Regioselective rearrangement

Details of the regioselective preparation of a variety of new 2,4-disubstituted oxazoles, using both iodide- and acid-promoted rearrangements of TV-acylaziridines, have been presented.584 It has been shown585 that two plausible mechanisms (S i and/or two 5n2 reactions) can account for the acid-catalysed transformation of 1-acylaziridines (447) to oxazolines (448), while the regioselective rearrangement of... 

BF3 Et20 is used for the regioselective rearrangement of polyprenyl aryl ethers to yield polyprenyl substituted phenols, e.g. coenzyme Q [92]. This reagent is used in the Fries rearrangement for example, 5-acetyl-6-hydroxycoumaran is obtained in 96 % yield from 6-acetoxycoumaran by use of this reagent (Eq. 48) [93]. 

BF3 Et20-promoted regioselective rearrangements of polyprenyl aryl ethers provide a convenient route for the preparation of polyprenyl-substituted hydroquinones (Eq. 51) which can be oxidized to polyprenylquinones [97]. 

Regioselective rearrangement to allyl alcohols can also be attained with dialkylboryl-trifluoromethane sulfonate in the presence of tertiary amines (Eq. 152). ... 

Allylphenols. A regioselective rearrangement of 2-alkenyl aryl ethers to the brominated o-position is realized via the lithio derivative (via reaction with r-BuLi) by treatment of the latter species with CuCN-LiBr. 

Zhu and coworkers have reported a regioselective rearrangement of the Diels-Alder cycloadduct 180, derived from furan 178 and acetylene 179, to form the 1,4-difunctionalized 2,3-bis(trifluoromethyl)benzene system 181 in one chemical operation (equation 129). 

The effect of alkyl groups as substituents at either Cl or C2 of such compounds is less pronounced, usually giving mixtures of isomeric photoproducts. Phenyl groups tend to stabilize intermediate radical centers and thus also induce regioselective rearrangements. ... 

Diethyl l-substituted-3,4-epoxybutylphosphonates are treated with n-BuLi at low temperature in THF, and the resulting anions regioselectively rearrange on warming into diethyl 1-substituted-... 

An alternative process for the production of (-)-carvone has recently been elaborated. Starting from (-i-)-limonene 1,2-epoxide, a regioselective rearrangement of the epoxide leads to (-)-carveol (trans- -.[2102-58-1] cis- -.[2102-59-2]). The reaction is effected by the use of a catalyst consisting of a combination of metal salts and phenolic compounds. 

For further examples of regioselective rearrangements with organoaluminum reagents see refs 123 and 129. For organoaluminum-promoted rearrangements of allylphenyl ethers see ref 140. 

In regioselective rearrangements, (/T)-alkene moieties react more rapidly than (Z)-alkene moieties, e.g., reaction of 3 to give predominantly (Z,E)-4356. 

A full account of the palladium-catalysed, highly regioselective rearrangement of 0-allyl phosphorothioates to their S-isomers has appeared (a preliminary announcement appeared in Organophosphorus Chemistry , Vol. 12, p. 101). 

Iron(III) tetraphenylporphyrin has been developed as an efficient catalyst for the regioselective rearrangement of simple monoalkyl-substituted epoxides into the corresponding aldehydes. The acid- and BF3-catalysed rearrangement of methylpropene... 

In addition to these enolate reactions, -silyl ketones can be thermally isomerized to silyl enol ethers by a regioselective rearrangement (eq 9), or treated with another Grignard reagent to provide alkenes through Peterson alkenation reactions. 

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