The Effect of Lewis Acids on the Cycloaddition of 3,3,6‐Trimethylcyclohex‐5‐ene‐1,2,4‐trione: Hydrogen Transfer versus Cycloaddition with Cyclopentadiene

Abstract

Exposure of 3,3,6-trimethylcyclohex-5-ene-1,2,4-trione to catalytic amounts of Lewis acids revealed two disparate reactions in the presence of cyclopentadiene. The expected cycloaddition was found to be reversible for the title com-

The Golden Age of Transfer Hydrogenation

“…Reports on catalytic TH involving Lewis acids, ferrocenylimidazolium salts, and bases , have also recently appeared.…”

Perfluoroalkylated Main‐Group Element Lewis Acids as Catalysts in Transfer Hydrogenation

“…Different Lewis acids as catalysts have been screened in the reaction of a cyclohexenetrione derivative with cyclopentadiene. [10] A diamidocarbene derivative has been shown to facilitate transfer hydrogenation of 1,4-cyclohexadiene and 9,10-dihydrophenanthrene. [11] The electrophilic phosphonium cation [P(C 6 F 5 ) 3 F] + catalyzes the dehydrocoupling and simultaneous hydrogenation of olefins.…”

“…Recently, the range of suitable catalysts has been extended to include strong Lewis acids. Different Lewis acids as catalysts have been screened in the reaction of a cyclohexenetrione derivative with cyclopentadiene . A diamidocarbene derivative has been shown to facilitate transfer hydrogenation of 1,4‐cyclohexadiene and 9,10‐dihydrophenanthrene .…”

Transition‐Metal‐Catalysed Transfer Hydrogenation Reactions with Glycerol and Carbohydrates as Hydrogen Donors

“…Nevertheless, in the case of TH, sacrificial hydrogen donors are utilised, which are easily accessible, inexpensive, and commercially available. [10] Numerous advancements have been made in this field using homogeneous, [11][12][13][14][15][16] heterogeneous catalysts, [13,[17][18][19][20][21][22] organocatalysts, [23,24] Lewis acids [25] and bases [26,27] including asymmetric TH reactions. [28][29][30][31][32] Although several hydrogen donors have been studied in TH reactions, non-toxic and renewable hydrogen sources are highly fascinating in the rise of green chemistry.…”

“…Nevertheless, in the case of TH, sacrificial hydrogen donors are utilised, which are easily accessible, inexpensive, and commercially available [10] . Numerous advancements have been made in this field using homogeneous, [11–16] heterogeneous catalysts, [13,17–22] organocatalysts, [23,24] Lewis acids [25] and bases [26,27] including asymmetric TH reactions [28–32] …”