Cycloaddition reactions of 5,6-dihydro-1,3,2-oxazine 3-oxide and conformational analysis of the resultant bicyclic isoxazolidines

The rate constants for several addition reactions of a heterocyclic nitrone , 5,6-dihydro-1,3,2-oxazine 3-oxide (7), have been determined by a H-1 NMR technique. The heterocyclic nitrone is found to be as reactive as its carbo cyclic counterparts. The nitrone underwent regio- and stereo-selective cycl oaddition reaction with several alkenes to afford bicyclic isoxazolidines e fficiently. The NMR studies showed that the isoxazolidines prefer the confo rmer with cis ring fusion having an equatorially oriented nitrogen lone pai r capable of manifesting an endo anomeric effect.