A new and convenient approach for the synthesis of P-stereogenic intermediates bearing a tert-butyl(methyl)phosphino group

Facile Synthesis of H-Phosphinates from P(OR)3 or ClP(OR)2 via SiO2-Promoted Hydrolysis

H-Phosphinates represent a valuable class of organophosphorus building blocks and catalytic ligands. The existing synthetic approaches are generally associated with the use of strong acids, the need for meticulous treatment of intermediates, and the limitation of only P-aryl introductions. Following a comprehensive investigation into the unexpected SiO2-promoted hydrolysis observed during the chromatography workup of the crude R'P(OR)2 intermediates, we have developed an extremely simple and general synthetic route to H-phosphinates from commercially available Grignard reagents and P(OR)3. An alternative approach involved the use of ClP(OR)2 in place of P(OR)3, which proved to be a valuable strategy for the preparation of sterically hindered ArMgBr substrates bearing bulky ortho-substituted motifs. A library of 36 structurally diverse P-(cyclo)alkyl and P-(hetero)aryl H-phosphinates was thus obtained in moderate to high yields using this practical protocol. Furthermore, the CuCl2-mediated P(O)-H bond derivations were also examined, resulting in the formation of the corresponding EtOPhP(O)-X (X = O, N, S) compounds in nearly quantitative yields.

Cu(II)-Mediated direct 18F-dehydrofluorination of phosphine oxides in high molar activity

BACKGROUND

The 18F/19F-isotope exchange method employing P(V)-centered prosthetic groups demonstrates advantages in addressing mild one-step aqueous 18F-labeling of peptides and proteins. However, the molar activity (Am) achieved through isotope exchange remains relatively low, unless employing a high initial activity of [18F]F-. To overcome this drawback, our work introduces a novel approach through a Cu-mediated direct 18F-dehydrofluorination of phosphine oxides. This method leverages the straightforward separation of the 18F-labeled product from the phosphine oxide precursors, aiming to primarily increase Am.

RESULTS

Through a 19F-dehydrofluorination efficiency test, Cu(OAc)2 was identified as the optimal oxidative metal salt, exhibiting a remarkable 100% conversion within one hour. Leveraging the straightforward separation of phosphine oxide precursors and phosphinic fluoride products, the Am of an activated ester, [18F]4, sees an impressive nearly 15-fold increase compared to the 18F/19F-isotope exchange, with the same initial activity of [18F]F-. Furthermore, this Cu(II)-mediated 18F-dehydrofluorination approach demonstrates tolerance up to 20% solvent water content, which enables the practical radiosynthesis of 18F-labeled water-soluble molecules under non-drying conditions.

CONCLUSIONS

The direct 18F-dehydrofluorination of phosphine oxide prosthetic groups has been successfully accomplished, achieving a high Am via Cu(II)-mediated oxidative addition and reductive elimination.

Enantioseparation of P-Stereogenic 1-Adamantyl Arylthiophosphonates and Their Stereospecific Transformation to 1-Adamantyl Aryl-H-phosphinates

A focused library of 1-adamantyl arylthiophosphonates was prepared in racemic form. An enantioseparation method was developed for P-stereogenic thiophosphonates using (S)-1-phenylethylamine as the resolving agent. Under optimized conditions, three out of the five arylthiophosphonates were prepared in enantiopure form (ee > 99%). The subsequent desulfurization of optically active arylthiophosphonates gave the corresponding H-phosphinates without significant erosion of enantiomeric purity (ee = 95-98%). Hence, this reaction sequence can be considered an alternative method for the preparation of 1-adamantyl aryl-H-phopshinates. The absolute configuration of the (S)-1-adamantyl phenylphosphonothioic acid was assigned using single-crystal XRD and it allowed the confirmation that the removal of the P = S group proceeds with retention of configuration. The organocatalytic applicability of (S)-1-adamantyl phenylphosphonothioic acid was also evaluated as a P-stereogenic Brønsted acid.

Asymmetric Synthesis of P-Stereogenic Secondary Phosphine-Boranes by an Unsymmetric Bisphosphine Pincer-Nickel Complex

The first highly enantioselective catalytic synthesis of P-stereogenic secondary phosphine-boranes was realized by the asymmetric addition of primary phosphine to electron-deficient alkenes with a newly developed unsymmetric bisphosphine (PCP') pincer-nickel complex. Various P-stereogenic secondary phosphine-boranes were obtained in 57-92% yields with up to 99% ee and >20:1 dr. The follow-up alkylation upon P-C bond formation with alkyl halides provided a practical way to access P-chiral compounds with diverse functional groups.

Synthesis and application in asymmetric catalysis of P-stereogenic pincer–metal complexes

P-stereogenic pincer: synthesis and application in asymmetric catalysis.

The construction of three C–P bonds of P-stereogenic tertiary phosphines containing (l)-menthyl

A wide range of R_P or S_P-(l)-menthyl-containing SPOs were prepared via the reaction of 1,1′-bi(2-naphthol) derived phosphonite with a metallic reagent with excellent yield and dr.

Functional Phosphine Derivatives Having Stationary and Flexible Chiralities: Their Preparation and Chirality Controlling

Various functional secondary and tertiary phosphines, or their derivatives, containing stationary chiral phosphorus and flexible chiral axis were prepared, which could be further modified to afford diversely chelating ligands. The flexible axial chirality was fixed by stereogenic phosphorus via a cyclic linkage of chemical bonds or coordination with a metallic ion.

Synthesis and coordination chemistry of enantiopure t-BuMeP(O)H

Enantioselective synthesis of t-BuMeP(O)H and its coordination chemistry towards several transition metals are described, showing a variety of coordination modes.