Spirokonjugation

Abstract

Professor Georg Wittig gewidmetSpiroverbindungen mit senkrecht zueinander angeordneten n-Elektronensystemen (,,Spire-polyene") weisen eine neue Art der Homokonjugation auf, die als Spirokonjugation bezeichnet wird. Spiro-polyene sind z. B. durch Cycloaddition, durch Eliminierung von Distickstoff aus 1,2-Diazaspiro-polyenen und durch Cyclisierung von Carbeniumionen oder Carbanionen gut zuganglich. Die GroBe des Effektes, den die Spirokonjugation bewirkt, wird durch Modellrechnungen abgeschatzt. Der Nachweis gelingt u. a. durch Vergleich der Elektronen-und Photoelektronenspektren von Spiro-polyenen und analogen Verbindungen, die nicht die' Moglichkeit zu dieser Wechselwirkung haben. Synthesen von Spiro-polyenen CycloadditionSpiroverbindungen konnen im Prinzip auf sehr einfache Weise synthetisiert werden. Als allgemeines Reaktionsprinzip Angew. Chem. 90,591 601 ( 1 9 7 8 ) Angew. Chem. 90.591-601 (1978)

A Spiro‐Fused Triarylaminium Radical Cation with a Triplet Ground State

“…By consideration of symmetry it can be deduced that the two fragment MOs can interact with each other only when they are antisymmetric (AA) to both planes. [7] The fragment MOs of a triarylamine such as 1 indeed have AA symmetry, as illustrated in Figure 2. Hence, the resulting HOMO for 1 is expected to be doubly degenerate.…”

“…[3] With regard to molecule-based magnetism, Dougherty et al elaborately examined the possibility of generating 1,4,6,9-spiro [4.4]nonatetrayl. [6] From the viewpoint of magnetic interaction, the spin preference in spirobiradicals is determined by the balance between two contributions: 1) the two perpendicular p systems, which favor ferromagnetic interaction resulting from the degeneracy of the magnetic orbital derived from the two ring systems, and 2) so-called spiroconjugation, [7] which can lift the degeneracy of the two magnetic orbitals and thus lead to a singlet spin state. [6] From the viewpoint of magnetic interaction, the spin preference in spirobiradicals is determined by the balance between two contributions: 1) the two perpendicular p systems, which favor ferromagnetic interaction resulting from the degeneracy of the magnetic orbital derived from the two ring systems, and 2) so-called spiroconjugation, [7] which can lift the degeneracy of the two magnetic orbitals and thus lead to a singlet spin state.…”

“…[4,5] Recently, Frank et al reported the synthesis of a spiro-fused bis(nitronyl nitroxide) biradical and the magnetic interaction between the two radical centers. [6] From the viewpoint of magnetic interaction, the spin preference in spirobiradicals is determined by the balance between two contributions: 1) the two perpendicular p systems, which favor ferromagnetic interaction resulting from the degeneracy of the magnetic orbital derived from the two ring systems, and 2) so-called spiroconjugation, [7] which can lift the degeneracy of the two magnetic orbitals and thus lead to a singlet spin state. In fact, the biradical reported in ref.[3] exhibited a weak antiferromagnetic interaction, probably because of the second contribution.…”

para‐Phenylene‐Bridged Spirobi(triarylamine) Dimer with Four Perpendicularly Linked Redox‐Active π Systems

“…[16] When both fragment MOs are antisymmetric to only one of the two symmetry planes (AS and SA), the orbital degeneracy gives rise to a parallel spin alignment between two unpaired electrons; when both fragment MOs are antisymmetric to both symmetry planes (AA), so-called spiro conjugation lifts the orbital degeneracy and thus leads to an antiparallel spin alignment between two unpaired electrons. With regard to the spin preference in spirobiradicals, Dougherty and coworkers examined the possibility of generating 1,4,6,9-spiro-A C H T U N G T R E N N U N G [4,4]nonatetrayl from both theoretical and experimental points of view, [4,5] and Kahn and co-workers reported the synthesis of a spiro-fused bis(nitronyl nitroxide) and the weak intramolecular antiferromagnetic interaction (J intra / k B = À5.8 K) between the two radical centers, which is probably due to the spiro conjugation.…”

ICl‐Induced Intramolecular Electrophilic Cyclization of 1‐[4′‐Methoxy(1,1′‐biphenyl)2‐yl]alkynones—A Facile Approach to Spiroconjugated Molecules

“…Base [mol %] Solvent Yield of 3 a [%] [b] 1 [c] no base CH 3 [d] Na 2 HPO 4 CH 3 CN 69 10 [e] Na 2 HPO 4 CH 3 CN 99 11 [e] no base CH 3 CN 88…”