Transition Metal-Free Synthesis of Halobenzo[ b ]furans from O -Aryl Carbamates via o -Lithiation Reactions.

A straightforward and transition metal-free one-pot protocol to synthesize halobenzo[ b ]furans has been developed employing simple and easily available starting materials such as O -aryl carbamates and alkynylsulfones. The fine-tuning of the different steps involved was key to achieving a successful one-pot procedure. Initially, a directed ortho -lithiation process, which uses the carbamate as the directed metalation group, was crucial in providing access to O -2-alkynylaryl N,N -diethyl carbamates by a direct alkynylation of the o -lithiated carbamate, with arylsulfonylalkynes as electrophilic reagents. Cyclization of the generated o -alkynylaryl carbamates was successfully accomplished through a strategy involving in situ carbamate alkaline hydrolysis under conventional heating or microwave irradiation, coupled with a subsequent heterocyclization step delivering the desired benzo[ b ]furans. A wide variety of new halobenzo[ b ]furans has been synthesized and their utility has been demonstrated by their further transformation.