To obtain a new monoazo compound excellent in tone, capable of providing a vivid image having magenta color and high color concentration, excellent in light resistance, weatherability, heat resistance and heat-resistant transfer property and useful for heat-sensitive transfer sheets.

This compound is represented by the formula [X1 and X2 are each H, a halogen or CN, especially a halogen such as Cl; Y1 is H, an alkyl, a halogen such as Cl or OH; Y2 is H or a lower alkyl; R is H, a (substituted) alkyl, an aryl or a (substituted)aryl; (n) is 1 or 2, especially 2], e.g. 6-[(6,7- dichlorobenzothizol-2-yl)azo]-1-(2-methoxyethyl)-1,2,3,4-tetrahydroquinoline. The compound of the formula is obtained by diazotizing the corresponding 2- aminobenzothiazole derivative according to a conventional method and subjecting the resultant diazo solution to coupling with the corresponding 1,2,3,4- tetrahydroquinoline derivative or indoline derivative in an acid medium at -5 to 20°C.