R1 and R4 are each independently an atom or group selected from hydrogen, a linear or branched C1-8 alkyl group, a deuterated linear or branched C1-8 alkyl group, an aralkyl group, or a substituted aryl group; R2 is independently an atom or group selected from halogens, a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group; and R3 is independently an atom or group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group. The compound is useful as a reaction intermediate for the synthesis of PQQ. A process in which CAN is used as an oxidant in the synthesis of PQQ in existing patents and literatures is replaced. This makes the process cheaper and more efficient.