A sterically demanding TBS-substituted oligosilane (4, TBS=t-butyldimethylsilyl) was stepwisely formed by reactions of oligosilanyl potassium compound and the corresponding chlorosilane. Although a well-established method, the ring closure reaction of compound 4 in the presence of t-BuOK and 18-Cr-6 with SiX4 (X=Cl, Br) failed. The silyl potassium compound was then transformed to silyl Grignard compound 5, which can be used to react with SiX4 to give the dihalocyclopentasilanes (6, X=Cl; 7, X=Br) successfully. The molecular structures of 3–7 have been confirmed by X-ray single-crystal analyses.