Recent Biomimetic and Organocatalytic Syntheses of ?-Tocopherol

Abstract

Abstract:Wereporthereonoureffortstodevelopnewstrategiesforthesynthesisofa-tocopherol,thebiologicallymostsignificantmemberofthevitaminEfamily.Thisreviewcomprisesfivenewmethodstogeneratethechiral chromaneofa-tocopherolwithoverallupto29%yieldfromcommerciallyavailablematerialandupto94%de.

Copper(II) Complexes of Sulfonated Salan Ligands: Thermodynamic and Spectroscopic Features and Applications for Catalysis of the Henry Reaction

“…The reaction of nitroalkanes with aldehydes or ketones is a synthetically useful reaction resulting in β-nitro alcohols, which can yield important compounds upon further transformations (e.g., nitroalkenes by dehydration or β-amino alcohols via reduction). − ,, The reaction is catalyzed by various bases; however, transition-metal catalysts are used increasingly, especially for the enantioselective synthesis of β-nitro alcohols. Copper complexes were found to be effective catalysts in this reaction. ,,,, The Henry reaction of benzaldehyde with nitromethane (Scheme ) is often studied to establish the basic catalytic properties of new types of catalysts. − …”

“…Below we report the equilibrium and structural study of copper­(II) complexes with several HSS-type ligands, as shown in Scheme . Furthermore, the catalytic activity of these complexes was also studied in aqueous media in the Henry or nitroaldol reaction of aldehydes and nitroalkanes, a synthetically important C–C bond-forming process. − …”

Regioselective and Enantioselective Domino Aldol–Oxa‐Michael Reactions to Construct Quaternary (Chroman) Stereocenters

“…Nevertheless, direct enantioselective processes are rare and mainly achieved by using chiral transition-metal complexes (Pd, [13] Ru, [14] Au, [15] or Pt [16] ) or organocatalysts. [1,17,18] Previously, we developed a diastereoselective domino aldol-oxaMichael reaction between a salicylaldehyde (A) and an α,β-unsaturated aldehyde (B) as a key step using a Jorgensen/ Hayashi catalyst (R)-1 (TES = triethylsilyl) to achieve the total synthesis of α-tocopherol (Scheme 1). [19] The synthetic methodology was further successfully applied to synthesize other chroman-related natural products.…”

“…Therefore, continuous efforts including catalytic synthesis methods, to build such stereogenic centers have been made in recent years. Nevertheless, direct enantioselective processes are rare and mainly achieved by using chiral transition‐metal complexes (Pd,13 Ru,14 Au,15 or Pt16) or organocatalysts 1,17,18. Previously, we developed a diastereoselective domino aldol–oxa‐Michael reaction between a salicylaldehyde ( A ) and an α,β‐unsaturated aldehyde ( B ) as a key step using a Jorgensen/Hayashi catalyst ( R )‐ 1 (TES = triethylsilyl) to achieve the total synthesis of α‐tocopherol (Scheme ) 19.…”

Aufbau quartärer Chroman‐Stereozentren durch asymmetrische Redox‐Organokatalyse: ein neuer Zugang zu Vitamin E

“…[6] Woggon und Mitarbeiter konnten in einer Domino-Aldol-oxa-Michael-Reaktion als organokatalytischem Schlüsselschritt das tertiäre ChromanolStereozentrum aufbauen und gleichzeitig die chirale Seitenkette anfügen. [7] Auch diese eleganten Zugänge liefern insgesamt oder teilweise ausgezeichnete Selektivitäten, nachteilig schlagen jedoch z. B. die aufwendige Herstellung der Ausgangsstoffe, vielstufige Vervollständigung der Synthesesequenz oder hohe Katalysatorbeladung zu Buche.…”