1, 3‐Cycloadditions to Highly Substituted, Strained Double Bonds: Spiro β‐lactams from α‐methylidene‐β‐lactams by reactions with diphenylnitrilimine, acetonitrile oxide, nitrones, and diazomethane

Substituted dihydropyrazole‐spiro‐β‐lactams and isoxazolidine‐spiro‐β‐lactam derivatives are regio‐ and stereoselectively prepared by 1, 3‐cydoadditions between substituted α‐methylidene‐β‐lactams and diazomethane, nitrones, or the in‐situ‐prepared dipoles ‘diphenylnitrilimine’ and acetonitrile oxide. These reactions represent examples for 1, 3‐cycloadditions to the highly substituted, strained double bonds of α‐methylidene‐β‐lactams, and they need special experimental conditions as all reaction products are relatively unstable. Especially in solution, the reverse reaction is highly favoured. Regioselectivity and stereoselectivity of the reactions are elucidated mainly by NMR techniques such as 2D‐INEPT, ATP, and NOE experiments.