Intramolecular ring closure via ether bond in reaction of α,α′ halogeno bicyclo[3.3.1]nonanediones under basic conditions

The stereoselectivity of halogenation of bicyclo[3.3.1]nonan-2-one 1 and bicyclo[3.3.1]nonane-2,6-dione 2 with molecular bromine and chlorine was studied. The transformation of alpha-bromo- and chloro-bicyclo[3.3.1]nonanones 3-5 under Favorskii reaction conditions was studied. The reaction of alpha,alpha'-dihalogeno diones in the presence of sodium methoxide, ethoxide, propoxide and potassium cyanide led to the intramolecular ring closure via C-O bond formation giving the highly functionalized chiral 2-oxatricyclo[4.3.1.0(3,8)]decane (2-oxaprotoadamantane) structure. Enantiomers of this cage structure were resolved by chiral GLC. The intramolecular ring closure pathway involving the intermediate alkoxybicyclo[3.3.1]nonanolate structure was proposed.