A compound selected from those of formula : <IMAGE> in which {HEAD ~ the meanings} of R, {TAIL ~ R1}, R2 and X are as defined in the specification, and medicinal products containing the same which are in treating or in preventing a disorder of the melatoninergic system 
A compound selected from those of formula : < IMAGE > in which { HEAD ~ the meanings } of R , { TAIL ~ R1 } , R2 and X are as defined in the specification , and medicinal products containing the same which are in treating or in preventing a disorder of the melatoninergic system
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