Recent Developments in the [1,2]-Phospha-Brook Rearrangement Reaction

The [1,2]-phospha-Brook rearrangement serves as a powerful synthetic strategy that enables efficient carbonyl umpolung through phosphoryl group migration, providing direct access to α-hydroxyphosphoryl compounds-a privileged class of synthons with broad applications in organophosphorus chemistry, medicinal chemistry, and materials science. This review provides a comprehensive overview of recent progress in synthetic methodologies, possible mechanisms, and asymmetric transformations, highlighting key breakthroughs and future directions in this rapidly evolving field.

Organophosphates as Versatile Substrates in Organic Synthesis

This review summarizes the applications of organophosphates in organic synthesis. After a brief introduction, it discusses cross-coupling reactions, including both transition-metal-catalyzed and transition-metal-free substitution reactions. Subsequently, oxidation and reduction reactions are described. In addition, this review highlights the applications of organophosphates in the synthesis of natural compounds, demonstrating their versatility and importance in modern synthetic chemistry.

Formation of N,N,N',N'-tetramethylethylenediamine via coupling of the two charge reversed C-N bonds of Me3NO in the presence of an Eu(II) bis(trimethylsilyl)amide complex

An N,N,N',N'-tetramethylethylenediamine (TMEDA) complex of Eu(II) was synthesized via an unprecedented self-aminomethylation of Me3NO in the presence of Eu[N(SiMe3)2]2(THF)2. The neutral TMEDA ligand is formed via the coupling of two charge reversed carbon centres from the same precursor Me3NO. In contrast, the reactions of LnII[N(SiMe3)2]2(THF)2 (Ln = Yb, Sm) with Me3NO led to the oxygen-bridged dinuclear complexes of Ln(III).

Stereoselective Reductive Coupling Reactions Utilizing [1,2]-Phospha-Brook Rearrangement: A Powerful Umpolung Approach

[1,2]-Phospha-Brook rearrangement entails the generation of α-oxygenated carbanions via the umpolung process. Recently, these anionic species have been widely utilized for several C-C bond forming strategies, providing various useful frameworks that are difficult to access through conventional approaches. However, the application of this powerful methodology in the development of chiral strategies is still at the nascent stage due to challenges involved in controlling chemoselectivity and enantioselectivity. This synopsis provides a detailed summary of diastereo- and/or enantioselective chemical transformations using [1,2]-phospha-Brook rearrangement.

Ynamides in Radical Reactions: A Route to Original Persubstituted 2-Aminofurans

Mn(OAc)₃/Cu(OAc)₂-mediated reaction between ynamides, derived from oxazolidone or 3-methylindole carboxylate, and cyclic α-dicarbonyl radicals led to the one-pot synthesis of 2-aminofurans. The transformation involves addition of the α-dicarbonyl radical to ynamide, oxidation to ketene-iminium, and polar cyclization steps to provide original persubstituted 2-aminofurans in good to excellent yields. This work represents the first radical route for the synthesis of furans from ynamides.

Synthesis of 2-Aminofurans and 2-Aminothiophenes through Elemental Sulfur-Promoted Switchable Redox Condensation Reaction of Enaminones with Methylene Nitriles

Herein, we report an elemental sulfur-promoted switchable redox condensation reaction that can selectively prepare 2-aminofurans and 2-aminothiophenes from the corresponding enaminones and methylene nitriles, respectively. Mechanistic studies demonstrated that the enaminones, as dual nucleophiles, reacted with nitrile acetate to produce 2-aminofurans via 3,5-annulation under promotion by elemental sulfur. These reactions used readily available starting materials, transition metal-free, eco-friendly procedures, gram-scale syntheses, and wide functional group tolerance. The methodology may be useful for the construction of 2-aminofuran and 2-aminothiophene derivatives with potential biological activity.

Brønsted base-catalyzed 1,2-addition/[1,2]-phospha-Brook rearrangement sequence providing functionalized phosphonates

A new methodology for the introduction of functional groups into an organic molecule in which a keto or a formyl group is used as the connecting site was developed by utilizing the 1,2-addition/[1,2]-phospha-Brook rearrangement sequence under Brønsted base catalysis. The reaction of aromatic aldehydes and ketones with phosphinates having functional groups such as alkynyl, bromoalkyl, N-Boc amino, and boryl groups efficiently proceeded with the aid of phosphazene base P2-tBu as the catalyst, providing densely functionalized phosphonates in good yields.

Diastereoselective 1,6-Addition of α-Phosphonyloxy Enolates to para-Quinone Methides

The addition of α-ketoamide to p-quinone methide initiated by dialkylphosphite in the presence of organic base 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) is explored. Coupling of dialkylphosphites to α-ketoamides in the presence of a base follows [1,2]-phospha-Brook rearrangement, generating corresponding α-phosphonyloxy enolates that are subsequently seized by p-quinone methides (p-QMs). The two-step one-pot 1,6-conjugate addition provides effective access to a series of isatin-incorporated phosphate-bearing 1,6-adducts having two vicinal tertiary carbons with up to 90% yield and >20:1 dr.

Stereoselective Synthesis of Dihydrocoumarins via [1,2]-Phospha-Brook Rearrangement in Three-Component Coupling Reaction of α-Ketoesters, o-Quinone Methides, and Dialkyl Phosphites

A highly regio- and diastereoselective approach for the synthesis of phosphate substituted dihydrocoumarins via Brønsted base catalyzed [1,2]-phospha-Brook rearrangement is reported. The two-step, one-pot Michael addition of α-phosphonyloxy enolates proceeds by coupling of dialkyl phosphite and α-ketoesters to o-quinone methides, followed by an intramolecular cyclization, providing 3,4-dihydrocoumarin frameworks.

Direct Synthesis of CF2H-Substituted 2-Amidofurans via Copper-Catalyzed Addition of Difluorinated Diazoacetone to Ynamides

The significance of molecules containing difluoromethyl groups is driven by their potential applications in pharmaceutical and agrochemical science. Methods for the incorporation of lightly fluorinated groups such as CF₂H have been less well developed. Here we report the use of difluorinated diazoacetone as a practical reagent for the direct synthesis of CF₂H-substituted 2-amidofurans through addition to ynamides. These newly designed difluorinated amidofurans were elaborated to create new nitrogen-containing frameworks that would be challenging to obtain otherwise.

Synthesis of Tetrasubstituted Furans through One-Pot Formal [3 + 2] Cycloaddition Utilizing [1,2]-Phospha-Brook Rearrangement

An efficient method for the synthesis of tetrasubstituted furans was developed by utilizing the [1,2]-phospha-Brook rearrangement under Brønsted base catalysis. The two-step one-pot formal [3 + 2] cycloaddition involves the nucleophilic addition of a propargyl anion, which is catalytically generated through the [1,2]-phospha-Brook rearrangement, to an aldehyde and the subsequent intramolecular cyclization mediated by N-iodosuccinimide to provide 2,4,5-trisubstituted-3-iodofurans. The present method with readily available substrates provides new access to a wide range of well-organized tetrasubstituted furans.

Construction of α-methoxyimidoyl ketonitrones via phosphite-mediated addition of α-keto N-tert-butanesulfinyl imidates to nitrosoarenes

A dimethyl phosphite-mediated addition of α-keto N-tert-butanesulfinyl imidates to nitrosoarenes was developed. Nitrosoarenes were successfully used as electrophiles to trap aza-enolate intermediates that were generated from nucleophilic addition of deprotonated phosphite to α-keto N-tert-butanesulfinyl imidates and following phospha-Brook rearrangement, allowing efficient construction of ketonitrones with excellent (Z)-geometries.

Recent developments in functionalization of acyclic α-keto amides

This review describes the synthetic utility of α-keto amides to synthesize various important molecules via mono, dual and triple functionalization reactions.

Regioselective addition of phosphites to acyl cyclopropanes and following rearrangements: a facile access to enol phosphates

This work describes a novel method of preparing functionalized enol phosphates with acyl cyclopropanes through a regioselective cascade reaction.

Preparation of 2-Amino-5-homoallylfurans via Palladium-Catalyzed Tandem Cycloisomerization/Heck-Type Coupling of Homoallenyl Amides with Allyltrialkylsilanes

The direct access to 2-amino-5-homoallylfurans has been realized by a palladium-catalyzed tandem cycloisomerization/Heck-type coupling between homoallenyl amides and allyltrialkylsilanes, using a novel DDQ/MnO₂ combination as the efficient oxidant. The reaction exclusively affords γ-allylation products in good to excellent yields with broad substrate scope under exceptionally mild reaction conditions. It represents one of the rare examples of the Pd-catalyzed intermolecular Heck-type coupling of allytrialkylsilanes terminated by β-silyl elimination, thus complementing traditional allylation methods because of the excellent γ-selectivity.