Synthesis of Medium and Large Cyclic Amines in Rhodium-Catalysed Reactions of Aminoalkenes with H2/CO

Abstract

Rhodium-catalysed reactions of N-benzyl- or N-alkyl-aminoalkenes (6) with H₂/CO can give cyclic amines (7) (7–13 ring size) in good to excellent yields when BIPHEPHOS is used as a ligand. Hydrogenation of the aminoalkene becomes a competing reaction for the smaller rings but can be overcome by using a H₂/CO gas ratio of 1 : 5. Reactions of 2-alkenyloxybenzylamines (13) gave 9-, 12- and 17-membered rings (14) in 30–40% yield, but dimer formation (16) and/or hydrogenation were competing reactions. Similar reactions of alkenylamides and ortho-alkenylanilines gave only non-cyclized amino aldehydes as products in low isolated yields.