Lignans neolignans, and related compounds

Biomimetic Synthesis of Lignans

“…Of these, Ag 2 O and Ag 2 CO 3 are the most commonly employed metal catalysts, and HRP-H 2 O 2 is the most common enzyme-mediated system [3][4][5][6][7][8][9][10][11][12][13][14].…”

“…In this instance, the application of CuSO 4 under an O 2 atmosphere in aqueous acetone perfected the reaction to deliver racemic (±)-43 in 90% yield (Scheme 18.6) [43]. In recent years, Tl III and Mn III metal species have proven equally effective in promoting high yielding β -β phenolic couplings for the biomimetic synthesis of racemic furofurans [3][4][5][6][7][8][9][10][11][12][13][14]32]. …”

“…To date, all benzoxanthenones identified have been isolated as single diastereomers, and produced in Nature as racemates. The first member of this class, carpanone (18) was isolated along with an ortho-methoxystyrene named carpacin (48). Brophy of carpacin to produce 49, β -β phenolic coupling to deliver trans-ortho-quinone methide 50, followed by an endo-selective inverse electron demand Diels-Alder to afford carpanone (18) (Scheme 18.7).…”

“…This chapter will focus on the biomimetic synthesis of lignans. In Nature, lignan chemotypes 4-14 are produced as either racemates (though usually a single diastereomer) or, in some cases, as single enantiomers [3][4][5][6][7][8][9][10][11][12][13][14]. In Scheme 18.2 One-electron oxidation of (E)-coniferyl alcohol (19) to multiple quinone methide mesomeric radicals 21-23, which combine to give rise to neolignans (coupling products other than .…”

“…This lack of stereocontrol is observed with both metal-catalyzed (Ag I , Mn II , I III , Cu II , Co II , Fe II ) oxidative phenolic couplings as well as enzyme-mediated [horse radish peroxidase (HRP), laccases, oxidases] oxidative phenolic couplings [3][4][5][6][7][8][9][10][11][12][13][14]. In Nature, the stereochemical outcome of these radical couplings is somehow controlled to provide enantiopure lignans.…”