Cyclic Allenes Up to Seven‐Membered Rings

Catalytic Formation of Five-Membered Zirconacycloallenoids and Their Reaction with Carbon Dioxide

“…All of the remaining 13 C NMR framework signals (C3, C2, C1) are in the olefinic range, although the C(2) 13 C NMR resonance is markedly shifted to lower values in comparison to those for typical allene compounds . Again, a description of the zirconacycloallenoid by the resonance structures 9a and 9a ′ seems justified (see Scheme ).…”

Strain-Activated Diels–Alder Trapping of 1,2-Cyclohexadienes: Intramolecular Capture by Pendent Furans

“…Well-known reactive intermediates based on strained unsaturated rings such as arynes and cyclohexynes have been established as valuable synthetic building blocks that undergo Diels–Alder cycloaddition and various ionic processes under mild conditions . The corresponding cyclic allenes have recently become attractive alternatives as reactants in strain-driven cycloadditions; although less strained than cyclohexynes, 1,2-cyclohexadienes still exhibit a high degree of bond angle strain, estimated at ca. 32 kcal/mol .…”

Synthesis of Imidazopyridinium-Fused Metallacycloallene via One-Pot Reaction of η2-Alkynol-Coordinated Osmacycle with 2-Aminopyridine

“…Allenes are a unique class of unsaturated compounds containing two orthogonal cumulative CC bonds, which has aroused ever-increasing interest from both experimental and theoretical chemists . The synthesis of small cyclic allenes encounters substantial challenges due to the ring strain associated with the highly distorted cumulative double bonds. , The incorporation of a metal moiety in cycloallenes has been established as an efficient strategy to release the ring strain, leading to a number of stable metallacycloallenes. As shown in Figure , the reported small metallacycloallenes can be classified into two types, in which a CH 2 group (type A ) or a CH group (type B ) of the corresponding carbocyclic analogues is formally replaced by a transition-metal fragment.…”