The reaction of 1-(dichloromethyl)bicyclo[1.1.1]pentane (10a) with MeLi afforded 1-chloro-2-methylbicyclo-[2.1.1]hexane (14) and 1,2-dichloro-2-methylbicyclo[2.1.1]hexane (15) in yields of 15 and 11%. 1-(Trichloromethyl)bicyclo[1.1.1]pentane (10b) and MeLi led to a 62% yield of 15. [C-12]-Labeling of the trichloromethyl group (10e) showed that the label was exclusively found in the C-1 position of 15, indicating an overall two CC bond breaking and two CC bond forming process. Treatment of 10b, 10c, and 10d with MeLi or NaN(SiMe(3))(2) in the presence of 2,5-dimethylfuran, cyclohexene, and tetramethylethylene, respectively, gave rise to spiroadducts 24a, 25, and 27, respectively, in yields of 29, 10, and 10%. The last two reactions were accompanied by the formation of trihalides 26 (16%) and 28 (25%). 10d, NaN(SiMe(3))(2), and triethylsilane produced a 34% yield of silane 29, The results are interpreted on the basis of a carbene (19) --> bridgehead olefin (20) --> carbene (21) rearrangement.