Process for manufacturing chromenes which are intended for the preparation of thermosetting resins, comprising the step of transforming an aromatic propargyl ether of general formula below in which: R 1 and R 5 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group, on condition that at least one from among R 1 and R 5 represents a hydrogen atom; R 2 and R 4 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne such as propargyl, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group such as an O-propargyl; and R 3 represents a hydrogen atom, a O-(C 1 -C 6)alkyl or a C 2 -C 6 alkene group, the alkene group being optionally substituted with a group of general formula below in which: R 6 and R 9 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group, on condition that at least one from among R 6 and R 9 represents a hydrogen atom; and R 7 and R 8 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne such as propargyl, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group such as an O-propargyl; on condition that at least one from among R 1, R 2, R 3, R 4 and R 5 does not represent a hydrogen atom or a O-(C 1 -C 6)alkyl group; and the cis/trans isomers thereof and the optical isomers thereof and the racemic mixtures thereof into a chromene by flash vacuum thermolysis, at a temperature of between 300 and 600°C, advantageously between 400 and 450°C, at a pressure of between 4 and 10 000 Pa, advantageously between 5 and 7000 Pa. R 1 and R 5 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group, on condition that at least one from among R 1 and R 5 represents a hydrogen atom; R 2 and R 4 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne such as propargyl, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group such as an O-propargyl; and R 3 represents a hydrogen atom, a O-(C 1 -C 6)alkyl or a C 2 -C 6 alkene group, the alkene group being optionally substituted with a group of general formula below in which: R 6 and R 9 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group, on condition that at least one from among R 6 and R 9 represents a hydrogen atom; and R 7 and R 8 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne such as propargyl, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group such as an O-propargyl; on condition that at least one from among R 1, R 2, R 3, R 4 and R 5 does not represent a hydrogen atom or a O-(C 1 -C 6)alkyl group; and the cis/trans isomers thereof and the optical isomers thereof and the racemic mixtures thereof into a chromene by flash vacuum thermolysis, at a temperature of between 300 and 600°C, advantageously between 400 and 450°C, at a pressure of between 4 and 10 000 Pa, advantageously between 5 and 7000 Pa. R 6 and R 9 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group, on condition that at least one from among R 6 and R 9 represents a hydrogen atom; and R 7 and R 8 represent, independently of each other, a hydrogen atom, a C 2 -C 6 alkene, C 2 -C 6 alkyne such as propargyl, O-(C 1 -C 6)alkyl, O-(C 2 -C 6)alkene or O-(C 2 -C 6)alkyne group such as an O-propargyl; on condition that at least one from among R 1, R 2, R 3, R 4 and R 5 does not represent a hydrogen atom or a O-(C 1 -C 6)alkyl group; and the cis/trans isomers thereof and the optical isomers thereof and the racemic mixtures thereof into a chromene by flash vacuum thermolysis, at a temperature of between 300 and 600°C, advantageously between 400 and 450°C, at a pressure of between 4 and 10 000 Pa, advantageously between 5 and 7000 Pa.