Syntheses, Structures, and Reactions of Highly Strained Dihydro- and Tetrahydroacepentalene Derivatives

Abstract

A versatile approach towards the highly strained acepentalene 3 via the readily accessible dipotassium acepentalenediide (10 a) and the highly strained tetraenes 7 is reported. An unexpected [42] cycloaddition dimer 14 is formed upon protonation of the dipotassium acepentalenediide (10 a) in 93 % yield, and the monomeric 4,7-dihydroacepentalene (7 a), as the reactive intermediate, can be trapped with anthracene to form the corresponding Diels ± Alder adduct 16 in 15 % yield. In contrast, the highly strained, but sterically protected monomeric bridgehead ± bridgehead alkenes 7 c, d can be isolated upon reaction of 10 a or 10 b with bulky electrophiles, such as Me 3 -SiCl and Me 3 SnCl, respectively. The Xray crystal structure analysis of 7 d exhibits a highly pyramidalized central double bond. The bisstannane 7 d is an ideal precursor for acepentalene (3), which would be formed by removal of the two trimethylstannyl substituents. It can also be transmetallated to give the pure crystalline dilithium acepentalenediide (10 b) in 78 % yield. According to its 1 H, 7Li and 13 C NMR spectra, the bowl-shaped 12 p-dianion in 10 b is an aromatic species, and it undergoes a rapid bowl-to-bowl inversion at room temperature.

Three-Dimensional Hydrocarbon Cores Based on Multiply Fused Cyclopentane and Indane Units: Centropolyindanes

“…Besides the discussion on the long-assumed homoconjugative interaction between the π bonds of 18 , − the generation and properties of the triquinacene-10-yl cation was put forward. ,, Many bridgehead-functionalized derivatives of triquinacene, such as 19 , − a few centro -substituted ones, e.g., 20 , , and peripherally functionalized ones, e.g., the interesting all- exo -hexaol 22 , have been described and studied, mainly with respect to their reactivity toward complexation with metal carbonyl fragments, reduction, and elimination. The deprotonation/dehydrogenation pathways of 18 and some derivatives by use of superbases have also been studied in great detail, ,− and the existence of neutral acepentalene ( 23 ), having remained elusive in condensed media, was demonstrated in the gas phase . More recently, the azatriquinacenes, including the parent, convex/concave heterocentropolyquinane 24 , have attracted some attention because of the particularly exposed basic nitrogen center. −

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Unsaturated Oligoquinanes and Related Systems

“…The sp 2 -hybridized carbon atoms of the central double bond in these dihydroacepentalene derivatives 65 are highly pyramidalized with an angle between the two adjacent five-membered rings of 143°(see Fig. 13) [64,65]. Therefore, the central double bond in compounds of type 65 is highly reactive towards electrophiles, e.g., 65a adds water and alcohols under acid catalysis, and organic acids readily at room temperature to yield the 1-substituted 4,7-bis(trimethylsilyl)triquinacenes 67.…”

“…The 4,7-bis(trimethylstannyl)dihydroacepentalene 65b also turned out to be perfectly suited for the generation of pure dilithium acepentalenediide 71 by transmetallation (Scheme 17) [63,65]. Treatment of 65b with salt-free methyllithium in dimethoxyethane yielded a crystalline compound which according to an X-ray crystal structure analysis turned out to be an interesting dimeric aggregate of two ion triplets held together by dimethoxyethane ligands (Fig.…”

GIAO-DFT study of13C NMR chemical shifts of highly pyramidalized alkenes

“…Some of the most recent examples of highly pyramidalized alkenes include cubene, 2 several unsaturated dodecahedranes, 3 tricyclo[3.3.0.0 3,7 ]oct-1( 5)-ene and related compounds, 4 tricyclo[3.1.0.0 2,6 ]hex-1(6)-ene, 5 and others. 6 Due to the instability of these compounds, their physical and chemical properties have been studied only on the less pyramidalized ones. 7 Ab initio methods are a powerful tool for predicting properties of unstable compounds and many computational predictions carried out on pyramidalized alkenes have experimentally been confirmed.…”