Dihaloadamantanes: Ring Closure versus Rearrangement or Halogen-Displacement Reactions

Three dihaloadamantanes [i.e., 2‐bromo‐1‐(chloromethyl)adamantane (1), 1‐(bromomethyl)‐2‐chloroadamantane (2) and 2‐bromo‐1‐(bromomethyl)adamantane (3)] were synthesized, and their corresponding ring‐closing reactions, performed by using Na metal or alkyllithium reagents, were studied. Compound 1 reacted with Na in toluene or in tetraglyme to afford 1,2‐methanoadamantane (4) as the major product. However, the corresponding reactions, when performed by using 2 and 3 as substrates, produced methyladamantane (5) or 4‐methyleneprotoadamantane (6) as the major reaction products. The corresponding reactions of 1 and 2 with tBuLi or nBuLi afforded small quantities of 4, 5 and 6 along with the corresponding monohalides, that is, 1‐(chloromethyl)adamantane (7) and 2‐chloro‐1‐methyladamantane (8), which constituted the major products of these reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)