Enantiocontrolled macrocycle formation by catalytic intramolecular cyclopropanation

Stereoselectivity in intramolecular cyclopropanation reactions resulting in cyclopropane fusion with ten- and larger-membered rings has been examined using chiral copper(I) and dirhodium(II) catalysts. The influence of alkene structure and catalyst has been obtained using the 1,2-bonzenedimethanol linker between the allylic double bond and diazoacetate. Control features in the addition reaction, especially those for diastereoselectivity and enantioselectivity, have been elucidated, and they are associated with the metal itself or its attendant ligands that influence the trajectory of the alkene to the carbene center. The influence of ring size, from five- to twenty-membered rings, on stereoselectivity has been determined with selected copper(I) and dirhodium(II) catalysts, and the changes in stereocontrol as a function of ring size can be understood as being due to a change in the olefin trajectory to the carbene center. Hydride abstraction from a benzylic position accompanies addition when dirhodium catalysts are employed, and intramolecular C-H insertion into an allylic site to form a nine-membered ring has been observed as a major competing reaction but with negligible enantiocontrol. The use of 1,8-naphthalenedimethanol. as a linker results in lower enantioselectivity than does use of 1,2-benzenedimethanol.