A mixture consisting of 12 g. of piperonal 8.4 ml. of p-fluorobenzaldehyde, 6 g. of potassium cyanide, and 80 ml. of 65% ethanol is reacted as described in Example 20, giving 11.7 g. of 4'-fluoro-3,4-methylenedioxybenzoin as an uncrystallizable oil. 9.0 g. of this benzoin is converted to its methanesulfonate ester by the procedure of Example 20, yielding 9.8 g. of ester as an uncrystallizable oil. The reaction of 4.9 g. of the crude methanesulfonate ester, and 1.16 g. of hexahydro-2H-1,3-diazepin-2-thione in 80 ml. of acetone, followed by treatment with 5 ml of 2 N ethanolic hydrogen chloride gives the title compound melting at 211°-213° C.
