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
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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, the 4,6‐ and 4,7‐diyl dianions when using nBuLi/tBuOK, and the 4‐yl anion (1–) after quenching the dianions with THF. Reaction of the anions with Me3SnCl 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 Me3SiCl and Me3PbCl 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[3.2.2.02,4]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 endo1‐type transition structure. – The new compounds 1b – i, 2d, 2i, 3b and 3c are characterized with emphasis on the NMR data including 1H, 13C, 119Sn, 207Pb signal shifts and various heteronuclear couplings. Copyright © 1993 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim
author list (cited authors)
Blümel, J., & Köhler, F. H.