Showing papers on "Claisen rearrangement published in 1972"

The ortho-Claisen rearrangement of phenyl allyl ethers in trifluoroacetic acid

Abstract: Phenyl allyl ethers spontaneously rearrange when dissolved in trifluoroacetic acid; rate constants for several para-substituted compounds are estimated to be ca. 105 times as great as those observed in the thermal rearrangement.

A novel Claisen rearrangement producing a furo[3,2-b]pyrone

Abstract: The thermal rearrangement of prop-2-ynyl kojate (2) to the novel furo[3,2-b]pyrone (6) in high yield is described.

Claisen rearrangement of allyl imidates and thioimidates derived from lactams and thiolactams

Abstract: Allyl imidates N=C(OCH2CH=CH2)CH2, derived from lactams, rearrange on heating to yield the corresponding C-allyl and N-dlyl lactams,I NHCOCHCH2CH=CH2 and N(CH2CH=CH2)COCH2 while allyl thioimidates yield only the C-allyl thiolactams. The C-allylation is postulated to occur through a ketene acetal intermediate by way of a quasi-chair transition state. The yield of 3-allylhexahydro-2H-azepin-2-one obtained in such a rearrangement is significantly increased by the presence of 2-pyridone.

Furano compounds. XX. Synthesis of angular and linear furoxanthones

Abstract: The three isomeric furoxanthones viz. 4-methoxy-2-methyl-5-H-furo[3,2-b]xanthen-5-one 11, 4-methoxy-2-methyl-11-H-furo [2,3-a]xanthen-11-one 16 and 5-methoxy-2-methyl-6-H-furo[2,3-c]-xanthen-6-one 23 have been synthesised starting with 1,3-dihydroxy xanthone and building a furan ring on the 2:3, 1:2, and 3:4 positions respectively after partial tosylation of the 3-hydroxyl and following the sequence of reactions: allylation, CLAISEN rearrangement, acetylation, bromine addition and dehydrobromination with appropriate modification, viz. methylation and detosylation in the sequence depending on the individual case.

Synthesis and reactions of 3,3-dimethylallyl derivatives of acetylacetone and other poly-β-carbonyl compounds

Abstract: Alkylation of acetylacetone, and of a number of related triketones and lactones, with 3,3-dimethylallyl bromide and 3,3-dimethylallyl diphenyl phosphate gives C-alkylated products under a variety of experimental conditions. The C- and O-(3,3-dimethylallyl) derivatives of acetylacetone undergo ready cyclisation and Claisen rearrangement reactions, respectively, to give products whose isoprenoid part-structures are similar to those found in phenolic isoprenoids. Acetylacetone is converted into 4-bromopent-3-en-2-one under mild conditions by treatment with triphenylphosphine dibromide.

Some reactions of 7-hydroxy- and 7-mercapto-3-methylbenzo[b]thio-phen

Abstract: Bromination of 7-hydroxy-3-methylbenzo[b]thiophen gave the 4- and the 6-monobromo- and the 4, 6-dibromo-derivative. Nitration gave the 6-nitro- and the 4,6-dinitro-derivative, and formylation by the Gattermann reaction gave the 6-formyl derivative. 7-Allyloxy-3-methylbenzo[b]thiophen underwent the Claisen rearrangement to give the expected 6-allyl compound, whereas Fries rearrangement of the 7-acetoxy-compound gave 2-acetyl-7-hydroxy-3-methylbenzo[b]thiophen. With ethyl acetoacetate in the presence of gaseous hydrogen chloride, 7-hydroxy-3-methylbenzo[b]thiophen condensed to give 3,6-dimethylthieno[3,2-h][1]benzopyran-8-one, 7-Mercapto-3-methylbenzo[b]thiophen and 2-bromopropionic acid in alkaline solution gave 2-(3-methyl-7-benzo[b]thienylthio)propionic acid, which was cyclised in hot polyphosphoric acid to give 7.8-dihydro-3-methyl-thieno[3,2-h][1]benzothiopyran-6-one.

Nucleophilic addition and substitution reactions of polyhalogenated norbornadienes with alkenoxide and alkenoxide anions. A novel Claisen rearrangement of allyl norbornadienyl ethers

Abstract: Rational syntheses of polyhalogenonorbornadienes (including the hepta- and octa-chloro-compounds and their bromo- and dibromo-hexachloro-analogues) and their reactions with alkoxide and alkenoxide anions in the presence (or otherwise) of dipolar aprotic solvents are described. Vinylic chlorine or bromine substitution, together with addition of alcohols appear to be the more important of their reations with these bases. Hydrolysis of the resulting divinylic ethers gives polyhalogenonorbornane-2,5-diones exhibiting unusual Iong-range n.m.r. spin couplings. Mild thermolysis of the derived allyl vinyl ethers results in Claisen [3,3] sigmatropic rearrangements new to the norbornadienes. Comment is made on the stereochemistry of this rearrangement and on addition reactions of norbornenes.

Claisen rearrangement of 1-hydroxy-3-(3-methylbut-2-enyl)oxyxanthones

Abstract: Claisen rearrangement of three 1-hydroxy-3-(3-methylbut-2-enyl)oxyxanthones at 200° for 3 h yields the corresponding deprenylated xanthones and linear and angular furoxanthones, in contrast to previous results.

Synthesis of unsaturated aldehydes by sequential Claisen and Cope rearrangements

Abstract: The reaction of hexa-1,5-dien-3-ols with 2-methyl-1,1,3-triethoxybutane gives unsaturated aldehydes by a Claisen rearrangement which undergo two Cope rearrangements to give 2,5,9-unsaturated aldehydes; the reactions proceed with high stereospecificity when secondary hexa-1,5-dien-3-ols are used, resulting in the 2-trans-5-trans isomer.

Synthesis of Naphthalimide Derivatives by the Claisen Rearrangement and their Fluorescence Spectra

Abstract: 5, 9-Dimethyl-5, 6-dihydro- (or-5, 6, 8, 9-tetrahydro-) 4H-benzofuro- [5, 6, 7-de] isoquinoline-4, 6-dione (5a, 8a) were synthesized by the Claisen rearrangement of 4-allyloxynaphthal-N-methylimide. Similarly, 8-phenyl derivatives of (5a) and (8a), (5b, 8b) were obtained from 4-cinnamyloxynaphthal-N-methylimide. In addition to (8b), in the latter case, 5-methyl-8-phenyl-5, 6-dihydro-4 H, 10 H- [1] benzopyrano [6, 7, 8-de] isoquinoline-4, 6-dione (9) was formed as a by-product.Furthermore, several 3-substituted-4-methoxynaphthal-N-methylimides [e. g. propenyl (11a), α-phenylpropenyl (11b), carboxy (12), methoxycarbonyl (13), carbamoyl (14) and benzoyl (16)] were derived from the 3-allyl- (10a) or 3-α-phenylallyl-4-methoxy derivative (10b). The fluorescence spectra of these compounds were determined and the relationship between their structures and spectra was discussed.The results are as follows. 1) The annellated dihydrofuran ring (5a), (5b) causes a shift (30 mμ) to longer wavelength at the fluorescence maximum and a slight increase in the fluorescence intensity, compared with 4-methoxynaphthal-N-methylimide as the standard sample. 2) On the other hand, the annellated furan ring (8a) results in only 10mμ shift and its intensity falls to 1/10 of that of the standard sample. 3) Fluorescence intensities of (8b), (9), (11b) and (16) are too weak to be measured under the conditions probably due to the non-planarity between their phenyl group and the naphthalene nucleus.

Stereochemie einer claisen-umlagerung in der sterin-seitenkette

Abstract: Es werden alle Faktoren untersucht, die bei der Claisen-Umlagerung des Keten-O.N-acetals 2 zur stereospezifischen Bildung der Sterin-amide (24S,25R)-3, (24R.25S)-3, (24R.25R)-3 und (24S,25S)-3 und daraus der Sterine (24S)- und (24R)-4 beitragen. Durch Abbau der Amide 3 wird deren Konfiguration bestimmt und damit auf chemischem Wege bewiesen. das dem in Cucurbitaceen vorkommenden Sterin 4 die ungewohnliche (24S)-Konfiguration zukommt. Stereochemistry of a Claisen Rearrangement in the Sterol Side Chain All the factors are examined which in the Claisen rearrangement of the ketene O.N-acetal 2 contribute to the stereospecific formation of the sterol amides (24S,25R)-3, (24R.25S)-3, (24R.25R)-3 and (24S,25S)-3 and further to that of the sterols (24S)- and (24R)-4. The configuration of the amides 3 is determined by degradation, which gives a chemical proof for the unusual (24S)-configuration of the sterol 4, which occurs in Cucurbitaceae.

Stereochemie der claisen-umlagerung mit 1-dimethylamino-1-methoxy-propen-(1)

Abstract: Bei der Umsetzung der Allylalkohole 2, 7 und 11 mit dem Titelreagens (1) erhalt man mit hoher Stereoselektivitat aus den trans-Formen die erythro-Amide 3, 8 und 12 und aus den cis-Formen die entsprechenden threo-Amide. Mit diesen Befunden last sich ein sesselformiger Ubergangszustand (6a, b) beschreiben und die direkt nicht erfasbare Z-Konfiguration der Keten-O.N-acetal-Doppelbindung beweisen. Stereochemistry of the Claisen Rearrangement with 1-Dimethylamino-1-methoxy-1-propene Reaction of the allylic alcohols 2, 7 and 11 with the title reagent (1) gives the erythro amides 3, 8 and 12 from the trans-forms and the corresponding threo amides from the cis allylic alcohols with high stereo-selectivity. These results indicate a chair-like transition state (6a, b) with Z-configuration of the ketene O.N-acetal double bond, which cannot be observed directly.