Q1(b). Nitrene transfer to an alkene

Answer in brief

Trapping of the generated butylnitrene gives 1-butyl-2,2,3,3-tetramethylaziridine.

Key points

• Base removes the N–H proton of BuNH–O–SO₂Ar; cleavage of the N–O bond expels sulfonate and generates Bu–N:, an electron-deficient nitrene.
• The alkene π bond supplies electrons to the nitrene nitrogen while a second C–N bond closes the three-membered ring; singlet nitrene adds stereospecifically.
• Both alkene carbons retain their two methyl groups; nitrogen retains the n-butyl group and becomes the third ring atom of the aziridine.
• Alkylnitrenes can also undergo rapid 1,2-H migration to imines; the alkene is the trapping reagent.