1-Benzopyran-4(4H)-ones as novel activated alkenes in the Baylis–Hillman reaction: a simple and facile synthesis of indolizine-fused-chromones

Rapid Access to Triarylmethanes (TRAMs) Enabled by Direct Electrolysis of Indolizines with Carbonyls

A fast, scalable, transition metal-free, electrochemical sp2 geminal functionalization of carbonyls enabled by anodic oxidation of non-prefunctionalized chromone-fused indolizines to access the triarylmethanes (TRAMs) is disclosed for the first time. This momentary electrochemical approach features the use of readily available carbonyls, implantation of the C(sp3) center (well-known for dramatically improving biological active potency), a broad substrate scope, and excellent yields of TRAMs with fluorescence properties.

Electrochemical direct C-H mono and bis-chalcogenation of indolizine frameworks under oxidant-free conditions

Herein, we disclosed a sustainable electrochemical approach for site-selective C-H mono and bis-chalcogenation (sulfenylation or selenylation) of indolizine frameworks. Diversely functionalized disulfides and diselenides possessing EDGs and EWGs were successfully reacted with a variety of indolizines to directly access sulfenylated/selenylated indolizines in 40-96% yields. A mechanistic radical pathway was also validated with control experiments and cyclic voltammogram data.

Iodine-Mediated Domino Cyclization for One-Pot Synthesis of Indolizine-Fused Chromones via Metal-Free sp3 C-H Functionalization

An efficient method for the synthesis of new indolizine-fused chromones has been accomplished from ethyl (E)-3-(2-acetylphenoxy)acrylates and pyridines in a "one-pot" manner. Facile operation in open-air, metal-free, and mild conditions renders this protocol particularly practical and attractive. Moreover, this method can simultaneously construct two molecular fragments of chromone and indolizine. Scale-up experiment and the construction of natural products further prove the practicability of this strategy.

A simple and convenient synthesis of 3-salicyloylquinoline-4-carboxylic esters from chromone and isatin

A simple and convenient synthesis of 3-salicyloylquinoline-4-carboxylic esters has been developed through an AlCl3-catalyzed reaction of easily available Baylis-Hillman adducts from chromones and isatin-derivatives. This reaction involves esterification, cyclization and ring opening in a one-step process, and provides an efficient approach for easy access to a series of valuable salicyloylquinoline derivatives with high yields. Moreover, this protocol offers several advantages, such as availability of starting materials, economic availability, operational simplicity and mild reaction conditions.

Tandem synthesis of 4-aminoxanthones is controlled by a water-assisted tautomerization: a general straightforward reaction

Iminolactone-aminofuran tautomerization is the rate-determining step in the multicomponent synthesis of xanthones from 3-carbonylchromones, isocyanides and dienophiles.

The Baylis–Hillman reaction: a new continent in organic chemistry – our philosophy, vision and over three decades of research

This mini review describes in brief the way in which our research has contributed towards the development of the Baylis–Hillman reaction as a powerful tool in synthetic chemistry, offering unending opportunities and intellectual challenges to understand and address the present day requirements in the area of organic chemistry.

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.

A direct method for the synthesis of indolizine derivatives from easily available aromatic ketones, pyridines, and acrylonitrile derivatives

A concise and efficient strategy has been proposed to synthesize indolizine derivatives from easily available aryl or heteroaryl methyl ketones, pyridines, and acrylonitriles. The mechanistic pathway involved the integration of iodination, pyridinium ylide synthesis, and 1,3-dipolar cycloaddition. The protocols were found to be highly efficient in terms of high yields, operational simplicity, mild reaction conditions, and easy workup. This method has provided an important supplement for the synthesis of indolizine derivatives via a novel tandem synthesis.

Reaction of polyhaloalkyl-substituted chromones, pyrones, and furanones with salicylaldehydes as a direct route to fused 2H-chromenes

Polyhaloalkyl-substituted chromones, gamma-pyrones, and beta-furanones react with salicylaldehydes in the presence of piperidine to give a wide variety of fused 2H-chromenes in good yields. This novel annulation reaction presumably proceeds by a tandem intermolecular oxa-Michael addition and subsequent intramolecular Mannich condensation.

The Baylis–Hillman reaction: a novel source of attraction, opportunities, and challenges in synthetic chemistry

The Baylis-Hillman reaction is a successful, useful, and atom-economical carbon-carbon bond forming reaction, which has grown from an obscure level to the level of high synthetic popularity due to its operational simplicity and also due to the enormous applications of the Baylis-Hillman adducts in organic synthesis. In this tutorial review, we briefly describe the way this reaction has grown to its present heights and the opportunities, attractions, and challenges the reaction offers with respect to its asymmetric and intramolecular versions, and mechanistic aspects.

Simple and One-Pot Protocol for Synthesis of Indene-spiro-oxindoles Involving Tandem Prins and Friedel−Crafts Reactions

[reaction: see text] A simple and one-pot protocol for the synthesis of indene-spiro-oxindole derivatives via TiCl4-mediated reaction between 1,1-diarylethylenes and isatin derivatives involving construction of two carbon-carbon bonds through tandem Prins and intramolecular Friedel-Crafts (PFC) reactions has been described. A plausible mechanism for this transformation is also presented.

Hydroxyalkylation of Conjugated Nitroalkenes with Activated Nonenolizable Carbonyl Compounds

[reaction: see text] The Morita-Baylis-Hillman reaction of a variety of conjugated nitroalkenes with activated nonenolizable carbonyl compounds such as glyoxylate, trifluoropyruvate, pyruvaldehyde, and ninhydrin in the presence of 40-100 mol % of DMAP in acetonitrile or 100 mol % of imidazole in CHCl(3) or THF provided the adducts in decent to good yields. In most cases, the reactions catalyzed by DMAP in acetonitrile were faster and provided the desired MBH adducts in higher yields as compared to the imidazole catalyzed reactions.

Palladium-Catalyzed Arylation and Heteroarylation of Azolopyrimidines

A comparative study of the palladium-catalyzed arylation and heteroarylation of 5-bromoazolopyrimidines shows that aryl and electron-rich heteroaryl boronic acids gave higher yields than those obtained using the corresponding aryl and heteroaryl tributyl stannanes. In contrast, the reaction with electron-poor heteroaryl tributyl stannanes gave better results than the corresponding boronic acids.

Efficient Baylis-Hillman reactions of cyclic enones in methanol as catalyzed by methoxide anion

The Baylis-Hillman reactions of cyclic enones with a variety of aldehydes were investigated. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) was found to be a viable catalyst in promoting the reactions of sterically retarded substrates in methanol. The reactions showed clear solvent dependence and only occurred in hydroxylic solvents, especially in methanol. Further consideration on the steric character of DBU and its high basicity jointly with other experimental observations suggests that the methoxide anion should be the "true" Baylis-Hillman catalyst. This has been confirmed by the effectiveness of similar reactions directly employing methoxide as the catalyst. The reaction pathways of this type of catalysis are proposed to depend on the choice of substrates. Supporting experimental observations were demonstrated and discussed in relation to mechanistic considerations. This study also reveals that both DBU and sodium methoxide can be successfully applied as effective catalysts in methanol to promote the Baylis-Hillman reactions for a range of cyclic enones including cyclopent-2-enones, cyclohex-2-enones, gamma-pyrone, and 1-benzopyran-4(4H)-ones.

Straightforward Asymmetric Entry to Highly Functionalized 3-Substituted 3-Hydroxy-β-lactams via Baylis−Hillman or Bromoallylation Reactions

The reaction of various activated vinyl systems, including 2-cyclopenten-1-one, with enantiopure azetidine-2,3-diones 1 was promoted by DABCO to afford the corresponding optically pure Baylis-Hillman adducts 2 without detectable epimerization. However, the reaction of alpha-keto lactams 1 with but-3-yn-2-one was not as successful, giving the corresponding beta-halo Baylis-Hillman adduct in low yield. Metal-mediated bromoallylation reaction between 2,3-dibromopropene and azetidine-2,3-diones 1 was investigated in aqueous media. Surprisingly, indium was unable to promote the bromoallylation reaction of alpha-keto lactams 1, but the Sn-Hf(4)Cl-promoted bromoallylation of ketones 1 proceeded efficiently to achieve bromohomoallyl alcohols 5 as single diastereomers. On this basis, simple and fast protocols for the asymmetric synthesis of the potentially bioactive 3-substituted 3-hydroxy-beta-lactam moiety were developed.