Revisitation of Cycloheptatriene Derivatives as a Building Block for Various Substituted and Fused 1,6-Methano[10]annulenes and Substituted 4,9-Methanothia[11]annulenes

Abstract

Cl Cl Br Br Br Br 1 6 4 3 2 5 7 8 9 10 11 1 Scheme 1. Vogel's first method of synthesizing 1.Abstract: A synthetic maneuver from 1,6-diacetyl-and 1,6-diformyl-1,3,5-cycloheptatrienes toward various 1,6-methano[10]annulenes, such as diaryl-substituted, cyclobutene-annulated, and thiophene-annulated derivatives and its quinodimethane-type compound, and 4,9-methanothia[11]annulenes is spotlighted based on our recent research efforts. The crystal structure analysis of the annulenes, discussion of mechanistic details of a key cyclization step and application of some annulene derivatives to a material in organic electroluminescent devices are also described.

11,11-Dimethyl-1,6-methano[10]annulene—An Annulene with an Ultralong CC Bond or a Fluxional Molecule?

“…The PEC is still obtained in a SW+1S form where 2b is now 11.5 rather than 5.3 kcal/mol higher in energy than the annulene form at the potential minimum at R = 2.256 Å (X-ray: 2.235 Å). The corresponding Δ H (298) and Δ G (298) values are 10.2 and 10.3 kcal/mol, respectively, in line with experimental observations. − ,− ,− ,,, Clearly, 2 has to be considered as [10]annulene rather than a bicyclic, homoaromatic π-system because R = 2.256 Å is too large to lead to sizable through-space interactions …”

“…The corresponding ΔH(298) and ΔG(298) values are 10.2 and 10.3 kcal/mol, respectively, in line with experimental observations. [24][25][26][27][29][30][31][33][34][35]37,47,48 Clearly, 2 has to be considered as [10]annulene rather than a bicyclic, homoaromatic π-system because R = 2.256 Å is too large to lead to sizable throughspace interactions. 10 These results show clearly that CCSD(T) and BD(T), although they may account for some nondynamical effects besides the dynamical electron correlation effects, fail to describe the TS region and 3b correctly, which can also be observed for 2b, as too much stability is assigned to the norcaradiene forms.…”

“…The target system 1 investigated in this work (see Figure ) belongs to the group of bridged [10]annulenes, the parent member of which, 1,6-methano[10]annulene ( 2 ), was first synthesized by Roth and Vogel in 1964 . Annulene 2 was experimentally characterized as an aromatic 10π-system fulfilling the Hückel 4 n + 2 rule, however with a distorted ring perimeter and a C1C6 distance R of 2.235 Å; , that is, it adopts structure 2a rather than that of the bisnorcaradiene (tricyclo[4.4.1.0 1,6 ]undeca-2,4,7,9-tetraene) form 2b (see Figure ), as was verified in dozens of experimental investigations − as well as computational investigations. ,− Therefore, it was an unexpected result when in the early 1970ies the 11,11-dimethyl derivative 1 , also synthesized by the Vogel group, was found to adopt according to X-ray diffraction studies a “tricyclic” structure with an R value close to 1.8 Å (1.827 and 1.771 due to 2 molecules in the unit cell) that speaks in favor of structure 1b rather than 1a . With the discovery that the corresponding 11-cyano-11-methyl derivative had similar R values and the dicyano derivative had even an R value of 1.558 Å, , the existence of a bisnorcaradiene form was fully confirmed.…”