Thiohydantoins. IX. Tautomerism of some Methylation Products

Abstract

The methylation product of 5,5-pentamethylene-2-thiohydantoin has been shown by U.V. and i.r. spectral studies to exist predominantly as 2-methylthio-4,4-pentamethylene-2-imidazolin-5-one in chloroform or cyclohexane, and as 2-methylthio-5,5-pentamethylene-2-imidazolin-4-one in water. The tautomerism of the methylation product of 5,5-pentamethylene-2,4-dithiohydantoin exhibits a similar sensitivity to solvent.Des etudes dans 1'u.v. et dans 1'i.r. demontrent que le produit fourni par l'action d'iodure de methyle sur , le pentamethylene-5,5 thio-2 hydantoine existe comme methylthio-2 pentamethylkne-4,4 2-imidazoline-5-one en solution de chloroforme ou de cyclohexane, mais comme methylthio-2 pentamethylene-5,5 2-imidazoline-4-one en solution aqueuse. Le produit fourni par la methylation de pentamethyldne-5,5 dithio-2,4 hydantoi'ne dkmontre une tautomerie semblable.Canadian Journal of Chemistry, 50, 2423Chemistry, 50, (1972 Carrington and Waring (1) obtained a product (112, X = 0 ) from the methylation of 5,5-pentamethylene-2-thiohydantoin (3, X = 0 ) to which they assigned the unconjugated structure 1 (X = 0 ) on the basis of analogies which cannot be considered conclusive. Edward and Martlew (2) pointed out that the U.V. spectral characteristics reported for the compound supported rather the conjugated structure 2 (X = 0). Recently it has been shown (3) that the related spiroimidazolone 112 (X = 0 ; H in place of SMe) exists practically exclusively as the unconjugated tautomer in chloroform solution. However, in aqueous solution it exists as an approximately 70:30 mixture of the unconjugated : conjugated tautomer, and this proportion should be decreased by the presence of the 2-methylthio group.In the present work we show that 112 (X = 0 ) can exist almost entirely in one tautomeric form or the other depending on its solvent. This has been done by U.V. and i.r. studies making use of 4 and 5 (X = 0 ) as models for 1 and 2 (X = 0 ) . The compound 4 (X = 0 ) had already been synthesized by Carrington and Waring (I), and' 5 (X = 0 ) , hitherto unknown, was prepared by treating 1-methyl-5,5-pentamethylene-2-thiohydantoin (6; X = 0 ) with methyl iodide in ether (cf. ref. 4) ; and decomposing the hydriodide thus obtained with aqueous bicarbonate. The structure 5 (X = 0 ) was proved by hydrolyzing the compound with dilute acid to methanethiol and 1-methyl-5,5-pentamethylenehydantoin.The U.V. spectra of these model compounds (Table 1 and Fig. 1) were similar to those of the simpler compounds 4 and 5 (X = 0 , H in place of SMe) studied earlier (3), the conjugated compound 5 (X = 0 ) absorbing at longer wavelength than the unconjugated 4 (X = 0 ) . The

2-S-Methyl-5,5-dimethylimidazolin-4-one: chemical behaviour and crystal structure of its Δ1 tautomer

“…~' ( 1 ) ~'(11) This tautomerism, defined as annular desmotropy, was studied by ir and uv spectroscopies in several hydantoin derivatives (1,2). Lempert et al (2) determined the X-ray structures of the two desmotropes of 2-S-methyl-5,5-diphenylimidazolin-4-one in 1973, and showed that the polarity of the solvent is crucial in obtaining one of the two tautomers.…”