Syntheses based on nitrile oxides. 1. Reaction of aromatic nitrile oxides with N-cyanimides

The reaction of trialkylaminocyanimides with aromatic nitrile oxides leads to trialkylamino-(3-aryl-1,2,4-oxadiazol-5-yl)imides, while the corresponding reactions with sulfylcyanimines and phosphincyanimides do not take place. Using x-ray structural analysis the principal structural features of the 1,2,4-oxadiazole products have been elucidated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2084–2089, September, 1990.     

Reactions of nitrile oxides with nitrogen oxides. 1. Reactions with nitrogen tetroxide

We have studied the reaction of nitrile oxides with nitrogen tetroxide. It was shown that the reaction is selective: acetonitrile oxide yields ethylnitrolic acid, -oximinophenylacetonitrile oxide gives a mixture of isomers of phenylnitrofuroxan, and aromatic nitrile oxides give aryltrinitromethanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1620–1622, July, 1990.     

Polyfluorinated nitrile oxides

(2+3)-Cycloaddition of polyfluorinated aliphatic nitrile oxides, generated in situ, to donor dipolarophiles takes place regioselectively to give the 5-substituted isoxazolines, and is limited by the donor and steric properties of the dipolarophiles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, 663–667, May, 1989.     

Reactions of nitrile oxides with nitrogen oxides. 2. Reactions with nitrogen monoxide and nitrogen sesquioxide

We have studied the reactions of aromatic nitrile oxides with nitrogen monoxide and nitrogen sesquioxide. It was shown that nitrogen monoxide removes an oxygen atom from the nitrile oxide with formation of the corresponding nitrile and nitrogen dioxide. The reaction products with nitrogen sesquioxide are formed as a result of reactions of the nitrile oxide with nitrogen monoxide and nitrogen tetroxide.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1623–1625, July, 1990.     

Syntheses based on nitrile oxides

Interaction of aromatic nitrile oxides with bis-trimethylsilylthiodiimide results in 2-amino-4-aryl-1,2,3,5-oxathiadiazoles, the first representatives of a new class of heterocyclic compounds.For Part 2, see ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 742–743, April, 1993.     

Phosphorylinitrile oxides. 7. Quantum chemical study of the dimerization of nitrile oxides

A semiempirical MNDO calculation was carried out for the singlet potential energy surface for the dimerization of acetonitrile oxide leading to dimethylfuroxane. The dimerization of nitrile oxides proceeds by a two-step mechanism. The rate-limiting step is formation of a dinitrosoethylene intermediate. A semiempirical AMI calculation was carried out to study the effect of phosphoryl substituents on formation of the transition state of the rate-limiting step in the dimerization of dimethoxyphosphorylnitrile oxide. Independently of the initial orientation of the two phosphorylnitrile oxide molecules, a gauche-oriented dimerica species is formed in the first step in the dimerization. There is hardly any specific effect ofthe phosphoryl substituents in the first step of phosphorylnitrile oxide dimerization.Communication 6, see ref. [1].Kazan State Technological University, 420015 Kazan, and Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1269–1273, September, 1994. Original article submitted August 5, 1994.     

Heterocycles from nitrile oxides. II . 1,2,4-oxadiazin-6-ones

Condensation of arylnitrile oxides with α-amino acid esters, other than those of glycine and analine, has been found to constitute a synthetic route to the hitherto unknown 1,2,4-oxadiazin-6-ones 7. α-Amino alcohols yield with nitrile oxides the corresponding acyclic N-(arylhydroxamoyl)amino alcohols, which are also accessible by borohydride reduction of compounds 7 . In contrast, the adducts formed from nitrile oxides and α-amino acids are unstable; they decompose readily into the aldehyde, derived from the amino acid, together with the aldoxime, derived from the nitrile oxide. Both decomposition products are also formed when compounds 7 are subjected to mild hydrolysis.     

1,3-Dipolar cycloaddition reactions of nitrile oxides and nitrile imines with 2-methoxyvinyl phenyl ketone

Nitrile oxides react regioselectively with 2-methoxyvinyl phenyl ketone 1 to give 4-benzoylisoxazoles 4 via elimination of methanol from the primary cycloadducts 3 . After heating with an excess of nitrile oxide bis-cycloadducts 5 were also formed. Reactions of nitrile imines with 1 are less regioselective yielding both 4-benzoylpyrazoles 9 and 5-benzoytpyrazoles 10 , whereas no bis-cycloadducts were isolated.     

Amine-promoted cyclocondensation of highly substituted aromatic nitrile oxides with diketones

Base-promoted cyclocondensation of hindered nitrile oxides and cyclic diketones affords highly functionalized, sterically-encumbered isoxazole products in good yield. The mild reaction conditions (NEt₃, EtOH) are tolerant to a wide variety of functionality and permit the preparation of precursors to complex polycycles typically inaccessible via direct, intermolecular carboncarbon bond forming reactions. The ability to effect the cyclocondensation reaction with a catalytic amount of amine points to the intermediacy of an ammonium enolate as a key reactive species. A convenient, single step preparation of crystalline, stable nitrile oxides from the corresponding oximes enhances the advantages of this methodology for the preparation of functionalized polycycles.     

Stereoconvergent and stepwise 1,3-dipolar cycloadditions of nitrile oxides and nitrile imines

The first example of stereoconvergent 1,3-dipolar cycloaddition of nitrile oxides and nitrile imines with E/Z isomeric mixture of electron-deficient olefins is reported, delivering isoxazolines and pyrazolines bearing two vicinal stereogenic tertiary and trifluoromethylated quaternary carbon centers with perfect regioand diastereoselectivities. The possibility of concerted cycloaddition/epimerization sequence under basic condition to form the thermodynamically stable diastereomers is excluded th...     

Reaction of some aromatic nitrile oxides with dimedone

1,3-Dipolar cycloaddition of benzonitrile and m-nitrobenzonitrile oxides to the enol form of dimedone gives the corresponding 4-oxotetrahydrobenzisoxazoles. A second reaction path — nucleophilic addition of the enol to the N-oxide to give a hydroxamic acid derivative — is observed in the case of m-nitrobenzonitrile oxide. The tetrahydrobenzisoxazoles are converted to enamine derivatives of benzoyldimedone under catalytic hydrogenation conditions.     

Cycloaddition of nitrile oxides to substituted vinylphosphonates

Cycloaddition of nitrile oxides to substituted vinylphosphonates was performed. A series of 4,5‐dihydroisoxazoles containing phosphonyl group were synthesized under very mild condition in excellent regiospecificity. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:309–311, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10149     

Intramolecular 1,3-dipolar cycloadditions of norbornadiene-tethered nitrile oxides.

Efficient routes to the synthesis of norbornadiene-tethered nitrile oxides have been developed, and their intramolecular 1,3-dipolar cycloadditions were studied. The cycloadditions occurred in good yields for a variety of substrates and were found to be highly regio- and stereoselective, giving single regio- and stereoisomers in most cases.     

Reaction of 2-azabicyclo[2.2.1]heptenes with nitrile oxides

The reaction of 2-azanorbornene derivatives with nitrile oxides (generated in situ by dehydrohalogenation of N-hydroxyimoyl halides) affords two regioisomers with the exo-arrangement of the isoxazoline ring.     

Tetraacetylethylene and nitrile oxides: Synthesis of spirofuranisoxazoles

trans and cis-3-Hexen-2,5-dione, 2 , reacted with nitrile oxides to give 4,5-dihydroisoxazoles 3a-c with the trans configuration. On the contrary the reaction between 3,4-diacetyl-3-hexen-2,5-dione, 1 , with nitrile oxides yielded 3-aryl-8,9-diacetyl-7-hydroxy-7-methyl-1,6-dioxa-2-azaspiro[4.4]nona-3,8-dienes 9a-e. The reaction is completely regiospecific. The cycloadducts show ring-open chain tautomerism.     

Activation of nitriles by hydrogen bonding in cycloadditions with nitrile oxides

The dipolarophilic activity of aromatic nitriles in cycloaddition with benzonitrile oxides is remarkably enhanced by ortho-acylamino substituents. The activation depends upon the solvent and can be ascribed to a hydrogen bond which assists cycloaddition.     

Asymmetric 1,3-dipolar cycloaddition of nitrile oxides with optically active vinylboronic ester

Pinanyldioxy styrylboronic ester (1) was employed for asymmetric 1,3-dipolar cycloaddition with nitrile oxides, optically active △2-isoxazolines (3) or 4-hydroxy-△2-isoxazolines (4) were obtained. The effect of different bases on the selectivity of the cycloaddition reaction was studied.     

Reaction of polyfluorinated cyclohexa-2,4-dienones with aryl nitrile oxides

Reaction of 1,3-dipolar cycloaddition of 6-chloropentafluorocyclohexa-2,4-dienone, 6-chloro-3-(pentafluorophenoxy)tetrafluorocyclohexa-2,4-dienone, and perfluoro-6-phenoxycyclohexa-2,4-dienone with aryl nitrile oxides proceeds highly stereoselectively at the c C=O group of the dienone providing in a high yield mixtures of diastereomeric fluorine-containing 3-aryl-1,4-dioxa-2-azaspiro[4,5]deca-2,6,8-trienes. The reaction of the latter with sodium pentafluorophenolate proceeds along the type of allyl substitution affording polyfluorinated 3-aryl-8-phenoxy-1,4-dioxa-2-azaspiro[4,5]deca-2,6,9-trienes.