Claisen Rearrangement Routes

Compound 1, 2,2-diniethyl-4-pentenal, has been prepared by the Claisen rearrangement route described above and by reaction of isobutyraldehyde with allyl chloride in the presence of aqueous sodium hydroxide and a phase-transfer catalyst. Both routes are applicable to the synthesis of a variety of substituted 4-pentenals. 

Claisen rearrangements routes to multiply substituted pyranoside diquinanes, J. Org. Chem. 54 5357 (1989). 

Eor an early summary of the chloromethylation route , the Claisen rearrangement route and the quinonemethide route see C. D. Gutsche, in Calixarenes A Versatile Class of Macrocyclic Compounds (Eds. J. Vicens and V. Bohmer), Kluwer, Dordrecht, 1990, p. 3. 

With the p-positions of the calixarenes made available by de-tert-butylation, a wide variety of p-functionalization procedures have been explored. A number of these were developed in the 1980s (see ref. 1, pp. 135-144), including the electrophilic substitution route 4 , 5 , 6 , etc. 169 (E = NO2, SO3H, COR, COAr, CH2CI), the p-Claisen rearrangement route 4 , 5 , 6 , etc. -> 173 174, and the... 

A highly successful route to stereoisomers of substituted 3-cyclohexene-l-carboxylates runs via Ireland-Claisen rearrangements of silyl enolates of oj-vinyl lactones. The rearrangement proceeds stereospeaifically through the only possible boat-like transition state, in which the connecting carbon atoms come close enough (S. Danishefsky, 1980 see also section 4.8.3, M. Nakatsuka, 1990). 

Final remarks. The 14C-KIE and 2H-SKIE data presented in this Section (VLB) clearly indicate the usefulness of isotope effect methodology in studies of mechanistic details of thermally induced Claisen rearrangement, which provides a synthetic route to y,5-unsaturatcd carbonyl compounds. The primary and secondary 14C KIE supplement strongly the deuterium SKIE. Especially easy for interpretation are 14C and 2H isotope... 

In a variation of this method, a dimethylamine adduct can be used in the same way as the methanol adduct described previously [Eq. (20)]. Nickel(II) and palladium(II) complexes with allyl-substituted NHCs are accessible by this route. These compounds cannot be prepared by the cleavage of an electron-rich olefin vide infra) because of an amino Claisen rearrangement of the tetramino-substituted olefin. However, [(NHC)M(CO)4] (M = Cr or Mo) were accessible via cleavage of electron-rich olefins with [M(CO)6] as the precursors but for the very same NHC. ... 

Secondary aliphatic amines were found to give higher yields of thienothiophenes than did tertiary amines, which are weaker bases. A maximum ratio of thienothiophenes to thienothiopyrans of about 4 1 was achieved at 145° with diisopropylamine as cat yst and DMSO as solvent. Only thienothiopyrans were formed in DMF in the presence of the same catalyst The amines promote nucleophilic cyclization of Claisen rearrangement products into thienothiophenes. Since thienothiophenes are resistant to treatment with potassium t-butoxide in DMSO and thienothiopyrans form resinous products under these conditions, the method is a convenient route to pure thienothiophenes 35 and 42 in yields of up to 40%. ... 

Scott G. Nelson of the University of Pittsburgh has developed (J. Org. Chem. 2005, 70,4375) a highly diastereocontrolled route to substituted cyclohexanones using the intramolecular Sakurai reaction. The requisite ally silane 12 was prepared by Claisen rearrangement of the allylic alcohol 10, followed by homologation. The Ti enolate from the Sakurai addition was trapped with isobutyraldehyde to give 13. Although 32 diastereomers of 13 are possible, the diastereomer illustrated was the dominant product from the cylization. Note that use of the enantiomerically-pure form of the alcohol 10 would have led to enantiomerically-pure 13. 

The Claisen rearrangement of lactonic enolates provides a new route to cycloalkenes. Cyclocitral was converted to the lactone (642) through a multistep sequence, the lactone deprotonated with LDA in THF at -78 °C, and the enolate quenched with f-butyldimethyl-chlorosilane (80JA6889, 6891). The crude ketene acetal (643) was heated at 110 °C for 10 h, and the product treated with fluoride ion to afford a single acid. Replacement of the quaternary carboxyl group by hydroxyl was accomplished through use of the carboxy inversion reaction (Scheme 147). The product (645) of this last reaction was identical with an authentic sample of widdrol in all respects excluding its optical rotation. 

Similar reactions were carried out on 17,29 18,30 and 19.30 The last gave thiochromans and 2,3-dihydrothiophenes from an apparent cyclization at the ortho methyl substituent, but in fact involving a variety of hydrogen and methyl shifts. The route to the two main products [Eq. (7)] of the thio-Claisen rearrangement has been suggested to be via the thiirane intermediate (20).31... 

D. B. Tulshian, R. Tsang, and B. Fraser-Reid, Out-of ring Claisen rearrangements are highly stereoselective in pyranoses Routes to gem-dialkylated sugars, J. Org. Chem. 49 2347 (1984). 

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 formation of the coumarin (388) from 7-allyloxy-3-methylf avone via a Claisen rearrangement and oxidation with DDQ is of a similar nature to the previous route, though yields are considerably lower (77TL473). 

Asymmetric induction has been reported for a ketene Claisen rearrangement of the adducts of dichloroketene to chiral allyl thioethers as a route to precursors of optically active y-butyrolactones [504], An example of this sigmatropic step is given hereafter. 

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