Dichloro as well as monochloro derivatives of 1, 6-C2B4H6 and 2, 4-CzBSH7 are prepared, and the effect of the first chlorine substituent on the position of the entering second chlorine substituent is discussed. Both mono-and dichloro derivatives of C2BsH7 rearrange at approximately 300 OC to a mixture of isomers.