Cycloisomerization of Bifunctionalized Allenes: Synthesis of 3(2H)-Furanones in Water

Synthesis of 3(2H)-furanone derivatives: p-TsOH/halotrimethylsilane promoted cycloketonization of γ-hydroxyl ynones

A p-TsOH/halotrimethylsilane facilitated cycloketonization of γ-hydroxyl ynones is detailed. This methodology enables the one-step synthesis of polysubstituted 3(2H)-furanone products. It is remarkable that the reaction exhibits excellent regio- and chemoselectivity by the addition of very small quantities of p-toluenesulfonic acid and water.

Palladium-Catalyzed Oxidative Cyclization of α-Allenols in the Presence of TBN: Access to 3(2H)-Furanones

A new palladium-catalyzed oxidative cyclization of α-allenols is described. The readily accessible α-allenols participate in intra-molecular oxidative cyclization in the presence of TBN to grant access to multisubstituted 3(2H)-furanones, which are common motifs in several biologically important natural products and pharmaceuticals.

Cyanoacetylenic Alcohols: Molecules of Interstellar Relevance in the Synthesis of Essential Heterocycles, Amino Acids, Nucleobases and Nucleosides

Cyanoacetylenic alcohols, R1R2C(OH)C≡C–CN, the closest derivatives of cyanoacetylene, an abundant interstellar molecule, are now becoming important compounds in the area of modern organic synthesis that tends to mimic Nature. The presence of highly reactive C≡C and C≡N bonds in close proximity to a hydroxy group endows cyanoacetylenic alcohols with a chemical trinity of mutually influencing functions, leading to a myriad number of chemical transformations. All reactions of cyanoacetylenic alcohols parallel modern organic synthesis, whilst being biomimetic. To react, they do not need transition metals (and in most cases, no metals at all, except for physiologically indispensable Na+ and K+), proceed at ambient temperature and often in aqueous media. Fundamentally, their reactions are 100% atom-economic because they are almost exclusively addition processes. Typically, the cyano, acetylene and hydroxy functions of cyanoacetylenic alcohols behave as an inseparable entity, leading to reaction products with multiple functional groups. This allows hydroxy, carbonyl, carboxylic, imino, amino, amido, cyanoamido, cyano, various P-containing, ether and ester functions, along with double bonds, different fundamental heterocycles (furans, furanones, pyrazoles, oxazoles, pyridines, pyrimidines, purines, etc.) and diverse polycyclic systems to be integrated in a single molecular architecture. This review focuses on an analysis and generalization of the knowledge that has accumulated on the chemistry of cyanoacetylenic alcohols, mostly over the past 15 years.

1 Introduction

2 Nucleophilic Addition to Cyanoacetylenic Alcohols and Subsequent Transformations of the Adducts

3 Annulation with Nonaromatic Nitrogen Heterocycles

4 Annulation with Aromatic Nitrogen Heterocycles

5 Modification of Amino Acids

6 Modifications of Nucleobases

7 Modification of Nucleosides

8 Conclusion

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

The allene functionality has participated in one of the most exciting voyages in organic chemistry, from chemical curiosities to a recurring building block in modern organic chemistry. In the last decades, a special kind of allene, namely, allenol, has emerged. Allenols, formed by an allene moiety and a hydroxyl functional group with diverse connectivity, have become common building blocks for the synthesis of a wide range of structures and frequent motif in naturally occurring systems. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This Review summarizes the most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products.

Palladium-Catalyzed Multicomponent Synthesis of Fully Substituted Alkylidene Furanones

In the presence of a catalytic amount of Pd(OAc)₂ and XantPhos, the three-component reaction of ynones, imines, and aryl iodides affords fully substituted alkylidene-furan-3(2H)-ones via a sequence of the Mannich reaction followed by chemo- and regioselective oxypalladation and reductive elimination. One carbon-oxygen and two carbon-carbon bonds are generated to afford the heterocycle in good to excellent yield.

Ultrasonochemical synthesis of 2,3-dihydrofuranediones in aqueous medium

2,3-Dihydrofuranediones were prepared by an efficient one-pot multicomponent Knoevnagel-like condensation between pyrazolecarbaldehydes or indole-3-carbaldehyde, ethyl pyruvate and bromine, followed by an intramolecular cyclization in aqueous medium.

The Current Status of O-Heterocycles: A Synthetic and Medicinal Overview

O-Heterocycles have been explored in the field of medicinal chemistry for a long time, but their significance has not been duly recognised and they are often shunned in favour of N-heterocycles. The design of bioactive molecules for nearly every pathophysiological condition is primarily focused on novel N-heterocycles. The main reasons for such bias include the ease of synthesis and possible mimicking of physiological molecules by N-heterocycles. But considering only this criterion rarely provides breakthrough molecules for a given disease condition, and instead the risks of toxicity or side effects are increased with such molecules. On the other hand, owing to improved synthetic feasibility, O-heterocycles have established themselves as equally potent lead molecules for a wide range of pathophysiological conditions. In the last decade there have been hundreds of reports validating the fact that equally potent molecules can be designed and developed by using O-heterocycles, and these are also expected to have comparably low toxicity. Even so, researchers tend to remain biased toward the use of N-heterocycles over O-heterocycles. Thus, this review provides a critical analysis of the synthesis and medicinal attributes of O-heterocycles, such as pyrones, oxazolones, furanones, oxetanes, oxazolidinones, and dioxolonones, and others, reported in the last five years, underlining the need for and the advantages guiding researchers toward them.

Organocatalytic asymmetric domino Michael/O-alkylation reaction for the construction of succinimide substituted 3(2H)-furanones catalyzed by quinine

Asymmetric domino reaction of maleimides with γ-halogenated-β-ketoesters catalyzed by quinine is developed to give succinimide substituted 3(2H)-furanones in good enantioselectivities.

A Serendipitous Synthesis of Bis-Heterocyclic Spiro 3(2H)-Furanones

(Z) Enol triflates 6, 11b-d, (E) enol triflate 11e, and phenol triflate 11a, derived from β-keto esters or 2-carboalkoxy phenols, respectively, react with N-Boc 2-lithiopyrrolidine (5a), N-Boc N-methylaminomethyllithium (5b), or 2-lithio-1,3-dithiane (14) to afford 3(2H)-furanones in modest to good yields (38-81%). Product and carbanion reagent studies suggest that the 3(2H)-furanone is formed in a cascade of reactions involving nucleophilic acyl substitution, enolate formation, trifluoromethyl transfer, iminium or sulfenium ion formation, and subsequent ring closure to form the 3(2H)-furanone. The use of 2-lithio-1,3-dithiane affords a cyclic α-keto-S,S,O-orthoester in which the functionality can be selectively manipulated for synthetic applications.

Base catalysed intermolecular cyclisation of N-protected o-amino benzaldehyde/acetophenone with phosphorus/sulphur based allenes: facile synthesis of substituted quinolines

Base catalyzed reaction of N-Bz protected o-aminobenzaldehyde with allenylphosphonates affords O-phosphorylated quinolines via a route involving a thermal rearrangement.

A tandem Mannich addition-palladium catalyzed ring-closing route toward 4-substituted-3(2H)-furanones

A facile route towards highly functionalized 3(2H)-furanones via a sequential Mannich addition–palladium catalyzed ring closing has been elaborated. The reaction of 4-chloroacetoacetate esters with imines derived from aliphatic and aromatic aldehydes under palladium catalysis afforded 4-substituted furanones in good to excellent yields. 4-Hydrazino-3(2H)-furanones could also be synthesized from diazo esters in excellent yields by utilising the developed strategy. We could also efficiently transform the substituted furanones to aza-prostaglandin analogues.

Bifunctionalized allenes. Part XIII. A convenient and efficient method for regioselective synthesis of phosphorylated α-hydroxyallenes with protected and unprotected hydroxy group

The paper describes a convenient and efficient method for regioselective synthesis of phosphorylated α-hydroxyallenes using an atom economical [2,3]-sigmatropic rearrangement of intermediate propargyl phosphites or phosphinites. These can be readily prepared via reaction of protected alkynols with dimethyl chlorophosphite or chlorodiphenyl phosphine respectively in the presence of a base.

Allenylphosphine oxides as simple scaffolds for phosphinoylindoles and phosphinoylisocoumarins

A range of phosphinoylindoles was prepared in one-pot from functionalized propargyl alcohols and a suitable P(III) precursor via a base-mediated reaction. The reaction proceeds via the intermediacy of allenylphosphine oxides. Similarly, phosphinoylisocoumarins were prepared from allenylphosphine oxides in a trifluoroacetic acid-mediated reaction; the latter also acts as a solvent. Interestingly, in the presence of wet trifluoroacetic acid, in addition to phosphinoylisocoumarins, phosphorus-free isocoumarins were also obtained. Key products were characterized by single crystal X-ray crystallography.