METALATED 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 tBuLi/TMEDA, t he 4,6- and 4,7-diyl dianions when using nBuLi/tBuOK, and the 4-yl ani on (1-) after quenching the dianions with THF. Reaction of the anions with Me3SnCl gives the 6-, 7-, and 4-monostannylated bicyclo[3.2.2]non a-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 1 g, respectively. Reaction of 1- with Me3SiCl and Me3PbCl leads to the corresponding 4-silyl derivative 1 h and its plumbyl analogue 1i. Inve rsely, cleavage of 1d with MeLi allows to generate 1- under particular ly 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 po sitions. - On heating 1d and 1i rearrange to yield 9-trimethylstannylb arbaralane (2d) and its plumbyl analogue 2i quantitatively. The reacti vity decreases on passing from 1i to 1d whereas 1h does not react. Mer cury and zinc derivatives of 1- are so labile that only dibarbaralylme rcury (2j) and -zinc (2k) are observed by NMR spectroscopy. The title rearrangement proceeds by a 1,5-homodienyl metallatropic shift which i nvolves an endo-type transition structure. - The new compounds 1b-i, 2 d, 2i, 3b and 3c are characterized with emphasis on the NMR data inclu ding H-1, C-13, Sn-119, Pb-207 signal shifts and various heteronuclear couplings.