Synthesis of the core ring system of the yuzurimine-type Daphniphyllum alkaloids by cascade condensation, cyclization, cycloaddition chemistry.

Addition of hydroxylamine to substituted 4-chlorobutanals gives intermediate nitrones that undergo tandem cyclization and then intramolecular dipolar cycloaddition to give the core ring system of the yuzurimine-type natural products. Ring-opening of the isoxazolidines gives amino alcohols that can be converted to 1,3-oxazines, representing the tetracyclic core of alkaloids such as daphcalycic acid and daphcalycine.