Hydroximates, rearrangement

The discoveiy that a mixture of (Z)-(94a) and (Z)-(94b), on treatment with LDA, forms only (Z)-(95a) and (Z)-(95b) is consistent with an intramolecular mechanism (e.g. Scheme 6) for this new imino-Wittig rearrangement of hydroximates alternative radical pathways have also been discussed for reactions of Z- and. E-isomers.169... 

A diastereoselective imino [1,2]-Wittig rearrangement of allyl hydroximates provides for the preparation of optically active a-hydroxy oxime ethers when R3 is designed (g) as shown to participate in the reaction (Scheme 5).8... 

The Lessen rearrangement differs from the Hofmaim rearrangement only in that the leaving group is carboxylate anion rather than bromide ion. The starting material is the ester of hydroxamic add (RCONHOH), which is decomposed in presence of base. The hydroxamic acids exhibit tautomerism - the keto-form is termed hydroxamic form while the enol-form is called hydroximic add. As the reaction is normally carried out in water, the process furnishes the amine directly (Scheme 6.39). 

Vedejs has reported an oxaza-Claisen rearrangement to construct the pyrrole derivative 38. In presence of ethyl propiolate, the vinylogous hydroximic acid 35 imdergoes a conjugate addition followed by sigmatropic rearrangement to produce the aldehyde 37. Cyclization and dehydration resulted 38. ... 

The imino [1,2]-Wittig rearrangement was originally reported by Katritzky in 1981, and has been subsequently explored by Uneyama and Naito These transformations involve rearrangements of benzyl or allyl hydroximates to a-hydroxy oximes. An illustrative example involves the... 

The imino [1,2]-Wittig rearrangement of hydroximates has also been employed in the construction of natural products. For example, ( )-cytoxazone (88) was prepared fi om intermediate 87, which was generated via [1,2]-Wittig rearrangement of 86. An asymmetric synthesis of (+)-... 

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