Untersuchungen an Siebenring-Systemen, VIII. Darstellung und Reaktivität konformationsisomerer Tetraphenyl-tribenzocycloheptatriene (1.2.3.4-Tetraphenyl-9 H-tribenzo-[a.c.e]cycloheptene)

TLDR: The tetraphenyl-tribenzocycloheptene (1.2.3.4-9H-tibenzo) series has a very high energy barrier for ring inversion (ΔG≠ ≧ 31 kcal/Mol) as discussed by the authors.

Abstract: Die Darstellung, Spektren und Reaktionen von konformationsisomeren Tetraphenyl-tribenzocycloheptatrienen (1.2.3.4-Tetraphenyl-9H-tribenzo[a.c.e]cycloheptenen. 1–3, 5–7) werden beschrieben. Aufgrund der hohen Energiebarriere fur die Ringinversion des zentralen Siebenringes (ΔG≠ ≧ 31 kcal Mol) ist es moglich, Konformere A und B mit quasi-aquatorialen und quasi-axialen Substituenten zu isolieren. Derivate des Typs A erweisen sich bei Solvolyse-Versuchen als -reaktionstrage, was z. B. die Isolierung des Chlorosulfits 2A ermoglicht. Andererseits gehen die Konformeren B leicht nucleophile Substitutionen unter bevorzugter Konformationserhaltung ein. Die konformativ bedingten Reaktivitatsunterschiede sowie die Struktur des „Tetraphenyl-tribenzotropylium-Ions 10” werden an Hand von Modellbetrachtungen diskutiert. Studies on Seven-Membered Ring Systems, VIII. Preparation and Reactivity of the Conformational Isomers in the Tetraphenyl-tribenzocycloheptatriene (1.2.3.4-Tetraphenyl-9H-tribenzo[a.c.e]cycloheptene) Series The synthesis, spectra and reactions of conformational isomers in the tetraphenyl-tribenzocycloheptatriene (1.2.3.4-tetraphenyl-9H-tribenzo[a.c.e]cycloheptene) series (1–3, 5–7) are described. It is possible to isolate the conformational isomers A and B with quasi-equatorial and quasi-axial substituents, because the central seven-membered ring system shows a very high energy barrier for ring inversion (ΔG≠ ≧ 31 kcal/Mol). Compounds of the type A are remarkably stable under solvolysis conditions; as a consequence the chlorosulfite 2A can be isolated. On the other hand, conformers of the type B readily undergo nucleophilic substitutions with high retention of conformation. These remarkable reactivity differences between the conformational isomers and the structure of the tetraphenyl-tribenzotropylium ion 10 are discussed on the basis of model considerations.