A process for manufacturing chromenes which are intended for the preparation of thermosetting resins, includes transforming an aromatic propargyl ether of general formula (I) into a chromene by flash vacuum thermolysis, at a temperature of between 300 and 600° C., at a pressure of between 4 and 10 000 Pa. It also concerns a process for preparing a material made of thermoset resin, including successively: a) implementation of the above process; b) polymerization of the reaction product obtained in a) so as to obtain the material made of thermoset resin; c) recovery of the material made of thermoset resin obtained in b).