Photochemical Formation of Heteromethylenecyclopropanes, 27. Annulated Tetrazolium Salts

Abstract

RI-R2-H -(CH2)2-Me -(CH2)2-3b, 4b Me -(CH2)3-H -MqC-C&-CMq-H -(CH2)3-H -(CH&-Lithiation of the annulated tetrazoles 6a, c with butyllithium yields the N-lithiotetrazoles 7a, c which are allowed to react with alkyl halides. Alkylation at the a-carbon atom is observed in the reaction with methyl iodide (+ 6b, d), l-bromo-2chloroethane (7c + 14a), and 1,3-dibromopropane (+ 16, 17), while 1,2-dichloro-and 1,2-dibromoethane give other products, viz. 11 -13. Quaternisation of 6 with dimethyl sulphate affords mixtures of 1-methyl-(1) and 2-methyltetrazolium salts (8) (3:l-4:l) from which the hexafluorophosphates 1 .PF6 are obtained by crystallisation. Methyl triflate converts the a-azidonitriles 9 into the N-methylnitrilium triflates 10 which immediately undergo an intramolecular 1,3-dipolar cycloaddition to afford the 1-methyltetrazolium triflates 1 . F3CS03. Cyclisation of 16 by intramolecular N-alkylation furnishes the bisannulated tetrazolium bromide 3a . Br. Attempts to obtain the lower homologue 15, either from 14a or from 17, met with failure. Instead, 17 rearranges via 15b into 14b. The a-branched tetrazole 24 is synthesised from ethyl cyanoacetate and the bromide 18. Double cyclisation of 24 affords the bisannulated tetrazolium chloride 3b . C1. The analogous scheme, envisaged for the synthesis of the lower homologue 32, failed in the last step owing to the high strain of this system. Deprotonation of 1,4-substituted 5-alkyltetrazolium salts affords 5-alkylidenedihydrotetra~oles[~~~] which undergo a number of interesting reactions. Photoextrusion of molecular nitrogen yields diastereoselectively iminoaziridines in the E configuration[*]. Iminoaziridines are also formed on thermolysis, besides products derived from cycloadducts of fragments like methyl azide or 1,3-diazabutadienes to the exocyclic double bond of 5-alkylidenedihydrotetrazole~[~]. This double bond is extremely electron-rich and polari~ed[~] and hence even adds normally unreactive 1,3-dipoles such as alkyl azidesL6]. Electrophilic azides afford zwitterions, that are intermediates of non-concerted 1,3-dipolar cycloaddition reactions['], or 5-imino-l,4,5,6-tetrahydro-l,2,3,4tetrazines via [3 + 21 cycloaddition followed by extrusion of molecular nitrogen with concomitant ring expansion[*]. With the view of exploiting and extending the rich chemistry of 5-alkylidenedihydrotetrazoles, we embarked on the synthesis of a number of annulated tetrazolium salts of type 1 and 3 which yield the annulated alkylidenedihydrotetrazoles 2 and 4, respectively, on deprotonation[']. Three different routes were envisaged: Alkylation of known annulated tetrazoles, cyclisation by intramolecular N-alkylation, and intramolecular [3 + 21 cycloaddition of o-azidonitrilium salts. The results are reported here. . . N=N X-N=N 1 2 3 2 6 H 7 R -7 G Q 4 R a R \ I N=N \ I N=N X-2 1 3 4Annulated Tetrazoles f114,1s1) and hydrogenation of tetrazolo[ 1,5-a]pyridine The annulated tetrazoles 6a, c, and f, which were needed ( 6~' '~~) .The tetramethyl compound 6e was now obtained as starti...

Photoextrusion of Molecular Nitrogen from Annulated 5-Alkylidene-4,5-dihydro-1H-tetrazoles: Annulated Iminoaziridines and the First Triplet Diazatrimethylenemethane

“…[16] Accordingly, the unsubstituted and 12a were prepared as described. [1] oxyallyl shows a slight preference for a triplet ground state…”

“…232°C (dec.)]. These structural requirements are much more stringent [1,2,3,4]tetrazole (5a): A than in the case of tris(imino)methanes, the only other trip-suspension of 4a (54 mg, 0.2 mmol), KH (28 mg, 0.4 mmol) and let heterotrimethylenemethanes that have been identified ex-18-crown-6 (3 mg, 10 µmol) in [D 8 ]tetrahydrofuran (0.6 ml) was magnetically stirred at Ϫ78°C in an NMR sample tube attached perimentally as yet. [22] to a bubble counter.…”

“…230Ϫ233°C (dec.) [ref. [1] : 50% (in two steps), m.p. tions that furnish monoradicals or EPR-silent products.…”

“…Solutions the parent diazatrimethylenemethane (30) are calculated on of alkylidenedihydrotetrazoles in sealed tubes were stored in the the CCSD(T)/UHF level to possess triplet ground states. [16] dark at 77 K. [1] in CHCl 3 (90 ml) was placed into 3 thick-walled glass tubes (30 ϫ 4 cm). Dry HCl was introduced for persistence of its EPR signal in low-temperature matrices.…”

“…4, 6, 8, 10, and 12. [1] We now report on their deprotonation and the irradiation of the resulting annulated 5-alkylidenedihydrotetrazoles. This study was stimulated by the hope that the additional strain imposed by the second rings might render the formation of iminoaziridines difficult, if not impossible, and thus help to observe triplet diradicals generated by extrusion of nitrogen, e.g.…”