No abstract

A novel and efficient synthesis of aza-eight-membered ring-fused indolines has been developed. This process is realized by zinc-catalyzed C2 alkylation of indoles and subsequent base-promoted ring expansion of the newly formed six-membered ring with alkynes. Easily accessible starting materials, good functional group tolerance, and high atom economy make this procedure attractive.

An atom economic procedure for the regioselective synthesis of bridged seven-membered-ring compounds from simple reactants such as ynones and indene-1,3-dione has been developed. This process was realized through the one-pot reactions of ring-expansion of indene-1,3-dione with alkynyl ketones and successive formal [4+2] cycloaddition. The Michael addition reaction is the key for the regioselectivity of the formal [4+2] cycloaddition.

Methods for the synthesis of 3-phenylsulfonylcoumarins by radical sulfonylation cyclisation of phenyl propiolates with sulfinic acids or sodium sulfinates as sulfonyl sources have been developed. A combination of potassium persulfate as oxidant and silver nitrate as catalyst, or tert-butyl hydroperoxide as oxidant and potassium iodide as catalyst were used. The products were formed by an ipso-cyclisation/1,2-ester migration mechanism. The toleration of functional groups is broad and the yield is up to 96%.

A novel and efficient copper-catalyzed transannular ring-closing reaction of eight-membered rings has been developed that provides a straightforward way to synthesize bicyclo[3.3.0]octane derivatives in good yields. Mechanistic studies revealed that the reaction pathway might involve chlorination followed by the Kornblum reaction. Readily accessible starting materials and good functional group tolerance make this procedure attractive.