remains challenging, since the multiple unbiased C[double bond, length as m-dash]C bonds of terpenes lead to difficulty in controlling the regioselectivity. Herein, a cobalt(iii)-catalyzed C-H activation strategy has been developed to facilitate hydroxymethylarylation of terpenes with formaldehyde and arenes with high chemo- and regio-selectivities. These (chemo- and regio-) selectivities are governed by