XOzS-N* ,N\ nS\ (Sa), X = F 85 1 2 6 -( S b ) , X = C1 2 9 90 XOzS-N CRs (SC), X = CF3 3 4 . 5 7 9Formation of ( 9 ) in the presence of a large excess of ethyl isocyanate is regarded as evidence for the intermediacy of (7): (46) + (2b) + CzH,-NCO ( e x c e s s ) (733 ClOZS-N* ,N\ --.+ @S, ,C=O + R3C-NCO C102S-N N I (9) CZH5 Compounds ( 8 ) were characterized by elemental analysis, as well as mass, IR, and NMR spectra. The 'Hand 19F-NMR spectra contain only singlets [ ( 8 a ) : dSF= +60.7, hCH= + 1.6251; as in other four-membered ring ketones14], the C O stretching vibrations appear at high wavenumbers [vco: (80) 1840, (86) 1842, (8c) 1840 cm-'1. The spectroscopic data hardly permit any distinction between (8) and ( 5 ) ;it took an X-ray structure analysis performed on (8a) to rule out the alternative ( 5 ) . (8 a ) forms orthorhombic crystals [Pnma, a = 16.075(4), b=l2.990(3),~=8.071(2)W;at -120"C:P212121r a= 15.936(4), b= 12.794(3), c=7.934(2)& Z=4]. The structure was solved from low-temperature diffractometer data by direct methods &=+1.646; ( 8 b ) : d o = +1.646; ( 8~) : 6 0 = -78.1, 1.538 Fig. 1. Molecular structure of crystalline thiadiaretidinone ( 8 a ) with bond lengths and angles (standard deviation 0.002 to 0.004 A and 0.2", respectively). and refined to R=2.8 %. Figure 1 depicts the molecule with averaged bond parameters. The mutually perpendicular fragments SN=S=NS and C-N(:>N-C are almost planar (angles in ring: NSN 79.5(1), SNC 92.0(2), NCN 96.5(2)"). Procedure a ) Bis(tert-butylimido)halosulfonylimidosulfiof VT) ( 4 ) : A solution of halosulfonyl isocyanate ( 2 ) (8.4 mmol) in pentane (60ml) is added dropwise at + 10°C to ( I ) (2.0g, 8.16mmol) in pentane (120ml). After stirring for 16 h, the resulting colorless solution is decanted from the polymer adhering to the vessel wall and cooled to -100°C. The precipitated product is filtered off at this temperature under nitrogen. Yield 58 % ( 4 a ) [NMR: &F= +54.0 (s), ~~( c H~)~c = f1.46 (s); MS: m/e= 271 (2.3%) M + ] and 63% ( 4 b ) [NMR: S(CH,)~C= +1.49 (s); MS: m/e=287 (1.5%) M']. b ) li6,2,4-Thiadiazetidin-3-ones (8): Analogous reaction of ( I ) , but with 24.8mmol of sulfonyl isocyanate. ( 8 a ) is purified by sublimation (oil pump vacuum, 50-55°C); (8 b ) and ( 8 c ) by crystallization from pentane [MS: M + at m/e=396 (2.3 %), 428 (2.0 %), and 496 (1. 8 %), respectively]. Electron impact induced dissociations, which are actually the result of special neighboring group effects (e.g. anchimeric participations""] or ortho-effects" bl), have already been reported in the literature on several occasions ["]. We report here on the first example of a system in which the rupture of a C-C bond cannot be described in terms of a simple homolysis, but rather in terms of an intramolecular, rate-determining H-migrationr2].On electron impact ionization (70 eV) of methyl isobutyrate (1) the mass spectrum shows an intense signal for the methyl elimination from M" (13% total ion current (TI)). In the case of unimolecular dissociation of metastable molecular ions of...
