Stereoselectivity of intramolecular cyclisations of nitrones derived from 3-oxahept-6-enals

Intramolecular [1,3]-dipolar cycloadditions of nitrones 33, derived from 3-oxahept-6-enals 7, substituted at either the 4- or 5-position and prepared using a variety of approaches, give good to excellent yields of the cycloadducts 34–37, with good levels of stereoselectivity, especially when the substituent is adjacent to the alkene. The cyclisations appear to proceed via well-defined transition state conformations which should be of predictive value.