Rearrangement 1,2-acyloxy migration

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 gold-catalysed synthesis of substituted furans via [3,3]-sigmatropic rearrangements and/or [l,2]-acyloxy migration based on propargyl ketones has been investigated... 

VCP-substituted propargylic ester 65 rearranged to the seven-membered product 66 in the presence of [RhCl(CO)2]2 (Scheme 2.53) [74]. 1,3-Acyloxy migration generated VCP-substituted allene, which acts as a seven-carbon component in rhodium-catalyzed cycloisomerization. The subsequent ring opening produced methylenecycloheptadiene. 

Cycloisomerization of 73 in the presence of copper catalysts and base afforded the corresponding 2,3,5-trisubstituted furans 74 in good to high yields (Scheme 27.27) [37]. The reaction proceeds via prototropic rearrangement to form allene intermediate 75 and subsequent 1,2-acyloxy migration via dioxolenylium intermediate 76. 

Metal complexes such as Pd(II), Pt(II), Ru(II), Au(I), or Au(III) have been reported to activate efficiently propargyl carboxylic esters to form complexes 174, that evolve toward 1,2- and/or 1,3-acyloxy migration ([3,3] rearrangement) to generate... 

Sulfonate esters and halides can also migrate in this reaction. a-Halo and a-acyloxy epoxides undergo ready rearrangement to a-halo and a-acyloxy ketones,... 

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