The crystal and molecular structures of 3-methyl-2,4-diphenyl-(1,3)-thiazolidine-5-spiro-2′-adamantane and 3-methyl-2,4,5,5-tetraphenyl-(1,3)-thiazolidine are investigated showing the existence of C(sp 2 )-H‚‚‚S and C(sp 2 )-H‚‚‚N intramolecular contacts. The use of the Bader theory shows that C-H...S interactions existing in crystal structures may be treated as weak H bonds. The C-H...N and C-H...S interactions are also analyzed here for simple modeled complexes of (1,3)-thiazolidine as the proton acceptor and simple proton donators: HF, H 2 O, C 2 H 4 , and C 2 H 2 molecules. The calculations for these complexes were performed within the DFT method, B3LYP/6-311++G** level of theory. The bond critical points (BCPs) were found for these modeled systems and the analysis of the electron densities and their Laplacians at BCPs was performed.

4085isomer, (-)-(2S,8&)-2 (entries 7 and 13). Asymmetric enolate oxidation of 2-methyltetralone (6) with (+)-(2R,8aS)-1 gave much lower stereoselectivities (entries [15][16][17][18][19]. Changing the base or solvent failed to increase the asymmetric induction. Asymmetric oxidations using (-)-(S,S)-3 also reduced the asymmetric induction for 4a,b (entries 8 and 14) but nearly doubled it from 16% ee to 23.5% ee for ketone 6 (compare entries 17 with 20).The results summarized in Table I are best understood in terms of an open transition state, where nonbonded steric interactions are principally responsible for the chiral recognition.10 Dreiding models and an X-ray crystal structure of the conformationally locked oxaziridine (+)-(2R,8aS)-1, suggest that in the vicinity of the active site oxygen the most sterically demanding region is the bridgehead 5-4a bond.12 We consider, by analogy with recent studies by Heathcock and co-workers,13 that the largest enolate group is the "OM" (M = Li, Na) solvent aggregate complex. The two extreme geometries for the oxidation of the si-faces of the metal (2)-enolates of 4a,b by (+)-(2R,8aS)-l are depicted in Scheme I. From a consideration of the nonbonded interactions, the planar transition-state geometry is favored over the spiro form.14 The lower enantioselectivities noted for 2-methyltetralone (6) are consistent with this hypothesis because all rotational conformations of this enolate are sterically demanding. It is interesting to note that planar transitionstate geometry is also preferred for asymmetric epoxidations of alkenes by chiral oxaziridineslg and certain conformationally restricted peracids.lg If our assumptions concerning the factors that control the transition state geometries are correct, then it follows that "NaO" can also be considered as a large group. The higher enantioselectivities associated with sodium vs. lithium enolates of 4a,b probably reflect the lower temperature of oxidation for the former counterion (Table I).2o We speculate that the generally lower stereoselectivities seen in the presence of HMPA (entries 2,4,10,12, 16) and for the potassium enolates (entries 5, 13, 18) are the result of a smaller effective size for "OM" group. K+ is a poorer chelating metal than either Li+ or Na+, and HMPA is (10) No change in the 'H or 13C NMR spectra of oxaziridine (+)-(2R,BaS)-A and the shift reagent Pr(fod), at 1:l molar ratios could be detected. (11) Davis, F. A.; Towson, J. T., manuscript in preparation. (12) Details of the X-ray structure of (+)-(2R,BaS)-l will be published elsewhere." (13) (a) Heathcock, C. H.; Henderson, M. A.; Oare, D. A.; Sanner, M. A. J. Org. Chem. 1985,50,3019. (b) Heathcock, C. H.; Oare, D. A. J. Org. Chem. 1985,50, 3022. (14) In analogy with other studies,lB the enolate and oxaziridine are considered to approach in a perpendicular fashion. Recent ab initio calculations by Houk and Paddon-Row suggest that the transition state for reaction of MeF with the acetaldehyde enolate is product-like; Le., MeF approaches the enolate at an angle o...

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640 1 unilateral electron flow should result, establishing one bond between the reactants, Le., generation of a zwitterionic intermedi~te.~ Sulfur and carbon possess the same electronegativity on the Pauling scale. Absence of the more electronegative 0 or N atoms brings thiocarbonyl ylides6 close to the high M O energies of the allyl anion, electronic prototype of 1,3-dipoles. An aliphatic thiocarbonyl ylide and an ethylene derivative bearing four electron-attracting substituents offer a reactant pair with extremely different M O energies.

The atmospherically highly relevant methylsulfinyl radical CH3(O)S˙ was generated thermally under flash pyrolysis conditions and isolated in Ar matrices at 10 K; the allyl radical is a byproduct. CH3(O)S˙ and its D3- and (13)C-isotopologues were characterized through the excellent agreement between experimental and computed IR and UV/Vis spectra.