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)₁₀Hydrocarbons

Abstract

6-Trimethylsilyl- (1 b), 6-hydroxymethyl- (1 e), and 6-methyldiademane (1 f) have been prepared by irradiation of the corresponding snoutene derivatives, in 23, 2.8, and 17 % yields, respectively, together with the isomeric 1-trimethylsilyl- (10 b) and 1-methyldiademane (10 f) (8 and 2 % yields, respectively). The starting 4-trimethylsilyl- (9 b) and 4-(trimethylsilyloxymethyl)snoutene (9 d) were prepared from the correspondingly substituted cyclooctatetraenes 4 b and 4 c in several steps in 20 and 8 % overall yields, respectively. Upon heating, as well as under the conditions of gas-chromatographic separation, diademanes 1 b, 10 b, 1 f, and 10 f rearranged into the corresponding C10- and C1-substituted triquinacenes 3 b, 3 f, 11 b, and 11 f, respectively. Rough kinetic measurements of these rearrangements indicate some acceleration of the reaction caused by the presence of a methyl substituent and retardation by that of a trimethylsilyl substituent, relative to the parent diademane 1 a. At this insufficient precision, however, the activation energies (E(a)) of 29.0 and 28.1 kcal mol(-1), respectively, are essentially the same as that reported for 1 a (28.3 kcal mol(-1)). An X-ray crystal structure analysis of trimethylsilylsnoutene 9 b revealed a significant lengthening of the distal (with respect to the substituent) bond (1.534 versus 1.505 A) in the unsubstituted cyclopropane ring. In the substituted cyclopropane ring, the two proximal bonds are lengthened (1.530 A) and the distal bond is slightly shortened 1.492 A). This indicates a small, but significant electron-withdrawing effect of the trimethylsilyl group in 9 b. An X-ray crystal structure analysis of 6-hydroxymethyldiademane 1 e showed pronounced alternation of the bond lengths in the six-membered ring, with 1.494(4) between and 1.539(4) A within the three cyclopropane moieties, in close agreement with computations at different theoretical levels. This structural feature corroborates a predisposition of the tris-sigma-homobenzene skeleton of this molecule in the ground state to undergo the facile [sigma(2)(s) + sigma(2)(s) + sigma(2)(s)] cycloreversion to the triquinacene skeleton observed for the parent diademane 1 a, its derivative 1 b and 1 f, as well as for other tris-sigma-homobenzene derivatives.

4,7,11‐Triheterotrishomocubanes – Propeller‐Shaped Highly Symmetrical Chiral Molecules Derived from Barrelene

“…The X-ray crystal structure analysis of the trisether (-)-12 ( Figure 3) disclosed almost ideal D 3 symmetry for this molecule in which the six C-C bonds adjacent to the bridgehead atoms C2, C9 [1.559(3) Å] are slightly lengthened as compared to the other three C-C bonds [1.530(3) Å] and to a normal C sp 3-C sp 3 bond length (1.536 Å [35] ) mostly due to their being in- corporated in a polycyclic skeleton. [16,36] The bicyclo[2.2.2]-octane core in 12 is twisted with dihedral angles of Φ = -63.8 and τ = -40.7°.…”

Synthesis of propellanes containing a bicyclo[2.2.2]octene unitviathe Diels–Alder reaction and ring-closing metathesis as key steps

“…Later, this strategy was extended to design the basketene 17 and anthracene-based propellane derivatives 45 and 50 respectively. Recently, our group reported the synthesis of cage propellanes, 18 however, the basketene-based propellane synthesis is a worthy target for high energy systems.…”

Boryl‐ and Silyl‐Substituted Mixed Sandwich Compounds of Scandium

“…Solvents were dried by standard procedures. The compounds Na[C 5 H 5 ], K 2 [C 8 H 8 ], Na[C 5 H 4 B(NMe 2 ) 2 ], Li[C 5 H 4 SiMe 3 ], C 8 H 7 Br, C 8 H 7 SiMe 3 , and ClB(NMe 2 ) 2 were prepared according to published procedures. The NMR spectra were recorded on a Bruker Avance 500 spectrometer.…”

“…The compounds Na[C 5 H 5 ], [32] K 2 [C 8 H 8 ], [33] Na[C 5 H 4 B(NMe 2 ) 2 ], [25] Li[C 5 H 4 SiMe 3 ], [34] C 8 H 7 Br, [35] C 8 H 7 SiMe 3 , [36] and ClB(NMe 2 ) 2 [37] were prepared according to published procedures. Solvents were dried by standard procedures.…”