Intermolecular reactions nitrile trapping

The most widely used, and often most convenient reagents for such one-pot reactions are sodium hypochlorite (45) or hypobromite (16). These reactions are performed in the presence of an organic base (generally triethylamine) that normally enhances the yield of cycloaddition products (45). This method was employed for many intermolecular reactions (71) and also seems especially suited for intramolecular ones (72-77) as well as for the solid-phase synthesis (78) of 2-isoxazolines. Hypohalite can also be replaced by sodium broruite in combination with a catalytic amount of tri-u-butyltin chloride (79). In a related method, O-tributylstannyl oximes were treated with tert-butyl hypochlorite to produce nitrile oxides that were trapped with aUcenes or alkynes to afford the corresponding isoxazolines or isoxazoles in moderate to good yield (80). 

In contrast to the diverse insertion chemistry of vinylpalladium intermediates discussed in Sects. IV.3 and IV.5, the reactions of vinylpalladium complexes with electrophiles had not been reported until recently. Although a single report on the annulation of the o-mer-curio benzaldehyde with diphenylacetylene into the corresponding indenols and inde-nones catalytic in palladium and stoichiometric in copper had been communicated in 1992, the more synthetically useful protocol for the catalytic version of this type of transformation remained unknown until 1999. In this section the intermolecular carbopalladation of alkynes with aryl halides followed by the intramolecular trapping of the formed vinylpalladium species with ketones, aldehydes, and nitriles will be discussed. 

The in situ generation of nitrile oxides 119 and subsequent intra- or intermolecular 1,3-dipoIar cycloaddition reactions with alkenes and alkynes represent one of the most exploited strategies for the preparation of diverse isoxazoline 121 and isoxazole 120 derivatives. Ciufolini et al. [89] reported that PIDA in combination with a substoichiometric amount of TFA efficiently oxidize aldoximes 118 to nitrile oxides 119, which were trapped in situ with olefins to afford... 

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