Synthesis of hexahydroisoindole-3a-carboxylates by IMDA reaction of Morita–Baylis–Hillman adduct-derived dienes bearing a Z-alkenyl tether

An intramolecular Diels–Alder (IMDA) reaction of Morita–Baylis–Hillman adduct-derived dienes bearing a Z-alkenyl dienophile tether afforded hexahydroisoindole-3a-carboxylates in excellent yields and stereoselectivity.     

Synthesis of 1H-benzo[g]indazole derivatives: propargyl–allenyl isomerization and 6π-electrocyclization involving two aromatic π-bonds

An efficient synthesis of 1H-benzo[g]indazoles starting from Morita–Baylis–Hillman (MBH) adducts is disclosed. The synthesis was carried out from MBH bromide via a sequential copper-catalyzed alkynylation, one-pot synthesis of pyrazole, propargyl–allenyl isomerization, and a 6π-electrocyclization involving two aromatic π-bonds and an allenyl π-bond.     

Enantioselective Morita–Baylis–Hillman reaction catalyzed by a chiral phosphine oxide

An application of a hypervalent silicon complex, generated from a chiral phosphine oxide catalyst and silicon tetrachloride, to the enantioselective organocatalytic Morita–Baylis–Hillman reaction is described. A chloride anion liberated from the hypervalent silicon complex smoothly generated a γ-chloro silyl enol ether that subsequently reacted with an aldehyde to afford the Baylis–Hillman adducts in good yields and with good enantioselectivities.     

Catalytic asymmetric one-pot synthesis of α-methylene-γ-lactams

An organocatalytic enantioselective synthesis of α-methylene-γ-lactams has been developed. The reaction between protected 2-aminomalonates and Morita–Baylis–Hillman carbonates is catalyzed by chiral Lewis bases to afford the corresponding lactams in excellent yields and moderate to good enantioselectivities, after work-up.     

An easy access to halogenated and non-halogenated spiro-hexadienones

We describe an improved protocol for the synthesis of spiro-hexadienones from Morita–Baylis–Hillman adducts. Solvent modification and temperature resulted in a significant increase in the yield. This protocol was used to synthesize mono- and dibrominated spiro-hexadienones in good overall yields. This report is the first to describe the synthesis of halogenated spiro-hexadienones from Morita–Baylis–Hillman adducts.     

Highly regioselective synthesis of 3-alkylthio-2-oxindoles via DABCO-catalyzed allylic α-substitution of Morita–Baylis–Hillman carbonates of isatins with various thiols

The first Lewis base-catalysed allylic sulfuration of Morita–Baylis–Hillman (MBH) adducts derived from ketones (isatins) has been developed, which affords C3-quaternary oxindole derivatives bearing thio-group at 3-position in good to excellent yield (up to 98% yield) under mild reaction conditions. Significantly, the potential utility of the protocol also has been demonstrated by gram-scale synthesis of 3-alkylthio-2-oxindole (3ae), a low catalyst loading (0.3 mol %) and facile conversion of resulting product (3ad) into functionalized pyrrolidinone (5ad).     

Solvent-dependent Baylis–Hillman reactions for the synthesis of 3-benzyl-3-hydroxyoxindoles and benzo-δ-sultams

We have developed a solvent-dependent method for the preparation of novel benzo-δ-sultam and 3-benzyl-3-hydroxy-N-methyloxindole scaffolds. A variety of 3-(methoxy(phenyl)methyl)-1-methyl-1H-benzo-[c][1,2]thiazine 2,2-dioxides and 3-benzyl-3-hydroxy-1-methylindolin-2-ones were obtained in moderate to high yields via DBU-catalyzed Baylis–Hillman reaction of a number of (E)-N-(2-formylphenyl)-N-methyl-2-phenylethenesulfonamides in DMF and MeOH, respectively. The proof of the structures relies on analytical investigation and X-ray crystallography. Whereas reaction of (E)-N-(2-formylphenyl)-N-methyl-2-phenylethenesulfonamides in MeOH presumably proceeds through intramolecular Baylis–Hillman/dehydration, 3-hydroxy-N-methyloxindoles seem to have been generated via intramolecular Baylis–Hillman/1,3-H shift/oxidation/intramolecular cyclization tandem sequences in DMF.     

The Morita–Baylis–Hillman reaction for non-electron-deficient olefins enabled by photoredox catalysis

A strategy for overcoming the limitation of the Morita–Baylis–Hillman (MBH) reaction, which is only applicable to electron-deficient olefins, has been achieved via visible-light induced photoredox catalysis in this report. A series of non-electron-deficient olefins underwent the MBH reaction smoothly via a novel photoredox-quinuclidine dual catalysis. The in situ formed key β-quinuclidinium radical intermediates, derived from the addition of olefins with quinuclidinium radical cations, are used to enable the MBH reaction of non-electron-deficient olefins. On the basis of previous reports, a plausible mechanism is suggested. Mechanistic studies, such as radical probe experiments and density functional theory (DFT) calculations, were also conducted to support our proposed reaction pathways.

A strategy for overcoming the limitation of the Morita–Baylis–Hillman (MBH) reaction, which is only applicable to electron-deficient olefins, has been achieved via visible-light induced photoredox catalysis in this report.     

A general,flexible, ring closing metathesis (RCM) based strategy for accessing the fused furo[3,2-b]furanone moiety present in diverse bioactive natural products

A simple and straightforward methodology of general utility to construct sterically encumbered furo[3,2-b]furanone scaffolds present in a diverse range of bioactive natural products is delineated. The methodology emanates from readily available Morita–Baylis–Hillman adducts and employs sequential ring closing metathesis and oxy-Michael addition cascade as the key steps.     

Stereoselective synthesis of benzofulvenes via a palladium-catalyzed cyclization of 1,3-dienes derived from Morita–Baylis–Hillman adducts

A facile synthesis of benzofulvenes was carried out starting from the Morita–Baylis–Hillman adducts of 2-bromobenzaldehyde. The synthesis was carried out via the sequential bromination, Wittig reaction with aldehyde, and Pd-catalyzed intramolecular Mizoroki–Heck reaction. The stereochemistry of benzofulvenes was dependent on the reaction condition, especially on the kinds of base and reaction time, and the substituent of starting materials.     

Studying the reactivity of alkyl substituted BODIPYs: first enantioselective addition of BODIPY to MBH carbonates

The first enantioselective addition of alkyl BODIPYs to Morita–Baylis–Hillman (MBH) carbonates is reported. This is the first reported enantioselective methodology using the methylene position of BODIPYs as a nucleophile. The reaction is efficiently catalyzed by cinchona alkaloids, achieving high enantioselectivities and total diastereoselectivity. The use of cinchona alkaloid pseudo enantiomers (chinine/cinchonine) allows us to obtain both pairs of enantiomers in similar yields and enantioselectivities, a common issue in this type of reaction. The photophysical study of these dyes (absorption and fluorescence) has been performed in order to determine their parameters and explore future possible application in bioimaging. In addition, electronic circular dichroism (ECD) studies supported by time-dependent density functional theory (TD-DFT) calculations were also performed.

The first enantioselective addition of alkyl BODIPYs to Morita–Baylis–Hillman (MBH) carbonates is reported.     

Synthetic studies on polymaxenolides: model studies for constructing dihydropyran portion and synthesis of lower portion

With a goal of the total synthesis of polymaxenolide, the first hybrid marine natural product, the model studies for constructing the dihydropyran portion based on the originally proposed biosynthesis (C–C bond formation followed by dehydrative cyclization) and the synthesis of the lower portion (the C1–C3, C7–C17 portion) based on an iodide-induced Morita–Baylis–Hillman type reaction (a three-component assembly) followed by Suzuki–Miyaura cross-coupling are described.     

Valine-derived phosphinothiourea as organocatalyst in enantioselective Morita–Baylis–Hillman reactions of acrylates with aromatic aldehydes

A new type of chiral bifunctional phosphinothiourea derived from l-valine is synthesized and used as an organocatalyst in the enantioselective Morita–Baylis–Hillman reaction of aromatic aldehydes with acrylates. The desired products were obtained in good enantioselectivities (up to 83% ee) and in excellent yields (up to 96%) under mild reaction conditions.     

Study of the stereoselectivity of the nucleophilic epoxidation of 3-hydroxy-2-methylene esters

The diastereoselectivity of the nucleophilic epoxidation of 3-hydroxy-2-methylene esters has been studied. The 3-hydroxy-2-methylene esters were obtained through a Morita–Baylis–Hillman reaction. The resulting epoxyesters were treated with thiophenol for transformation into 2,3-dihydroxy-2-((phenylthio)methyl), which upon treatment with triphosgene afforded the corresponding cyclic carbonates.     

Diastereoselective Mukaiyama aldol reaction of (N-alkyl) isatins with 2-(trimethylsilyloxy)furan by using lanthanum triflate

An efficient vinylogous Mukaiyama aldol reaction (VMAR) of 2-(trimethylsilyloxy)furan with various (N-alkyl)isatins is described in the presence of lanthanum(III) triflates (5 mol %). The reaction proceeds rapidly and affords the corresponding 3-hydroxy-(5-oxo-2,5-dihydrofuran-2-yl)indolin-2-one in high yields with good diastereoselectivities (threo:erythro ratio up to ≤95:5).     

A tactical approach for the synthesis of novel β-lactam-substituted,polycyclic-fused isoxazolidine derivatives via an intramolecular [3+2] cycloaddition reaction

The synthesis of functionalized β-lactam-substituted, tricyclic chromenoisoxazolidine and tetracyclic naphthopyranoisoxazolidine derivatives by intramolecular nitrone cycloaddition reaction is described. The O-allyl hydroxyaldehyde derivatives, obtained from Baylis–Hillman adducts (BHA) derived from β-lactam aldehyde underwent intramolecular cycloaddition reaction to give β-lactam-substituted, polycyclic isoxazolidine derivatives in good yield. All the products were confirmed by spectral analysis. The products with a β-lactam substituent may find good applications in biological chemistry.     

Access to P-chiral sec- and tert-phosphine oxides enabled by Le-Phos-catalyzed asymmetric kinetic resolution

The synthesis of P-stereogenic building blocks is extremely difficult. Herein we report an efficient kinetic resolution of secondary phosphine oxides via a Le-Phos-catalyzed asymmetric allylation reaction with Morita–Baylis–Hillman carbonates. This method provides facile access to enantioenriched secondary and tertiary P-chiral phosphine oxides with broad substrate scope, both of which could serve as P-stereogenic synthons, and can be rapidly incorporated into a given scaffold bearing a P-stereocenter. The highly desirable late stage modifications demonstrate the practicability of our method and can be a critical contribution to obtaining optimal P-chiral catalysts and ligands.

Herein we report an efficient kinetic resolution of secondary phosphine oxides via a Le-Phos-catalyzed asymmetric allylation reaction with Morita–Baylis–Hillman carbonates.     

Organocatalytic formal [5+1] annulation: diastereoselective cascade synthesis of functionalized six-membered spirocyclic indane-1,3-diones/oxindoles via Michael–aldol reaction

An efficient cascade protocol has been developed for the diastereoselective synthesis of functionalized six-membered spirocyclic compounds. The reaction proceeded smoothly between indane 1,3-diones/oxindoles/coumaranone as the dinucleophilic components and (E)-5-nitro-6-aryl-hex-5-en-2-one as the dielectrophile to give the desired products with reasonable to high chemical yields (30–84%) and high levels of diastereoselectivities (upto >95:5 dr). The reaction proceeded smoothly via cascade Michael–aldol reaction.     

Bifunctional chiral phosphine-containing Lewis base catalyzed asymmetric Morita–Baylis–Hillman reaction of aldehydes with activated alkenes

A series of novel bifunctional chiral phosphine-containing Lewis bases were synthesized and successfully applied to the asymmetric Morita–Baylis–Hillman reaction of aldehydes with methyl vinyl ketone (MVK) and ethyl vinyl ketone (EVK) to give the corresponding adducts in moderate yields and enantioselectivities under mild reaction conditions.     

Combining palladium and ammonium halide catalysts for Morita–Baylis–Hillman carbonates of methyl vinyl ketone: from 1,4-carbodipoles to ion pairs

Here we report that Morita–Baylis–Hillman carbonates from diverse aldehydes and methyl vinyl ketones can be directly utilised as palladium-trimethylenemethane 1,4-carbodipole-type precursors, and both reactivity and enantioselectivity are finely regulated by adding a chiral ammonium halide as the ion-pair catalyst. The newly assembled intermediates, proposed to contain an electronically neutral π-allylpalladium halide complex and a reactive compact ion pair, efficiently undergo asymmetric [4 + 2] annulations with diverse activated alkenes or isatins, generally with high regio-, diastereo- and enantio-selectivity, and even switchable regiodivergent or diastereodivergent annulations can be well realised by tuning the substrate or catalyst assemblies. An array of control experiments, including UV/Vis absorption study and density functional theory calculations, are conducted to rationalise this new double activation mode combining a palladium complex and an ammonium halide as an ion-pair catalyst.

A double activation catalytic system combining a palladium complex and an ammonium halide was developed to promote the asymmetric [4 + 2] annulations of Morita–Baylis–Hillman carbonates of methyl vinyl ketone.