Metallated Bicyclo[3.2.2]nona‐2,6,8‐trienes, Their Rearrangement to Barbaralanes, and a Short Synthesis of the Bicyclo[3.2.2]nona‐2,6,8‐trien‐4‐yl Anion

Five different anions are formed when bicyclo[3.2.2]nona‐2,6,8‐triene ( 1a ) is deprotonated: the 6‐ and 7‐yl anions when using t BuLi/TMEDA, the 4,6‐ and 4,7‐diyl dianions when using n BuLi/ t BuOK, and the 4‐yl anion ( 1 – ) after quenching the dianions with THF. Reaction of the anions with Me 3 SnCl gives the 6‐, 7‐, and 4‐monostannylated bicyclo[3.2.2]nona‐2,6,8‐trienes 1b, 1c , and 1d as well as the exo ‐4,7‐, endo ‐4,6‐, and endo ‐4,7‐distannylated bicyclo[3.2.2]nona‐2,6,8‐trienes 1e, 1f , and 1g , respectively. Reaction of 1 – with Me 3 SiCl and Me 3 PbCl leads to the corresponding 4‐silyl derivative 1h and its plumbyl analogue 1i . Inversely, cleavage of 1d with MeLi allows to generate 1 – under particularly mild conditions. The metallation of tricyclo[3.2.2.0 2,4 ]nona‐6,8‐diene ( 3a ), which was tested for an alternative route to 1 – , gives two stannyl derivatives 3b and 3c which are substituted in the vinylic positions. – On heating 1d and 1i rearrange to yield 9‐trimethylstannylbarbaralane ( 2d ) and its plumbyl analogue 2i quantitatively. The reactivity decreases on passing from 1i to 1d whereas 1h does not react. Mercury and zinc derivatives of 1 – are so labile that only dibarbaralylmercury ( 2j ) and ‐zinc ( 2k ) are observed by NMR spectroscopy. The title rearrangement proceeds by a 1,5‐homodienyl metallatropic shift which involves an endo 1‐type transition structure. – The new compounds 1b – i, 2d, 2i, 3b and 3c are characterized with emphasis on the NMR data including 1 H, 13 C, 119 Sn, 207 Pb signal shifts and various heteronuclear couplings.