Rearrangement Of Methyl Research Articles

Two-atom azirine ring expansion reaction of methyl 2-diazo-3-(4-methoxyphenyl)-3-oxopropanoate via a dirhodium tetraacetate-catalyzed Wolff rearrangement

Rh2(OAc)4-catalyzed Wolff rearrangement of methyl 2-diazo-3-(4-methoxyphenyl)-3-oxopropanoate gave methoxycarbonyl(4-methoxyphenyl) ketene that was added to 2Н-azirines, resulting in opening of the three-membered ring at the N–C(2) bond and leading to the formation of 3,4-dihydro-2Н-pyrrol-2-one derivatives. Depending on the structure of the obtained products, they isomerized to the more stable 1Н-pyrrol-2(3H)-one derivatives or added a water molecule at the C=N bond.

Regioselectivity of the thermal van Alphen–Hüttel rearrangement of 4- and 5-mono- and 4,5-disubstituted 3,3-diphenyl-3H-pyrazoles

Thermal van Alphen–Huttel rearrangement of methyl 3,3-diphenyl-3H-pyrazole-4-carboxylate, 3,3-diphenyl-3H-pyrazole-4-carbonitrile, and methyl 5-methyl-3,3-diphenyl-3H-pyrazole-4-carboxylate involves completely regioselective migration of one phenyl group from the 3-position to N2 with formation of aromatic 1H-pyrazole system. Thermal rearrangement of methyl 3,3-diphenyl-3H-pyrazole-5-carboxylate leads to the formation of methyl 4,5-diphenyl-1H-pyrazole-3-carboxylate as a result of migration of the 3-phenyl group exclusively to the C4 atom and subsequent prototropic isomerization. Under analogous conditions, methyl 4-methyl-3,3-diphenyl-3H-pyrazole-5-carboxylate, methyl 5-(methanesulfonyl)-3,3-diphenyl-3H-pyrazole-4-carboxylate, methyl 5-(benzenesulfonyl)-3,3-diphenyl-3H-pyrazole-4-carboxylate, and dimethyl 3,3-diphenyl-3H-pyrazole-4,5-dicarboxylate have been regioselectively converted into the corresponding 4H-pyrazoles. Thermolysis of 5-(4-methylbenzenesulfonyl)-3,3-diphenyl-3H-pyrazole-4-carbonitrile gives rise to a mixture of 1H- and 4H-pyrazoles, the former considerably prevailing, whereas the corresponding 1H-pyrazoles are formed as the only product from 5-(methanesulfonyl)- and 5-(benzenesulfonyl)-3,3-diphenyl-3H-pyrazole-4-carbonitriles.

Facile Synthesis of 1H, 4H-cyclopenta[c]pyrrolo[1,2-b]isoquinolin-2(3H)-one

A novel and facile method for the synthesis of 4H-cyclopenta[c]pyrrolo[1,2-b] isoquinolin-2(3H)-one has been developed by employing the [2, 3] Stevens rearrangement of methyl N-allyl-N-benzylpyrrolidine 2-carboxylate to methyl 2-allyl-l-benzyl-pyrrolidine 2-carboxylate and acid-lactonisation as key transformations. The synthetic strategy from readily available materials provided a model skeletal analogue of cephalotaxine and should have general applicability in the synthesis of Cephalotaxus alkaloids.

Specific degradation of pectins via a carbodiimide-mediated Lossen rearrangement of methyl esterified galacturonic acid residues

A specific, chemical degradation of the methyl esterified galacturonic acid residues of pectins is described. These residues are converted, with hydroxylamine, to hydroxamic acids, and then, with a carbodiimide, to isoureas; the latter undergo a Lossen rearrangement on alkaline hydrolysis. The isocyanates formed are hydrolysed to 5-aminoarabinopyranose derivatives, which spontaneously ring open to give 1,5-dialdehydes. The latter are reduced, in situ, to avoid peeling reactions, with sodium borohydride to give substituted arabitol residues. Thus, overall, partially esterified pectins are specifically cleaved to generate a series of oligogalacturonic acids bearing an arabitol residue as aglycone. Analysis of oligomers so generated discloses the pattern of contiguous nonesterification in a variety of pectins of differing degrees of esterification. Other potential applications are described.

Enantioselective conversion of linoleate hydroperoxide to an α, β‐epoxy alcohol by niobium ethoxide

AbstractNiobium (V) ethoxide [Nb(OC2H5)5] catalyzed the rearrangement of methyl 13(S)‐hydroperoxy‐9(Z),11(E)‐octadecadienoate (Me‐HPODE) to epoxy hydroxy isomers. At low temperature (5°C) in aprotic solvent, Me‐HPODE was converted to the diastereomeric α, β‐epoxy alcohols, methyl 11(R,S),12(R,S)‐epoxy‐13(S)‐hydroxy‐9(Z)octadecenoate. These products are referred to as oxylipids and structurally resemble those obtained from the vanadium‐ and epoxygenase‐catalyzed rearrangement of Me‐HPODE but are distinct from products obtained from ferrous iron‐, hematin‐, and hemoglobin‐catalyzed rearrangements. Because the product of the niobium‐catalyzed rearrangement of Me‐HPODE was predominantly the erythro diastereomer, the rearrangement is distinguished from that produced by a titanium catalyst, in which the threo diastereomer [methyl 11(R), 12(R)‐epoxy‐13(S)‐hydroxy‐9(Z)‐octadecenoate] predominates, and from that produced by a vanadium catalyst, in which both diastereomers are produced in equal proportion. The synthesis of alcohol epoxide by Nb(OC2H5)5 was inhibited by traces of water, but inclusion of molecular sieves in the reaction medium did not improve yield, as the alcohol epoxide rearranged to ketonic materials.

Synthesis of isochroman-3-ylacetates and isochromane-γ-lactones through rearrangement of aryldioxolanylacetates

Lewis acid catalysed rearrangement of methyl 4,5-trans-4-aryldioxolan-5-ylacetates 1 provides a convenient route to substituted methyl isochroman-3-ylacetates 2 and isochromane-γ-lactones 3. The choice of Lewis acid is determined by the substitution pattern of the aromatic ring. The two contiguous isochromane stereocentres are transferred unchanged from the parent dioxolanes, while the configuration of the isochromane methyl group is dependent upon the aryl substitution, the reagent and the reaction conditions. Thus treatment of the C-2 epimeric 3′,5′-dimethoxyphenyldioxolanes 4 and 5 with camphorsulfonic acid afforded a mixture of the C-5 epimeric isochromane lactones 26 and 29, the former being favoured at lower acid concentrations, the latter at higher concentrations. Titanium tetrachloride isomerised the analogous 2′-chloro-5′-methoxyphenyldioxolanes 6 and 7 into the methyl isochroman-3-ylacetate 38, which could be lactonised to the isochromane lactone 27. Phosphoric acid converted the 2′,5′-dimethoxyphenyldioxolanes 8 and 9 into a mixture of the isochromane lactones 28 and 31, while similar treatment of the hydroxylactone 22 in the presence of acetaldehyde afforded the isochromane lactone 28 directly and with complete diastereoselectivity. Oxidative demethylation and annulation of this isochromane lactone 28 afforded 5-epi-7-deoxykalafungin 41.

ChemInform Abstract: Sulfoxide Induced Sigmatropic Rearrangement (SISR) of Methyl 1‐ Methylsulfanylvinyl Sulfoxides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Rearrangement of Methyl 11,12‐Di‐O‐methyl‐6,7‐didehydrocarnosate in Basic Medium. Easy Hemisynthesis of Miltirone.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Unprecedented Stereochemical Reversal from Alkyl to Aryl Substituents in the Johnson-Claisen Rearrangement of Methyl 3-Hydroxy-2-methylenealkanoates

An unprecedented stereochemical reversal from alkyl to aryl substituents in the Johnson-Claisen rearrangement of methyl 3-hydroxy-2-methylenealkanoates with triethyl orthoacetate with a plausible mechanism has been described.

Rearrangement of methyl 11,12-di-O-methyl-6,7-didehydrocarnosate in basic medium. Easy hemisynthesis of miltirone

Methyl 11,12-di-O-methyl-6,7-didehydrocarnosate 3, obtained from the abundant natural product carnosol 1, undergoes an interesting rearrangement when treated with potassium tert-butoxide in dimethyl sulfoxide to give 11,12-dimethoxy-20(10→7)abeo-abieta-5(10),8,11,13-tetraen-20-oic acid 4, in which an additional double bond is formed between C-5 and C-10 and the carboxylic acid group has migrated from C-10 to C-7. Deprotection of the two methyl ether moieties in 4 with BBr3 allows spontaneous air oxidation and decarboxylation of the catechol derivative to give the potent benzodiazepine agonist miltirone 10. The structure of 6 has been unequivocally elucidated by X-ray diffraction analysis and indirect chemical correlation between 4 and 6 has been established.

Synthesis of novel piperideine- and pyridine-containing long-chain fatty ester derivatives from methyl iso-ricinoleate

Oxidative rearrangement of methyl 9-azido-12,13-epoxy-stearate 2 with MeI, NaI and DMF and short-time concomitant ultrasonication at 120 °C yields exclusively 1,4- and 1,5-azido-oxo isomers 3 and 4, whereas prolonged heating furnishes pyrrole and pyridine derivatives 5 and 6; cyclization of 3 and 4 with Ph3P gives pyrroline 7 and Δ1piperideine 8; and oxidative aromatization of 8 with PtO2 yields compound 6 as an alternative route.

Preferred Conformation of a New Ring B-Homo Diterpene, Rearrangement Product of Methyl 9α-Hydroxy-11α-Methanesulfonyloxy-(-)-Kauran-19-oate

Abstract The preferred conformation of a ring B-homo diterpene, obtained by the rearrangement of methyl 9α-hydroxy-11α-methanesulfonyloxy-(-)-kauran-10-oate 1 with potassium t-butoxide in t-butanol, was determined on the basis of the n.O.e. experiments and molecular dynamics calculations.

ChemInform Abstract: Synthesis of a 2,3‐Dideoxy‐2,3‐difluorofuranose with the D‐lyxo Configuration. An Intramolecular Rearrangement of Methyl 5‐O‐Benzoyl‐2, 3‐dideoxy‐2,3‐difluoro‐D‐lyxofuranoside Observed During the Attempted Synthesis of 1‐(2,3‐Dideoxy‐2,3‐difluoro‐β‐D‐lyxofuranosyl) thymine.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The contribution of quantum mechanical tunneling to the 1,2-hydrogen rearrangement of methylbromocarbene

The rate constants for the 1,2-hydrogen rearrangement of methyl- and methyl-d3-bromocarbene have been determined as a function of temperature. The Arrhenius plots are curved, and the intermolecular isotope effect is small and may increase with increasing temperature. We believe that although the rearrangement proceeds classically at high temperatures, as suggested by theory, quantum mechanical tunneling contributes significantly to the reaction at low temperatures. Alternative explanations are presented and discussed.

Synthesis of cyclopentathiophenacetic acid derivatives. Reactivity of methyl 6‐oxo‐4,5‐dihydro‐6H‐cyclopenta[b]thiophen‐4‐acetate

AbstractOxodihydrocyclopentathiophenacetic acids 4, 5 and 6 were synthesized from suitable 2‐ or 3‐formylthiophenes. Reactivity of the carbonyl group or the carboxylic group of these bicyclic systems was investigated. The Beckmann rearrangement of methyl 6‐oximino4,5‐dihydro‐6H‐cyclopenta[b]thiophen‐4‐acetate 12 is an interesting route to methyl 7‐oxo‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridin‐4‐acetate (13).

Synthesis of some further C-3 branched 3-amino-2,3,6-trideoxysugars, related to daunosamine, as potential components for structurally modified anthracyclines

A Hofmann-type, oxidative rearrangement of methyl 4,6- O-benzylidene-3- C-carbamoyl-3- C-cyano-3-deoxy- α- d-glucopyranoside ( 1) by mercuric acetate and N-bromosuccinimide resulted in a 2-oxazolidinone ring fused to the pyranoside. Deoxygenation by tributylstannane of the 2- O-phenoxythio-carbonyl derivative of 1 led to its 2,3-dideoxy analog. The latter was subjected to Hofmann rearrangement with lead tetraacetate followed by reduction of the cyano group, with simultaneous N-tert-butoxycarbonylation in both steps, to give methyl 4,6- O-benzylidene-3- tert-butoxycarbonylamino-3- C- tert-butoxycarbonylaminomethyl-2,3-dideoxy- α- d-glucopyranoside. Hanessian reaction of this acetal yielded the corresponding 6-bromo-6-deoxy 4-benzoate which by dehydrobromination with DBU produced a blocked 3- C-aminomethyl-2,3,6-trideoxy-3,6-iminohexopyranoside. Methyl 3-amino-3,6-dideoxy-3- C-methoxycarbonyl- α- l-galactopyranoside was partially blocked atNH 2-3 and OH-4 by N-tert-butoxycarbonylation and N,O-isopropylidenation, and then converted into a 2-xanthate. Subsequent Barton deoxygenation followed by hydride reduction of the methyl ester function and methylation of the resulting primary alcohol gave 3,4-protected derivatives of 3-amino 2,3,6-trideoxy- l- lyxo-hexose ( l daunosamine) branched at C-3 by methoxycarbonyl, hydroxymethyl, and methoxymethyl groups.

On the Methyl‐Transfer Reaction in Crystalline Methyl 2‐(Methylthio)benzenesulfonate: a Thermally Induced Non‐Topochemical Solid‐State Reaction

AbstractThe rearrangement of methyl 2‐(methylthio)benzenesulfonate (1) to the zwitterionic 2‐(dimethyl‐sulfonium)benzenesulfonate (2) is known to proceed in solution by intermolecular Me transfers. The same rearrangement has been observed to occur in crystalline 1, but the crystal structure shows that the molecular packing is not conducive to intermolecular Me transfer. The reaction has been carried out with mixed crystals composed of 1 and deuteriomethylated (D6)‐l. By fast‐atom‐bombardment mass spectroscopy, it has been shown that the product consists of a 1:2:1 mixture of the non‐, tri‐, and hexadeuterated species, the mixture expected, if the solid‐state reaction proceeds by intermolecular Me transfers. From this result, together with the slower rates of conversion in the single crystal compared with the melt, it can be concluded that the reaction must occur not topochemically but rather at defects such as microcavities, surfaces, and other irregularities in the ordered crystal arrangement.

Theoretical study of the mechanism of halogenotropic rearrangement in dichlorovinylsulphones

The rearrangement of methyl β,β-dichlorovinylsulphone to methyl Z-α,β-dichlorovinylsulphone is studied using the MNDO method. It is shown that the Z-α,β-isomer is the most stable, thus suggesting the thermodynamic nature of the motive force of the rearrangement. The corresponding vinyl anions of all isomers are also calculated. The α-vinyl anion CH 3SO 2CCCl 2 appears to be a real stationary point on the potential energy surface contrary to the, β-vinyl anion CH 3SO 2CClCCl which is shown to be unstable against dissociation into methyl sulphinate anion CH 3SO 2 − and dichloroacetylene. The configurational stability of the α-vinyl anion is shown with a barrier of degenerated isomerization of about 324 kJ mol −1. The, β-vinyl anion appears to be configurationally unstable which could be responsible for stereospecific formation of the Z-α,β-isomer within the framework of both inter- and intramolecular mechanisms of the rearrangement under investigation.

Efficient, highly regioselective fries rearrangements of methyl 3-(2-acyloxy-4-methoxyphenyl)propanoates: The first total syntheses of the linear acylated coumarins geijerin and dehydrogeijerin.

Aluminium chloride catalysed para-Fries rearrangement of methyl 3-(2-acyloxy-4-methoxyphenyl)propanoates ( 5)in nitromethane furnishes the corresponding 5-acylated products ( 6) cleanly and in high yield. The rearrangement products may be converted into 6-acyl-7-methoxycoumarins ( 2) including the naturally occurring geijerin ( 2a) and dehydrogeijerin ( 2b).

ChemInform Abstract: Methoxide‐Catalyzed Rearrangement of Methyl (S)‐Dihydroorotate to Methyl Hydantoin‐5‐acetate.

AbstractMethyl S‐dihydroorotate (Ia) is consecutively converted to the racemic hydantoin‐5‐acetates (II).