Imidoyl halides nitrile ylides from

Intramolecular azomethine ylide cycloaddition to the C—O double bond of an aldehyde was reported in 197369 and cycloaddition to the C—C double bond was first reported in 1975.70 Competition between 1,1- and 1,3-cycloaddition is observed in intramolecular reactions, although intermolecular reactions give only 1,3-cycloaddition. Photolysis of 2//-azirines is one generation method of nitrile ylides applicable to intramolecular cycloaddition.70 Another method involves the base-catalyzed 1,3-elimination of hydrogen halide from alkenyl imidoyl halides. Still other procedures involve thermolytic and photolytic cycloreversions of oxazolinones and dihydrooxazaphospholes. 

A number of other methods have also been used to generate nitrile ylides. Access to this 1,3-dipole has been realized by (a) treatment of imidoyl halides (5) with base, (b) thermal or photochemical elimination of phosphoric acid ester from 4,5-dihydro-1,3,5-oxazaphospholes (6), (c) 1,3-dipolar cycloreversion of 1-azetidines (7), (d)loss of carbon dioxide from 3-oxazolin-5-ones (g)44-47 treatment of boron-containing isonitriles (9) with base ... 

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