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