Isoxazolidines retro 1,3-dipolar cycloaddition

Isoxazolidines sometimes undergo retro 1,3-dipolar cycloaddition to give back alkenes and nitrones (77AHC(2D207). 

The key step in the synthesis of 4-354 is the retro-1,3-dipolar cycloaddition of the isoxazolidine 4-351 to give the nitronate 4-352, which underwent an intramolecular 1,3-dipolar cycloaddition. The obtained cycloadduct 4-353 can be transformed in a few steps into the desired target 4-354 (Scheme 4.78). 

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