Unprecedented catalyst-controlled divergent cyclizations of Morita-Baylis-Hillman carbonates have been established using either Cs2CO3 or quinuclidine as the catalyst. 1,2-Dihydroquinolines and 4H-3,1-benzoxazines were efficiently synthesized via SN2' and SN2'-SN2' processes, respectively. DFT calculations have led to a deeper understanding of these reaction modes and chemoselectivity.