Three-substituted bicyclo[1.1.1]pent-1-yl radicals (5), generated from additions of radicals to [1.1.1]-propellane (1), are found to have high propensities to react with three-coordinate phosphorus molecules. For example, the 3-ethylbicyclo[1.1.1]pent-1-yl radical (5d) reacts with (EtO)(3)P in a free-radical Arbuzov process to yield dimethyl 3-ethylbicyclo[1.1.1]pent-1-ylphosphonate (13). By contrast, the ethyl radical does not react with (EtO)(3)P to yield EtP(O)(OEt)(2). However, the highly reactive phenyl radical yields PhP(O)(OEt)(2). Moreover, attack of the n-pentylbicyclo[1.1.1]pent-1-yl radical (5b) on n-C5H11P(OMe)(2) results in a free-radical substitution process that gives dimethyl 3-n-pentyl[1.1.1]bicyclopent-1-ylphosphonite (7b) and the primary alkyl radical n-C5H11.. Thus, 5 has a propensity to bond to three-coordinate phosphorus that is greater than that of a primary alkyl radical and similar to that of phenyl radical. Reaction of 2-benzyl-4-methyl-1,3,2-dioxaphospholane (9) with 5a is found to proceed with predominant inversion of configuration at phosphorus. Furthermore, 3-phenylmethylbicyclo[1.1.1]pent-1-yl radical, 5a (from reaction of benzyl radical with 1), participates in reasonably efficient radical chain reactions with PhCH(2)OP(OMe)(2) (11) and PhCH(2)P(OMe)(2) (6a) (chain lengths 30-50) to provide structurally novel products of new radical-Arbuzov and radical-substitution reactions. Dimethyl 3-phenylmethylbicyclo[1.1.1]pent-1-ylphosphonate (12) from 11 and dimethyl 3-phenylmethylbicyclo[1.1.1]pent-1-ylphosphonite (7a) from 6a incorporate the bicyclo[1.1.1]pent-1-yl moiety. The high propensity of various 5 to react with three-coordinate phosphorus molecules reflects the highly pyramidal nature of 5 which is accompanied by the increased s-character of the SOMO orbital of 5 and the strength of the phosphorus-carbon bond in the presumed phosphoranyl radical intermediates (3 and 4) formed. Figure 1 depicts the thermodynamics of three classes of free radical substitution and Arbuzov reactions with three-coordinate phosphorus molecules.