Aryl nitrile oxides

It was found that the reaction of 5-acetoxy- and 5-benzoyloxy-2(5//)-furanones 174 with aryl nitrile oxides afforded only one cycloadduct, the condensed isox-azoline 233 (88TL5317). In principle, there are four possible cycloadducts 233 and 234 resulting from the anti approach of the 1,3-dipolarophile to the acetoxy group (with exo configuration of the acetoxy substituent), and two further isomers... 

Catalytic enantioselective crossed aldehyde-ketone benzoin cyclizations of ketoaldehydes, such as 13, readily obtained from an aryl nitrile oxide and a 1,3-diketone, were studied in order to perform the synthesis of complex molecules. Significant asymmetric induction was observed with chiral triazolium salts such as 14, in the presence of DBU as base, leading to compound 15 in high yield and with 99% ee in favor of the R enantiomer <06AG(E)3492>. 

The reactions of nitrones with 165 have been described (277-279). In the approach described by Koskinen and co-workers (279), the bulky nitrone 166 was used in a reaction with 165 to give a 20 1 mixture of 167 and an unidentified diastereomer (Note Opposite enantiomers are shown here). Reactions of less bulky nitrones gave lower selectivities (277,278). Kim et al. (280,281) described reactions of 165 with silyl nitronates (Scheme 12.52). The configuration of the direct isoxazolidine products was not determined. Instead, diastereoselectivities of 66-88% de of 169 were found after elimination of the silyloxy group. The reaction of various nitrile oxides proceeded to give the same isoxazoline products 169 as obtained for nitronates (Scheme 12.52). For the reactions of 165 with various alkyl and aryl nitrile oxides 170, the products 169 were obtained with diastereoselectivities of 62-90% de (282-286). In a theoretical study, it was proposed that the... 

Kurabayashi and Grundmann have reported the preparation of the 1,2,4-oxadiazoles (34) from 1,3,5-triazine and aryl nitrile oxides in the presence of boron trifluoride. The mechanism has not been fully elucidated, but it is most likely that the initial stage is the formation of the complex (33) (78BCJ1484). 

Similar [34-2] cycloadditions with C-aryl nitrile oxides and other terminal fluoroalkylated al-kenes (Rf = C-2F5, and fluoroalkylated alkynes provide high yields of cycloadducts. 

Similar [3 4-2] cycloadditions with C-aryl nitrile oxides and other terminal fiuoroalkylated al-kenes (RF = C2F5, C6F13) and fiuoroalkylated alkynes provide high yields of cycloadducts.86,87 The nitrile oxides can be generated by various methods. Generation from bromoaldoximes in a chloroform/sodium hypochlorite biphase medium is efficient.86... 

In a search for new isoxazole-based liquid crystalline compounds, a 22-member library of 3,5-diaryl isoxazoles 628 was prepared by parallel synthesis on solid phase (Rink resin) through 1,3-dipolar cycloaddition of supported phenylacetylene units with suitable aryl nitrile oxides generated in situ from hydroxyiminoyl chlorides. Cleavage from the resin under acidic conditions allowed the generation of the cyano moiety <2004TL2277>. 

Dipolar cycloadducts 176 are available from the reactions of cyclopropenes with azomethine ylids, pyridinium ylids aryl nitrile oxides " ", alkyl nitrile... 

After consideration of the moderate complexity of our target 10 b, it was clear that the best hope for multi-kilo preparations would still incorporate the useful [3+2] cycloaddition of an aryl nitrile oxide with a properly functionalized propylene to quickly establish the 2,5-disubstituted isoxazoline ring. Once that is assumed, there remained three conceptual routes to 10b (Fig. 8). 

An elegant and flexible strategy for the assembly of a synthon for the ort/to-hydroxyaryl-1,3-diketone required for a chromone synthesis depends on the use of an isoxazole as surrogate for the 1,3-diketone unit (25.7). An isoxazole was produced by the cycloaddition (25.12.1.2) of an aryl nitrile oxide to tri-n-butylstannylacetylene, the product coupled with 2,4,6-trihydroxyiodobenzene and then the N-0 bond hydrogenolytically cleaved. ... 

Recent examples of 1,3-dipolar addition reactions include the additions of aryl nitrile oxides, ethyl diazoacetate, or tert-buty azidoacetate to dialkyl (perfluoroalk-l-ynyl)phosphonates , and further reactions of the nitrilimine (520) have been reported. ... 

Aryl nitrile oxides Aryl nitrile oxide and (ii) 61... 

The following 1,3-dipoles will be considered (a) aryl azides (b) diazoalkanes (c) aryl nitrile oxides (d) nitrile imines (e) azomethine imines (/) azomethine oxides (g) azomethine ylides. (a) to (d) represent 1,3-dipoles with a double bond in their sextet structure, while the last three, from (e) to (g), are without a double bond . All of them have nitrogen as the central atom of the 1,3-dipole. They will be formulated as allyl-like systems, having their negative charge distributed (according to an unspecified balance) at the two sides of the positive nitrogen, e.g. 

Dioxadia%ines. Dimerization of aryl nitrile oxides (Scheme 34) - currently unclear how conditions (e.g., inclusion/exclusion of added base) influence which product (1,4,2,5-dioxadiazine or 1,2,5-oxadiazole A-oxide (fur-oxan)) is favored. 

Elsewhere, x-ray crystallographic analyses have been used to define the structure of a dimeric product from A (2)-acetylation of 4-phenyl-5/f-2,3-benzodiazepine <84JCS(P1)2027>, and confirm 2-ethoxycarbonyl-5-methyl-l0-aryl-l,2,9-triaza-8-oxabicyclo[5.3.0 ]-3,5,9-decatrienes (10), as the main class of products from cycloaddition of aryl nitrile oxides and l-ethoxycarbonyl-5-methyl-l//-... 

Construction of stmcturally inspiring spiroisoxazolines 13COS661. Functional 3-arylisoxazoles and 3-aryl-2-isoxazolines from reaction of aryl nitrile oxides and enolates ... 

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