Migration acyloxy groups

Whereas diaryl ditellurium compounds and copper powder in refluxing dioxane yielded diaryl tellurium derivatives (p. 419), bis[3-chloro-2-acyloxypropyl] ditellurium compounds lost both tellurium atoms under these conditions. The tellurium-free products were propenes. During the reaction the acyloxy group migrated to take the place of the chlorine atom5. 

Shortly after, a similar Pt(II)-catalyzed transformation of alkynylpyridines 338 providing 2-acyloxy-substituted indolizines 339/340 via a 1,2/1,3-acyloxy group migration was disclosed by Sarpong (Scheme 9.117) [298]. Although a variety of... 

FIERON reactions of 7V-acyloxy-7V-alkoxyamides would be expected to favour migration of acyloxyl groups since anomeric effects are strongest in this direction... 

The formation of anhydrides 101 in the thermal decomposition reactions of TV-acyloxy-TV-alkoxyamides in non-polar mesitylene (Scheme 21, pathway (ii)) can thus be attributed to HERON migration of acyloxyl groups. However, the similarity of Eas for the two isomeric transition states raises the possibility that in these reactions some, or all of the ester might be generated by HERON migration of the alkoxyl substituent (Scheme 21, pathway (iii)). 

Ion pair collapse in the acyloxy migration is so rapid as to preclude nucleophilic trapping of the contact ion pair even by intramolecular nucleophiles, which essentially precludes the use of acetates as leaving groups in tandem rearrangement reactions of the types discussed below [111, 127]. 

The 1,2 migration of an acyloxy group in (3-(acyloxy)alkyl radicals has been the subject of numerous synthetic and mechanistic studies [25]. These... 

Scheme 6.13 A stepwise pathway via five-membered cyclic intermediate radical 66 in the 1,2 migration of an acyloxy group...

A convenient preparation of 2-deoxy sugars [204] from glycosyl halides is based on the rapid and irreversible migration of an acyloxy group from C-2 to the anomeric center upon generation of the glycosyl radicals. This is a thermodynamically controlled reaction because it restores a d-a-d arrangement. 

Another reaction of such azides attached to the benzene part of benzo[7>]thiophene is the formation of benzoxazoles when heated in a mixture of carboxylic acid and PPA. The mechanism has been discussed in detail (79AG(E)900) and involves insertion of the singlet nitrene into the anhydride, followed by migration of the acyloxy group to the ortho position, and cyclization. The 5- and 6-azides thus given angularly fused benzoxazoles (Scheme 147). 

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