Synthesis of (E,E)-Dienones and (E,E)-Dienals via Palladium-Catalyzed γ,δ-Dehydrogenation of Enones and Enals

Abstract

A new strategy for the synthesis of conjugated (E,E)-dienones and (E,E)-dienals via a palladium-catalyzed aerobic g,d-dehydrogenation of enones and enals has been developed. The method can be employed in the direct and efficient synthesis of various (E,E)-dienones and (E,E)-dienals, including nonsubstituted a-, band nd g-and/or d-substituted (E,E)-dienones and (E,E)-dienals. The protocol is featured by the ready accessibility and elaboration of the starting materials, good functional group compatibility, and mild reaction conditions. Furthermore, the reaction is of complete E,E-stereoselectivity and uses molecular oxygen as the sole clean oxidant.

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes: synthesis of (E,E)-dienamides

“…The broad synthetic utility and important biological potential of this structure have resulted in numerous methods for the efficient synthesis of these useful dienamide compounds. The traditional methods to access conjugated dienamides include: the alkenylation reactions of carbonyl compounds, such as the Wittig reaction and its variants; 1 e ,3 the dehydrogenation of unsaturated amides; 4 and other reactions. 5 Multistep synthesis is usually needed for these reactions.…”

Synthesis of 2,3-Benzotropones via Palladium(II)-Catalyzed Aerobic Dehydrogenation from 1-Benzosuberones and Sequential Diels–Alder Reaction to Yield Benzobicyclo[3.2.2]nonenones

“…First, 1-benzosuberone 1a reacts with Pd­(II) to form palladium­(II) enolate A . Pd­(II)-catalyzed dehydrogenation converts 1-benzosuberone 1a into 8,9-dihydro-5-benzocycloheptenone 2a via β-hydride elimination. , α,β-Unsaturated carbonyl structure 2a can be activated by palladium to afford π-allylpalladium intermediate B , which can generate γ-palladation enone C . β-Hydride elimination yields α,β,γ,δ-unsaturated carbonyl product 3a , and the Pd(0) species is regenerated to Pd­(II) through oxidation under molecular oxygen conditions .…”

Sequential hydrozirconation/Pd-catalyzed cross coupling of acyl chlorides towards conjugated (2E,4E)-dienones

“…As outlined in Scheme 2 , a variety of methods has been reported for the synthesis of conjugated dienones, mostly via addition/elimination reactions such as Knoevenagel condensation or Claisen–Schmidt condensation of enals 6 with aldehydes 7a or ketones 7b [ 6 – 11 ], isomerization of alkynones 8 [ 12 – 15 ], Horner–Wadsworth–Emmons reaction of unsaturated phosphonates 9 and aldehydes 10 [ 16 – 17 ], and dehydrogenation of enones 11 [ 18 ]. Further, Claisen rearrangement of vinyl propargylic ethers 12 [ 19 ] and metal-catalyzed cross coupling of alkenes 13 and enones 14 [ 20 – 21 ] have been reported.…”

“…However, these reactions face multiple disadvantages such as limited substrate scope, use of hazardous solvents and harsh reaction conditions such as high temperatures or acidic/basic conditions, which might be incompatible with existing functional groups and/or the stereochemical integrity [ 18 , 22 ]. Especially in natural product synthesis, dienone functional groups suffer from isomerization and polymerization [ 23 ].…”