Ortho esters, reactions with allylic alcohols

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... 

The mechanism and stereochemistry of the ortho ester Claisen rearrangement are analogous to those of the Cope rearrangement. The reaction is stereospecific with respect to the double bond present in the initial allylic alcohol. In acyclic molecules, the stereochemistry of the product can usually be predicted on the basis of a chairlike transition state.158 When steric effects or ring geometry preclude a chairlike structure, the reaction can proceed through a boatlike transition state.159... 

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. 

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]. 

Substiluled acrylic acids a-methylene-y-butyrolactones. The reaction of 1 with the allylic alcohol 2 at 170° gives the product (3) of Claisen ortho ester rearrangement. Oxidative elimination of GsHsSeOH gives the 2-substituted acrylic ester 4. 

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. 

The aliphatic version of this rearrangement is associated with the names of Cope and Ciaisen. It also converts a C-O bond in an ether into a C-C bond in the product. An allylic alcohol (40) or (43) is converted into a vinyl ether (41) or (44) by reaction with another vinyl ether (to give aldehydes or ketones) or with an ortho ester (to give esters). The rearrangement is rapid at 100 150 C and gives y,5-unsaturated carbonyl compounds (42) and (4S). 

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. 

The Johnson rearrangement involves reaction of an allylic alcohol with ethyl orthoacetate to give a mixed ortho ester that loses ethanol and then undergoes... 

Chemical characteristics. The most broadly used allyl resins are prepared from the prepolymers of either DAP or DAIP which have been condensed from dibasic acids. The diallyl phthalate monomer is an ester produced by the esterification process involving a reaction between a dibasic acid (phthalic anhydride) and an alcohol (allyl alcohol) which yields the DAP ortho monomer, as shown in Fig. 2.1. Similar reactions with dibasic acids will yield the DAIP (iso) prepolymer. Both prepolymers are white, free-flowing powders and are relatively stable whether catalyzed or not, with the DAP being more stable and showing negligible change after storage of several years in temperatures up to 90°C. 

The ortho-ester Claisen rearrangement continues to provide a versatile method for the preparation of unsaturated esters. Reaction of trimethyl-methoxyorthoacetate with an allyl alcohol furnishes a-methoxy-Y,d-unsaturated esters in 22—55% yields. A stereospecific synthesis of both enantiomers of the insect pheromone methyl E-2,4,5-tetradecatrienoate involves the conversion of the R-acetylenic alcohol (65) (Scheme 53) into the R-allenic ester (66) as its key step. This process was repeated with the 5-alcohol to provide the enantiomer of (66). The optically active erythro-alcohol (67), readily available... 

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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