Diastereoselective Synthesis of Spiro-?-lactams via Staudinger Reaction

In this work, eleven new spiro-?-lactams have been prepared using the Staudinger reaction of isomaleimides (1a-d) and carboxylic acids (chloroacetic acid, (-)-menthoxyacetic acid (7) and an oxazolidinone derived acid (10)) in the presence of triphosgene under mild condition. All reactions have been shown to be stereoselective. The new stereogenic centers were assigned by X-ray diffraction.