Remote oxidations

Remote Oxidation (functionalization) Comprehensive Organic Synthesis 1991, 7, 39. 

Yields up to 50% are obtained in a remote oxidation procedure developed by Bres-low. If, for example, the hydroxyl group of 3er-stigmastanol is esterified with 4 -... 

SO2 0-0.5 ppmv (urban) 20-200 pptv (remote) Oxidation of fossil fuel S Oxidation of S gases, volcanoes Direct reaction with earth surface, oxidation to sulfate... 

It has proved possible to convert CH2 to C=0 groups, even if they are not near any functional groups, indirectly, by the remote oxidation method of Breslow (see... 

As part of their study of enzyme models capable of remote oxidation, Breslow and co-workers have used a benzophenone derivative to function-... 

To determine whether a more rigid conformation would increase the degree of selectivity of this remote oxidation, Breslow and Baldwin studied a similar system using the 3-a-cholestanol moiety,(77)... 

A literature method for preparation of chromyl acetate by interaction of chromium trioxide and acetic anhydride was modified by omission of cooling and agitation. The warm mixture exploded violently when moved [1], A later publication emphasised the need for cooling, and summarised several such previous occurrences [2], An earlier reference attributes the cause of chromium trioxide-acetic anhydride oxidation mixtures going out of control to presence of nitric acid or nitrates in the chromium trioxide, and a simple test to check this point is given [3], Mixtures used as a reagent for the remote oxidation of carboxylic esters are potentially explosive, and must be made up and used at below 25 °C under controlled conditions [4], An attempt to purify the anhydride by warming with 2% w/v of trioxide led to an explosion at 30°C [5],... 

Tab. 4 Remote oxidation of ketones in acetonitrile/lithium perchlorate...

Tab. 5 Remote oxidation of esters in acetonitrile/LiCl04 or TEABF4 ...

Remote oxidation of ketones 9-34 Dimerization of silyl enol ethers or of lithium enolates... 

Breslow s template-directed remote oxidation of steroids utilizes an aryl iodide as a template to direct the oxidation of steroid tertiary carbons by the radical relay mechanism, in which a chlorine radical is transferred from a [9-1-2] [PhICl] radical to the iodine atom of the template and then relayed to a geometrically accessible hydrogen atom. This method allows a highly regioselective functionalization of nonactivated carbon atoms of steroids [Eq. (78)] [137,138]. 

Reactions have been described for RH = amines, alcohols, aromatics, aliphatics, perfluoroalkyls, hydrogen halides, and thiols (167). Another recent use of S2OfiF2 in organic chemistry has been in the synthesis of lactones by the remote oxidation of carboxylic acids using a... 

Our principal target in P-450 mimics was the selective oxidation of saturated carbons directed by geometric control, not by intrinsic reactivity. In our first study, we examined selective geometrically controlled attack on aliphatic C-H bonds by photo-excited benzophenones [145]. In a process we labeled remote oxidation", photolysis of a long-chain ester 69 of benzophenone-4-carboxylic acid afforded insertion into CH2 groups far into the chain. 

Sonication of the steroidal bromohyrins 176 in the presence of DAIB-I2 enables remote oxidation of the C-19 methyl group leading, via alkoxy radicals, to the C-19 furan derivatives 177 (99TL8711). 

Two novel variations on remote oxidation involve radical relay mechanisms. Chlorine radicals generated by photolysis of iodobenzene dichloride are carried by the iodine atom of a suitable iodo-aryl ester of 5a-cholestan-3a-ol to permit hydrogen abstractions from C-9 or C-14, depending upon the ester employed.237 The m-iodobenzoate (293) afforded the 9a-chloro- and thence the cholest-9(ll)-ene derivative (294), whereas the p-iodophenylacetate similarly gave a 14-ene. 

---