A fresh guanidine solution prepared from 5.6 g of guanidinium chloride and 1.6 g of sodium in 40 ml of ethylene glycol dimethyl ether is added to a solution of 1.2 g of 2-methyl-4-(1-cyclopentene-3-yl)-5-methylsulfonylbenzoyl chloride [obtainable by reaction of methyl 2-methyl-4-bromo-5-methyl-sulfonyl-benzoate with cyclopentene in the presence of Pd(II)acetate and tri-o-tolylphosphine, separation of the two isomers by means of a Prebar® stainless steel cartridge 250-50, filled with LiChroprep RP-18; eluent 0.1 m NaH2PO4 buffer/acetonitrile 9:1 with an increasing gradient to 1:1, and subsequent hydrolysis and conversion into the acid chloride with SOCl2 ], in 20 ml of ethylene glycol dimethyl ether with ice-cooling and the mixture is stirred at room temperature for 2 hours. The reaction mixture is then poured onto ice-water, acidified and washed with ethyl acetate and the pH of the solution is adjusted to 10. Customary working-up gives N-diaminomethylene-2-methyl-4-(1-cyclopentene-3-yl)-5-methylsulfonylbenzamide, which can be recrystallized from acetonitrile/diethyl ether, melting point 212°-214°.
