1,2-Diacylation of Alkynes Using Acyl Fluorides and Acylsilanes by P(III)/P(V) Catalysis

Phosphine-catalyzed reaction of cyclopropenones with water: divergent synthesis of highly functionalized γ-butenolides, trisubstituted α,β-unsaturated acids and anhydride

The reaction between cyclopropenones and water catalyzed by different phosphines has been thoroughly investigated. Under the catalysis of trimethylphosphine, highly functionalized γ-butenolides were successfully synthesized from the simple starting material, cyclopropenones, and water in 35%-81% yields with excellent diastereoselectivities. Under the catalysis of triphenylphosphine, cyclopropenones were transferred to trisubstituted α,β-unsaturated acids with sufficient water in 78%-99% yields, while α,β-unsaturated acid anhydrides were obtained with trace water.

Sb-to-P Metathesis: A Direct Route to Structurally Constrained, Cationic PIII Compound

Structurally constrained, cationic PIII compound [LP][SbCl4] with an OCO pincer-type ligand (L) having a central carbene donor was directly synthesized via an Sb-to-P metathesis reaction between PCl3 and LSb-Cl. [LP][SbCl4] was isolated and its reactivity with small molecules (ROH and RNH2) was studied, showing that [SbCl4]- is not an innocent counter anion, but an active participant in these reactions. When the [SbCl4]- was replaced with the [CB11H12]- ([Cb]-) anion, the reactions were redirected to [LP]+ cation only. The reactions with alcohols and amines led to the equilibrium between the products of the formal E-H (E=O, N) bond oxidative addition to the P-center and products of the P-center/ligand-assisted bond activation. Remarkably, [LP]+ activated the PhO-H and PhN(H)-H bonds in a reversible, thermoneutral fashion.

Transition from Kwon [4+2]- to [3+2]-cycloaddition enabled by AgF-assisted phosphine catalysis

Phosphine catalysis generally relies on the potential of carbanion-phosphonium zwitterions that are generated via nucleophilic addition of phosphine catalyst to electrophilic reactants. Consequently, structural modification of zwitterions using distinct electrophilic reactants has emerged as a prominent strategy to enhance catalysis diversity. Herein, we present an alternative strategy that utilizes AgF additive to expand phosphine catalysis. We find that AgF can readily transform the canonical carbanion-phosphonium zwitterion into silver enolate-fluorophosphorane intermediate, eventually furnishing a P(III)/P(V) catalytic cycle. This strategy has been successfully applied to the phosphine-catalyzed reaction of 2-substituted allenoate and imine, resulting in the transition from Kwon [4 + 2] cycloaddition to [3 + 2] cycloaddition. This [3 + 2] cycloaddition features remarkable diastereoselectivity, high yield, and broad substrate scope. Experimental and computational studies have validated the proposed mechanism. Given the prevalence of carbanion-phosphonium zwitterions in phosphine catalysis, this AgF-assisted strategy is believed to hold significant potential for advancing P(III)/P(V) catalysis.

(3+2) Annulation of 4-Acetoxy Allenoate with Aldimine Enabled by AgF-Assisted P(III)/P(V) Catalysis

A phosphine-catalyzed (3+2) annulation of 4-acetoxy allenoate and aldimine with the assistance of AgF is described. The success of this reaction hinges on the metathesis between the enolate-phosphonium zwitterion and AgF, leading to a key intermediate comprising of silver enolate and a fluorophosphorane P(V)-moiety. The former is able to undergo a Mannich reaction with aldimine, whereas the latter initiates a cascade sequence of AcO-elimination/aza-addition, thus furnishing the P(III)/P(V) catalysis. By taking advantage of the silver enolate, a preliminary attempt at an asymmetric variant was conducted with the combination of an achiral phosphine catalyst and a chiral bis(oxazolinyl)pyridine ligand (PyBox), giving moderate enantioselectivity.

Metal-Free Tunable 1,2-Difunctionalization of Terminal Alkynes: Synthesis of β-Substituted α,β-Unsaturated Ketones

A metal-free tunable 1,2-difunctionalization of the terminal alkynes showcasing a tandem installation of C-C and C-S bonds has been developed. The key enabling factor for the approach is the use of acetic acid as an acyl source to synthesize β-substituted α,β-unsaturated ketones. The reaction at room temperature leads to the regioselective acylation at the terminal carbon of alkynes, whereas at -78 °C, the acylation occurs at the more substituted carbon.

Bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction for construction of 5-oxazoylmethyl α-silyl alcohol

A bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction was developed. The reaction proceeded well with a broad range of N-propargylamides and acylsilanes, affording the target chiral 5-oxazoylmethyl α-silyl alcohols in up to 95% yield and 99% ee under mild conditions. Importantly, this facile protocol was available for the late-stage modification of several bioactive molecules. Based on the mechanistic study and control experiments, a possible catalytic cycle and transition state are proposed to elucidate the reaction process and enantioinduction.