Conjugated Olefin Enabled Rollover Cyclometallation of Distant C-H Bonds: Regioselective Annulation of o-Alkenyl Phenols with Alkynes.

Although challenging, the distant C-H functionalization with precision is quite rewarding and has long been intriguing. Tailoring an appropriate template accomplishes the job but the prerequisite sets the limitation. We herein unveil our discovery of annulation of alkynes on to two distant (from directing group) C-H bonds through rollover cyclometallation assisted by conjugated C=C bond. The annulation follows a concomitant cyclization rewarding a rare triple C-H functionalization. The annulation is totally regioselective with an array of unsymmetrical alkynes, taking the leverage of an extended conjugation or a tertiary hydroxyl co-ordination. The mechanism is supported by control experiments, KIE & labelling studies and Mass spectrometry.