Reaction of Donor‐Acceptor Cyclobutanes with Indoles: A General Protocol for the Formal Total Synthesis of (±)‐Strychnine and the Total Synthesis of (±)‐Akuammicine

A ligand‐promoted catalytic [4+2] annulation reaction using indole derivatives and donor‐acceptor (D‐A) cyclobutanes is reported, thus providing an efficient and atom‐economical access to versatile cyclohexa‐fused indolines with excellent levels of diastereoselectivity and a broad substrate scope. In the presence of a chiral SaBOX ligand, excellent enantioselectivity was realized with up to 94 % ee. This novel synthetic method is applied as a general protocol for the total synthesis of (±)‐akuammicine and the formal total synthesis of (±)‐strychnine from the same common‐core scaffold.