B. Albert, D. Elsasser, H.-D. Martin, B. Mayer, T. J. Chow, A. P. Marchand, C.-T. Ren, M. N. Paddon-Row Small and Medium Rings, 78'' zyxwvuts Cage Dimers of Norbornadiene with Perpendicular Arrangement of Subchromophores: Orbital Interaction in the zyx Heptacyclo[6.6.0.02~6.03~13.04~11.05~9.010~14]tetradecane System Bernhard Albert", Dominik Elsassera, Hans-Dieter Martin*", Bernhard Mayera, Tahsin J. Chow* b, Alan P. Marchand*', Chien-Tai Ren', and Michael N. Paddon-Row*d lnstitut fur Organische Chemie und Makromolekulare Chemie der Universitlt Diisseldorf", Universitatsstr. 1, W-4000 Diisseldorf 1, F.R.G. Institute of Chemistry, Academia Sinicab, Nankang, Taipei, Taiwan, Republic of China Department of Chemistry, University of North Texas", P.O.Box 5068, Denton, Texas 76203, U.S. A. Department of Organic Chemistry, University of New South Walesd, P. 0. Box 1, Kensington, N. S.W. 2033, Australia Received July 3, 1991 Key Words: Polyquinanes zyxwvutsrq / Norbornadiene dimers / Orbital interaction, t..rough- -3n Orbitals, precanonical / Switches, molecular / PE spectroscopy / 2871 The syntheses of functionalized norbornadiene dimers 1 are described. These cage compounds feature remarkably high zyxwvuts Dzd symmetry as regards the dimethylene and dioxo deriva- tives Id and le. On the other hand, the mixed enone com- pound 1 f behaves differently: zyxwvutsrqp rCc and lone-pair nco orbitals mix strongly with each other, albeit only by means of the interveningfive-bondosystem.Al1theoretical conclusions have been verified by using PE spectroscopy. A comparison is made between systems 1 and the geometrically similar adamantanes 2, on the one hand, and the attractive but still unknown de- rivatives of garudane 3 on the other hand. The latter exhibit the interesting parallel topology of suitable chromophores, thus making these polycycles 3 desirable candidates for trans- mission studies. Thc chemistry of cage-shaped hydrocarbons (polyhedranes, pris- manes, polyquinanes, adamantanes) and their derivatives has at- tracted wide interest among both, theoretical and synthetic chemists'!. These aesthetically fascinating compounds continue to represent a synthetic challenge because of their increasing practical importance. For instancc, their application as energy materials') and as medicinal substances4', e. g. antiviral agcnts5),has been re- ccntly discusscd. Bcsidcs thcsc practical purposes cage-shaped hy- drocarbons often provide conformationally fixed carbocyclic skel- etons with a defined inherent symmetry. In this regard they become particularly interesting objects of spectroscopical and theoretical studies. Scheme 1 1 2 3 a: X = Y = H1; b: X = 0, Y = Ha; E: X = CH2, Y = Hz; d: X = Y = 0; e: X = Y = CH2; f: X = CH,; Y = 0; g: X = OCH,CH>O, Y = 0; h: X = OCH2CH20, Y = H2 However, syntheses of such cage compounds are sometimes te- dious since assembling a highly compact structure is an entropy- disfavored process. One example how to overcome this difficulty by organometallic means is the efficient formation of the eight- membered polyquinane la (heptacyclo[6.6.0.02~6.0~~'3.04J~.05~9.0'oJ4]- tetradecane6)) which is commonly referred to as HCTD. The oc- taquinane la is formed in one step by metal-assisted dimerization of norbornadiene (NBD). This was first observed in 1961'land since then has been studied extensively". An ordinary dimcrization of NBD generally produces several isomers simultaneouslyY). Only a few stereospecific reactions have been known 'I. Recently, one of us reported a stereospecific endo-cis-endo coupling of NBD in the pres- ence of hexacarbonylmolybdenum 'I). The resulting cage dimer la is formed exclusively in a yield of 26%. Dimerization of 7-tert- butoxynorbornadiene12'and related NBD derivativesl3I gave access to HCTD derivatives oxygenated in the 7,12-p0sition'~). In the pres- ence of hexacarbonylmolybdenum the dimer of tert-butoxynorbor- nadiene was also formed in a stereospecific reaction 15), thus facili- tating the syntheses of monoketone lb and diketone ld'@. In the present communication we will report on the prep- aration of the corresponding olefines lc and le, respectively, as well as of the "mixed" enone lf, in order to provide a series of HCDT derivatives with a common structural fea- ture: Due to the stereospecific cross dimerization of NBD the carbocyclic skeletons of zyx 1 a- 1 f show the remarkable D2(, symmetry. As a consequence, the two double bonds in Chem. Ber. 124 (1991) 2871 -2878 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1991 0009 -2940/91/1212-2871 $ 3.50+ .25/0