G. Smets

Cycloaddition reactions of azides with electron-poor olefins : Isomerization and thermolysis of the resulting Δ2-triazolines

The cycloaddition reactions of phenyl azide and butyl azide with monosubstituted electronpoor olefins are highly regioselective (if not regiospecific) and lead to 1,4-disubstituted Δ2-triazolines or products derived therefrom: aziridines, diazocompounds, pyrazolines and 1,4-trisubstituted triazolines. As expected, the latter three products are not formed when a methyl group is introduced in the geminal position of the olefins, but Δ2-triazolines and aziridines are then obtained exclusively. In all cases studied the 1,4-substituted Δ2-triazolines derived from phenyl azide only give aziridines on thermolysis, whereas those derived from alkyl azides are thermally converted into a mixture of aziridine and enamine.

Reactions of aryl azides with α-keto phosphorus ylides

Abstract Acylmethylenetriphenylphosphoranes react with aryl azides in refluxing benzene to give 1-aryl-5-substituted-1,2,3-triazoles exclusively. The regiochemistry of the reaction was resolved by comparison of the triazoles with authentic samples, prepared by the Dimroth method. From the kinetic point of view, the reaction is accelerated by electron-withdrawing substituents on the azide and electron-releasing substituents on the ylide. The polarity of the solvent has only a small effect on the reaction rate. Finally, the low entropies of activation support a concerted cycloaddition in the first step of the reaction.

Reactions of azides with α-ester phosphorus ylids

Abstract The reactions of α-ester phosphorus ylids with several azides are described together with a kinetic investigation. The two reaction courses, leading either to diazo compounds or to vic -triazoles, are interpreted as proceeding by an addition elimination sequence. The low values of the entropies of activation provide evidence for a concerted addition in the first step of the reaction.

Synthesis and spectral characteristics of vinyltetrazolinones

Abstract Several methods have been worked out to synthesize 1 - vinyl - 4 - substituted - Δ 2 - tetrazolin - 5 - ones. NMR spectra showed typical AMX-patterns for the vinyl protons with chemical shifts and coupling constants almost independent of the nature of the other N-substituent. From the shielding increments, it was concluded that the tetrazolinone group exercises a strong inductive electron-withdrawing effect, but only a small resonance effect on the vinyl group. This paper also describes the first cycloreversions of azide adducts, induced by electron impact. Other significant fragmentation patterns of several mono- and disubstituted tetrazolinones are discussed.

Reactions of carbonyl azides with α-keto phosphorus ylides : Synthesis of N-2 acyl and N-2 carbethoxy-1,2,3-triazoles

Abstract A general method for the synthesis of N-2 acyl and N-2 carbethoxy-1,2,3-triazoles is provided by the title reaction. The corresponding N-1 triazoles were shown to be the precursors of the N-2 triazoles and their respective regiostructures were elucidated by NMR. New kinetic data are presented which fully support a concerted mechanism for the cycloaddition step.

A new synthetic method for 5-sulfonylimino-1,4,2-oxathiazoles

Abstract Nitrile oxides reacted with sulfonyl isothiocyanates to give 3-substituted-5-sulfonylimino-1,4,2-oxathiazoles ( 4a-i ) in moderate to good yields. Although thermolysis of the adducts at ca. 200° furnished a complex mixture of reaction products, decomposition in methanol or dimethylamine proceeded cleanly and yielded respectively urethanes and ureas.

Reactions of carbethoxyalkylidenetriphenylphosphoranes with aryl azides

Abstract The title reaction has been shown to give a complex mixture of products from which triazoles (12 and 17), maleates (13), fumarates (14), triphenylphosphine oxide (15), iminophosphoranes (16) and triazenes (18) have been isolated. Their formation is rationalized by two reaction paths, involving addition of the azide onto the CC and CP bonds of the ylide. Diazoesters 5 and 19, which should result from CP addition, were not isolated, but are believed to give rise to compounds 13,14 and 18.

Reactions of ethyl azidoformate and substituted benzoyl azides with carbonyl-stabilized sulfonium ylides

Abstract The title reactions proceed by nucleophilic attack of the ylides either on the terminal nitrogen atom, or on the carbonyl function of the azides. The first pathway produces vinyl triazenes (6), cyclopropyl triazenes (7) or their presumed decomposition products, amides (14 and 17). In solution, several triazenes (6a and 7e-g) exist in the Δ2-triazoline form (8 and 11e-g), which can eventually decompose to N-acyl amides (15) when strong electron-withdrawing groups are attached to the N1-nitrogen atom. The second pathway, leading to new stabilized sulphur ylides (18), is observed in the reactions of m- and p-nitrobenzoyl azide with carbethoxymethylenedimethylsulphurane. Spectral data which led to structure elucidation are discussed.

UMSETZUNG VON ACYLMETHYLENTRIPHENYLPHOSPHORANEN MIT BENZONITRILOXID

Bei der Umsetzung des Ylids (III) mit Benzonitriloxid (II) in Methylenchlorid entstehen nebeneinander das Isoxazol (I) in 8%iger und das stabile Ylid (IV) in 21,5%iger Ausbeute.