O-migration

Direct proof of an oxaziridine intermediate was achieved in photolysis experiments in an organic glass at 77 K (80JA5643). Oxaziridine (75), formed by photolysis of A/-oxide (74) and evidenced by UV spectroscopy under the above conditions, decomposed at higher temperature to form the imino ether (76) by N—O bond cleavage and C -> O migration of an aryl group. 

S1P-, S1P (nM) SPC (pM) Ubiquitous Gj/o Migration f, proliferation, survival, cell-cell-contacts, angiogenesis, lymphocyte trafficking... 

Mobile phase Acetic acid (99 o) Migration distance 12 cm... 

The most widely used reaction of organoboranes is the oxidation to alcohols, and alkaline hydrogen peroxide is the reagent usually employed to effect the oxidation. The mechanism, which is outlined below, involves a series of B to O migrations of the alkyl groups. The R—O—B bonds are hydrolyzed in the alkaline aqueous solution, generating the alcohol. 

Another recent disclosure examined silicon-to-copper transmetallation as a mild means of synthesizing alkenyl-copper reagents from stable precursors. The method requires activation of the silyl group by an allylic alcohol. Again, the silanes in this work are produced by circuitous means but should be accessible by ruthenium-catalyzed hydrosilylation. Treatment of the silyl alcohol with a stoichiometric amount of copper(l) /rz -butoxide results in the C-to-O migration of the silyl group to produce a vinylcuprate shown to be competent for subsequent allylation to produce 1,4-diene products (Scheme 17). 

Desilylation may involve initial attack of F on the carbonyl group followed by C to O migration of the silyl group to give QHsCXFJOSKCH-,), or direct displacement of the benzoyl union. 

Means, J.L., Crerar, D.A., and Duguid, J.O., Migration of radioactive wastes Radionuclide mobilization by complexing agents, Science (Washington, DC), 200, 1477, 1978. 

Irradiation of oompound 218 (R = OMe) in DMSO at Aexo 436 nm induces both acylotropic N —> O migration and partial decomposition. 

A number of o-quinol diacetates have been prepared and they rearrange smoothly to triacetoxyben-zenes o — o migration is preferred unless the latter position is blocked or sterically crowded, when acetoxy shift is directed to another aryl site. The range of possibilities is indicated by the conversions of the o-quinol diacetates (131)-(134) to the 1,2,3- or 1,2,4-triacetoxybenzenes (135)-(138), in 56-90% yields. 

TBAF, SiO, 100% yield or TBAF, DMF, 20min. In the following case, TAS-F and other fluoride reagents proved ineffective.It is likely that the more acidic reagents cause N to O migration in the threonine fragment. 

Free radical-mediated cyclisation of 206 or 207 provided convenient access to the 1,2-oxasilepine spiro products 208 in moderate yield <05T2037>. The other products isolated in minor yield were 209 and 210. The key step in the formation of 208 is the rapid 1,5-cyclisation and silicon C to O migration of the first formed carbon centred radical Irom Br atom abstraction. 

The most obvious thing to do is to react the carbonyl compound with a peroxyacid. After all, double bonds react to give epoxides and enols are more nucleophilic than double bonds. Unfortunately, peroxyacids are nucleophilic as well as electrophilic and form hemiacetals with carbonyl compounds which decompose by the C to O migration 195 known as the Baeyer-Villiger rearrangement. 

Magnesium oxide has been investigated by Robertson and by Henney and Jones. Surface diffusion was identified as the dominant mechanism of transport in both of these studies. The activation energies appeared excessive for this interpretation. In the reevaluation of these data it was shown that interpretation as volume diffusion produced = 0.02 exp (—70,000/i 7, which is in agreement with the tracer and mass spectrometer results compiled by Harrop in which the mean activation energy for Mg and O migration is 70,500 cal/mole. 

Several benzo-fused tetrahydropyrans have been prepared either from aryl-propanhydroperoxides in the presence of iron(II) and copper(II) salts, from the corresponding arylpropanol either by oxidation with FeS20g, or in a photochemical reaction with iodine and mercury(II) oxide (type III radical precursors). These reactions are considered to proceed via alkoxyl radical intermediates which add to the aromatic part of the molecule. Subsequent C- or O-migration in spirocyclized intermediates affords substituted chromanes. However, ionic cyclizations may significantly interfere with the key step of the C-O bond formation [57-59]. 

A concept of redox shuttle has been proposed before the advent of lithium-ion cells. The principle is depicted in Fig. 4.16. A compound R with a reversible redox potential is added into the electrolyte solution. The R is oxidized to compound O on the cathode, and then O migrates to the anode and is reduced to the original form R. The following properties are required for the compounds ... 

Details of the O migration mechanisms were deduced from the particle trajectories which were analyzed by using molecular graphics techniques. The O vacancies migrated between 0(1), 0(4) and 0(5) sites but not to 0(2) or 0(3) sites. The possible 0-ion jump paths were observed to be 0(l)-0(5), 0(l)-0(4) and 0(4)-0(5). X.Zhang, C.R.A.Catlow Physical Review B, 1992, 46[1], 457-62... 

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