A compound selected from those of formula : <IMAGE> in which {HEAD ~ the meanings} of R, R1, {TAIL ~ 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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A compound selected from those of formula : < IMAGE > in which { HEAD ~ the meanings } of R , R1 , { TAIL ~ 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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