Organocatalytic Regiodivergent Ring Expansion of Cyclobutanones for the Enantioselective Synthesis of Azepino[1,2-a]indoles and Cyclohepta[b]indoles.

A regiodivergent organocatalytic enantioselective Michael addition/three-atom ring expansion sequence of electron-withdrawing group activated cyclobutanones with 2-nitrovinylindoles was developed. A series of azepino[1,2-a]indoles were obtained with exclusive regioselectivities and high diastereo- and enantioselectivities (up to >20:1 dr, 96% ee) with the application of the N1 nucleophilic site of the indole nucleus. Meanwhile, various cyclohepta[b]indoles could be accessed with high enantiopurity (up to 96% ee) through the Michael addition/boron-trifluoride-etherate-promoted indole C3-attack ring expansion process.