Synthesis of spiropyrans via the Rh(III)-catalyzed annulation of 3-aryl-2 H -benzo[ b ][1,4]oxazines with diazo ketoesters.

Rh(III)-Catalyzed 1 : 2 coupling of 3-aryl-2 H -benzo[ b ][1,4]oxazines with α-diazo-β-ketoesters has been realized for the mild synthesis of spiropyrans. The reaction proceeded via twofold C-H activation followed by unusual [3+3] and [4+2] annulation with decent functional group tolerance. Moreover, a pyranoid-skeleton intermediate was isolated as a key intermediate as a result of monoalkylation and enol oxygen annulation, which offers direct mechanistic insight.