A Ceric Ammonium Nitrate N-Dearylation of N-p-Anisylazoles Applied to Pyrazole, Triazole, Tetrazole, and Pentazole Rings: Release of Parent Azoles. Generation of Unstable Pentazole, HN5/N5 -, in Solution
Butler, Richard N. and Hanniffy, John M. and Stephens, John C. and Burke, Luke A. (2008) A Ceric Ammonium Nitrate N-Dearylation of N-p-Anisylazoles Applied to Pyrazole, Triazole, Tetrazole, and Pentazole Rings: Release of Parent Azoles. Generation of Unstable Pentazole, HN5/N5 -, in Solution. JOC - Journal of Organic Chemistry, 73 (4). pp. 1354-1364. ISSN 0022-3263
The reaction of cerium(IV) ammonium nitrate (CAN) with a range of N-(p-anisyl)azoles in acetonitrile or methanol solvents leads to N-dearylation releasing the parent NH-azole and p-benzoquinone in comparable yields. The scope and limitations of the reaction are explored. It was successful with 1-(panisyl) pyrazoles, 2-(p-anisyl)-1,2,3-triazoles, 2-(p-anisyl)-2H-tetrazoles, and 1-(p-anisyl)pentazole. The dearylation renders the p-anisyl group as a potentially useful N-protecting group in azole chemistry. The azole released in solution from 1-(p-anisyl)pentazole is unstable HN5, the long-sought parent pentazolic acid. p-Anisylpentazole samples were synthesized with combinations of one, two, and three 15N atoms at all positions of the pentazole ring. The unstable HN5/N5 - produced at -40 °C did not build up in the solution but degraded to azide ion and nitrogen gas with a short lifetime. The 15N-labeling of the N3 - ion obtained from all samples proved unequivocally that it came from the degradation of HN5 (tautomeric forms) and/or its anion N5 - in the solution.
Repository Staff Only: item control page