A smiles rearrangement in the pyridazine series

In the hydrazinolysis of 6-chloro-3-(-phthalimidoethoxy)-pyridazine a rearrangement takes place with the formation of 6-chloro-3-(-hydroxyethylamino)pyridazine. The action of thionyl chloride on the latter has given 6-chloro-2,3-dihydroimidazo[1,2-b]pyridazmium chloride. The reaction of -hydroxyethylguanidine with 3,6-dichloropyridazine leads to 6-chloro-3-(-hydroxyethylguanidino)pyridazine.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 124–126, January, 1974.     

Comparative study of the cope rearrangement of hexa-1,5-diene and barbaralane

The classical rules for Cope rearrangements predict a transition state with chair form to be favored over the boat form. On the other hand, bridged homotropylidenes, which allow only a boat-form transition state by steric reasons, have extremely low barriers. A controversy about the correct pathway and the different possible intermediates and transition states of the reaction has gone on for years. In this work, the hypersurfaces of barbaralane, in comparison with the boat- and chair-form of hexa-1,5-diene, are computed by the ab inito CASSCF (6,6)/6-31G** method starting with UMP2/6-31G** natural orbitals (NO's). All three hypersurfaces show characteristic features, and, moreover differ from each other. A hitherto undiscussed intermediate, bicyclo[2.2.0]hexane, was localized on the boat-hexa-1,5-diene pathway. So it is noteworthy that our transition state for the boat-hexa-1,5-diene does not correspond to the transition states found by other authors for this conformation. The computed enthalpies of activation of boat- and chair-hexa-1,5-diene, and barbaralane are in good agreement with the experimental data.     

Synthesis of 1,2,4-oxadiazines and their rearrangement to pyrimidines

Several amide oximes underwent condensation reactions with dimethyl acetylene dicarboxylate to afford 1:1 adducts. Under basic conditions, these adducts underwent ring closure to afford several methyl [3-(substituted)-4,5-dihydro-5-oxo-6H-1,2,4-oxadiazin-6-ylidene]acetates. The reactions of these compounds with a variety of amines resulted in addition-rearrangement reactions with the formation of the corresponding methyl 2-substituted-5-substituted amino-1,6-dihydro-6-oxo-4-pyrimidine carboxylates.     

20-hydroxyecdysone oximes and their rearrangement into lactams

(E)-Oximes derived from 20-hydroxyecdysone diacetonides and 7,8-dihydro analog were converted into the corresponding lactams (6-oxo-5a-aza-5a-homo derivatives) via Beckmann rearrangement. 14,15-Anhydro-20-hydroxyecdysone (Z)-oxime under analogous conditions (reaction with p-toluenesulfonyl chloride in acetone in the presence of Na₂CO₃) gave rise to 20-hydroxyecdisone 20,22-acetonide (Z)-O-tosyloxime which did not undergo Beckmann rearrangement.     

Nitrosophenols and their rearrangement products

It is shown that the benzene ring is opened (via the scheme of the Beckmann rearrangement) during the nitrosation of 6-hydroxyquinoline and subsequent reaction with acylating agents; the products are -(3-cyano-2-pyridyl)acrylic acids.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 504–508, April. 1971.     

The wolff-kishner reduction of 2-acetonyl pyrazines and pyridines. A novel rearrangement

Wolff-Kishner reduction of 1-(6-methylpyrazin-2-yl)-2-propanone leads to the formation of 2-isopropyl-6-methylpyrazine ( 2a ), in addition to the expected 6-methyl-2-n-propylpyrazine. The by-product 2a is suggested to arise via a spirocyclopropylidene aza-anion, which serves as a conduit between the initial less-stable secondary 1-(2-pyrazinyl)-2-propyl carbanion and the more stable primary 2-(2-pyrazinyl)-1-propyl carbanion. Similar results were observed for the 1-(3-methylpyrazin-2-yl) and 1-(6-methylpyridin-2-yl)-2-propanones. The extent of by-product formation diminished in the pyridine ring system. Electrophilic activation of the ring appears essential since the benzene analog phenylacetone gave no detectable cumene under identical reaction conditions.     

Lewis acids catalysed Fries rearrangement of isopropylcresol esters

Summary In the course of the Fries rearrangement, aluminium chloride frequently induces migration or elimination of alkyl groups. The results obtained with titanium tetrachloride for the synthesis of vicinalo-hydroxyketones are compared with those obtained with aluminium chloride for some aliphatic and aromatic esters of isopropylcresols. In order to understand the migration and elimination processes occurring, the stabilities of theo-hydroxyketones are studied in the presence of aluminium chloride at different temperatures. Furthermore, all-vicinalo-hydroxyketones were prepared by the Fries rearrangement of 6-tert-butyl-p-thymol with titanium tetrachloride.

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Lewis-Säure-katalysierte Fries-Umlagerung von Isopropylkresolestern

Zusammenfassung Im Verlauf der Fries-Umlagerung induziert Aluminiumchlorid des öfteren eine Wanderung oder Eliminierung von Alkylgruppen. Die Resultate mit Titantetrachlorid bei der Synthese von vicinaleno-Hydroxyketonen werden mit denen mit Aluminiumchlorid für einige aliphatische und aromatische Ester des Isopropylkresols verglichen. Um zu einem Verständnis der auftretenden Wanderungs-und Eliminierungsprozesse zu gelangen, wurden die Stabilitäten vono-Hydroxyketonen bei verschiedenen Temperaturen in der Gegenwart von Aluminiumchlorid untersucht. Außerdem wurden all-vicinaleo-Hydroxyketone mittels Fries-Umlagerung von 6-tert-Butyl-p-thymol mit Titantetrachlorid hergestellt.

     

Structure and Reactivity of Xanthocorrinoids. Part III. The first example of a pinacol-type rearrangement in the corrin series

The transformation of the c-acetic-acid chain of hexamethyl Coα, Coβ-dicyanocobyrinate into an ethyl group (→ 2 ) as well as the synthesis of the pentadecaalkyl-cobalticorrin 6d from commercial cyanocobalamin are described. On reaction of 2 or 6d with O₂ in the presence of ascorbic acid, migration of the CH₃ group at C(5) to the vicinal position C(6) takes place concomitantly with the introduction of a carbonyl group at C(5).     

Transformation of a spirobarbituric acid via aminobarbituric acid‐hydantoin rearrangement

A successful application of the aminobarbituric acid‐hydantoin rearrangement to produce a bicyclic carbamoylhydantoin from an intermediate spirobarbituric acid is reported. 7a‐Phenylcarbamoyl‐tetrahydro‐1H‐pyrrolo[1,2‐c]imidazole‐1,3(2H)‐dione ( 8 ) was obtained in a one‐pot multistep reaction of 1‐acetyl‐2,2‐bis(ethoxycarbonyl)pyrrolidine ( 5 ) and phenylurea in the presence of sodium ethoxide. Under less severe conditions, 5 and phenylurea were reacted to afford 1‐acetyl‐7‐phenyl‐triaza[4,5]decane‐6,8,10‐trione ( 6 ). The structural elucidation of the bicyclic hydantoin 8 and the spirobarbituric acid 6 was based on relevant nmr signals in accordance with those of reference compounds, i.e. monocyclic hydantoins 4a,b and acetamidobarbituric acids 2a‐c. The latter compounds were newly prepared from diethyl acetamidomalonates 1 and phenylurea.     

The adamantane rearrangement of 1,2-trimethylenenorbornanes. Part IV. Hydride-ion abstraction in 1,2-exo-trimethylenenorbornane

In the AlBr₃-catalyzed adamantane rearrangement in CS₂ of 1,2-exo-trimethylenenorbornane ( 1 ) to 2-endo,6-endo-trimethylenenorbornane ( 3 ), hydride-ion abstraction occurs at C(6) from the exo-side. The k_H/k_D value for competition between 1 and 5 (D_exo-C(6)) was 1.58 ± 0.05, whereas no kinetic isotope effect was operative for competition between unlabeled 1 and 4 (D_endo-C(5)) and between 1 and 6 (D_endo-C(6)).     

Evidence for a double intramolecular trimethylsilyl rearrangement

A double trimethylsilyl rearrangement ion, m/z 287, C₆H₅S(OSi(CH₃)₃)₃, was observed in the isobutane chemical ionization mass spectrum of 3-trimethylsilyl-9-(2-trimethylsilylethylthio)-1-phenyl-3-phenylsulfonylnonane. The daughter mass spectrum of the protonated molecule produced the rearrangement ion, m/z 287, suggesting that the double trimethylsilyl rearrangement occurred intramolecularly.     

Ab initio and RRKM evidence that the McLafferty rearrangement of ionized n-butanal is stepwise

Hartree-Fock calculations with geometry optimization at a series of C(2)? C(3) distances predict a negligible reverse critical energy for the second step of the McLafferty rearrangement of ionized n-butanal, in contrast to a previous conclusion. The most favorable geometry for departure of the C₂H₄ has a dihedral angle of about 90° between the parting fragments. RRKM calculations were used to estimate rates of reactions associated with the McLafferty rearrangement These calculations indicate that the McLafferty rearrangement of the n-butanal ion is stepwise. The RRKM calculations predict competition of H exchange with decomposition up to much higher energies than actually occurs.     

New rearrangement reactions of the trichothecane framework]

Treatment of the apotrichothecane derivative 4 with H₂SO₄ in dioxan gave the acetal 6 and with H₂SO₄ in acetone the ketal 9 . Whereas the oxidation of 4 with Ag₂CO₃ yielded the hydroxy aldehyde 7 , the reaction with CrO₃ or MnO₂ led to the α,β-unsaturated ketone 8 . Upon treatment of 8 with base the cyclic keto ether 11 was obtained due to 1,4-addition. Acetylation of the latter compound gave a mixture consisting of the enolacetate 13 and the acetylketone 14 . The oxim 15 of ketone 14 was transformed to the nitrile 16 and not the Beckmann fragmentation product 18 . For the identification of the C(11) hydrogen atom in biosynthetic studies the triol 22 was oxidized to the keto aldehyde 26 which, upon treatment with methanolic K₂CO₃, gave the spirolactol 30 and the cyclic acetal 29 as second product when the reaction was carried out in dilute solution. The spirolactol 30 was oxidized to the spirolactone 31 . The corresponding 19 possessing the intact 12,13-epoxy group underwent rearrangement to the apotrichothecane derivatives 20 and 21 under the same conditions. Oxidation of the triol 22 with MnO₂ or CrO₃ gave a mixture of the acetal 23 and the keto acid 24 . – The mechanisms of the rearrangements observed are discussed.     

Skeletal rearrangement for water loss from molecular protonated ions of t-butoxycyclohexane

Isotopic labelling and chemical substitution support the proposition that the skeletal rearrangement for water loss from molecular protonated ions of t-butoxycyclohexane involves competition between three reaction pathways. The principal reaction pathway (83%) involves migration of the t-butyl group to the 2-(6-) position of the cyclohexyl ring with reciprocal hydrogen transfer. A second reaction pathway (12%) involves ring contraction followed by reciprocal exchange of the t-butyl group with the 2-(5-) hydrogen atom of the nascent cyclopentyl ring. The third reaction pathway (5%) involves rearrangement of a proton-bound complex to permit ipso attack by isobutene. Stereospecific substitutions indicate that the principal reaction pathway is susceptible to 1,3-diaxial interactions.     

Synthesis of transparent and thermally stable polycyanurates and their thermal rearrangement

Transparent and thermally stable polycyanurates, whose solubility can be changed by thermal rearrangement, have been synthesized as functional films used in the multilayer coating process. Before the synthesis of polycyanurates, the model compound, 2,6‐bis(4‐methoxyphenyl)?6‐methoxy‐1,3,5‐triazine as a cyanurate is prepared and rearranged to an isocyanurate, 1,3‐bis(4‐methoxyphenyl)?5‐methyl‐1,3,5‐triazinane‐2,4,6‐trione in an excellent yield by thermal treatment. Based on this result, polycyanurates are prepared by the phase‐transfer‐catalyzed polycondensation of 2,4‐dichloro‐6‐methoxy‐1,3,5‐triazine with bisphenol monomers in the presence of quaternary ammonium salts. The polycyanurate obtained from 9,9‐bis(hydroxyphenyl)fluorene exhibits a high glass transition temperature at 251 °C. The solubility of polycyanurate films containing 1 wt % of tetrabutylammonium bromide can be changed by thermal rearrangement. The partially rearranged films keep high transparency and low birefringence. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3950–3955     

Sommelet-hauser rearrangement of an ammonium ylide derived from the HIV-1 reverse transcriptase inhibitor nevirapine

Functionalization at the 3-position of the dipyridodiazepinone nevirapine ( 1 ) has been accomplished by Sommelet-Hauser rearrangement of an ylide derived from 1 . Treatment of N-cyanomethylpyrrolidinium salt 4 with potassium tert-butoxide in a mixture of dimethylsulfoxide and tetrahydrofuran at ?10°, followed by acid hydrolysis, afforded a mixture of compounds 5 and 6 in a ratio of 1:1.8. Upon treatment of 4 with sodium amide in liquid ammonia, 5 and 6 were obtained in a ratio of 1.5:1 and a combined yield of 83%. Compound 5 is the desired product resulting from Sommelet-Hauser rearrangement of 4 , whereas 6 derives from competing Stevens rearrangement and intramolecular cyclization of the aldehyde produced upon hydrolysis. Baeyer-Villiger oxidation of 5 afforded the 3-hydroxy derivative 2 , a recently identified metabolite of nevirapine.     

1,2,4-Triazoles from formic acid-Induced rearrangement of 6-(Phenylhydrazino)uracils

The structure of a rearrangement product of 6-(phenylhydrazino)uracil + formic acid has been proved to be 1-phenyl-3-carboxamidomethyl-1,2,4-triazole: hydrolysis of this compound and thermal decarboxylation of the intermediate acid gave the known 1-phenyl-3-methyl-1,2,4-triazole. Yields of triazoles from substituted 6-(phenylhydrazino)uracils follow inversely yields of pyrimidoindoles derived from Fischer-type cyclization [J. Heterocyclic Chem., 13 , 539 (1976)]. The lack of formation of a triazole from 3-methyl-6-(phenylhydrazino)uracil suggests that an intermediate in this rearrangement, ie., that resulting from formylation of the anilino nitrogen atom followed by intramolecular cyclization involving the uracil 1-nitrogen atom, must undergo conjugate elimination of water to generate the triazole ring.     

Synthesis and thermal rearrangement of allylic 3,5,6-trimethyl-2-pyrazinylacetates: A heterocyclic carroll rearrangement

The synthesis of allylic 3,5,6-trimethyl-2-pyrazinylacetates 2–4 has been achieved by the reaction of 3,5,6-trimethyl-2-pyrazinylacetic acid lithium salt ( 1 ) with phenyl dichlorophosphate followed by addition of the allylic alcohol. On thermolysis, the allylic β-heteroaromatic esters underwent a rearrangement, analogous to the Carroll rearrangement, to generate the corresponding γ,δ-unsaturated heteroaromatic compound. The configuration of the double bond formed in the product was the E-isomer. The rate of the rearrangement was dependent on the substitution pattern of the allylic portion of the molecule with 4>2>3 . The ester enolate version of the heterocyclic Carroll rearrangement was investigated with 2 , however these conditions did not promote the rearrangement.     

Ring closure and rearrangement reactions of 4-azido-2-oxoquinoline-3-carboxylates and 4-azidocoumarin-3-carboxylates

4-Azido-2-oxoquinoline-3-carboxylates and 4-azidocoumarin-3-carboxylates 6 , which were obtained from the corresponding 4-hydroxy derivatives 1 via 4-tosylates 2 or 4-chloro compounds 4 , cyclized upon thermolysis to 3-alkoxyisoxazolo[4,3-c]quinolin-4(5H)-ones or the corresponding coumarins 8 , whereas at slightly higher temperatures a 3-O, 4-O-rearrangement took place to give the 4-alkoxy-isoxazolo[4,3-c]-quinolin-3-ones and the corresponding coumarins 9. The necessary reaction conditions could be obtained easily with the help of differential scanning calorimetry.     

ipso-Substitution with Sodium-N-alkyl-(p-nitrobenzene)sulfonamide. A novel anionic rearrangement

Reaction of N-benzyl-N, N-di-(p-nitrobenzene)sulfonamide ( 3 ) with NaCN/HMPA at 140° affords N-benzyl-p-nitroaniline ( 4 ). The same product is obtained upon heating of the sodium salt of N-benzyl-(p-nitrobenzene)sulfonamide ( 5 ). The transformation 5 → 4 is believed to proceed via an anionic episulfonyl compound 6 .