Catalytic Asymmetric Cyclopropanations with Nonstabilized Carbenes.

Cyclopropanes are common building blocks in pharmaceuticals, agrochemicals, and organic materials. The most general methods for the synthesis of chiral cyclopropanes are catalytic additions of diazoalkanes to alkenes. However, a limitation of this approach is that diazoalkanes can only be safely handled on preparative scales if they possess stabilizing substituents. Here we show that gem-dichloroalkanes can serve as precursors to nonstabilized carbenes for asymmetric cyclopropanation reactions of alkenes. The process uses a cobalt catalyst and is proposed to involve the formation of a cationic carbenoid species bearing structural resemblance to the Simmons-Smith reagent. High levels of enantioselectivity are observed for monosubstituted, 1,1-disubstituted, and internal alkenes. The reaction is compatible with alkyl-substituted carbenes, which are susceptible to undergoing competing 1,2-hydride shifts.

Synthesis of Acridines through Alkyne Addition to Diarylamines.

A new synthesis of substituted acridines is achieved by palladium-catalyzed addition of terminal acetylenes between the aryl rings of bis(2-bromophenyl)amine. By including a diamine base and elevating the temperature, the reaction pathway favors the formation of acridine over a double Sonogashira reaction to form bis(tolan)amine. This method is demonstrated with several aryl-alkynes and alkyl-alkynes.