1,3-dipolar cycloaddition reactions unsymmetrical alkene

Unsymmetrical silaketals 201 having a 1,2-disubstituted double bond and a nitro group were prepared and transformed upon treatment with phenyl isocyanate in the presence of Et3N under mild reaction conditions into 2-oxazoline derivatives 202 by a regiospecific intramolecular 1,3-dipolar cycloaddition, as shown in Scheme 36 <1997SL1208>. The /ra r-stereochemistry of the alkene 201 was transported to the 2-isoxazoline product 202, which was confirmed by the H NMR spectroscopic data. 

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