Synthesis of Furo[2,3-b]pyran-2-ones through Ag(I)- or Ag(I)–Au(I)-Catalyzed Cascade Annulation of Alkynols and α-Ketoesters

Abstract

Ag(I)- or Ag(I)-Au(I)-catalyzed cascade annulation of alkynols (5-hexyn-1-ol systems) with α-ketoesters involving a dual activation process (π and σ) has been developed for the first time. This reaction proceeds through cycloisomerization of alkynol to give the 6-endo-enol ether followed by annulation with an α-ketoester to furnish furo[2,3-b]pyran-2-ones in good yields. Chemical structures of all products were rigorously confirmed by single crystal X-ray analysis and analogy.

Intramolecular Pd‐Catalyzed Formal anti‐Carboalkoxylation of Alkynes: Access to Tetrasubstituted Enol Ethers

“…Phenolates stabilized by electron‐withdrawing groups ( 5 a – 5 c ), but also compound 5 d , which is able to eliminate carboxylate (see catalytic cycle in Scheme b), underwent this further transformation. In all cases, the corresponding ketals 6 a – 6 d were isolated in good to excellent yields (54–99 %) . The structure of ketal 6 a was confirmed by X‐ray crystallography .…”

“…In all cases, the corresponding ketals 6a-6d werei solated in good to excellent yields (54-99 %). [19] The structure of ketal 6a was confirmed by X-ray crystallography. [20] In contrast to 5d,t he corresponding TMSmaskedalkyne 5e did not undergo the domino process including the Tsuji-Trost-type rearrangement, most probably because of the b-silyl effect,w hich raises the activation barrier of this process (Scheme 3).…”

A silver-catalyzed [3 + 3]-annulation cascade of alkynyl alcohols and α,β-unsaturated ketones for the regioselective assembly of chromanes

“…They participated in the initial 1,2-addition reaction with the carbonyl functionality of α-ketoesters 3 and subsequent annulation (Scheme 1, entry b). In continuation of this work, we were curious to explore the reactivity of alkynyl alcohols 2 with readily accessible α,β-unsaturated ketones 4 employing our previously identified σ and π-dual activating 16 catalytic systems, 14,15,17 which may deliver either ketals (spiro/fused) P5 and P6 through [4 + 2]-cycloaddition (IED-HDA), or regio-isomeric chromanes P7 or 5 via [3 + 3]-annulation pathways (Scheme 1, entry c).…”

Biomimetic approach to the catalytic enantioselective synthesis of tetracyclic isochroman

“…The establishment of the enantioselective biomimetic polyketide oligomer synthesis requires the methods for the generation of isochromene and o -QM intermidiates and a catalyst capable of promoting the stereoselective HDA reaction. It is known that Au(I) complexes have been used in the cascade reactions 35 – 39 and could promote the intramolecular cyclization of benzyl alcohol-functionalized alkynes to isochromene intermediate 40 , 41 , and the o -QM intermidiate could be generated from the proper precursor in the presence of either acid or base.…”