Microflow systems were found to serve as powerful tools for mechanistic studies on reactions involving highly unstable intermediates such as o-bromophenyllithium, which is known to decompose to benzyne very quickly even at -78 degrees C. Precise residence time control and precise temperature control of microsystems are responsible. Based on the information thus obtained, the Br-Li exchange reaction of o-dibromobenzene followed by reactions with electrophiles without benzyne formation was achieved using a microflow system. Sequential use of two bromine atoms in o-dibromobenzene with Br-Li exchange reactions followed by the reactions with electrophiles using the microsystem consisting of four micromixers and four microtube reactors was also accomplished.