Carbon–hydrogen bond insertion reactions of 3-acetoxy-aminoquinazolin-4(3H)-ones with cyclic dienes: stereochemistry and mechanism

Reaction of 2-substituted-3-acetoxyaminoquinazolin-4(3H)-ones (QNHOAc) with cyclohexa-1,3-diene or cyclohexa-1,4-diene (2 equiv.) gives, besides the expected aziridination products, stable dihydroaromatic by-products formally arising by insertion of [QN̈:] into one of the doubly allylic C–H bonds. An analogous insertion into the methylene C–H bonds of 9,10-dihydroanthracene or xanthene (1.5–2 equiv.) occurs. Using 3-acetoxyamino-2-[(S)-2,2-dimethyl-1-hydroxypropyl]quinazolin-4(3H)-one (Q1NHOAc) in the presence of titanium(IV) t-butoxide, insertion into cyclohexa-1,3-diene takes place completely diastereoselectively and the configuration at the cyclohexadienyl ring carbon has been correlated with that at the 6-position of the major aziridine diastereoisomer co-produced in the reaction. A mechanism involving concerted insertion into the C–H bond of the diene by QNHOAc is proposed with endo-overlap of both double bonds of the diene with the Q group in the transition state.