Showing papers on "Claisen rearrangement published in 1981"

Synthèse totale des acides (+) et (–) nonactique à partir de carbohydrates

Abstract: The synthesis of (−) and (+) nonactic acids (2a) and (2b) has been achieved starting from D-mannose (7) and D-gluono-γ-lactone (22) respectively. The key step in the synthesis is the [3,3]-sigmatropic rearrangement of the silylated ketene-acetals IV leading to control of the C-2 configuration of nonactic acid. The ketene-acetals were prepared from aliphatic esters of furanoid-glycals II, which were prepared in ten steps from the carbohydrate precursor. The chiral sites of the glycals arise from the corresponding centres in the starting monosaccharide. This type of ketene-acetal Claisen rearrangement leads to products containing the aldol portion required. At the same time knowledge of the absolute configuration of the chiral carbon atom of nonactic acid allows for the determination of the chair or boat form of the transition state of the [3,3]-sigmatropic rearrangement. [Journal translation]

Experiments directed towards the synthesis of anthracyclinones. V. Double Claisen rearrangement of 1,4-Bis(allyloxy)anthraquinones

Abstract: The Claisen rearrangements of 1,4-bis(prop-2'-enyloxy)anthraquinone (4) and 1,4-bis(2'-chloroprop- 2'-enyloxy)anthraquinone (3) in o-dichlorobenzene have been examined. The former gives a low yield of 1,4-dihydroxy-2,3-bis(prop-2'-enyl)anthraquinone (22), and 1,4-dihydroxy-2-(prop-2'-eny1)- anthraquinone (5) as the major product. Also formed is 1-hydroxy-4-propanoyl-2-(prop-2'-enyl)- anthraquinone (6) which arises from an unprecedented rearrangement of one allyloxy group. 1,4-Bis(2?-chloroprop-2'-enyloxy)anthraquinone (3) gives mainly 2-(2'-chloroprop-2'-enyl)-4-(2'- chloroprop-2'-enyloxy)-1-hydroxyanthraquinone (11) and a variety of minor products which are dependent on the time of reaction. Treatment of compound (11) with ethanolic potassium hydroxide, followed by a further Claisen rearrangement, gives a high yield of the synthetically useful 4-(2'-chloro-prop-2'-enyl)-5-hydroxy-2-methyl-6,11-dihydroanthra[1,2-b]furan-6,11-dione (19).

Some rearrangements of unsaturated phosphonate esters

Abstract: α-Hydroxyalk-2-enylphosphonates undergo Claisen orthoester rearrangement on heating with orthoesters, and their arylsulphenates undergo [2,3]-sigmatropic rearrangement to give 3-arylsulphinylalk-1-enylphosphonates. The addition of allyloxide anion to the central carbon of the allene Me2CCCHP(O)(OEt)2 is followed by rapid Claisen rearrangement of the resulting allylic carbanion to give the two possible β-ketoalkylphosphonates. Allenic phosphonates of the general formula R1R2CCH[CH2]nCR3CCHP(O)(OEt)2 have been prepared: when R1= R2= H, R3= Me, and n= 2, Cope rearrangement occurs to give isomeric dienes; when R1,R2,R3= Me and n= 0, [1,5] hydride shift gives a triene which then cyclises to a cyclohexadiene; when R1= Me, R2= H, R3= H or Me, and n= 0, the diene component can be used in Diels–Alder reactions.

Claisen rearrangement of meta-substituted allyl phenyl ethers

Abstract: Electron-releasing substituents at the 3-position of allyl phenyl ethers favour Claisen rearrangement of the allyl group to the 6-position, whereas electron-acceptors favour migration to the 2-position. 2-Acylhydroquinone 4-allyl ethers yield, predominantly, the 3-allyl isomers, probably because internal hydrogen bonding confers naphthalenoid character on the aryl residue.

The mechanism of catalysis of the thio-Claisen rearrangement

Abstract: The cyclization-induced rearrangement mechanism proposed by Overman to account for nucleophilic catalysis of the thio-Claisen rearrangement has been tested by application of two criteria, viz., the secondary kinetic deuterium isotope effect at the ..beta.. (side chain) carbon in phenyl allyl sulfide and the substituent rate effect. The results (k/sub H/k/sub D/ = 1.05 and log k/sub xp/k/sub H/ = 0.25 sigma/sup +/) do not support the mechanism. Instead, they can be construed to support the previously validated mechanism of nucleophilic triggering of sigmatropic rearrangement.

1,6-Dihydro-3(2H)-pyridinones as synthetic intermediates. A convenient total synthesis of (.+-.)-cleavamine.

Abstract: A novel and convenient total synthesis of (±)-cleavamine (1) starting from ethyl 1, 6-dihydro-3 (2H)-pyridinone-1-carboxylate (2) is described.

Synthetic utility of a fluorine-facilitated claisen rearrangement: a novel synthetic method for 2,4-alkadienoic acids using 2,2,2-trifluoroethyl phenyl sulfoxide

Abstract: A novel synthetic method for 2,4-alkadienoic acids from allylic alcohols and 2,2,2-trifluoroethyl phenyl sulfoxide is described which involves the in situ Claisen rearrangement facilitated by the fluorine. This method was applied to the stereocontrolled synthesis of pellitorine, a natural insecticide.

Synthesis of Demethylgorgosterol and Its Stereoisomers

Abstract: A stereoselective synthesis of demethylgorgosterol (2) is described. Alkylation at the C-22 position of the steroidal 23-aldehyde (5) was achieved by Claisen rearrangement of the piperidine enamine to give the (22S)-22-aldehyde (10a) predominantly. Compound 10a was transformed to the 22-hydroxymethyl-24-aldehyde mesylate (15a). When the mesylate was treated with potassium t-butoxide, the 22, 23-cyclopropyl 24-aldehyde (19a) was obtained in high yield. An isopropyl group was introduced at the C-24 position by means of the Grignard reaction and subsequently the hydroxy group was oxidized to provide the 24-ketone (25a). Wittig reaction of 25a followed by hydroboration and then LiAIH4 reduction of the mesylate gave 2, which was identical with the natural compound in all physical properties. Three other epimers, the (22R, 23R, 24S)-isomer (32), (22S, 23S, 24R)-isomer (34) and (22S, 23S, 24S)-isomer (35), were prepared by the same procedure. These four isomers can be separated by gas-liquid chromatography on a glass capillary column coated with OV-17.

Amino-Claisen Rearrangement. II. Quaternary Amino-Claisen Rearrangement of Anilinium Compounds with ortho Substituents

Abstract: Amino (N)-Claisen rearrangement of quaternary aniline derivatives with ortho substituents was investigated in relation to that of corresponding tertiary anilines. N-Allylated anilinium compounds 1 with a freely rotating ortho substituent such as a methyl or methoxy group yielded mostly the deallylated products 4 along with minor amounts of rearrangement products 2 and 3. The corresponding tertiary anilines yielded ortho rearrangement products 6 together with para ones 7. The quaternary N-Claisen rearangement of N-allylated 1, 2, 3, 4-tetrahydroquinolinium salts 14 and indolinium salts 22 in which the ortho substituents are locked in rings afforded the ortho rearrangement products 15 and 23, respectively in good yields. N-Claisen rearrangement of the corresponding aromatic tertiary amines 18 also took place in good yield. The above rearrangements could be rationalized on the basis of mechanistic considerations.

Experiments directed towards the synthesis of anthracyclinones. VI. Claisen rearrangements of 1,4-Bis(prop-2'-enyloxy)anthraquinone

Abstract: The Claisen rearrangement of 1,4-bis(prop-2'-enyloxy)anthraquinone (1) in N,N-diethylaniline and acetic anhydride has been examined. New products include compounds (3), and (6) and (14) in which a double bond has also migrated. Rearrangement of the compound (3) in o-dichlorobenzene affords the ketone (2), which supports an earlier mechanistic proposal.

Thermische Umlagerungen von 1-Allyloxy- und 1-Propargyloxy λ5-phosphorin-Derivaten

Abstract: Die thermische Umlagerung von 1-Allyloxy-λ5-phosphorin-Derivaten 1, fuhrt im Gegensatz zu der formal ahnlichen Claisen-Umlagerung von Allylphenylethern im irreversiblen Primarschritt in einer“ anti-Woodward-Hoffmann”-[3s5s]-Allylwanderung zu 4-Allyl-1,4-dihydro-λ5-phosphorin-Derivaten 2. –Die Reaktion verlauft, wie Kreuzungsexperimente beweisen, intramolekular und stereospezifisch nach einer Reaktion 1. Ordnung. Sie wird durch elektronenabgebende Substituenten in R4 und elektronenanziehende substituenten am Phosphor gefordert, ist jedoch wenig loungsmittelabhangig. Ihr folgt in einem irreversiblen Schritt unter erneuter Allyl-Umkehr eine [3s3s]-Cope-Umlagerung zu 2-Allyl-1,2-dihydro-λ5-Phosphorin-Derivaten 3. Bei etwas hoherer Temperatur gehen diese eine intramolekulare [4 + 2]-Cycloaddition zum Tricyclus 4 ein. Dessen Rontgenstrukturanalyse sowie die eindeutigen Deuterierungsergebnisse sprechen fur einen stereochemisch einheitlichen verlauf der Umlagerungen. Sterische und elektronische Einflusse auf einige analoge Umlagerungen werden untersucht, der Mechanismus wird diskutiert. Thermal Rearrangements of 1-Allyloxy- and 1-Propargyloxy-λ5-phosphorin Derivatives The thermal rearrangements of 1-allyloxy-λ5-phosphorin derivatives 1 affords – contrary to the formally similar Claisen rearrangement of allyl phenyl ethers - in the irreversible step an “anti-Woodward-Hoffmann” [3s5s] allyl shift to 4-allyl-1,4-dihydro-λ5-phosphorin derivatives 2. – The reaction is, as cross experiments prove, intramolecular and stereospecific according to 1st order law. It is accelerated by electron donating substituents in position 4 and by electron attracting substituent at the phosphorus, but is not much solvent-dependant. In a next step, again with allyl-inversion, a [3s3s] Cope rearrangement follows to give 2-allyl-1,2-dihydro-λ5-phosphorin derivatives 3. At somewhat higher temperature, by an intramolecular [4 + 2]-cycloaddition from 3j a tricyclus 4 is formed. Besides the experiments with deuterium marked compounds, the X-ray analysis of 4 proves the uniform stereochemic way of all these rearrangements. Steric and electronic influences on some analogous rearrangements are studied, the mechanism is discussed.

Thermal rearrangement of 1-(3-methylbut-2-enyloxy)-4-prop-1-enylbenzene (feniculin): a new synthesis of anisoxide and re-investigation of the constituents of star anise oil

Abstract: At 153 °C feniculin (1) undergoes Claisen rearrangement to the 1,1-dimethylallylphenol (3), which is slowly converted into the 1,2-dimethylallylphenol (4); the products of abnormal Claisen rearrangement, phenol (4) and anisoxide (2), are formed at 185 °C. Anisoxide was shown by g.l.c. analysis to be absent in star anise oil and in the seeds of Illicium verum and Foeniculum vulgare, and is believed to have been obtained previously as a result of prolonged distillation of anise oil.

Partially fluorinated heterocyclic compounds. Part 14. Syntheses of 4,5,6,7-tetrafluoro-2,3-dihydro-2-methyl-1-benzothiophen and 5,6,7,8-tetrafluorothiochroman from pentafluorophenyl prop-2-enyl sulphide via the Claisen rearrangement intermediate and the related reaction of prop-2-enyl 2,3,5,6-tetrafluorophenyl sulphide. Reactions which appear to proceed via homolytic fission of an aliphatic carbon–fluorine bond

Abstract: Prop-2-enyl 2,3,4,5-tetrafluorophenyl sulphide (1) undergoes a Claisen rearrangement in NN-diethylaniline to give 4,5,6,7-tetrafluoro-2,3-dihydro-2-methyl-1-benzothiophen (4) and 5,6,7,8-tetrafluorothiochroman (5). Pentafluorophenyl prop-2-enyl sulphide (3) in NN-diethylaniline also gave (4) and (5) accompanied by prop-2-enyl 3,4,5,6-tetrafluoro-2-(prop-2-enyl)phenyl sulphide (10), ethyl pentafluorophenyl sulphide (9), and perfluoropoly(phenylene sulphide). Prop-2-enyl 2,3,5,6-tetrafluorophenyl sulphide (2) reacted similarly to give 4,6,7-trifluoro-2,3-dihydro-2-methyl-1-benzothiophen (6), 5,7,8-trifluorothiochroman (7), ethyl 2,3,5,6-tetrafluorophenyl sulphide (8), and N-ethylaniline. Homolytic fission of the aliphatic C–F bond in the respective Claisen rearrangement intermediates from (3) and (2) is proposed to account for the formation of (4), (5), and (10), and of (6) and (7). Compounds (8)–(10) were synthesised by other methods.

Experiments Directed Towards the Synthesis of Anthracyclinones. VI* Claisen Rearrangements of

Abstract: The Claisen rearrangement of 1,4-bis(prop-2'-eny1oxy)anthraquinone (1) in N,N-diethylaniline and acetic anhydride has been examined. New products include compounds (3), and (6) and (14) in which a double bond has also migrated. Rearrangement of the compound (3) in o-dichiorobenzene affords the ketone (2), which supports an earlier mechanistic proposal.

Sequential [2,3]wittig and claisen rearrangement: a facile synthetic method for (e,e)-4,7-alkadienals and -alkadienoic acids. a new formal synthesis of (±)-cerulenin

Abstract: The regioselective [2,3]Wittig rearrangement of bis-allylic ethers followed by the Claisen rearragement permits ready access to (E,E)-4,7-alkadienals and -alkadienoic acids. The versatility of the sigmatropic sequence is demonstrated within the context of a new formal synthesis of (±)-cerulenin possessing an interesting spectrum of biological activities.

Rearrangement of a 2-aryloxycyclohex-2-enone. A new enolate Claisen rearrangement?

Abstract: The base-catalysed rearrangement of the 2-aryl-oxycyclohex-2-enone (3) to the enone (4a) is suggested to occur by an enolate-promoted 3,3-sigmatropic rearrangement of the enolate aryl ether (7)

Preparation of 4*77nonadienal

Abstract: PURPOSE:To obtain the titled compound useful as a synthetic intermediate for cerulenin from inexpensive substances readily in a short step, by isomerizing 1- methyl-2-propenyl allyl ether in the presence of a strong base, and reacting the isomerized ether with a vinyl ether CONSTITUTION:1-Methyl-2-propenyl allyl ether of formula V is isomerized in the presence of a strong base, eg methyllithium, preferably in the atmosphere of an inert gas and in an organic solvent at 0--100 degC, to give 1,5-heptadien-3-ol of formula III by the selective [2,3]sigmatropic rearrangement The compound of formula III is then reacted with a vinyl ether of formula IV in the presence of a mercury compound catalyst at 100-150 degC to form an intermediate of formula II, which is subjected to the selective Claisen rearrangement to afford the titled compound of formula I

Mechanism of the thio-claisen rearrangement of 3-methylallyl phenyl sulfide

Abstract: The thio-Claisen rearrangement of isomeric 3- and 1-methylallyl phenyl sulfides was investigated. It is demonstrated that the thio-Claisen rearrangement of the 3-methyl isomer is preceded by its thioallyl rearrangement to the 1-methyl isomer. The latter undergoes thio-Claisen rearrangement to o-(3-methylallyl)thiophenol, which is cyclized to 2-ethyl-2,3-dihydrobenzothiophene and 2-methylthiochroman under the reaction conditions.