Organopolylithium compounds have recently been the subjects of numerous theoretical calculations which predicted intriguing structural features; among them is the planar geometry at C-1 of 1,1-dilithiocyclopropane, 21;Lithium (alpha)-lithiocyclopropanecarboxylate, a possible precursor to 21, was alkylated by iodomethane, allyl bromide, benzyl chloride or bromide in contrary to an earlier report. Treatments of 1,1-dibromotetramethylcyclopropane with excess n-butyllithium or t-butyllithium in various solvent systems showed no evidence for a consecutive double Li-Br exchange but the usual products from coupling, disproportionation, and exchange. Pentamethylcyclopropyl lithium and 2,2,3,3-tetramethylcyclopropyl lithium were iodinated unexpectedly with iodomethane;2,3-trans-Dimethoxymethyl-2,3-dimethylcyclopropylidene bromolithiocarbenoid, 72, were studied with ('13)C NMR (('13)C-enriched compound was used) and ('7)Li NMR. Spectroscopic evidences for the inversion at the carbenoid carbon and a mechanism for the inversion process were presented. Carbenoid 72 formed a hitherto unknown stable cyclopropylidene carbenoid: alkyllithium complex below -40(DEGREES)C with n-butyllithium. Treatments of 72 with t-butyllithium gave, among others, the 1,1-dilithio species whose C-1 was observed only by ('7)Li decoupled ('13)C NMR;1,1-Dibromotetramethylcyclopropane was converted to various 1-substituted-2,2,3,3-tetramethylcyclopropyl bromide, 99, by trapping the carbenoid with methanol, iodomethane, chlorotrimethylsilane, ethyl formate, acetic anhydride, chloro ethylformate, and carbon dioxide. Flash pyrolysis of 99 constituted a convenient method for the synthesis of functionalized 2,4-dimethyl-1,3-pentadienes;Electrophilic additions to 4.3.1propell-3-ene showed a preference for the endo approach. In case of 10,10-dibromo4.3.1propell-3-ene or allylic derivatives of 10,10-dibromo4.3.1propell-2-ene, the endo approach was exclusive regardless of the allylic substitution. The steric effect of the syn bromine was dominating and led to unexpected products.