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.     

Synthesis and spectral properties of the 1-aryl-2-phenyl-4-oxo-4,5,6,7-tetrahydroindole oximes and of their beckmann rearrangement products

Under Beckmann conditions the oximes of the 1-aryl-2-phenyl-4-oxo-4,5,6,7-tetrahydroindoles 2a-k are rearranged yielding as the sole product, 1-aryl-2-phenyl-4-oxo-1,4,5,6,7,8-hexahydropyrrolo[3,2- c ]azepine 3a-k . The spectral data (ir, uv, ms) of these two classes of compounds are also discussed.     

Carbon-13 NMR study of some acetylenic amines,the N-oxides and their rearrangement products

Carbon-13 NMR chemical shifts of some N, N-dialkyl-4-acetoxybut-2-ynylamines and their corresponding N-oxides have been analysed. These N-oxides undergo thermal rearrangement to O-allenyl hydroxylamine for which the ¹³C NMR spectral assignments were also carried out. The effect of N-oxidation on the chemical shifts is calculated.     

Unexpected rearrangement products from animations of 5-bromo-2-nitrothiazole

While reaction of 2-bromo-5-nitrothiazole ( 2 ) with weakly basic secondary aliphatic amines gives the expected 2-amino products from nucleophilic displacement of the bromine, reaction of the isomeric 5-bromo-2-nitrothiazole ( 3 ) with such amines gives mixtures of the expected 5-amino products together with 2-aminated 5-nitrothiazole rearrangement products. The identity of the latter were detemined by alternative synthesis, and by X-ray crystallographic determination of a derivative. The mechanism proposed is a slow thermal isomerization of 5-bromo-2-nitrothiazole ( 3 ) to the much more reactive 2-bromo-5-nitro isomer 2 which competes, in the case of relatively weak amine nucleophiles, with the direct (but slow) nucleophilic displacement of the 5-bromo group to form the normal displacement products.     

Total synthesis of myxol and deoxymyxol stereoisomers and their application to determining the absolute configurations of the natural products

The total synthesis of myxol stereoisomers 1a,b and deoxymyxol (plectaniaxanthin) stereoisomers 2a,b was accomplished by Wittig reaction of (S)- and (R)-C₁₀-phosphonium salts 8a,b bearing a silyl-protected 1,2-dihydroxy-ψ end group with C₃₀-apocarotenals 6 and 7. The phosphonium salts 8a,b were derived from aldehydes 11a,b possessing a cyclopentylidene ketal moiety, prepared via Sharpless asymmetric epoxidation of allylic alcohol 12 followed by regioselective cleavage of the oxirane ring. We established an analytical HPLC method using a chiral column to separate stereoisomers 1a,b and 2a,b and thus determined the absolute configurations of the natural products. The HPLC analyses established that both myxol and deoxymyxol isolated from bacteria have the 2′S-configuration.     

Introduction of a triflate group into sterically-hindered positions in 1-aryl-4,6-diamino-1,3,5-triazines and their dimroth rearrangement products

Decomposition of 1-(azidophenyl)-4,6-diamino-1,3,5-triazines 11–13 and their 4-amino-6-(azidoanilino)-1,3,5-triazine isomers 31–33 in trifluoromethanesulphonic acid at 0° led to the introduction of the triflate group (OSO₂CF₃) into the aryl group. This method can be employed to introduce a bulky substituent into the hindered position ortho to the triazinyl substituent. Dimroth rearrangement of 1-(aryl)-4,6-diamino-1,3,5-triazines is best effected in refluxing ethanolic pyridine.     

Reexamination of the thermolytic rearrangement of 4-halophenyl azides to 2-aminophenols and other products

Summary The halogenation of derivatives of 2-aminophenol with N-chloro- and N-bromosuccinimides at ambient temperatures in acetic acid was studied. With the necessary compounds available, a reexamination of the thermolytic rearrangement of 2-halophenyl azides to 2-aminophenols and other products was undertaken. It is certain that the rearrangement of 4-halophenyl azides to 2-aminophenols occurs but the products identified in this study differ significantly from those reported previously by Suschitzky et al. (1963, 1966).

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Neuuntersuchung der thermolytischen Umlagerung von 4-Halogenphenylaziden zu 2-Aminophenolen und anderen Produkten

Zusammenfassung Es wurde die Halogenierung von 2-Aminophenol-Derivaten mit N-Chlor- und N-Bromsuccinimid bei Raumtemperatur in Essigsäure untersucht. Mit den zur Verfügung stehenden Verbindungen konnte eine Neuuntersuchung der thermolytischen Umlagerung von 4-Halogenphenylaziden zu 2-Aminophenolen und anderen Produkten unternommen werden. Diese Umlagerung findet sicherlich statt, allerdings differieren die dabei beobachteten Produkte signifikant von denen, die Suschitzky et al. 1963 und 1966 beschrieben.

     

2-fluoro- and 5-fluoro-3,4-dimethylphenethylamine derived from claisen rearrangement products

The Claisen rearrangement of 2-allyloxy-3-fluoroanisole followed by methylation provided the $\text{para}$-rearranged product along with the unexpected 3-(3,4-dimethoxy-2-fluorophenyl)-1-propene.     

Synthesis of 1-arylmethyl-2-(2-cyanoethyl)aziridines and their rearrangement into novel 2-(aminomethyl)cyclopropanecarbonitriles

1-Arylmethyl-2-(bromomethyl)aziridines were transformed into novel 2-(2-cyanoethyl)aziridines upon treatment with alpha-lithiated trimethylsilylacetonitrile in THF in an efficient and straightforward approach. The latter aziridines underwent ring opening by reaction with benzyl bromide in acetonitrile, affording 5-amino-4-bromopentanenitriles through a regiospecific ring opening of intermediate aziridinium salts by bromide. Further elaboration of these gamma-bromonitriles resulted in the synthesis of novel 2-[N,N-bis(arylmethyl)aminomethyl]cyclopropanecarbonitriles in high yields by means of a 1,3-cyclization protocol upon treatment with KOtBu in THF.     

The relation between the Claisen rearrangement of allyl ethers and their electronic structure Rearrangement of N-allylamines

The kinetics of a number of Claisen rearrangements have been studied and it is shown that the energy of activation of this reaction is a function of the bond orders and free valencies in the ethers undergoing rearrangement. In accordance with prediction from the derived equation, it was shown that N-allyl-1-naphthylamine rearranged smoothly and in high yield to 2-allyl-1-naphthylamine by a first order, intramolecular mechanism. This is the first recorded example of a Claisen rearrangement of an N-allyl compound. The behaviour of other ethers, whose rearrangements in the literature have been recorded as unusual or anomalous, is discussed in the light of these findings.     

The radical cation of syn-tricyclooctadiene and its rearrangement products

The syn dimer of cyclobutadiene (tricyclo[4.2.0.0(2.5)]octa-3,7-diene, TOD) is subjected to ionization under different conditions and the resulting species are probed by optical and ESR spectroscopy. By means of quantum chemical modelling of the potential energy surfaces and the optical spectra, it is possible to assign the different products that arise spontaneously after ionization or after subsequent warming or illumination of the samples. Based on these findings, we propose a mechanistic scheme which involves a partitioning of the incipient radical cation of TOD between two electronic states. These two states engage in (near) activation-less decay to the more stable valence isomers, cyclooctatetraene (COT*+) and a bis-cyclobutenylium radical cation BCB*+. The latter product undergoes further rearrangement, first to tetracyclo[4.2.0.0(2,4).0(3,5]oct-7-ene (TCO*+) and eventually to bicyclo[4.2.0]octa-2,4,7-triene (BOT*+) which can also be generated photochemically from BCB*+ or TCO*+. The surprising departure of syn-TOD*+ from the least-motion reaction path leading to BOT*+ can be traced to strong vibronic interactions (second-order Jahn-Teller effects) which prevail in both possible ground states of syn-TOD*+. Such effects seem to be more important in determining the intramolecular reactivity of radical cations than orbital or state symmetry rules.     

The radical cation of anti-tricyclooctadiene and its rearrangement products

The anti dimer of cyclobutadiene (anti-tricyclo[4.2.0.0(2.5)]octa-3,7-diene, TOD) is subjected to ionization by gamma-irradiation in Freon matrices, pulse radiolysis in hydrocarbon matrices, and photoinduced electron transfer in solution. The resulting species are probed by optical and ESR spectroscopy (solid phase) as well as by CIDNP spectroscopy (solution). Thereby it is found that ionization of anti-TOD invariably leads to spontaneous decay to two products, that is bicyclo[4.2.0]octa-2,4,7-triene (BOT) and 1,4-dihydropentalene (1,4-DHP), whose relative yield strongly depends on the conditions of the experiment. Exploration of the C8H8*+ potential energy surface by the B3LYP/6-31G* density functional method leads to a mechanistic hypothesis for the observed rearrangements which involves a bifurcation between a pathway leading to the simple valence isomer, BOT*+, and another one leading to an unprecedented other valence isomer, the anti form of the bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation (anti-BOD*+). The latter product undergoes a very facile H-shift to yield the radical cation of 1,3a-dihydropentalene (1,3a-DHP*+) which ultimately rearrranges by a further H-shift to the observed product, 1,4-DHP*+.     

Trimethylaluminium-induced diastereoselective methylation onto ethyl 2-oxocyclopentane-1-carboxylate and isomerization between the dimethylaluminium-alkoxide products

Methylation of α-disubstituted cyclopentanone 1 with Me₃Al in CH₂Cl₂ at 0 °C for 30 min gave diastereoselectively a mixture of (1R*,2S*)-2 and (1R*,2R*)-2 in a 96:4 ratio and 83% total yield. When the same methylation was carried out at 0 °C for 1 h and then at room temperature for 120 h, a diastereomeric mixture of (1R*,2S*)-2 and (1R*,2R*)-2 was obtained in a 12:88 ratio and in 88% total yield. The stereochemistry of the two diastereomers was determined by the results of acetalization of their diol derivatives 3 and 5. Isomerization between the Me₂Al-alkoxides of (1R*,2S*)-2 and (1R*,2R*)-2 and its possible mechanism were investigated by HPLC analysis of the methylation reaction process at 0 °C for 1 h and then at room temperature for 56 h and also by their mutual epimerization reactions.     

Bridging the gap between analytical R&D products and their use in practice

Identifying the key stakeholders (viz. R&D centers, routine laboratories, clients and producers of analytical tools) and their mutual relationships in Analytical Science, and pinpointing the objects through which knowledge and technology can be transferred among them, can help one recognize the weaknesses in the links connecting 'ivory towers' and industry with a view to developing ways to bridge the existing gap between the two.