Polyene compounds of the formula: ##EQU1## wherein R' is protected or unprotected hydroxyl or a group of the formula: ##EQU2## (in which R" and R"' are each carboxyl or a group convertible into carboxyl on hydrolysis), m is a positive integer and n is 0 or a positive integer, which are useful as intermediates in the synthesis of coenzyme Q, can be produced advantageously through a step for the dehydration of a compound of the formula: ##EQU3## wherein R', m and n are each as defined above.