1,4‐Cyclohexadienes—Easy Access to a Versatile Building Block via Transition‐Metal‐Catalysed Diels–Alder Reactions

Abstract

1,4-Cyclohexadiene derivatives are easily accessed via transition-metal cycloadditions of 1,3-dienes with alkynes. The mild reaction conditions of several transition-metal-catalysed reactions allows the incorporation of various functional groups to access functionalised 1,4-cyclohexadienes. The control of the regiochemistry in the intermolecular cobalt-catalysed Diels-Alder reaction is realised utilising different ligand designs. The functionalised 1,4-cyclohexadiene derivatives are valuable building blocks in follow-up transformations. Finally, the oxidation of the 1,4-cyclohexadienes can be accomplished under mild conditions to generate the corresponding arene derivatives.

Indium Tribromide‐Catalysed Transfer‐Hydrogenation: Expanding the Scope of the Hydrogenation and of the Regiodivergent DH or HD Addition to Alkenes

“…Dihydroaromatic compounds are relatively sensitive towards air and other mild oxidising agents and can be converted easily into the corresponding arenes. [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ] Based on these characteristics, dihydroaromatic compounds have found various applications[ 10 , 11 , 12 , 13 , 14 , 15 ] and the use as a surrogate for molecular hydrogen is one of the most prominent examples. [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ] Other applications of substituted 1,4‐cyclohexadienes are the transfer of HBr, [24] HCN[ 25 , 26 ] and many other hydrofunctionalisation reactions to transfer various groups[ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ] to unsaturated starting materials, which have been summarised recently.…”

Development and Applications of Double Diels‐Alder Reaction in Organic Synthesis

“…[20] Since then, numerous methods have been developed to accelerate the cycloaddition pathways, mainly, modified Lewis acid-catalysis systems and transition metal-promoted cycloadditions were evolved drastically. [21][22][23] It was concluded that, the reactivity of DA reaction depends on the energy separation gap between HOMO-LUMO of reacting partners, whereas, the factors affecting in lowering the energy gap certainly increase the rate of reaction. Nevertheless, Lewis-acid assistance accompanying intrinsic parameters such as steric and electronic factors were found to be practical to reduce the HOMO-LUMO gap and consequently allows reaction to proceed under milder conditions.…”

Synthesis of 1,4‐Cyclohexadiene Carboxylates through a Formal [2+4]‐Cycloaddition of Propiolates under Cobalt Catalysis

“…A catalytic system largely used by Hilt and coworkers for cycloadditions and hydrovinylations consists of a Co(II) pre‐catalyst, a chelating phosphine ligand and an external reductant [17] . This methodology has been used for the formal cycloaddition reaction between alkynes with dienes to form 6‐membered rings either with electron‐rich substituents or with subsequent in situ derivatization of the final products [18–26] . Based on this system, we decided to expand the scope of this method to substituted propiolates as dienophiles.…”