Rearrangements, Claisen with ortho acetate

A reaction which is related to the ortho ester Claisen rearrangement utilizes an amide acetal, such as dimethylacetamide dimethyl acetal, rather than an ortho ester in the exchange reaction with allylic alcohols.174 The stereochemistry of the reaction is analogous to that of the other variants of the Claisen rearrangement.175... 

An example of the formation of an ester of an -4,5-alkenoic acid 164 comes in a synthesis of chrysanthemic acid by Ficini and her group.31 Reduction gives the allylic alcohol 163 and [3,3] Claisen rearrangement with triethyl ortho-acetate gives the product 164 in one step. 

The Johnson Claisen rearrangement,31 also called the ortho ester Claisen rearrangement, involves the reaction of an allylic alcohol with an ortho ester, often triethyl orthoacetate, in the presence of a carboxylic acid such as propionic acid, usually at temperatures between 120 and 140 JC (Scheme 3).1 The intermediate kctcnc acetal rearranges stereoselectively. 

Ramamurthy and coworkers studied the photo-Fries rearrangement of phenyl acetate and phenyl benzoate and photo-Claisen rearrangement of allyl phenyl ether (Fig. 34) included in two types of zeolite (faujasites X and Y and pen-tasils ZSM-5 andZSM-11) [192], The photolysis was performed with the zeolite slurry in either hexane or iso-octane. One of the most remarkable observations is that the product distribution is altered within zeolites from that in isotropic solvent. Furthermore, while in solution, nearly a 1 1 mixture of ortho and para isomers 40 and 41 (Fig. 34) was obtained, within zeolites one is able to direct the photoreaction selectively toward either the ortho or the para products by conducting the reaction either within faujasites or pentasils, respectively (Fig. 34). 

The Pd(II)-catalysed reaction of an allylic alcohol with the ketene acetal 476 at room temperature generates the ortho ester 477. Its Claisen rearrangement via 478 in boiling xylene with a catalytic amount of PdCl2(PhCN)2 gives the y,S-unsaturated ester 479 [204]. 

The Johnson ortho-ester variant of the Claisen rearrangement provides access to y,5-unsaturated esters.The reaction entails heating the allylic alcohol with an ort/io-ester in the presence of a carboxylic acid to form a ketene acetal, which then rearranges to the trans-unsatmated ester.An elevated reaction temperature is necessary for the in situ formation of the ketene acetal but not for the rearrangement. 

Quaternary stereogenic centers / to C-6 do not exhibit a significant chiral induction. The simple Claisen rearrangement of cyclohexanone acetal 1 with butyl vinyl ether in the presence of mercury(II) acetate at 175 °C results in a 45 55 diastereomeric mixture of products 2. The ortho ester variation gives a similar result631. 

This is a classic Claisen [3,3]-sigmatropic rearrangement sequence starting with an allylic alcohol and forming a vinyl ether by acetal (or in this case ortho ester) exchange. The reaction is very trans selective. 

A reaction related to the ortho ester Claisen rearrangement utilizes N,N-dimethylacetamide dimethyl acetal and an allylic alcohol and produces N,N-dimethyl amides. The reaction can be carried out by heating the allyl alcohol with the A, A -dimethylacetamide dimethyl acetal, or with its elimination product 1-dimethylamino-l-methoxyethene, which can be prepared separately.The stereospecificity of this process is identical to that of the ortho ester Claisen rearrangement. 

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