TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): A diaminosilane derivative of formula (IV) is prepared by reacting a silane derivative of formula (II) with an amine derivative of formula (III). The cyclodisilazane derivative (I) is produced by intramolecular cyclization reaction of diaminosilane derivative (IV) with a silane derivative of formula (V) in the presence of 1-7C alkyllithium.X=halo.Preferred Method: The diaminosilane derivative (IV) is produced by reaction performed in the presence of a base of formula: N(R6)(R7)(R8) or 1-7C alkyllithium. A cyclodisilazane derivative of formula (I-2) is produced by reacting a halocyclodisilazane derivative of formula (I-1) with a metal hydride or an alkali metal derivative of formula (VIII). An aminosilane derivative of formula (VI) is produced by reacting a silane derivative of formula (II) with an amine derivative of formula (III). The resulting compound is subjected to intramolecular cyclization reaction in the presence of 1-7C alkyllithium to produce halocyclodisilazane derivative of formula (VII). The cyclodisilazane derivative of formula (IX) is obtained by reacting halocyclodisilazane derivative (VII) with a metal hydride or an alkali metal derivative of formula (VIII). The metal hydride is lithium hydride, sodium hydride, potassium hydride and/or lithium-aluminum hydride.R6-R8=1-7C alkyl;M=alkali metal;R10=H or 1-5C alkyl;andat least one of R1'-R3'=H, and remainder is H, 1-5C alkyl or 2-5C alkenyl. SPECIFIC COMPOUNDS - 9 Cyclodisilazane derivatives e.g. 1,3-diisopropyl-(1,3,2,4)diazadisiletidine of formula (Ia), 1,3-diisopropyl-2,4-dimethyl-(1,3,2,4)diazadisiletidine, 1,3-diisopropyl-2,2-dimethyl-(1,3,2,4)diazadisiletidine, 4-chloro-1,3-diisopropyl-2,2-dimethyl-(1,3,2,4)diazadisiletidine and 2,2,4-trichloro-1,3-diisopropyl-(1,3,2,4)diazadisiletidine are specifically claimed.    EXAMPLE - 100 g 1,3-diisopropyl-2,4-dichlorodimethyl cyclodisilazane and 200 ml organic solvent were added into a 1000 mL flame-dried Schlenk flask and stirred under anhydrous and inert atmosphere. 7.33 g Lithium hydride was slowly added and maintained at -15 degrees C. After the addition was completed, the temperature of the reaction solution was slowly raised to 65 degrees C, and the reaction solution was stirred for 12 hours. After the stirring was completed, the reaction solution was filtered, and a white solid obtained by the filtration was removed to obtain a filtrate. The solvent was removed from the filtrate under reduced pressure, and 60 g 1,3-diisopropyl-2,4-dimethylcyclodisilazane was obtained with yield of 80%.