New Spironorcaradienes. — Demonstration of a Reversible Norcaradiene‐Cycloheptatriene Valence‐Isomerization

Abstract

8] Further, no fluorescence is at first observed on 253.7-nm irradiation of ( l a ) and ( I b ) or ( 3 a ) and ( 3 b ) although indistinctly fluorescing by-products are formed on prolonged irradiation.[9] All the new compounds were characterized by elemental analysis and spectroscopic techniques. [lo] H! Tochtermann, K . Oppi,nliinder, and M . Nguyen-Duong Hoang,Liebigs Ann. Chem. 701, 117 (1967); H . Prinzbach, P. Wiirsch, P. Vogel, W Tochtermann, and C . Franke, Helv. Chim. Acta 51, 911 (1968); cf. footnote 10 in [Zb]. We thank Dr. W Tochtermann for a gift of (1 b ) and

Persistent Triplet Carbenes

“…124 FL reacts with benzene to give the equilibrating norcaradiene-cycloheptatriene mixture. 179 All of those behaviors are completely different from that observed for DPC (vide supra). FL is necessarily planar, but DPC being both bent and twisted may experience severe steric interaction in the transition state of the reaction.…”

“…There is no crossover product present in the FL−cyclohexane adduct when generated in an equimolecular mixture of cyclohexane and cyclohexane- d 12 . FL reacts with benzene to give the equilibrating norcaradiene−cycloheptatriene mixture …”

A New Spirocyclic System: Synthesis of a Silaspirotropylidene

“…Several spirotropylidenes having the ring structure shown as 1 were synthesized by Dürr and co-workers almost 30 years ago. , Although these compounds possess 10 π-electrons and so might be regarded as homoaromatic, they are actually rather unstable. NMR studies showed that all of the compounds of type 1 were in equilibrium with their spironorcaradiene valence isomers ( 2 ). , To our knowledge, no heteroatom-containing rings of type 1 or 2 have appeared in the literature.…”