Erratum: Assisted hydrolysis of cis-2-(3-phenylthioureido)cyclopentane-carbonitrile in alkaline solution. Solvent dependent switch from hydrolysis to rearrangement of the iminothiooxopyrimidine intermediate
| Autor: | Maria M. Toteva, Iva B. Blagoeva, Francis L. Chubb, Ergun Atay, Ivan G. Pojarlieff, John T. Edward |
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| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | Canadian Journal of Chemistry. 78:520 |
| ISSN: | 1480-3291 0008-4042 |
| DOI: | 10.1139/v00-069 |
| Popis: | The cis and trans isomers of 2-(3-phenylthioureido)cyclopentanecarbonitrile, 1, and the respective carboxamides, 3, and acids, 4, have been prepared. Acid cyclization of both nitriles, faster with the cis isomer, gave the more stable cis-2-thiooxo-cyclopenta(d)pyrimidin-4-one, 7. In base cis-1 formed the cis 4-imino-2-thiooxopyrimidine 2 which in aqueous alkali broke down via 3 to the acid 4; while in the presence of 66% acetonitrile 2 rearranged to the 4-phenyliminopyrimidine 5 to give as final product the thioureido acid 6 carrying no phenyl group. The 1 H NMR data for imino and phenylimino derivatives 2 and 5 showed strong bias for conformation A with 1-N pseudoaxial in the cyclopentane ring. Spectra of the E and Z isomers of the iminopyrimidine 2 under slow exchange could be recorded in DMSO-d6. The phenylimino tautomer of 5 is observed in CD3OD and in CDCl3 with the E and Z isomers in a 1:1 ratio. In DMSO-d6 the phenylamino tautomer 5a is also detected. The first process in aqueous KOH, the conversion of nitrile cis-1 into the imino intermediate 2, reaches an equilibrium which shifts towards the nitrile at higher alkalinities because of ionization of the phenylthioureido group (Ke =( 2)/(1) = 2.43 and pKAH = 12.74). The cyclization of 1 to 2 is first order in (OH - ) while the slower breakdown of 2 is pH independent. The latter is 10 4 times faster than the hydrolysis of acetonitrile evidencing substantial anchimeric assistance. The change in the reaction route towards the rearranged phenyliminopyrimidine 5 upon addition of acetonitrile can be caused by the lower dielectric constant favouring the elimination step leading to the intermediate isothiocyanate, and by increased activity of OH - accelerating the (presumably) second order elimination step as opposed to the pH-independent hydrolysis of the imino derivative 2. |
| Databáze: | OpenAIRE |
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