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We demonstrate here that even the most electron-poor olefins undergo Os0,-catalyzed oxidations. The reduced reactivity of chloroolefins relative to their fluorine counterparts is explained by a size effect; in all other respects the chloroolefins behave analog~usly.~~] The procedure is also applicable to strained fluoroolefins, for example norbornene derivatives.Our results cannot be rationalized with the frequently held conception of the mechanism of the osmylation as the electrophilic attack of osmium tetroxide on the olefin. The pyridine base effect discussed by Corey et al.

4] The twist angle I and the pyramidalization terms xc and lN were obtained from the primary torsion angle data 0,. w2. and w, as follows. 7 = (w, + w,)12; zN = (w2-(o, + x)mod2rr; xc = (w,-wJ + n)mod2x.Here we use the modified twist angle. 1;5 = (T) mod T I [Sa]. i maximizes at +90 and can he interpreted as the angle between the idealized positions of the px orbitals on C and N. The pyramidalization terms maximize at + 6 0 .[S] The other two classes are (1)cases where nonplanar amido-N ligands are thermodynamically favored over planar analogues accessible by isomeriza-