Rhodium(III)-Catalyzed Triple Aryl/Alkenyl C-H Bond Activation of Aryl Enaminones to Access Naphtho[1,8-bc]pyrans

Rhodium(III)-catalyzed triple C-H bond activation of aryl enaminones was achieved to access naphtho[1,8-bc]pyrans by oxidative annulation to internal alkynes. 1-Naphthols might be formed as the only products, depending on the steric and/or electronic environment around the aroyl moiety of the aryl enaminones or the electronic impact from the alkynes. With propargyl alcohols as the masked terminal alkynes, aryl enaminones underwent rhodium(III)-or rhodium(I)-catalyzed internal alkenyl C-H bond activation to afford functionalized but-2-ene-1,4-diones. The resultant naphtho[1,8-bc]pyrans are highly fluorescent and can be further transformed by chlorination, bromination, and difluoromethylation, demonstrating potential practicability of the synthetic protocol.

Automated summary

In this study, triple C-H bond activation of aryl enaminones was achieved to access naphtho[1,8-bc]pyrans through oxidative annulation. Depending on the steric and/or electronic environment around the aryl moiety of the enaminones or the electronic impact from the alkynes, 1-naphthols might be formed as the sole products. By using propargyl alcohols as masked terminal alkynes, functionalized but-2-ene-1,4-diones were obtained through rhodium(III)- or rhodium(I)-catalyzed internal alkenyl C-H bond activation. The resulting naphtho[1,8-bc]pyrans exhibited high fluorescence and could be further transformed by chlorination, bromination, and difluoromethylation, demonstrating the potential applicability of the synthetic protocol.