in III, where it can be seen that because of the large phenyl substituents it is understandably disfavored here. IllIn conclusion, then, the introduction of the "stiffened backbone" in dppee, as contrasted with the flexible backbone in dppe, leads to certain changes in the conformational characteristics of these molecules. These conformational changes then have consequences with respect to the way in which the molecules are assembled in the complete crystal structure.Acknowledgment. Support from the National Science Foundation (Grant No. CHE85-14588 to F.A.C. and Grant No. 85-06702 to R.A.W.) is gratefully acknowledged.Registry No. a-Re2Cl4(dppee)2-«-PrOH, 114720-22-8; /3-Re2Cl4-(dppee)2, 110329-68-5; a-Re2Cl4(dppe)2, 114720-23-9; (n-Bu4N)2Re2Cls, 14023-10-0; [ReCl2(dppe)2]Cl, 15628-22-5; (zi-Bu4N)2Re2Br8, 14049-60-6; a-Re2Br4(dppe)2, 114720-24-0; a-[Re2Cl4(dppee)2]PF6, 114720-26-2; (Cp2Fe)PF6, 11077-24-0; a-[Re2Cl4(dppp)2]PF6, 114720-28-4; a-Re2Cl4(dppp)2, 86436-61-5; Re, 7440-15-5; a-Re2Cl4(dppee)2, 1 10329-67-4. Supplementary Material Available: Full tables of bond distances and bond angles and tables of anisotropic displacement parameters for a-Re2Cl4(dppee)2.«-PrOH and 0-Re2Cl4(dppee)2 and a table of torsional angles for the ß isomer (14 pages); listings of observed and calculated structure factors for both compounds (45 pages). Ordering information is given on any current masthead page.

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Optically active oxirane-2-carboxylic esters, prepared from allylic alcohols employing the Sharpless epoxidation, were treated with sodium azide. The azido alcohols obtained were subsequently converted into aziridine-2-carboxylic esters by reaction with triphenylphosphine, in good yields and with high optical purity. Various racemic oxirane-2-carboxylic esters were subjected to the same sequence of reactions. Azidoh alcohols 6 Yield (%) 74 85 92 92 85 86 93 95 88 84 87 90 97 96 92 74 80 97 82 85 72 Johan Legters et al.