by deprotonation of the olefin-α-chloro-nitrone cycloadducts (see preceding communications) undergo a beautifully clean cycloreversion at ambient or slightly elevated temperatures. The sequence (2+4)-cycloaddition → deprotonation → (2′+4)-cycloreversion constitutes a potentially useful method for the oxidative cleavage of olefinic double bonds with concomitant extension of the carbon chain at one of the double bond termini (indirect «carboxolytic» cleavage of double bonds; see schemes 1 and 3).     

α-Chlor-nitrone V: Substitutionsreaktionen an Olefin- und Benzolderivaten. Eine Methode zur Darstellung von β,γ-un-gesättigten und β- arylsubstituierten Aldehyden. Stereospezifische Bildung von tetra-alkylsubstituierten Olefindoppelbindungen. Über synthetische Methoden, 9. (vorläufige) Mitteilung

The Ag⁺-induced α-chloro-aldonitrone/olefin reaction in polar solvents can proceed by substitution, thereby providing a method for the preparation of β, γ-unsaturated aldehydes. Positional as well as configurational retention of the olefinic double bond are mechanistically significant and preparatively useful characteristics of this process. Substitution also occurs with great ease at nucleophilic aromatic nuclei; this offers a simple preparative route to certain β-aryl-aldehydes. The results illustrate a general aspect of the chemistry of α-chloro-aldonitrones: the N-alkenyl-N-alkyl-nitrosonium-ions derived from them can serve as preparative equivalents of the elusive corresponding α-acyl-carbonium-ions.     

α-Chlor-nitrone VI: Ag+-induzierte Reaktion mit Acetylen-derivaten. Eine neue Bildungsweise von α,β-ungesättigten Carbonylsystemen Über synthetische Methoden, 10. (vorläufige) Mitteilung

α-Chloro-aldonitrones provide a novel synthetic pathway from acetylenes to αβ-unsaturated enone systems.     

Notiz über eine regiospezifische Methode zur Herstellung von konjugierten Cyclohexadienen Über synthetische Methoden, 11. Mitteilung

β,γ-unsaturated δ-hydroxy-cyclohexene carboxylic acids undergo a smooth decarboxylative elimination when treated with DMF-dineopentylacetal in an unpolar solvent. The reaction provides a method for the regiospecific preparation of 1,3-cyclohexadiene derivatives under non-isomerizing conditions, starting from easily accessible and structurally variable intermediates.     

Über Pterinchemie. 60. vorläufige Mitteilung [1]. Eine neue,regiospezifische Synthese von L-Biopterin

A new, regiospecific synthesis of L -biopterine Pure L -biopterine (I) is obtained in 35–40% yield by condensation of 5-desoxy-L -arabinose-hydrazone acetate with 2,4,5-triamino-6-hydroxy-pyrimidine, followed by oxidation of the formed tetrahydro-derivative and deacetylation of the L -bioterine diacetate. Catalytic reduction of the L -biopterine gives the expected mixture of two diastereomeric tetrahydro-L -biopterines.     

Sulfidkontraktion via alkylative Kupplung: Eine methode zur darstellung von β-dicarbonylderivaten. Über synthetische methoden, 1. Mitteilung

The experiments described in reaction schemes 1–12 indicate that sulfide contraction via alkylative coupling (see scheme p. 729) is a potentially general method for the synthesis of secondary vinylogous amides and enolizable β-dicarbonyl compounds.     

α,β-Epoxyketon → Alkinon-Fragmentierung II: Pyrolytischer Zerfall der Hydrazone aus α,β-Epoxyketonen und N-Amino-aziridinen. Über synthetische Methoden, 4. Mitteilung

Numerous examples illustrate the course of the thermolysis of hydrazones derived from α,β-epoxyketones and 2-phenyl- or trans-2,3-diphenyl-1-amino-aziridines. This process constitutes a preparatively useful method for the fragmentation of α,β-epoxyketones to acetylenic carbonyl compounds including acetylenic aldehydes. Monohydrazones from phenylglyoxal and substituted N-amino-aziridines decompose smoothly and stereospecifically to the corresponding olefins and diazoacetophenone; such a process might also be useful for the preparation of other α-diazocarbonyl compounds.     

Über die Stereospezifität der α-Alkylierung von β-Hydroxycarbonsäureestern. Vorläufige Mitteilung

About the Stereospecific α-Alkylation of β-Hydroxyesters It was found, that dianions derived from β-hydroxyesters with lithium diisopropylamide (LDA) at ?50 to ?20° were alkylated stereospecifically (Scheme 1). The stereospecificity was 95–98%, the threo-compound (threo -2, -3 and -4) being the main product. This was proved for threo -2 and -3 by preparing the β-lactones 7 and 8 , respectively, which were pyrolyzed to trans-1, 4-hexadiene (9) and trans-1-phenyl-2-butene (10) , respectively (Scheme 2). Moreover, the acid threo -6 from threo -3 was converted by dimethylformamide-dimethylacetal to cis-1-phenyl-2-butene (11) (s. footnote 6). The alkylation of α-monosubstituted β-hydroxyesters also turned out to be stereospecific. Reduction of 16 and 18 with actively fermenting yeast furnished (+) -17 and (+) -2. respectively (Scheme 4), which were each mixtures of the (2R, 3S)- and the (2S, 3S)-isomers. Alkylation of (+) -17 with allyl bromide yielded after chromatography (2S, 3S) -19 and of (+) -2 with methyl iodide (2R, 3S) -19 , the oxidation of which finally gave (S)-(?) -20 and (R)-(+) -20 , respectively.     

Über ein neues Verfahren zur Herstellung von. Acetylenverbindungen. Vorläufige Mitteilung

A new method for the preparation of acetylenes by reating α-halogeno- or α-sulfonyloxyketones with p-toluenesulfonylhydrazine is reported.     

Eine neue Methode zur Herstellung gemischter Disulfide. Vorläufige Mitteilung

A New Synthesis of Unsymmetrical Disulfides. A new synthesis of unsymmetrical disulfides 3a via alkylthio-dialkyl-sulfonium salts 6 is reported.     

Über Enolderivate der Chlorophyllreihe. Darstellung von 132,173-Cyclophäophorbid-enolen. Vorläufige Mitteilung

Enol derivatives in the chlorophyll series. Preparation of 13²,17³-cyclopheophorbide enols 13²,17³-Cyclopheophorbide enols have been prepared as model systems for studying the effect of ring E enolization upon the properties of chlorophyll derivatives.     

Notiz über Methoden zur Umwandlung von 1,2-Dicarbonsäuren in konjugiert ungesättigte Monocarbonsäuren. Über synthetische Methoden, 12.Mitteilung

A Note on Methods for the Transformation of 1,2-Dicarboxylic Acids into α, β-Unsaturated Monocarboxylic Acids. A model study using the Diels-Alder adduct of maleic anhydride and butadiene (see scheme 3) exemplifies the conversion of the succinic acid type of structure into α, β-unsaturated carboxylic acids via two complementary fragmentations of 3,6-dioxo-perhydro-1,2-oxazine derivatives.     

Über die Konstitution von Loroglossin. Vorläufige Mitteilung

The Constitution of Loroglossine. Loroglossine, a characteristic constituent of orchids, is shown to be bis-[4-(β-D -glucopyranosyloxy)-benzyl]-(2 R, 3 S)-2-isobutyl-tartrate ( 1 ). Hydrolysis and esterification gave 1 mol-equiv. of dimethyl (+)-2-isobutyl-erythro-tartrate ((+)-3) and 2 mol.-equiv. of a glucoside which, after acetylation, gave 4 , identical with a synthetic sample. The erythro configuration of (+)- 3 by oxidation of isobutyl-maleic acid with osmium tetroxide and subsequent esterification. The absolute configuration of (+)- 3 was based on Horeau experiments and NMR. data of the diastereomeric mixture of its esters 7 and 8 with S (+)- and R (?)-α-phenylbutyric acid respectively.     

Synthese von 1α-Hydroxycholecalciferol. Vorläufige Mitteilung

1α-hydroxycholesterol ( 4a ) was synthesized from cholesterol and transformed via its diacetyl derivative 4b into 1α, 3β-diacetoxycholesta-5, 7-diene ( 6b ). Irradiation of the ring-B-diene 6b followed by thermal isomerization and saponification gave 1α-hydroxycholecalciferol ( 7 ).     

Photochemie von Benzisoxazolen. (vorläufige Mitteilung)

The photochemical behaviour of benzisoxazoles 1 is remarkably solvent-dependent: Irradiation in H₂O or CH₃O or CH₃OH leads to benzoxazoles 2 in a virtually quantitative yield. However, at low concentrations of H₂O or CH₃OH in acetonitrile or hexane, photolysis of 3-alkyl-benzisoxazoles 1b–1e yields salicylamides 4 and salicylesters 5 , while under these conditions o-cyanophenol ( 3a ) is the only photoproduct of benzisoxazole ( 1a ). The course of these photochemical reactions is discussed from the standpoint of solvent-dependence, multiplicity and the behaviour at low temperatures.