CuOTf

These two compounds with S configuration on their oxazohne rings were tested as copper(I) catalysts for the cyclopropanation of styrene, the hgand 9 with S axial chirality being much more enantioselective than 10 with the R configuration. Thus, the catalytic system CuOTf-(S,S)-bis(oxazolyl)-binaphthyl (9, R = Bu) led to excellent enantioselectivities, particularly for the cyclopropanation of styrene with (-menthyldiazoacetate 95% ee for the trans-cyclopropane and 97% ee for the cis, with trans/cis = 68/32. 

CuOTf.PhCHa (5 mol %) CH2N2 / CH2CI2 (argon flow) CH2CI2 -40°C... 

Smooth and efficient cyclopropanation also occurs with copper(II) triflate and diazomethane. Intra- and intermolecular competition experiments show that, in this case, the less substituted double bond reacts preferentially251. The same is true for CuOTf and Cu(BF4)2, whereas with CuX P(OMe)3 (X = Cl, I), CuS04 and cop-per(II) acetylacetonate, cyclopropanation of the more substituted double bond predominates. An example is given for cyclopropanation of 1. 

The same difference in regioselectivity holds for cyclopropanation with ethyl diazoacetate 25 K It is assumed that Cu(OTf)2 or Cu(BF4)2 are reduced to the Cu(I) salts by the diazo compound the ability of CuOTf to form stable complexes with olefins may then explain why, with these catalysts, cyclopropanation is governed by the steric environment around a double bond rather than by its electron-richness. 

Thioacetals eliminate to vinylsulfides in the presence of CuOTf (Scheme 46).192 Cu1 and Cu11 triflates are mild Lewis acids for Friedel-Crafts acylation and alkylation reactions. CuOTf effectively catalyzes the reaction of anisole with selenoesters.193,194 Copper(II) sulfate promotes epoxide ring opening reactions in the presence of pyridine,195 with retention of configuration being observed. Cu(OTf)2 is a catalyst for the ring opening of aziridine by aniline.196... 

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