Photochemische Bildung von Hetermethylencyclopropanen, 16. 1,4,5‐Substituierte Tetrazoliumsalze durch Methylierung von 1,5‐substituierten Tetrazolen und [3 + 2]‐Cycloaddition von Alkylaziden an Nitrilium‐Ionen

Abstract

Ergiebige Synthesen isomerenreiner 1.4.5-substituierter Tetrazoliumsalze werden mitgeteilt: Durch Methylierung 1,s-substituierter Tetrazole 5 entstehen Gemische l,4,5-(1) und 1J.S-substituierter Tetrazoliumsalze 6. Das Verhiiltnis 1:6 hiingt nur wenig von den Reaktionsbedingungen und der Art dcr Methylicrungrcagenzien ab. Durch fraktionierende Kristallisation werden die isomerenreinen Tetrazoliumsalze la-e, g, j, k und 6j. k isoliert.rrrr-Butylierung von 5a. c mit terr-Butylalkohol/retranuoroborsiure ergibt nur die 3-rerr-Butyltetrazolium-tetranuoroborate 9a, c. Die N-Methylnitrilium-tetrafluoroborate. The ratio 1 :6 depends only little on the reaction conditions as well as on the methylating agents. The isomerically pure tetrazolium salts !a-e, g, j, k and 6j, k are isolated by fractionating crystallizations. rerr-Butylation of 5% c using terf-butyl alcohol/ tetrduoroboric acid produces only the 3-~ert-butyltetrazolium tetrduoroborates 9s, c The N-methylnitrilium tetrafluoroborates, fluorosulfonates or trinuoromethanesulfonates 7 s -e and e cycloadd the akyl azides 8a-d regioselectively to the tetrazolium salts la-c, e, f, h, i. Both rate and yield of the [3 + 23 cycloaddition decrcase with increasing size of the substituents. The Nterf-butylnitrilium tetrachloroferrate 7b (X = FeCI,) reacts with methyl azide @a) yielding the hydrogen tetrachloroferrate 4a . HFeCL of the imidoyl chloride 4a.rnit Alkaliaziden oder Ammoniumazid erhalt. Fur die Herstellung der N-Methylnitriliumsalze 7 a -e verwendeten wir FIuorsulfons~ure-methylester9~, Trifluormethansulfonsauremethylester'") oder Trimethyloxonium-tetrafluoroborat ll).In alteren Arbeiten wurden be1 der Quartarisierung von 1,5-substituierten Tetrazolen6'2,11~ fast imrnerl4) nur 1,4,5-substituierte Tetrazoliumsalze isoliert. Wir beobachteten dagegen anhand der 'H-NMR-Spektren der Rohprodukte ambidentes Verhalten der Tetrazole 5 gegeniiber allen Methylierungsreagenzien'5,16). Stets bildeten sich Gemische der 1,4,5-(1) und 1,3,5-substituierten Tetrazoliumsalze 6, deren Verhaltnis sich leicht 'H-NMR-spektroskopisch ermitteln lielj (Tab. 1). Urn ein moglichst groljes Verhaltnis 1 : 6 zu erhalten, untersuchten wir den Einflulj der Reaktionsbedingungen, Substituenten und Natur des Methylierungsreagens. Erwartungsgemalj nahm unter sonst gleichen Bedingungen die Methylierung voii N-4 rnit zunehmender GroRe des Substituenten an C-5 ab, also in der Reihe 5 c > 5d > 5b > 5a. Das

Triazenes by Acid‐Mediated Opening of the Dihydro‐1,2,3‐triazole Ring of1,3‐Dipolar Cycloadducts of Organic Azides to Cyclic Ketene N,N‐Acetals

“…The spiro carbon-13 signals at 100-105 ppm [9,10] are no longer observed while 1 H and 13 C NMR signals that are characteristic of 5-alkyl-1,4-dimethyltetrazolium ions make their appearance. [11] These results indicate that the dihydrotriazole ring of 1a and d was opened to yield a triazene. Addition of one equivalent of [D]hydrochloric acid to a solution of 1d in [D 4 ]methanol transformed 1d in the same way as the dihydrogen phosphate buffer.…”

“…IR: Perkin-Elmer 1420. The spirocycles 1a, d, [10] 1b, c, and 4 [11] were prepared according to known procedures. Tetrafluoroboric acid in diethyl ether (54 %, d = 1.19 g mL -1 ) was purchased from Merck, Darmstadt.…”

Reactions of some nitrogen heterocycles with chlorodifluoromethane under conditions of phase-transfer catalysis

“…Column chromatography was performed using Merck basic aluminiumoxid 90 (70-230 mesh) with hexane and ethyl acetate mixtures (gradient) as eluents. Chlorodifluoromethane (1) and heterocycles 2a-d,h were commercial materials, while benzimidazoles 2e [26], 2f [27], 2g [28], 2i,2j [29], benzotriazole 2k [30] and benzyltetrazole 6 [31] were prepared by literature procedures.…”

Comparative semiempirical calculations of tetrazole derivatives

“…Moreover, the significant localization of charges on the N(l) and N(4) atoms of 1-and 1,5-substituted tetrazoles accounts, to a certain extent, for their high reactivity in exhaustive alkylation [20,42,43] and complex-formation [45] reactions as compared to the corresponding 2-isomers. We have established a reliable correlation between the Mmo-calculated .rr-charges of nitrogen atoms and the chemical shifts of these atoms in "N-NMR spectra [30].…”

“…At the samt time, the calculated PA values obtained both in the present paper (Table 11) and using ab initio calculations [5] indicate that 1-and 1,5-substituted tetrazoles are characterized by a relatively small difference between the values of protonation energies for N(4) and Ng) atoms (e.g., APA is 8.3 and 9.5 kcal/mol, respectively, for 1-methyltetrazole 3 and 1,5-dimethyltetrazole a), whereas for 2-and 2,5-isomers, this difference is more significant (&A amounts to 22.8 and 20.9 kcal/mol, respectively, for 2-methyltetrazole 4 and 2,5-dimethyltetrazole 7). These data are in good agreement with the results of investigation of tetrazole derivative quaternization processes and explain, to a certain extent, the formation of a mixture of 1,3,5-and 1,4,5-tetrazolium salts with predomination of the 1,4,5-isomer upon exhaustive alkylation of 1-and 1,5-disubstituted tetrazoles and the high selectivity of the quaternization process of 2-and 2,s-disubstituted tetrazoles when alkylation occurs exclusively at the N(4) atom of the cycle [20,42,43].…”