Jochims, Johannes
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Nitrosation of sugar oximes : preparation of 2-glycosyl-1-hydroxydiazene-2-oxides
Oximes of glucose, xylose, lactose, fructose, and mannose have been prepared. Nitrosation of the oximes of glucose, xylose, and lactose with NaNO2/HCl afforded 2-(-glycopyranosyl)-1-hydroxydiazene-2-oxides, which were isolated as salts 13, 22, and 28. Nitrosation of fructose oxime 29 furnished fructose, whereas nitrosation of mannose oxime 30 with NaNO2/HCl afforded the 1-hydroxy-2-(-d-mannopyranosyl)diazene-2-oxide 32, from which the p-anisidinium salt 31 and the sodium salt 33 were prepared. However, nitrosation of 30 with isopentyl nitrite in aqueous solutions of CsOH or KOH resulted in the formation of the 2-(-D-mannofuranosyl)-1-hydroxydiazene-2-oxide salts 34 and 35, respectively. Methylation of the ammonium 2-(-D-glucopyranosyl)-1-hydroxydiazene-2-oxide 13 yielded the 1-methoxy compound, which was benzoylated to afford the tetra-O-benzoate 14 a, the structure of which was confirmed by X-ray diffraction analysis. From the glucose O-methyloximes 15 and 16 the N-methoxy-N-nitroso-2,3,4,6-tetra-O-acetyl--D-glucopyranosylamine 18 was prepared. The structure of this compound was confirmed by X-ray diffraction analysis. Treatment of acetobromoglucose with cupferron furnished the 1-(2,3,4,6-tetra-O-acetyl--D-glucopyranosyloxy)-2-phenyldiazene-2-oxide 20.
Synthesis of N-Acyliminium Salts by Reaction of Nitrilium Salts with Ketones
A new method for the preparation of N-acyliminium salts 3a-ab by reaction of nitrilium salts 1 with non-enolizable alkyl and aryl ketones 2 is described. Ketones without electron-releasing substituents react only with N-arylnitrilium salts 1. An X-ray structural analysis was carried out for the N-acyliminium salt 3j. From variable temperature NMR spectroscopy intramolecular conformational changes (essentially rotation around the iminium C=N double bond, coupled to rotation about the amide C-N single bond) of few compounds 3 were determined. The observed barriers to hindered rotation are compared with barriers calculated by the AM1 method.
On the Reaction of Nitrilium and N-Acylamidinium Salts with Oximes and Other Hetero Nucleophiles
Nitrilium salts 2 add oximes 1 to form stable alkylideneaminooxy-substituted iminium salts 4. Compounds 4 have been postulated by Meerwein as intermediates of the Beckmann rearrangement of oximes[1]. For (E)-4c an X-ray structural analysis is performed. Other intermediates of the Beckmann rearrangement are the N-acylamidinium salts 5, which are produced by the reaction of nitrilium salts with amides. As models for the transformation of 5 into amides, the end products of the Beckmann rearrangement, reactions of N-acylamidinium salts with nucleophiles, e.g. oximes, alcohols, water, amines, thiols, and benzophenone imine are studied.
N-acyliminium salts from the reaction of nitrilium salts with aldehydes
The nitrilium hexachloroantimonates 2a,d,g,p react with aromatic aldehydes to give isolable N-acyliminium hexachloroantimonates 10a-m. The N-aroyliminium salts (10g-m) and acyliminium salts with an aliphatic N-acyl group (10a-f) are of remarkably different stability. Contrary to the N-aroyliminium salts, compounds 10a-f are unstable in solution, e. g. react immediately with acetonitrile. With excess of aldehyde 10n,o give insertion products of the probable structures 12a,b. For 10b,f X-ray structural analyses have been carried out. The N-acylcyanamidium hexachloroantimonate 2p reacts with aldehydes to give new classes of cyclic N-acyliminium salts 13a-f, and 14f, respectively.
On alkylideneamidosulfenyl chlorides and 1-Thia-2-azoniaallene salts
X-Ray-diffraction analysis of tBu2CNSCl (4b) revealed an almost linear CNS unit with an SN bond order of ca. 1.9 (Fig. 1), in agreement with the structure of a 1-thia-2-azoniaallene chloride. With SCl2 and SbCl5, compound 4b was transformed into the imidosulfurous dichloride 6 (Scheme 2). With morpholine, compounds 4b and 6 afforded the sulfenamide 7and the aminosulfonium salt 8, respectively. The (diarylmethylene)amidosulfenyl chlorides 4g,h,i reacted with SbCl5 to give SbCl salts of the 1,2-benzisothiazoles 9a,b,d, most likely via 1-thia-2-azoniaallene intermediates 2 (Scheme 3).
Some reactions of 1,3-Dichloro-2-azoniaallene Salts with heteronucleophiles
1,3-Dichloro-2-azoniaallene hexachloroantimonates (1) reacted with H2S to give 1,2,4-dithiazolium salts 2. With hydrazines 1,2,4-triazolium salts (3, 4) were formed. 1,3-Dimethylurea, respectively 1,3-dimethylthiourea or ethyl allophanate, reacted with 1 to afford 2-oxo- or 2-thioxo-1,3,5-triazinium salts (5–7). With diphenylmethaneimines imino substituted 2-azoniaallene salts 8 were produced. From chloroacetonitrile dichloropyrimidines 9, and from the tricyanomethyl anion a hexatriene 10 and a triazine 11 could be prepared. The 1,5-dichloro substituted 2-azoniaallene salts 12 reacted as bifunctional electrophiles with nucleophiles such as benzophenone hydrazone or anilines, to furnish 1,3,5-triazinium salts 14. Against benzohydrazide the allene 12j behaved as trivalent electrophile giving the bicyclic 1,3,5-oxadiazinium salt 13j, the constitution of which has been secured by a crystal structural analysis. The vinyl-2-azoniaallene salt 1i cyclized on heating to the 1,3-thiazinium salts 16, 17. From 17 the triazinium salts 18 were prepared with alcohols.
On the Reaction of alpha,alpha-Dichlorocarbenium Ions with Isocyanates
Trichlormethanes 4 react with two equivalents of n-alkyl isocyanates R2-NCO in the presence of SbCl5 to furnish the 2,2-dichloro-5,6-dihydro-6-oxo2H-1,3,5-oxadiazinium salts (9). The structure of these heterocycles is confirmed by an X-ray analysis of 9d (R1 = ClC = CCl2, R2 = Et). p-Tolyl isocyanate is Friedel-Crafts alkylated by 4b in the presence of SbCl5. Subsequent ring closure affords the quinolinium salt 13, which is hydrolyzed to give inter alia the quinolone 16.
Cycloadditions of 1-aza-2-azoniaallene cations to isothiocyanates
Isothiocyanates react as S-nucleophiles with 1-aza-2-azoniaallene salts 1 to give different types of 1,3,4-thiadiazolium salts (9, 11, 12) and 1,2,4-triazolium salts (10). Which product is formed, depends on the one hand on the ability of a substituent of the heteroallene salt 1 to undergo a [1,2] shift as a positively charged migrant (generalized Wagner–Meerwein rearrangement) or to act as a cationic leaving group, and on the other hand on Dimroth rearrangement of the initially formed thiadiazolium salt 8 to triazolium salts. The structures of the thiadiazolium salt 9c and the triazolium salt 10d were confirmed by X-ray structural analyses.
On the Reaction of 1-Aza-2-azoniaallene Salts with Carbodiimides
1-Aza-2-azoniaallene cations 3, prepared in situ from geminal (chloroalkyl)azo compounds 2, react with carbodiimides 4 to give 4,5-dihydro-5-imino-1H-1,2,4-triazolium salts 7. An X-ray structural analysis was carried out for 71. According to AM1 calculations the cycloaddition of carbodiimides to 1-aza-2-azoniaallene cations occurs in a nonconcerted manner via cyanamidium cations 5 as intermediates. Hetero-Wagner-Meerwein rearrangements of the primary cycloadducts 6 provide the final products 7.
Reactions of 1-Thia-3-azoniabutatriene Salts with Alcohols, Carbonyl Compounds, Diazoalkanes, Nitrile Oxides, Nitrones, Enamines, and Butadienes
1-Thia-3-azoniabutatriene salts 1 react with alcohols, carbonyl compounds, diazo alkanes, nitrile oxides, nitrones, enamines, and 1,3-butadienes in all cases at the C=S double bond to yield new types of 2-azoniaallene salts (3, 9a, b, 13a, b, 18, 22) and other imines (2, 20). An X-ray diffraction analysis for 9b, the reaction product of 1b with 9-diazofluorene, confirms the proposed constitution.