Intramolecular Direct Dehydrohalide Coupling Promoted by KO(t)Bu: Total Synthesis of Amaryllidaceae Alkaloids Anhydrolycorinone and Oxoassoanine

A transition-metal-free intramolecular dehydrohalide coupling via intramolecular homolytic aromatic substitution (HAS) with aryl radicals has been developed in the presence of potassium tert-butoxide and an organic molecule as the catalyst. The methodology has been applied to a concise synthesis of Amaryllidaceae alkaloids viz. oxoassoanine (1b), anhydrolycorinone (1d), and other related structures. Interestingly, the method also works only in the presence of potassium tert-butoxide.