Carbene−Bridgehead Olefin−Carbene Rearrangement: Formation of the Tetracyclo[4.3.0.02,8.04,7]nonane Skeleton by Carbene CH Insertion1

Abstract

The sequence of rearrangements of carbenes 6 has been studied. Precursors for 6 were 1-halo-3-(n-halomethyl)bicyclo[1.1.1]pentane derivatives 11, which were obtained by addition of polyhalomethanes to the central bond of [1.1.1]propellane derivative 13 via radical chain processes. Reaction of compounds 11 with MeLi or sodium bis(trimethylsilyl)amide generates carbenes 6, which are stabilized by a carbene (6)−bridgehead olefin−carbene (9) rearrangement, followed by an intramolecular CH insertion reaction of carbenes 9 to afford tetracyclononane derivatives 15 in good yields. The carbenes 6 show only slight preferences in the rearrangement to alkenes 7 and 8. Both could be trapped with α-methylstyrene as ene adducts 16 and 17. The strongly twisted bridgehead olefin 7 has only the option to rearrange to carbene 9, whereas 8 could give 9 or 10, but prefers to give 9, in accordance with results of DFT calculations. The tetracyclononanes 15c and 15d contain halide atoms in the 1,3-positions; on treatment with t...