Abnormal Claisen

A so-called abnormal Claisen rearrangement has been observed on a number of occasions usually concurrently with the normal reaction. Here the /1-carbon atom in the ether becomes bonded to the ortho position in the phenyl group as in the formation of C from XCIX139, viz. ... 

Some allyl phenyl ethers with an alkyl substituent on the end carbon of the allyl group rearrange to give the normal ortho-Claisen product together with another isomeric O-allyl phenol. The latter, formed by the rearrangement of the normal product, has been established. This is called abnormal Claisen rearrangement, is illustrated by the following example. 

Another abnormal Claisen rearrangement is the product formed on heating phenyl propargyl ether. The normal product O-allenyl phenol rearranges by a [1, 5] hydrogen shift and then there is an electrocylic ring closure to give chromene which is the observed product. 

For reviews of these abnormal Claisen rearrangements, see Hansen Mech. Mot. Migr. 1971,3,177-236 Marvell Whalley, in Patai, Ref. 452, pt. 2, pp. 743-750. 

Reexamination of the extracts of some plants has made it possible to ascertain the presence and the structures of many minor compounds.98 Anisoxide, isolated from aniseed oil, the structure of which (39) has been established through synthesis,99 does not fit in with biogenetic theories and does not show the optical activity normally to be expected from a natural substance it is actually an artifact, formed during distillation by abnormal Claisen rearrangement from compound 40, which is present in the plant.100... 

In the furoquinoline series, Tarbell s technique may also be used 4-acetoxy-l-methyl-3-(l,2-dimethyl-2-propenyl)-2-quinolone (183), obtained by an abnormal Claisen reaction440 and treated with HBr + AcOH at 20° for 26 hours, gives a mixture of the isomeric furoquinolines 184 and 185. 

Explain the formation of the abnormal Claisen product 6.36, which is known to be produced from the normal product 6.35. 

Shifts in Neutral Species Shifts in Charged Species Shifts in Electron Deficient Centers Application of EMO Method Cope and Claisen Rearrangements Cope Rearrangement Oxy-Cope Rearrangement Claisen Rearrangement Some Other Examples Abnormal Claisen Rearrangement... 

A highly enantioselective and regioselective aromatic Claisen rearrangement was carried out using the reaction of catechol monoallyl ethers 192 with the chiral boron reagent 193. This reaction occurs without the formation of either the para-rearrangement or the abnormal Claisen rearrangement products (equation 89) . 

As shown by the examples in Table 1, the ring opening of carbonyl-substituted alkylcy-clopropanes is a general process. In fact, this isomerization has been shown to be part of the so-called enol-ene rearrangement which itself involves interchange of the ) - and <5-carbon atoms of ]S-alkyl-y,(5-unsaturated carbonyl systems, and which is also involved in the so-called abnormal Claisen rearrangement of y-alkylallyl phenyl ethers. ... 

In the abnormal" Claisen rearrangement29, a subsequent homodienyl [1,5] sigmatropic H-shift leads to the formation of isomeric allylphenols190 194. 

Photolysis of coumarin-3-carbonylazides gives nitrenes in the triplet state, and these have been trapped by hydrocarbons and by aniline. Prenyl ethers of 3-hydroxycoumarins undergo an abnormal Claisen rearrangement and give the 4-allyUc compound (193), but, in the presence of an 8-methoxy-group, the side-chain is further rearranged as in (192). ... 

Aromatic Claisen rearrangement. The presence of the silylating agent prevents the so-called abnormal Claisen rearrangement from occurring. 

Me), and a six-proton singlet at 8.84 (-CMe2) (207). Bucharidine appears to be a product of abnormal Claisen rearrangement of bucharaine (Scheme 24). Although this conversion was carried out in vitro by heating bucharaine in tetralin (203), the structure of the alkaloid is not yet certain the NMR resonance at 8.84 , for example, is at abnormally high field for a gem-dimethyl group in structure 285. 

The occurrence of (1,1-dimethylallyl)- and (l,2-dimethylallyl)quinoline derivatives in Flindersia and Ravenia species and the isolation of the prenyl ether 261 from Ravenia (Section V,B) suggested that the biosynthesis of this group of alkaloids might proceed via Claisen and abnormal Claisen rearrangements as in the synthetic route (Scheme 22, Section V, B). 

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