The reaction of K 2 (PMe) 4 · 2 THF with cis-1,2-dichloroethylene yields the hitherto unknown cyclocarbaphosphanes 1,2,3-trimethyl-1,2,3-triphosphole, (PMe) 3 C 2 H 2 (1), and 2,3,4,6,7,8-hexamethyl-2,3,4,6,7,8-hexaphosphabicyclo[3,3,0]octane, (PMe) 6 C 2 H 2 (2). Besides, (PMe) 5 , (PMe) 4 CH 2 , (PMe) 3 C 2 H 4 , and the new six-membered heterocycle (PMe) 2 (C 2 H 2 ) 2 are formed. The cyclocarbaphosphanes 1 and 2 were characterized by elemental analysis, mass, IR, Raman, and MR spectra. For the bicyclic compound 2 two diastereomers were obtained and separated. They differ in the position of the methine hydrogens and of the methyl substituents (cis-2 and trans-2). Compound 2 is also produced in the reaction of K2(PMe)4 * 2 THF with trans- 1,2-dichloroethylene whereas with 1,1,2,2- tetrachloroethane mainly (PMe)s is formed. In 1 and in each of the five-membered rings of cis-2 and trans-2 the methyl substituents at adjacent phosphorus atoms are situated on opposite sides of the ring.