Figure 1 : Transition metal-catalyzed [4+2] annulations and related strategies.

From: Merging rhodium-catalysed C–H activation and hydroamination in a highly selective [4+2] imine/alkyne annulation

Figure 1

(a) Catalytic [4+2] annulations between aromatic compounds and alkynes via cyclometalated intermediates (A); XH=H-substituted σ-donating functional group to direct aromatic C–H activation at the ortho-position. (b) Reported benzoheterocycle products from oxidative [4+2] annulations with NH or OH directing groups. (c) A Re–Mg bimetallic catalyst system for redox-neutral [4+2] annulation between benzamides and alkynes. (d) Divergent catalytic couplings between N–H aromatic ketimines and alkynes.