Influence of bicyclic anhydride structure on the outcome of the Castagnoli–Cushman reaction

The Castagnoli–Cushman reaction was carried out with various fused and bridged bicyclic anhydrides. The influence of the anhydride nature and, specifically, the size of fused anhydride rings on the reaction pathway were investigated. The negative outcome of the reaction in the case of small rings and bridged systems was mechanistically described. The scope and limitations of the procedure involving anhydrides and imines were discussed. The high diastereoselectivity of the method was proved and showed its correlation with the previous results. The reaction was optimized and scaled up to afford multigram amounts of products in a single run (up to 50 g).