(1H‑Tetrazol-5-yl)-Allenes: Building Blocks for Tetrazolyl Heterocycles

• Published in: Journal of organic chemistry Vol. 81; no. 19; pp. 9028 - 9036
• Main Authors: Cardoso, Ana L, Henriques, Marta S. C, Paixão, José A, Pinho e Melo, Teresa M. V. D
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 07.10.2016; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; FORMAL 3+2 CYCLOADDITIONS; ACID; 2-(TETRAZOL-5-YL)-2H-AZIRINES; ALLENOATES; REACTIVITY; CHEMISTRY; PYRROLES; AZIRIDINES; ALLENES; BETA-LACTAMS
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.6b01679

(1H-Tetrazol-5-yl)-allenes have been prepared for the first time, and their reactivity toward aziridines explored. Reaction of a (1-benzyl-1H-tetrazol-5-yl)-phosphonium chloride and acyl chlorides in the presence of triethylamine afforded the target allenes via Wittig reaction of the in situ generated phosphorus ylide and ketenes. 1-(1-Benzyl-1H-tetrazol-5-yl)­propa-1,2-diene and 3-methyl-, 3-ethyl- and 3-benzyl derivatives undergo microwave-induced formal [3 + 2] cycloaddition with cis-N-benzyl-2-benzoyl-3-phenylaziridine, through C–N bond cleavage, to give selectively tetrasubstituted pyrroles. In contrast, with (1H-tetrazol-5-yl)-allenes bearing bulkier substituents at C-3, such as i-propyl or a tert-butyl, 4-methylenepyrrolidines were obtained exclusively via [3 + 2] cycloaddition of the in situ generated azomethine ylide. The latter allenes also gave 4-methylenepyrrolidines on reacting with cis-2-benzoyl-N-cyclohexyl-3-phenylaziridine, whereas with the other allenes, pyrroles were obtained as major products together with the formation of 4-methylenepyrrolidines. All the studied (1H-tetrazol-5-yl)-allenes reacted with N-benzyl-cis-3-phenylaziridine-2-carboxylate to give the corresponding 4-methylenepyrrolidines exclusively.