SYNTHESIS OF [1.1.1]PROPELLANES BY BRIDGING OF BICYCLO[1.1.0]BUTANES

Several [1.1.1]propellanes were synthesized by bridging the 1,3-positi ons of the corresponding bicyclo[1.1.0]butane. The synthesis of 1-brom o-3-(chloromethyl)bicyclobutanes and the bridging were carried out in a one-pot reaction by addition of 2.0 equiv. of MeLi to 1,1-dibromo-2, 2-bis(chlormethyl) cyclopropanes 10. Three routes to 10 were investiga ted: Firstly, the Wittig reaction of 1,3-dichloroacetone leading to (c hloromethyl)allyl chlorides 6 was, with the exception of 6m, successfu l only with Wittig reagents derived from primary alkyl halides. Second ly, reduction of diethyl alkylidenemalonates with LiAlH4 in benzene af forded carbinols 12 which were converted into 6 by reaction with N-chl orosuccinimide/dimethyl sulfide. The cyclopropanation of 6 to 10 was a chieved by reaction with bromoform/NaOH under phase-transfer catalysis conditions. Finally, starting from diethyl alkylidene-malonates, the sequence of reduction and cyclopropanation could be interchanged, acco rding to the sequence 11 --> 13 --> 14 --> 10. Propellanes 5b and 3 we re reduced with LiAlH4 to bicyclo[1.1.1]pentanes 15b and e. 2-D INADEQ UATE NMR spectra of 5d and 5p indicate that the coupling constants J(C -13-C-13) between the bridgehead positions are very small, i.e. 0.47 a nd 0.53 Hz, respectively.