A novel catalytic enantioselective tandem transetherification–intramolecular hetero Diels–Alder reaction of methyl (E)-4-methoxy-2-oxo-3-butenoate with δ,ε-unsaturated alcohols
“…The catalytic asymmetric tandem transesterification‐intramolecular hetero‐Diels−Alder reaction was investigated for a series of catalysts such as the chiral TADDOL‐Ti IV and BOX‐Cu II complexes 28b. Careful optimization revealed that the chiral BOX‐Cu(OTf) 2 complex, in the presence of molecular sieves to avoid an acid‐catalyzed reaction, afforded the trans ‐fused hydropyranopyran derivative 24 in high yield and excellent enantioselectivity [Equation (15)].…”
The recent developments of mainly catalytic and enantioselective hetero-Diels−Alder reactions of ketones are presented. First, direct reactions of unactivated ketones are presented, focusing on the recent hydrogen bond-promoted hetero-Diels−Alder reactions with activated conjugated dienes. Then, direct catalytic enantioselective hetero-Diels−Alder reactions of activated ketones with conjugated dienes are outlined. The use of different chiral copper(II) and zinc(II) catalysts are shown and the use of the hetero-Diels−Alder adducts in organic synthesis presented. Finally, the inverseelectron demand hetero-Diels−Alder reactions of α,β-unsat-
“…The catalytic asymmetric tandem transesterification‐intramolecular hetero‐Diels−Alder reaction was investigated for a series of catalysts such as the chiral TADDOL‐Ti IV and BOX‐Cu II complexes 28b. Careful optimization revealed that the chiral BOX‐Cu(OTf) 2 complex, in the presence of molecular sieves to avoid an acid‐catalyzed reaction, afforded the trans ‐fused hydropyranopyran derivative 24 in high yield and excellent enantioselectivity [Equation (15)].…”
The recent developments of mainly catalytic and enantioselective hetero-Diels−Alder reactions of ketones are presented. First, direct reactions of unactivated ketones are presented, focusing on the recent hydrogen bond-promoted hetero-Diels−Alder reactions with activated conjugated dienes. Then, direct catalytic enantioselective hetero-Diels−Alder reactions of activated ketones with conjugated dienes are outlined. The use of different chiral copper(II) and zinc(II) catalysts are shown and the use of the hetero-Diels−Alder adducts in organic synthesis presented. Finally, the inverseelectron demand hetero-Diels−Alder reactions of α,β-unsat-
“…Next, chiral Lewis acid catalysts were used in this new type of transformation. Wada et al examined the catalytic asymmetric tandem transetherification-intramolecular HDA reaction of methyl ( E )-4-methoxy-2-oxo-3-butenoate 157 with δ,ε-unsaturated alcohols 158 (Scheme 29 ) [ 113 ]. The optically active catalyst derived from the ( S , S )- tert -Bu-bis(oxazoline) and Cu(SbF 6 ) 2 in presence of molecular sieves was a highly effective Lewis acid catalyst.…”
Section: Inverse-electron-demand Hetero-diels–alder Reactions Of 1-oxmentioning
This review is an endeavor to highlight the progress in the inverse-electron-demand hetero-Diels–Alder reactions of 1-oxa-1,3-butadienes in recent years. The huge number of examples of 1-oxadienes cycloadditions found in the literature clearly demonstrates the incessant importance of this transformation in pyran ring synthesis. This type of reaction is today one of the most important methods for the synthesis of dihydropyrans which are the key building blocks in structuring of carbohydrate and other natural products. Two different modes, inter- and intramolecular, of inverse-electron-demand hetero-Diels–Alder reactions of 1-oxadienes are discussed. The domino Knoevenagel hetero-Diels–Alder reactions are also described. In recent years the use of chiral Lewis acids, chiral organocatalysts, new optically active heterodienes or dienophiles have provided enormous progress in asymmetric synthesis. Solvent-free and aqueous hetero-Diels–Alder reactions of 1-oxabutadienes were also investigated. The reactivity of reactants, selectivity of cycloadditions, and chemical stability in aqueous solutions and under physiological conditions were taken into account to show the potential application of the described reactions in bioorthogonal chemistry. New bioorthogonal ligation by click inverse-electron-demand hetero-Diels–Alder cycloaddition of in situ-generated 1-oxa-1,3-butadienes and vinyl ethers was developed. It seems that some of the hetero-Diels–Alder reactions described in this review can be applied in bioorthogonal chemistry because they are selective, non-toxic, and can function in biological conditions taking into account pH, an aqueous environment, and temperature.
“…Kumaran and co-workers later demonstrated that a chiral copper complex could promote the intramolecular IEDHDA reactions between β,γ-unsaturated ketoesters and tri-substituted neutral olefins, while, very recently, Campagne and co-workers disclosed the intramolecular IEDHDA reaction of α,β-unsaturated acyl imidazole with tri-substituted neutral olefin in the presence of a Pybox/Fe(OTf) 3 complex. Despite being efficient and highly enantioselective, these two transformations featured a very limited scope 19 , 20 . Fig.…”
Inverse-electron-demand-hetero-Diels-Alder reactions of alkenes with α,β-unsaturated keto compounds allow rapid access to the tetrahydropyran ring found in numerous natural products and bioactive molecules. Despite its synthetic interest, catalytic asymmetric versions of this process remain underdeveloped, especially regarding the use of non-activated alkenes reacting with α,β-unsaturated ketone or aldehyde, for which no report can be found in the literature. Herein, we describe the catalytic inverse-electron-demand-hetero-Diels-Alder reactions between neutral alkenes and an α,β-unsaturated ketones or aldehydes to produce a variety of trans-fused [5,6,8] tricyclic structures containing a central, chiral tetrahydropyran ring. This complex transformation, which is achieved using a chiral phosphoric acid, allows for the formation of four stereogenic centers in a single step with high regio-, diastereo- and enantioselectivity (up to 99% ee). Such level of stereocontrol could be achieved by a key remote double hydrogen atom bonding interaction between the linear substrate and the catalyst.
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