MECHANISTIC DEFINITION OF TRIMETHYLSTANNYLATION OF 1,3-DIHALOADAMANTANES - DELOCALIZED RADICAL-ANIONS AS POSSIBLE INTERMEDIATES

A series of 1,3-dihaloadamantanes (3, X = Y = halogens) have been synthesized, characterized, and treated with (trimethylstannyl) alkali reagents (Me3SnM, M = Li or Na) in the absence and presence of tert-butylamine (TBA) and dicyclohexylphosphine (DCPH). The product distributions of these reactions have been established by C-13 and Sn-119 NMR spectroscopy and vapor-phase chromatographic analyses. Tin substitution via an S(RN)1-type pathway is shown to be a significant reaction for several of the derivatives of 3 (X = F, Y Br or I; X = Cl, Y = Br or I; X = Y = Br) but not for the bromo iodide or diiodide (3, X = Br, Y = I and X = Y = I). For the latter two compounds, the formation of 1,3-dehydroadamantane or propellane 8 is the predominant reaction product while tin substitution is insignificant. Propellane 8 formation is also a significant reaction product for some of the other dihalo derivatives of 3 (X = Cl, Y = I and X = Y = Br) but not for others (3, X = F, Y = Br or I and X = Cl, Y = Br). The mechanism of formation of 8 is perplexing in light of the trapping experiments in the presence of TBA and DCPH. A possible pathway is proposed in which the key intermediate is a delocalized radical anion.