O-transfer

Sulfonyloxaziridines were recently proposed as O-transferring reagents. Oxaziridine (89) converted thioethers to sulfoxides (90) and diaryl disulfides into their 5-oxides (91) (78TL5171). Epoxidations are also possible (81TL917). 

We do not refer to elements heavier than Se except for Mo and W since the others are not used in biological catalysts. Note the different use of early transition metals in O transfer (and N transfer), while later transition metals are used in H- and C-fragment transfer (see Section 2.20). 

It probably is as obscure as it sounds. Remember O = transfer of 2 electrons down the entire chain. 

Three possible mechanistic schemes can be suggested for this process. One involves elimination of the proton attached to the p-C atom of nitronate A or A followed by elimination of the OSi group from the intermediate anion (cf. Scheme 3.93). Another mechanism is associated with a 1,4-C,O-transfer of the proton from the p-C atom of nitronate A to the oxygen atom of the N—>0 fragment followed by elimination of silanol from hemiacetal B. The third mechanism is based on the concerted elimination of silanol from the minor cis isomer of SENA. 

The presence of ascorbic acid as a co-substrate enhanced the rate of the Ru(EDTA)-catalyzed autoxidation in the order cyclohexane < cyclohexanol < cyclohexene (148). The reactions were always first-order in [H2A]. It was concluded that these reactions occur via a Ru(EDTA)(H2A)(S)(02) adduct, in which ascorbic acid promotes the cleavage of the 02 unit and, as a consequence, O-transfer to the substrate. While the model seems to be consistent with the experimental observations, it leaves open some very intriguing questions. According to earlier results from the same laboratory (24,25), the Ru(EDTA) catalyzed autoxidation of ascorbic acid occurs at a comparable or even a faster rate than the reactions listed in Table III. It follows, that the interference from this side reaction should not be neglected in the detailed kinetic model, in particular because ascorbic acid may be completely consumed before the oxidation of the other substrate takes place. 

In 1973 it was shown that the monocation [Ir(NO)2(PPh3)2]+ undergoes reaction with CO to give [Ir(CO)3(PPh3)2]+, C02 and N20 (equation 39), and that the tricarbonyl cation is easily converted back to the dinitrosyl cation by reaction with NO. The reactions were recognized as the basis of a possible homogeneous catalytic O-transfer process. 

Under the appropriate conditions O transfer to the cluster unit has also been observed (equation... 

O-transfer reactions of peroxyl radicals are sometimes referred to as two-electron reductions (Bonifacic et al. 1991 Schoneich et al. 1991 Merenyi et al. 1994), in analogy to the one-electron reduction discussed above, although the reaction type is quite different. It requires the addition of the peroxyl radical to an electron-rich center and is thus reminiscent of the O-transfer in ozone reactions (Munoz and von Sonntag 2000 Munoz et al. 2001 Flyunt et al. 2003). In some cases, this complex may simply decay into an oxyl radical and an oxide as observed with diaryltellurides (Engman et al. 1995), phosphines (Engman et al. 1995) and disulfides [SchOneich et al. 1991 Bonifacic and Stefanic 2000 e.g., reaction (38)]. 

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