A conventional analytical HPLC system is modified by the addition of a catalytic Nafion-H® reactor column placed between the injector and a typical analytical column. The reactor column promotes cyclization reactions and the analytical column separates the reactant and product(s). In the reactions attempted, the analytical column has given baseline separation of the reactant from the desired product(s). Recoveries, yields and purities are generally equal to or better than those obtained with conventional synthesis and workup techniques. The advantages of this system are the rapidity of the reaction, separation, and ease of workup. Product(s) are readily recovered from the low-boiling solvents used and intact reactant may be recovered and reinjected. Three functional groups leading to cyclization are presented and the effects of solvent composition, temperature and flow rate are discussed in detail for one reaction.