Dihydroacepentalendiid, das Dianion des Acepentalens

Abstract

Dihydroacepentalendiid 22e, formal ein ethenoiiberbriicktes Dihydropentalendiid''], sollte wie dieses['**] nach semiempirischen Rechnungen ein geschlossenschaliges System seini31. Allerdings diirfte seiner Bildung die hohe Spannungsenergie in dem cyclisch und gekreuzt konjugierten Geriist rnit drei angular anellierten Flinfringenf4I entgegenstehen. Bisher war es offenbar nicht gelungen, 22e zu erzeugen, obwohl sich die Theoretiker schon lange fur Acepentalen (Cyclopenta[cd]pentalen) 2 interessiered". Neueste Versuche, die beiden Dialkylaminogruppen aus den als Vorstufen geeignet erscheinenden 4,7-Bis(dialkylamino)tricyclo[5.2.l.O4~'O]deca-l(l0),2,5,8-tetraenen131 reduktiv zu eliminieren, fuhrten lediglich zu 1,4,7-Tris(di-alky1amino)-substituierten M o n~a n i o n e n l~.~~. Um so iiberraschender ist es, wie einfach sich 22e direkt aus Tri-*

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

“…A more versatile approach to 4,7-disubstituted dihydroacepentalenes 65 is via the stable acepentalene dianion 64 as an easily accessible intermediate. Dipotassium acepentalenediide 64 can be obtained in virtually quantitative yield by treatment of triquinacene 10 with the superbasic mixture of potassium t-pentoxide and butyllithium [or even better potassium t-butoxide, butyllithium and tetramethylethylenediamine (TMEDA)] in hexane, the so-called Lochmann-Schlosser base (Scheme 15) [62,63]. Mechanistically this transformation has been shown to proceed via a threefold deprotonation at the three allylic positions in 10 and a subsequent hydride elimination of the central hydrogen from the intermediate trianion to form the dianion as in 64 [64].…”

Utility of the Tandem Pauson−Khand Reaction in the Construction of Tetracycles

“…During the last two decades interest in the study of molecules that contain significant amounts of strain energy in their molecular structure has increased. The questions of bonding character, π overlap, and Hückel stabilization are of great importance to computational and organic chemists. − The desire to better understand the bonding character of carbon has prompted the study of the synthesis of a number of strained molecules termed polyquinenes . Dicyclopenta[ a,e ]pentalene ( 1 ) and dicyclopenta[ a,f ]pentalene ( 2 ) (Figure ) have not been synthesized and have been discussed only from a computational point of view.…”