Claisen rearrangements ortho

The reactions of 2-hydroxy-2-(3-indolyl)ethanoamides and of ethyl 2-hydroxy-2-(2-pyrrolyl) ethanoates with trialkyl ortho-esters follow similar routes with the initial formation of the enol ethers (295) and (297), followed by an ortho- Claisen rearrangement to give the 2,3-disubstituted indoles (296) and pyrroles (298) (79JOC1885,80TL4335). 

The cholesteric mesophase formed by cholesteryl p-nitrobenzoate at 200 °C has been used as the solvent to effect an asymmetric synthesis lrans-but-2-enyl p-tolyl ether gave the product of an ortho-Claisen rearrangement, 2-(but-1 -en-3 -yl)-4-methylphenol. This material exhibited circular dichroism, although neither the optical yield nor the configuration of the product is yet known.262 Decarboxylation of ethylphenylmalonic acid in cholesteryl benzoate at 160 °C (cholesteric liquid-crystalline phase) also proceeded with asymmetric induction to give (R)-(—)-2-phenylbutyric acid, with 18% optical yield.263 Electric dipole moments are reported for some esters of 5a-cholest-8(14)-en-3j8-ol there is some slight correlation with melting points.264... 

Sigmatropic rearrangement of an allyl aryl ether gives an orr -dienone, which usually enolizes rapidly to the ortho-allyIphenol (ortho-Claisen rearrangement, 60 62, equation 10). If the ortho posi-... 

Figure 1. Mechanism of the ortho-Claisen rearrangement of allyl phenyl ether to 2-allylphenol. A typical reaction condition is heating at 200 °C for 6 h, yield 73% [2].

The ortho-Claisen rearrangement is characterised by the shift of the double bond in the allylic group. This allylic shift is absent in the para-Claisen rearrangement [1]. 

The preparative Claisen rearrangement was studied in aqueous media at temperatures up to 300 °C. The experiments were conducted in the recently created pressurized microwave batch reactor and in conventional heated autoclaves. It was found that allyl phenyl ether isomerizes in water during 10 min at 240 °C to give the ortho-Claisen rearrangement product in 84% conversion . 

Investigations into the lattice-controlled - asymmetric ortho-Claisen rearrangement of prostereogenic substrate 1 in a cholesteric liquid crystal solvent at 200 °C show that asymmetric induction can be achieved to some extent. However, the optical purity and absolute configuration of the product was reported654. 

Sol 3. The trans, tra j-hexa-2,4-dienylphenyl ether (I) provided on heating at 165 °C, in addition to the ortho Claisen rearrangement product III, mainly a mixture consisting of 94% 4-(l-methylpenta-2,4-dienyl)-phenol (II) and 6% 4-(hexa-2,4-dienyl)-phenol (IV). The migration I II, proceeding through a... 

A method for effecting ortho-Claisen rearrangements of benzyl vinyl ethers, reported last year (3, 189) has been extended to include furan, thiophen, and pyrrole derivatives, i.e. (100) (101). ... 

The Claisen rearrangement of benzyl vinyl ethers is not usually possible, so it is interesting to find that an ortho-Claisen rearrangement of ethyl mandelate derivatives can be effected (Scheme 29). Presumably this is due to the stabilizing influence of the ethoxycarbonyl group in the intermediate (135). Yields are in the range 20—80%, and the reaction can also be performed with 3-indolyl-glycolic esters. 

The oxy-Cope rearrangement generally is in competition with the retro-ene elimination reaction (6.112). These processes are considered in more detail in section 6.6. On occasions the Claisen rearrangement is also susceptible to side reactions. The first of these, the ortho-ortho Claisen rearrangement, involves... 

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