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‐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 MeLi to 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 LiAlH 4 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 LiAlH 4 to bicyclo[1.1.1]pentanes 15b and e . 2‐D INADEQUATE NMR spectra of 5d and 5p indicate that the coupling constants J ( 13 C‐ 13 C) between the bridgehead positions are very small, i.e. 0.47 and 0.53 Hz, respectively.