Recent contributions from the Baylis-Hillman reaction to organic chemistry

A Single-Flask Synthesis of Morita-Baylis-Hillman Adducts from Ethoxyacetylene and Carbonyl Compounds: Synthesis of Subamolides D and E

Sequential treatment of (ethoxyethynyl)lithium with aldehydes and/or ketones (2 and 4) and BF3·OEt2 gives rise to β-hydroxyenoates 5 in good to excellent overall yields. Similarly, the combination of 1 (M = Li) and dicarbonyl compounds 6 (X = O) or keto/aldehyde acetals (X = OMe) followed by the addition of a Lewis acid leads to five-, six-, and seven-membered hydroxycycloalkene carboxyates. The utility of this method is demonstrated in the synthesis of the α-alkylidene lactone natural products subamolide D and E.

Natural product inspired design and synthesis of β-carboline and γ-lactone based molecular hybrids

β-Carboline and γ-lactone moieties have been selected by nature as privileged scaffolds and display a wide range of pharmacological properties. Following nature, we envisaged the preparation of new β-carboline and γ-lactone based molecular hybrids incorporating both the pharmacophores. In this regard, a water-assisted In-mediated environmentally benign and easy to execute single-step tandem Barbier type allylation-lactonisation process has been devised in order to afford the targeted molecular architectures. It is anticipated that aqueous medium plays the key role in allylation as well as in the subsequent lactonisation process for the diastereo-selective synthesis of these conjugates. It is believed that water drives the reaction pathway through dual activation, it increases the electrophilic character of formyl and ester functionalities and simultaneously enhances the nucleophilic potential of the hydroxyl group to facilitate the in situ intramolecular condensation. Importantly, during this synthetic strategy no column chromatographic purification was required at any stage.

Synthesis and Spectral Characterization of Benzo-[6,7][1,5]diazocino[2,1-a]isoindol-12-(14H)-one Derivatives

A simple synthetic route affording 27%–85% yields of benzo[6,7][1,5]diazocino[2,1-a]isoindol-12(14H)-one ring systems from readily available 3-(2-oxo-2-phenylethyl) isobenzofuran-1(3H)-ones and 2-(aminomethyl)aniline starting materials in toluene and catalysed by p-toluene-sulfonic acid is developed. The ¹H- and ¹³C-NMR spectra of the final products were assigned using a variety of one and two-dimensional NMR experiments. The distinction between the two potential isomers of the final products was made on the basis of heteronuclear multiple bond connectivity (HMBC) NMR spectra.

Asymmetric α-amination of 3-substituted oxindoles using chiral bifunctional phosphine catalysts

A highly enantioselective α-amination of 3-substituted oxindoles with azodicarboxylates catalyzed by amino acids-derived chiral phosphine catalysts is reported. The corresponding products containing a tetrasubstituted carbon center attached to a nitrogen atom at the C-3 position of the oxindole were obtained in high yields and with up to 98% ee.

Formation of Thermally Robust Frustrated Lewis Pairs by Electrocyclic Ring Closure Reactions

The phosphorus/boron-substituted hexatriene systems 6 undergo thermally induced electrocyclic ring closure to yield the cyclohexadiene-derived P/B frustrated Lewis pairs (FLPs) 7. Subsequent TEMPO oxidation gives the phenylene-bridged FLPs 8. Both systems activate dihydrogen and the thermally robust FLPs undergo carbon-carbon coupling reactions at a mesityl group upon treatment with dimethyl acetylenedicarboxylate at elevated temperatures.

Application of 7-azaisatins in enantioselective Morita-Baylis-Hillman reaction

7-Azaisatin and 7-azaoxindole skeletons are valuable building blocks in diverse biologically active substances. Here 7-azaisatins turned out to be more efficient electrophiles than the analogous isatins in the enantioselective Morita-Baylis-Hillman (MBH) reactions with maleimides using a bifunctional tertiary amine, β-isocupreidine (β-ICD), as the catalyst. This route allows a convenient approach to access multifunctional 3-hydroxy-7-aza-2-oxindoles with high enantiopurity (up to 94% ee). Other types of activated alkenes, such as acrylates and acrolein, could also be efficiently utilized.

Synthesis and biological activities of indolizine derivatives as alpha-7 nAChR agonists

Human α7 nicotinic acetylcholine receptor (nAChR) is a promising therapeutic target for the treatment of schizophrenia accompanied with cognitive impairment. Herein, we report the synthesis and agonistic activities of a series of indolizine derivatives targeting to α7 nAChR. The results show that all synthesized compounds have affinity to α7 nAChR and some give strong agonistic activity, particularly most active agonists show higher potency than control EVP-6124. The docking and structure-activity relationship studies provide insights to develop more potent novel α7 nAChR agonists.

Nazarov cyclization of 1,4-pentadien-3-ols: preparation of cyclopenta[b]indoles and spiro[indene-1,4'-quinoline]s

The first Lewis acid-catalyzed intramolecular interrupted Nazarov cyclization of 1,4-pentadien-3-ols is described. Using FeBr3 as the catalyst, a series of new substituted cyclopenta[b]indoles was prepared-through a sequence of Nazarov cyclization, nucleophilic amination, and isomerization-with good yields and high diastereo- and regioselectivities. A similar catalytic process was also developed for the synthesis of structurally interesting spiro[indene-1,4'-quinoline]s.

Morita–Baylis–Hillman reaction in eutectic solvent under aqueous medium

Aqueous solvent-catalyst system formed by DES (1ChCl/2Gly) and DABCO is more useful and practical to the Morita–Baylis–Hillman reaction.

Catalyst-controlled switch of regioselectivity in the asymmetric allylic alkylation of oxazolones with MBHCs

A catalyst-controlled switch of regioselectivity in asymmetric allylic alkylation of oxazolones with MBHCs was described.

Asymmetric aza-Morita–Baylis–Hillman reactions of chiral N-phosphonyl imines with acrylates via GAP chemistry/technology

A series of aza-Morita–Baylis–Hillman acrylates have been synthesized by using chiral N-phosphonyl imines and GAP chemistry/technology.

Expedient Baylis–Hillman reaction protocol to functionalize cyclohexa-2,4-dienones

Several masked o-benzoquinone (MOBs) derivatives successfully took part in the Baylis–Hillman reaction with various aldehydes and ketones to furnish the corresponding condensation products in this study.

R, Sajith AM, K. V. D, C. S, Anwar S. Functionalised dihydroazo pyrimidine derivatives from Morita–Baylis–Hillman acetates: synthesis and studies against acetylcholinesterase as its inhibitors

Dihydroazo pyrimidine derivatives were synthesized at room temperature using MBH acetates and aminoazole derivatives. The in vitro studies carried on a couple of derivatives exhibited much higher potency for Alzheimer's disease (AD).

Hypervalent iodine catalysis for selective oxidation of Baylis–Hillman adducts via in situ generation of o-iodoxybenzoic acid (IBX) from 2-iodosobenzoic acid (IBA) in the presence of oxone

An efficient, eco-friendly protocol for selective oxidation of primary and secondary Baylis–Hillman alcohols to the corresponding carbonyl compounds in high yields has been developed with 2-iodosobenzoic acid (IBA).

Cinchona alkaloid and di-tert-butyldicarbonate–DMAP promoted efficient synthesis of (E)-nitroolefins

A simple and efficient metal-free methodology for the synthesis of β-nitroolefins has been developed from arylidinemalononitrile using bifunctional cinchona alkaloid along with di-tert-butyldicarbonate–DMAP in high yields with total selectivity.

Au(i)/Ag(i) co-operative catalysis: interception of Ag-bound carbocations with α-gold(i) enals in the imino-alkyne cyclizations with N-allenamides

A co-operative Au/Ag catalyst system has been developed to utilize N-allenamides as nucleophilic enal equivalents for the interceptive capturing of incipient carbocations generated through π-acid-triggered imino-alkyne cyclization.

Synthesis of 4H-chromenes by an unexpected, K3PO4-mediated intramolecular Rauhut–Currier type reaction

The K₃PO₄-mediated intramolecular Rauhut-Currier type reaction of chalcones having an enoate moiety leading to the formation of 4H-chromenes in moderate to good yields is demonstrated.

Protein self-assembly induces promiscuous nucleophilic biocatalysis in Morita–Baylis–Hillman (MBH) reaction

Self-assembled states of proteins render efficient promiscuous nucleophilic biocatalysis in MBH reaction in a green process.

Morita-Baylis-Hillman Reaction of β,β-Disubstituted Enones: An Enantioselective Organocatalytic Approach for the Synthesis of Cyclopenta[b]annulated Arenes and Heteroarenes

The first enantioselective organocatalytic intramolecular Morita-Baylis-Hillman (MBH) reaction of sterically highly demanding β,β-disubstituted enones is presented. The MBH reaction of β,β-disubstituted-α,β-unsaturated electron-withdrawing systems was previously considered to be unfeasible. Towards this end, designer substrates, which under simple and practical reaction conditions generate a variety of cyclopenta[b]annulated arenes and heteroarenes in excellent enantiopurities and near-quantitative yields in remarkably short reaction times, are described. The reason for the unusually facile nature of this reaction is attributed to the synergy guided and entropically favored intramolecular reaction. Further, this strategy provides easy access to a substantial number of bioactive natural products and pharmaceutically significant compounds.