Cyclodehydration reactions of methyl 9,10-; 10,12-; and 9,1 2-dioxostearates with 1,2-diaminoethane under ultrasonic irradiation.

Reaction of methyl 9,10-dioxostearate (1) and 9,12-dioxostearate (2) with 1,2-diaminoethane under concomitant ultrasonic irradiation (10-15 min, 60 degrees C) in water furnished the corresponding 2,3-dihydropyrazine (4, 79%) and 1,2,3,4-tetrahydro-1,4-diazocine (5, 70%) derivatives, respectively. Reaction of methyl 10,12-dioxostearate (3) with 1,2-diaminoethane was successful only when glacial acetic acid was used instead of water under ultrasonic irradiation (4 x 10 min, 70 degrees C) to give a 2,3-dihydro-1H-1,4-diazepine (6, 95%) derivative. The structures of these novel six-membered (4), seven-membered (6), and eight-membered (5) N-heterocyclic fatty ester derivatives were confirmed by a combination of infrared, nuclear magnetic resonance spectroscopic and mass spectral analyses.