Photochemische Stickstoff-Eliminierung aus 1-(1-Alkenyl)-4-tert-butyl-1,4-dihydro-5H-tetrazol-5-onen. Konkurrenz zwischen Methanol-Addition und Cyclisierung einer dipolaren Zwischenstufe

Aus dem 5-Chlortetrazol 7 und dem Tetrazolon 9 werden auf verschiedenen Wegen die 4-tert-Butyl-1-vinyltetrazolone 12a – c sowie die Tetrazolone 13 und 14 hergestellt. Bei der 254-nm-Photolyse der 1-Vinyltetrazolone 12 erhalt man in Abhangigkeit von Struktur und Reaktionsbedingungen das Imidazolon 16, die 4-Methoxyimidazolidinone 20 und/oder die N-(1,2-Dimethoxyalkyl)harnstoffe 22. Die Ergebnisse sprechen fur eine Konkurrenz zwischen Cyclisierung ( 15b 20b) und Methanol-Addition ( 21b 22b) einer dipolaren Photozwischenstufe. Die Struktur der Photoprodukte wird durch unabhangige Synthese von 16 sowie Hochfeld-1H-und 13C-NMR-Spektren bewiesen. Photochemical Elimination of Nitrogen from 1-(1-Alkenyl)-4-tert-butyl-1,4-dihydro-5H-tetrazol-5-ones. Competition between Addition of Methanol and Cyclization of a Dipolar Intermediate The 4-tert-butyl-1-vinylterazolones 12a – c and the tetrazolones 13 and 14 are synthesized from the 5-chlorotetrazole 7 and the tetrazolone 9via several routes. Bis(benzonitrile)palladium dichloride catalyses the O N-Claisen rearrangement 8 11, the allyl vinyl rearrangements 11a 12b and 11b 12c, as well as the equilibration 13 14. On 254 nm photolysis of the vinyltetrazolones 12 nitrogen is extruded and cyclic and/or acylic products of primary photo-intermediates are formed: In [D3]acetonitrile as solvent, 77% of 1-tert-butylimidazolone 16 arises from 12a, while the tetrazolones 12b, c produce only complex mixtures. In methanol as solvent, the methanol adduct 20a (23%) of the intermediate imidazolone 15a and the acyclic N-(1,2-dimethoxyethyl)urea 22a (32%) are obtained besides 45% of 16. In contrast, from 12c in methanol the corresponding urea 22c is formed almost quantitatively as the only product. In [D4]methanol solution of (E,Z)-12b a ratio of 4-methoxyimidazolidinone 20 b to the diastereomeric ureas 22 b of 22: 78 is observed. With decreasing amounts of [D4]methanol in [D4]methanol/[D3]acetonitrile mixtures, the imidazolidinone 20 b increases at the expense of the ureas 22 b. A 20 b: 22 b ratio of 98: 2 is reached in [D3]acetonitrile containing 3–6% [D4]methanol. This indicates a competition between the cyclization (affording 20 bvia15 b) and the methanol addition (producing 22 bvia21 b) of a dipolar photo-intermediate. The structure of the photo-products are confirmed by independent synthesis of 16 and by their high field proton and carbon-13 NMR spectra.