Isoxazoline special

In this approach, the SENA skeleton is assembled from nitroalkene (42) and nucleophile 56.With the exception of two examples (entries 1 and 2 in Table 3.2), the reaction does not stop at SENA 51, which either undergoes intramolecular cyclization through [3 + 2]-cycloaddition to give fused heterocycles (as a rule after elimination of trimethylsilanol) (198-200) or is involved in [3+ 2]-cycloaddition with specially added methyl vinyl ketone or methyl acrylate to form (after elimination of silanol) substituted isoxazolines in rather high yields (201). 

Wallace et al. (293) applied the boronic ester derivative 177 of Oppolzer s sultam acrylate for a special nitrile oxide cycloaddition (Scheme 12.53). This reaction has the advantage that it allows for the introduction of a hydroxy group in the 4-position of the isoxazoline product 178 after oxidative cleavage of the boronic... 

Thompson et al. have investigated the ecological role of the brominated isoxazoline alkaloids, aerothionin (Structure 2.84) and homoaerothionin (Structure 2.89), in Californian specimens of A. fistularis.134 139 The alkaloids caused behavioral modification in marine invertebrates, were toxic to dorid nudibranchs other than one specialized feeder, inhibited the settlement and/or metamorphosis of invertebrate larvae, and were strongly antimicrobial and cytotoxic. Sponges exuded significantly more of these two alkaloids when wounded,155 and, consistent with their defensive role, the metabolites were found to be localized in spherulous cells close to the aquiferous exhalant canals.156... 

As mentioned so far, methylnitroisoxazolone 10 serves as a precursor of carbamoylnitrile oxide 6 upon treatment with only water under mild conditions, in which any special reagents, conditions, and manipulations are not necessary. The nitrile oxide 6 reacts with alkynes 15, alkenes 17, nitriles 29, and 1,3-dicarbonyl compounds 34 to afford corresponding carbamoyl-substituted isoxazoles 16, isoxazolines 18, 1,2,4-oxadiazoles 28, and isoxazoles 33, respectively (Scheme 9.17). The electron-withdrawing carbamoyl group realizes the cycloaddition with electron-rich dipolarophiles, which is inverse electron-demand 1,3-dipolar cycloaddition. Furthermore, the carbamoyl group also plays a role of an activator of the dipolarophile. This mefliodology will be useful for the construction of a new library of functionalized compounds. 

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