The suprafacial hydroxylation of olefins by osmium tetraoxide, though a much used synthetic method,' would become even more important if three conditions could be met: (1) modification to achieve high and predictable enantioselectivity and acyclic diastereoselectivity, (2) clarification of reaction mechanism, and (3) facilitated recovery and recycling of osmium. This paper reports progress on all three fronts. Several other laboratories have been actively involved in the development of chiral ligands for enantioselective dioxyosmylation of olefins, most notably those of Sharpless,2 Tomioka,3 Narasaka,, S n~d e r ,~ Hirama,6 and Cinquini,' with a gratifying measure of success. On the mechanistic side, the picture has been very unclear,' not only in terms of stereochemical detail but also with regard to the matter of [3 + 21 cycloaddition (O=Os=O + C=C)* and [2 + 21 cycloaddition (Os=O + C=C)932a93b pathways.

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A system is described for the enantioselective hydroxylation of E olefins such as (I) that is unsurpassed in terms of enantioselectivity, ready availability and recoverability of the chiral controller ligand DMDPE, and recoverability of osmium.