Syntheses and Reactions of Alkylthio- and Arylthio-Substituted 1,6-Methano[10]annulenes

The treatment of bromo-substituted 1,6-methano[10]annulenes with sodium thiolates in DMF provides easy access to alkylthio- and arylthio-substituted 1,6-methano[10]annulenes (Schemes 2-4). These compounds are then brominated with N-bromosuccinimide ( NBS ) to study their reactivity in electrophilic substitution reactions (Schemes 5 and 6). The resulting brominated thio-1,6-methano[10]annulenes are, in a subsequent reaction, subjected to Heck coupling with (4-nitrophenyl)acetylene ( 13 ) to produce the alkynylated derivatives 14 in reasonable yield (Scheme 7).     

Vicarious nucleophilic substitution of hydrogen in nitro-1,6-methano[10]annulenes

Summary The 2- and 3-nitro-1,6-methano[10]annulenes and their 11,11-difluoro derivatives react with carbanions bearing leaving groups at the carbanionic center according to the Vicarious Nucleophilic Substitution of Hydrogen (VNS) scheme. The analogy between corresponding annulenes and naphthalenes with respect to reactivity is discussed.

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Vicarielle nucleophile Substitution von Wasserstoff in Nitro-1,6-methano[10]annulenen

Zusammenfassung 2- und 3-Nitro-1,6-methano[10]annulene und ihre 11,11-Difluoroderivate reagieren mit Carbanionen, die am carbanionischen Zentrum Abgangsgruppen aufweisen, nach dem Schema der vicariellen nucleophilen Substitution (VNS). Die Analogie zwischen entsprechenden Annulenen und Naphthalinen bezüglich ihrer Reaktivität wird diskutiert.

     

Aromaticity and Homoaromaticity in Methano[10]annulenes

Aromaticity and neutral homoaromaticity have been evaluated in methano[10]annulenes systems, 1,4-methano[10]annulene (1), 1,5-methano[10]annulene (2), and 1,6-methano[10]annulene (3). C-C bond lengths indicate that 1 presents higher bond alternation than 2 and 3. The relative energies were determined at the B3LYP/6-311+G(d,p) level, and they pointed out that 3 is the most stable isomer. Strain energies, evaluated employing homodesmotic reactions, show the same order as the relative energies. Through a decomposition of strain energies, it could be concluded that the rings absorb more tension than the bridges. The changes in aromaticity were evaluated by magnetic susceptibilities, chiM, HOMA, NICS, and resonance energies, RE. HOMA, RE, and chiM indicate that 2 and 3 are strongly, and 1 is fairly, aromatic. NICS does not provide reliable results, due to interference of ring and bridge atoms. NBO analysis presents some interactions that suggest the existence of neutral homoaromaticity. GPA indices (evaluated at the B3LYP/6-31G* level) point out that homoaromaticity plays a relevant role only in 3. Moreover, this work is the first in the current literature that studies 1,4-methano[10]annulene (1).     

1,6-methano[10]annulene-stabilized radicals

The rate of the methylenecyclopropane rearrangement is remarkably enhanced by the 1,6-methano[10]annulene group, which greatly stabilizes the biradical intermediate. The diastereomeric products argue against a concerted rearrangement mechanism and support a stabilized biradical intermediate that lives long enough to undergo rotation before ring closure. [structure: see text]     

Subphthalocyanine-dehydro[18]annulenes

A subphthalocyanine trimer built around a dehydro[18]annulene core was prepared. The synthesis was achieved through direct homocoupling of an ortho-diethynyl-functionalized subphthalocyanine, obtained by palladium-catalyzed cross-coupling of the corresponding diiodo-subphthalocyanine with an ethynyl derivative. The lower analogue dehydro[12]annulene did not form in these homocoupling conditions. The trimers were fully characterized and their electrochemical properties investigated.     

Propellanes—XLIV: Reaction of 11-substituted-1,6-methano[10]annulenes with 4-phenyl-1,2,4-triazoline-3,5-dione

Reaction of the bridged annulene derivatives and the dienophile mentioned in the title occurs through attack by the latter from below, anti- to the bridge. The mono-adducts obtained contain a substituted cyclopropane ring. Attempted nucleophilic displacement of suitable substituents was unsuccessful.     

Calculation of 1H chemical shifts of [n]annuleno[m]annulenes and [n]annulenyl[m]annulenes

The ring current and local anisotropic contributions to the ¹H chemical shifts of [n]annuleno[m]annulenes and [n]annulenyl[m]annulenes with n, m = 12, 14, 18 and n, m = 13, 15 are calculated. The agreement between experimental and calculated shifts for the few known compounds is very good so that the predictions for the as yet unknown compounds are reliable. The effect of an annulene ring on the shifts of the protons at the other ring in these bicyclic compounds is discussed for several types of fusion of the two constituent annulenes.     

Propellanes—XLIX : Relative diels-alder reaction of an unsubstituted and a substituted diene system in propellanes and 1,6-methano[10]annulenes

The relative reactivity of an unsubstituted cyclohexadiene ring and a substituted cyclohexadiene ring within a propellane system or a 1,6-methano[10]annulene system has been studied.