Easily accessible alkylbenzenes are highly valuable starting materials and solvents in synthetic organic chemistry for the production of pharmaceuticals, plastics, synthetic rubber, dyes, etc. Herein, by employing alkylbenzenes as precursors, an unprecedented one-pot protocol for the synthesis of buta-1,3-dienes under 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) visible-light photocatalysis has been reported. Also, a possible reaction mechanism has been described. Upon irradiation, in the first step, DDQ promotes the oxidative dehydrogenation of alkylbenzenes to olefins, which are then transformed to buta-1,3-dienes via a dehydrogenative C–H homocoupling reaction. The salient features of this transformation include eco-friendliness (free from metals and volatile organic solvents), cost effectiveness, good yield, use of clean visible-light as a source of energy, one-pot approach under ambient conditions and applicability to large-scale synthesis.