Cycloaddition reactions, in particular Diels‐Alder reactions, have attracted a lot of attention from organic chemists since they represent one of the most powerful methodologies for the construction ...of carbon‐carbon bonds. In particular, inverse‐electron‐demand hetero‐Diels‐Alder reactions have been an important breakthrough for the synthesis of heterocyclic compounds. Among all their variants, the organocatalytic enantioselective version has been widely explored since the asymmetric construction of diversely functionalized scaffolds under reaction conditions encompassed within the green chemistry field is of great interest. In this review, a profound revision on the latest advances on the organocatalytic asymmetric inverse‐electron demand hetero‐Diels‐Alder reaction is shown.
In this review, a profound revision on the latest advances on the organocatalytic asymmetric inverse‐electron demand hetero‐Diels‐Alder reaction is shown.
A synthetic protocol making use of a well‐defined cationic ruthenium complex 2 enabling the racemization of enantiomerically pure secondary alcohols in the presence of a weak base (K2CO3) is ...described. The compatibility of 2 with Candida Antarctica lipase B (Novozym 435) allows the development of an efficient dynamic kinetic resolution of sec‐alcohols in the absence of an additional strong base. This procedure involves the first example of a dynamic kinetic resolution of alcohols in the presence of a cationic ruthenium catalyst. In addition, we describe the conversion of ketones to the enantioenriched acetates in a one‐pot reaction, probing the versatility of complex 2.
Milder than before: A cationic ruthenium complex (1) has been used, for the first time, in the racemization of secondary alcohols. As a pre‐activation of the catalyst by a strong base is unnecessary, the racemization reaction is performed in the presence of a catalytic amount of K2CO3. The racemization system is fully compatible with the Candida Antarctica lipase B (CAL‐B) catalyzed enzymatic kinetic resolution of secondary alcohols.
A highly efficient enantioselective inverse-electron-demand aza-Diels–Alder reaction between aza-sulfonyl-1-aza-1,3-butadienes and silyl (di)enol ethers has been developed. The presented methodology ...allows the synthesis of benzofuran-fused 2-piperidinol derivatives with three contiguous stereocenters in a highly selective manner, as even the hemiaminal center is completely stereocontrolled. Density functional theory (DFT) calculations support that the hydrogen-bond donor-based bifunctional organocatalyst selectively triggers the reaction through the ipso,α-position of the dienophile, in contrast to the reactivity observed for dienolates in situ generated from β,γ-unsaturated derivatives. Moreover, the calculations have clarified the mechanism of the reaction and the ability of the hydrogen-bond donor core to hydrolyze selectively the E isomer of the dienol ether. Furthermore, to demonstrate the applicability of silyl enol ethers as nucleophiles in the asymmetric synthesis of interesting benzofuran-fused derivatives, the catalytic system has also been implemented for the highly efficient installation of an aromatic ring in the piperidine adducts.
A very general and efficient catalytic protocol for the selective reduction of carboxylic acids to their corresponding alcohols under mild conditions is described. Various carboxylic acids, including ...benzoic acids, were reduced in good yields using the presented methodology. The ruthenium‐catalysed method yields a highly chemoselective reduction permitting the reduction of a carboxylic acid functionality in the presence of numerous other potentially reducible moieties.
Inverse‐electron‐demand hetero‐Diels‐Alder reactions have been an important breakthrough for the synthesis of heterocyclic compounds. Among all their variants, the organocatalytic enantioselective ...version has been widely explored since the asymmetric construction of diversely functionalized scaffolds under reaction conditions encompassed within the green chemistry field is of great interest. A profound revision on the latest advances on the organocatalytic asymmetric inverse‐electron demand hetero‐Diels‐Alder reaction is shown, showing in detail the mode of action of the organocatalysts. For more information, see the Minireview by J. Alemán et al. on page 12509.
A highly diastereoselective Refortmatsky reaction to N-tert-butanesulfinyl propargylaldimines and ketimines is presented. The reaction proceeded with excellent yields and diastereoselectivities ...provided by the sulfinyl group in the presence of Me3Al. The use of TBSOTf as a Lewis acid promoter switched the sense of the stereoinduction. Thus, this methodology allowed the stereodivergent asymmetric synthesis of β-alkynyl β-amino acid derivatives, from the same sulfinyl configuration, by simply changing the Lewis acid promoter.
Abstract
A general methodology for the α‐arylation of ketones using a nickel catalyst has been developed. The new well‐defined Ni(IPr*)(cin)Cl (
1 c
) pre‐catalyst showed great efficiency for this ...transformation, allowing the coupling of a wide range of ketones, including acetophenone derivatives, with various functionalised aryl chlorides. This cinnamyl‐based Ni–N‐heterocyclic carbene (NHC) complex has demonstrated a different behaviour to previously reported NHC‐Ni catalysts. Preliminary mechanistic studies suggest a Ni
0
/Ni
II
catalytic cycle to be at play.
Herein, an enantioselective desymmetrization of cyclic keto sulfonium salts through enantioselective deprotonation/ring opening process by anion-binding catalysis is presented. We report a ...squaramide/HCO3- complex as catalytic active species which is able to stereo-differentiate two enantiomeric protons, triggering the ring opening event taking advantage of the great tendency of sulfonium salts to act as leaving groups. Thus, this desymmetrization methodology give rise to β-methylsulfenylated sulfa-Michael addition type products with excellent yields and very good enantioselectivities. The bifunctional organocatalyst has been demonstrated to be capable of activating simultaneously the base and the keto sulfonium salt by DFT calculations and experimental proofs.Although anion-binding processes are well-known for their crucial role in molecular recognition, this type of phenomenon has only recently been utilized for catalysis. Here, the authors present an enantioselective desymmetrization of cyclic keto sulfonium salts through enantioselective deprotonation/ring opening process by anion-binding catalysis.
A general methodology for the α-arylation of ketones using a nickel catalyst has been developed. The new well-defined Ni(IPr*)(cin)Cl (1 c) pre-catalyst showed great efficiency for this ...transformation, allowing the coupling of a wide range of ketones, including acetophenone derivatives, with various functionalised aryl chlorides. This cinnamyl-based Ni-N-heterocyclic carbene (NHC) complex has demonstrated a different behaviour to previously reported NHC-Ni catalysts. Preliminary mechanistic studies suggest a Ni(0)/Ni(II) catalytic cycle to be at play.
An interrupted Pummerer/nickel‐catalysed cross‐coupling strategy has been developed and used in the elaboration of styrenes. The operationally simple method can be carried out as a one‐pot process, ...involves the direct formation of stable alkenyl sulfonium salt intermediates, utilises a commercially available sulfoxide, catalyst, and ligand, operates at ambient temperature, accommodates sp‐, sp2‐, and sp3‐hybridised organozinc coupling partners, and delivers functionalised styrene products in high yields over two steps. An interrupted Pummerer/cyclisation approach has also been used to access carbo‐ and heterocyclic alkenyl sulfonium salts for cross‐coupling.
Feel free to interrupt: Styrenes were activated under metal‐free conditions by an interrupted Pummerer process. The resulting stable alkenyl sulfonium salts underwent nickel‐catalysed cross‐coupling under simple, mild conditions. The versatile sequence could be carried out as a one‐pot process with a range of organozinc partners to form di‐, tri‐, and tetrasubstituted alkene products.
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