Alkoxy alcohols rearrangement

Although no mechanism is proposed for the dimerization of lactic acid in the FSOsH-SbFs solution, the process may very well involve the superelectrophile 147. Other oxonium-carbenium 1,3-dications have been suggested in superacid promoted pinacolone rearrangments of diprotonated aliphatic glycols and alkoxy alcohols (eqs 49-50).58... 

Photolysis of PhI(OAc)2 with tertiary allylic alcohols 590 in the presence of iodine affords a-iodoepoxides 591 (50-72% yield) as a result of alkoxy radical rearrangement (Scheme 3.233) [632]. 

Cross-conjugated dienones are quite inert to nucleophilic reactions at C-3, and the susceptibility of these systems to dienone-phenol rearrangement precludes the use of strong acid conditions. In spite of previous statements, A " -3-ketones do not form ketals, thioketals or enamines, and therefore no convenient protecting groups are available for this chromophore. Enol ethers are not formed by the orthoformate procedure, but preparation of A -trienol ethers from A -3-ketones has been claimed. Another route to A -trien-3-ol ethers involves conjugate addition of alcohol, enol etherification and then alcohol removal from la-alkoxy compounds. 

This excellent method of oxidative cleavage (/) of carbon-silicon bonds requires that the silane carry an electronegative substituent (2), such as alkoxy or fluoro. Either hydrogen peroxide or mcpba may be used as oxidant, and the alcohol is produced with retention of configuration (3). Fluoride ion is normally a mandatory additive in what is believed to be a fluoride ion-assisted rearrangement of a silyl peroxide, as shown below ... 

Even though the radical attacking ethyl alcohol in the above reaction generated a-hydroxyethyl rather then ethoxy free radical, there seems to be little or no tendency for alkoxy free radicals to rearrange to a-hydroxyalkyl radicals. Thus in the reaction... 

Concerning the possible rearrangement of the lithiooxirane into the alkoxy carbene 155, calculations have also shown that the activation energies of the 1,2-H shifts (to cyclopentanone enolate or cyclopentenol) are extremely high (at least 23 kcalmol" ) from 155, whereas they are much lower (between —0.4 kcalmol" and 8.8 kcalmol" ) from carbene 154. This is explained by a strong intramolecular stabilization of the carbene by the alcoholate moiety, as depicted in Scheme 66. This stabilization could signify that the formation of a carbene from the carbenoid is a disfavored process, and that the carbenoid itself is involved in the rearrangement reaction. 

The 0ew-N3P3(NH2)2Cl4 when allowed to react with alkoxide ion in the corresponding alcohol gives rearranged cis and trans alkoxy derivatives, non-gem-N3P3(NH2)2(OR)4 (R = Me, Et, Pr" or Bu") (Eq. 29) [168-170]. However,... 

The different behavior of the alcohols probably arises from differences in bond dissociation energies. Experiments show that radical attack on methanol (4) and ethanol (27) leads to rupture of the C—H rather than the O—H bond. There appear to be no direct measurements of C—H bond energies in alcohols. However, D(R—OH) has been determined as 102 kcal. and does not appear to vary greatly with changes in R, provided R is a simple alkyl radical (16). Moreover, the heat of rearrangement of alkoxy radicals to hydroxyalkyl radicals has been determined from electron impact data (12). Considering, for example, 2-propanol and the following reactions... 

In the oxidation of 2-octenyl acetate, in addition to the normal oxidation, palladium-catalyzed allylic rearrangement and subsequent oxidation took place to give a small amount of 3-acetoxy-2-octanone as a byproduct. Ethers of secondary allylic alcohols also underwent the regioselective oxidation to give the corresponding 3-alkoxy ketones in 30-40% yields. But in this case too, by-products derived from the allylic reanangement a subsequent oxidation were also detected. Results of the oxidation of some allyl ethers are shown in Table 3. °... 

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