Straightforward synthesis of a vicinal double bridgehead iodo trimethylsilyl octacycle: unprecedented lack of reactivity of the silyl group in front of fluoride anions.

Abstract

Abstract: A convenient synthesis of an octacyclic compound containing an iodo and a trimethylsilyl group in vicinal double bridgehead positions, as a possible precursor of a pyramidalized alkene, is described. The key step of the synthesis consists of a double nucleophilic substitution of two neopentyl-type iodides by cyclopentadienide anions followed by two intramolecular Diels-Alder cycloadditions. All attempts to generate the expected pyramidalized alkene from the above precursor on reac-tion with different sources of fluoride failed. This octacyclic compound, which contains two disubstituted C=C bonds, underwent a chemo- and stereoselective Pd0-catalyzed co-cyclotrimerization with dimethyl acetylenedicarb-oxylate to give a nonacyclic cyclohexadiene derivative that can be aromatized upon reaction with CsF or transformed into a related fluoride upon reaction with AgF.