hydroximolactone 2 and tert-butyl hypochlorite (89%), was established by X-raycrystallographicanalysis. The [4 + 2] cycloadditions of 1 with the dienes 3 and 8–11 led to the N-unsubstituted 3,6-dihydro-2H-1,2-oxazines 6 and 12–16 in high enantiomeric excess (Table 1). Due to the additional α-alkoxy group, the reactivity of 2 is much superior to the one of known α-chloronitrosoalkanes. The reactive conformation