Metal‐Catalyzed Cycloetherification Reactions of β,γ‐ and γ,δ‐Allendiols: Chemo‐, Regio‐, and Stereocontrol in the Synthesis of Oxacycles

Abstract

Versatile routes that lead to a variety of functionalized enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines are based on chemo-, regio-, and stereocontrolled metal-catalyzed oxycyclization reactions of β,γ- and γ,δ-allendiols, which were readily prepared from (R)-2,3-O-isopropylideneglyceraldehyde. The application of Pd(II), Pt(II), Au(III), or La(III) salts as the catalysts gives controlled access to differently sized oxacycles in enantiopure form. Usually, chemoselective cyclization reactions occurred exclusively by attack of the secondary hydroxy group (except for the oxybromination of phenyl β,γ-allenic diols 3b and 3d) to an allenic carbon atom. Regio- and stereocontrol issues are mainly influenced by the nature of the metal catalysts and substituents.

Allenes in Catalytic Asymmetric Synthesis and Natural Product Syntheses

“…Since the first report of the palladium(II)-catalyzed cycloisomerization of 1,2-allenyl ketones by an oxypalladation process by Hashmi et al in 1997, [276] palladium(II)catalyzed cyclization/coupling reactions of allenoic acids, amides, allenols, allenic ketones, 1,2-allenyl phosphonic acids, and allenic amines in the presence of allylic halides, [277] or w-1-alkenyl halides, [278] alkenes, [279] alkynes, [280] allenylic alcohols or acetates, [281] allenes, [282] and bisallenes [283] have been established. These transformations allow the synthesis of a variety of different cyclic products, which are commonly observed units in natural products, with high efficiency of chirality transfer by an anti-nucleometalation mechanism (Scheme 110).…”

Recent developments in alkene hydro-functionalisation promoted by homogeneous catalysts based on earth abundant elements: formation of C–N, C–O and C–P bond

“…Appli-cation of La[N(TMS) 2 ] 3 have been tested by Alcaide et al on chiral β,γand γ,δ-allendiols leading to hydroxymethylfurane unlike Pt, Pd and Au salts. 76 In the course of studies, Dzudza and Marks et al have also reported that lanthanide triflates could be associated with ionic liquid (IL) to improve the catalytic efficiency of the functionalisation of alkenes (Scheme 25). 77 ILs have been chosen for their low volatility, their high polarity and their potential environmental benefit.…”

Silver and platinum-catalysed addition of O–H and N–H bonds to allenes

“…72 This aldehyde was not very stable, but could be trapped in situ by a stabilised Wittig reagent. The mechanism proposed for the formation of the oxidised product goes via the 6-endo oxyplatination of the activated π-complex to form, in the first instance the expected 25 (dihydropyranyl)methanol derivative.…”