Preparation and Properties of Centrally Bridgehead-Substituted Hexacyclo[4.4.0.0 2,1 .0 3,5 .0 4,8 .0 7,9 ]decanes (™Diademanes∫) and Related (CH) 10 Hydrocarbons Armin de Meijere,* [a] Chih-Hung Lee, [a] Bengt Bengtson, [a] Ehmke Pohl, [b] Sergei I. Kozhushkov, [a] Peter R. Schreiner,* [c] Roland Boese,* [d] and Thomas Haumann [d] Abstract: 6-Trimethylsilyl- (1b), 6-hy- droxymethyl- (1e), and 6-methyldiade- mane (1f) have been prepared by irra- diation of the corresponding snoutene derivatives, in 23, 2.8, and 17% yields, respectively, together with the isomeric 1-trimethylsilyl- (10b) and 1-methyldi- ademane (10f) (8 and 2% yields, re- spectively). The starting 4-trimethylsilyl- (9b) and 4-(trimethylsilyloxymethyl)- snoutene (9d) were prepared from the correspondingly substituted cycloocta- tetraenes 4b and 4c in several steps in 20 and 8% overall yields, respectively. Upon heating, as well as under the conditions of gas-chromatographic sep- aration, diademanes 1b, 10b, 1f , and 10f rearranged into the corresponding C10- and C1-substituted triquinacenes 3b, 3f , 11b,and 11f , respectively. Rough kinetic measurements of these rear- rangements indicate some acceleration of the reaction caused by the presence of a methyl substituent and retardation by that of a trimethylsilyl substituent, rela- tive to the parent diademane 1a. At this insufficient precision, however, the acti- vation energies (E a ) of 29.0 and 28.1 kcalmol 1 , respectively, are essen- tially the same as that reported for 1a (28.3 kcalmol 1 ). An X-ray crystal struc- ture analysis of trimethylsilylsnoutene 9b revealed a significant lengthening of the distal (with respect to the substitu- ent) bond (1.534 versus 1.505 ä) in the unsubstituted cyclopropane ring. In the substituted cyclopropane ring, the two proximal bonds are lengthened (1.530 ä) and the distal bond is slightly shortened 1.492 ä). This indicates a small, but significant electron-withdrawing effect of the trimethylsilyl group in 9b. An X-ray crystal structure analysis of 6-hydroxy- methyldiademane 1e showed pronounced alternation of the bond lengths in the six- membered ring, with 1.494(4) between and 1.539(4) ä within the three cyclo- propane moieties, in close agreement with computations at different theoretical lev- els. This structural feature corroborates a predisposition of the tris-s-homobenzene skeleton of this molecule in the ground state to undergo the facile [s 2 s  s 2 s  s 2 s ] cycloreversion to the triquinacene skele- ton observed for the parent diademane 1a, its derivative 1b and 1f , as well as for other tris-s-homobenzene derivatives. Keywords: alkenes ¥ hydrocarbons ¥ isomerization ¥ polycycles ¥ strained molecules ¥ structure elucidation Introduction Among the members of the (CH) 10 hydrocarbon family, which–like other (CH) n hydrocarbon families–is known for its multiple photochemical and thermal rearrangements, [1, 2] the one nick-named ™diademane∫ (hexacyclo- [4.4.0.0 2,10 .0 3,5 .0 4,8 .0 7,9 ]decane, 1a [3] ) draws the eye because of its molecular shape, resembling that of a closed crown. Diademane 1a is also remarkable because of its facile thermal rearrangement leading to triquinacene 3a, in which the C 3v symmetry of the precursor is retained. [4] It has been proposed that this rearrangement is a concerted [s 2 s  s 2 s  s 2 s ] cyclo- reversion, in which three cyclopropane s-bonds are opened and three p-bonds are formed simultaneously (Scheme 1). According to MINDO/3 [5] and B3LYP/6-311  G** [6] cal- culations, the transition structure 2 of this rearrangement has the same C 3v symmetry as the starting material 1a and the product 3a. To further test for this concept, we have prepared a number of centrally bridgehead-substituted derivatives. With the purpose of answering the important question of [a] Prof. Dr. A. de Meijere, Dr. C.-H. Lee, Dr. B. Bengtson, Dr. S. I. Kozhushkov Institut f¸r Organische Chemie der Georg-August-Universit‰t Gˆttingen Tammannstrasse 2, 37077 Gˆttingen (Germany) Fax: ( 49)551-399475 E-mail: armin.demeijere@chemie.uni-goettingen.de [b] Dr. E. Pohl European Molecular Biology Laboratory Hamburg Outstation Notkesstr. 85, 22603 Hamburg (Germany) E-mail: ehmke@embl-hamburg.de [c] Prof. Dr. P. R. Schreiner Institut f¸r Organische Chemie der Justus-Liebig-Universit‰t Giessen Heinrich-Buff-Ring 58, 35392 Giessen (Germany) Fax: ( 49)641-9934309 E-mail: peter.r.schreiner@org.chemie.uni-giessen.de [d] Prof. Dr. R. Boese, Dr. T. Haumann Institut f¸r Anorganische Chemie, Universit‰t Essen Universit‰tsstr. 3 ± 5, 45117 Essen (Germany) Fax: ( 49)201-183-2535 E-mail: boese@structchem.uni-essen.de FULL PAPER Chem.Eur.J. 2003, 9, 5481±5488 DOI: 10.1002/chem.200305114 ¹ 2003 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 5481