Y-Aromaticity:  Why Is the Trimethylenemethane Dication More Stable than the Butadienyl Dication?

Abstract

[reactions: see text] Resonance energies of the trimethylenemethane dication (1) and the butadienyl dication (4) were evaluated using two independent computational methodologies to provide insight into the validity of Y-aromaticity. One methodology employed density functional theory calculations and examined the resonance contribution of the C=C double bond toward the double hydride abstraction enthalpies of methylpropene (6) and 2-butene (8), yielding 1 and 4, respectively. These resonance contributions by the double bond were determined by calculating the double hydride abstraction enthalpies of both the parallel and perpendicular conformations of vinylogues of 6 and 8, in which n = 1-4 vinyl units were inserted between the central carbon-carbon double bond and each of the reaction centers. Extrapolation of the resonance contribution in each vinylogue to n = 0 yielded the resonance contribution in the respective parent molecules. The second methodology employed an orbital deletion procedure (ODP), which effectively allowed us to examine the energies of individual resonance structures. The resonance energy of each dication is computed as the difference between the most stable resonance structure and that of the delocalized species. The two methodologies are in agreement, suggesting that the resonance energy of the trimethylenemethane dication is substantially greater than that of the butadienyl dication. The origin of this difference in resonance stabilization is discussed.

Dendralene auf dem Vormarsch: kreuzkonjugierte Oligoene ermöglichen den schnellen Aufbau molekularer Komplexität

“…Wie in Schema 3 zusammengefasst, wurden die maskierten Dendralenintermediate durch eine Reihe von Stille-Kreuzkupplungen erhalten. Die Schlüsselbausteine waren Sweeneys Sulfolen (14), [24] 3-Iodsulfolen (15), Tributylvinylstannan (16), 1,1-Dibromethen (17) und 2,3-Bis(trimethylstannyl)-1,3-butadien (19). Cadogans [3] Später zeigte der Arbeitskreis um Sherburn, dass der Zugang in Schema 3 weiter verbessert werden konnte.…”

“…[4] Außerdem werden wir keine kreuzkonjugierten Kohlenwasserstoffe, in denen eine der terminalen Doppelbindungen eines [3]Dendralens durch ein aromatisches Ringsystem oder ein Alkin ersetzt wurde, berücksichtigen, da diese p-Systeme bereits ausführlich im Übersichtsartikel von Gholami und Tykwinski besprochen wurden. [7] Reaktive Intermediate mit einer kreuzkonjugierten Anordnung der p-Elektronen werden wir ebenfalls nicht behandeln (d. h. Radikale, [12,13] Carbokationen, [14] Carbanionen [15,16] und Radikalionen [17]…”

Synthesis and conformational features of sym N,N′,N″-triarylguanidines

“…16−20 Further, sym N,N′,N″-triarylguanidinium cations of 7-12 could be a promising scaffold to stabilize reactive anions of unusual structure given the extraordinary stability of guanidinium cations due to Yaromaticity. 21 One of the convenient routes envisaged for 7-12 would be guanylation of aryl amine with the respective sym N,N′-diarylcarbodiimide as previously reported for 1. 13 Unfortunately, this route is limited by sym N,N′-diarylcarbodiimides source.…”

A one-pot synthesis of functionalized 4,5-bis(phenylimino)-1,3-thiazolidine-2-thiones from primary amines, CS2 and N,N’-diphenyloxalimidoyl dichloride

“…The initial event may be the formation of dianione 5 from amine 1 and CS 2 . Dianione 5 is a heteroanalogue of guanidinium cation with noticeable resonance stabilization energy of Y-shaped species with 4n + 2 π-electrons, which suggest potential Y-aromaticity in these structures [24,25]. Formation of a Y-delocalized intermediate, such as the carbamodithioate dianione 5, may act as a driving force for chemical transformations.…”