Synthesis of [1.1.1]propellanes by bridging of bicyclo[1.1.0]butanes

Article abstract of DOI:10.1002/jlac.199619961103

Several [1.1.1]propellanes were synthesized by bridging the 1,3-positions of the corresponding bicyclo[1.1.0]butane. The synthesis of 1-bromo-3-(chloromethyl)bicyclobutanes and the bridging were carried out in a one-pot reaction by addition of 2.0 equiv. of MeLito 1,1-dibromo-2,2-bis(chlormethyl)-cyclopropanes 10. Three routes to 10 were investigated: Firstly, the Wittig reaction of 1,3-dichloroacetone leading to (chloromethyl)allyl chlorides 6 was, with the exception of 6m, successful only with Wittig reagents derived from primary alkyl halides. Secondly, reduction of diethyl alkylidenemalonates with LiAlH₄ in benzene afforded carbinols 12 which were converted into 6 by reaction with N-chlorosuccinimide/ dimethyl sulfide. The cyclopropanation of 6 to 10 was achieved by reaction with bromoform/NaOH under phase-transfer catalysis conditions. Finally, starting from diethyl alkylidenemalonates, the sequence of reduction and cyclopropanation could be interchanged, according to the sequence 11 → 13 → 14 → 10. Propellanes 5b and 3 were reduced with LiAlH₄ to bicyclo[1.1.1]pentanes 15b and e. 2-D INADEQUATE NMR spectra of 5d and 5p indicate that the coupling constants J(¹³C-¹³C) between the bridgehead positions are very small, i.e. 0.47 and 0.53 Hz, respectively. VCH Verlagsgesellschaft mbH, 1996.