Rhodium-Catalyzed Selective C( sp 2 )-H Activation/Annulation of tert -Butyl Benzoyloxycarbamates with 1,3-Diynes: A One Step Access to Alkynylated Isocoumarins and Bis-Isocoumarins.

We report here a Rh(III) catalyzed regio- and stereoselective synthesis of alkynylated and bis-isocoumarin from 1,3-dialkyne. Exclusive one-pot formation of 3,3-bis-isocoumarin isomers has been achieved by eliminating several other possibilities. This is the first example of transition metal catalyzed synthesis of alkynylated and bis-isocoumarin scaffolds. The protocol is compatible with a wide range of functional groups affording good to excellent yields. Several mechanistic investigations, including deuterium labeling experiments and kinetic isotope effect studies, have been carried out.