Synthesis of (Difluoromethyl)cycloalkenes from 2‐Cycloalkenones by Utilizing Phospha‐Brook Rearrangement

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.

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.

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.

Lanthanide Silylamide-Catalyzed Synthesis of Pyrano[2,3-b]indol-2-ones

A lanthanide silylamide-catalyzed tandem reaction of isatins, diethyl phosphite, and 2,3-diarylcyclopropenones has been developed. A series of pyrano[2,3-b]indol-2-ones were synthesized in high yields. The cooperation of the Lewis acidity of the lanthanide center and the Bronsted basicity of the N(SiMe₃)₂ anion may be the key factor affecting the catalytic activity of lanthanide amides.

Synthesis of difluoromethylated diarylmethanes via Fe(OTf)3-catalyzed Friedel-Crafts reaction of 2,2-difluoro-1-arylethyl phosphates

The Fe(OTf)₃-catalyzed Friedel-Crafts reaction of 2,2-difluoro-1-arylethyl phosphates with electron-rich (hetero)arenes afforded difluoromethylated diarylmethanes. Control experiments showed that Fe(OTf)₃ behaves as the Lewis acid, and that the phosphate leaving group and o- or p-alkoxy substituents on the substrates are necessary for the Fe(OTf)₃-catalyzed reaction to proceed under mild conditions.

Synthesis of 1-(Difluoromethyl)alk-1-enes via Palladium-Catalyzed SN2'-Type Substitution Reaction of Difluoromethylated Allylic Phosphates with 1,3-Dicarbonyl Compounds and Imides

Herein, we report the synthesis of 1-(difluoromethyl)alkenes via a palladium-catalyzed reaction of difluoromethyl-substituted allylic phosphates with 1,3-dicarbonyl compounds using PdCl₂(PPh₃)₂ as a precatalyst. 1,3-Dicarbonyl compounds attacked the γ-carbon with respect to the difluoromethyl group to afford their corresponding S_N2'-type substitution products irrespective of the substitution pattern in the allylic phosphates. This regioselectivity has been ascribed to the electronic environment of the unsymmetrical π-allylpalladium intermediate using density functional theory (DFT) calculations. The reaction of difluoromethyl-substituted allylic phosphates with imides was also carried out using a different catalyst system composed of [PdCl(η³-allyl)]₂ and di(diphenylphosphino)butane (dppb).

Enantioselective Lewis base catalyzed phosphonyldifluoromethylation of allylic fluorides using a C-silyl latent pronucleophile

The first enantioselective phosphonyldifluoromethylation is enabled by the use of a latent silylated C-centered pronucleophile in the Lewis base catalyzed substitution of allylic fluorides.