Phosphorylation of arenes, heteroarenes, alkenes, carbonyls and imines by dehydrogenative cross-coupling of P(O)-H and P(R)-H

Synthetic versatility: the C-P bond odyssey

C-P bond formation reactions have garnered significant attention due to the widespread presence of organophosphorus compounds in pharmaceuticals, phosphine-containing ligands, pesticides, and materials science. Consequently, various efficient methodologies have been established in recent decades for constructing C-P bonds. This review article traces the historical evolution of C-P bond research and explores the prospects of C-P bond formation. It contrasts biotechnological approaches with chemical synthesis, emphasizing the critical importance of precision and innovation in developing novel C-P structures. A forward-looking perspective is provided on the role of computational tools and machine learning in optimizing C-P bond synthesis and discovering new compounds. The article explores prospective avenues for reactions that form C-P bonds and advocates for enhanced interdisciplinary collaboration to propel scientific and technological advancements.

N-Protection Dependent Phosphorylation of Dehydroamino Acids to Build Unusual Phosphono-Peptides

An efficient Mn(III)-promoted phosphorylation of dehydroalanine (Dha) has been developed to give unusual α-amino acids bearing phosphonates/phosphine oxides and β-vinyl phosphonates/phosphinates depending on N-protection of amino acid. N,N-diprotected dehydroalanine reacted with H-phosphonates and H-phosphine oxides to give structurally diverse phosphorylated α-amino acids through conjugate addition of phosphorous radical generated by Mn(OAc)3.2H2O. Whereas, a highly Z-selective phosphorylation was observed in the case of mono N-Boc protected dehydroalanine via cross dehydrogenative coupling to give (Z)- β -vinyl phosphono amino acid. The method is successfully applied to short peptides to derive unusual phosphono-peptides under mild conditions.

Phototriggered Self-Catalyzed Phosphorylation of 3,4-Dihydroquinoxalin-2(1H)-ones with Diarylphosphine Oxides in EtOH

A highly effective external photocatalyst- and additive-free method for the phosphorylation of 3,4-dihydroquinoxalin-2(1H)-ones to produce phosphorylated dihydroquinoxalin-2(1H)-ones has been reported. A wide variety of phosphorylated products were formed in good to excellent yields. Preliminary mechanistic studies reveal that the phosphorylation process involves an EnT process, a SET process, a HAT process, and a deprotonation process.

Metal-Free Aminophosphonation: Eco-Friendly Synthesis and Photophysical Properties of Fluorescent 3-(Aminoimidazo[1,2-a]Pyridin-2-yl)Phosphonates

We report a novel, metal-free procedure for the direct aminophosphonation of imidazo[1,2-a]pyridines in green solvents under open air conditions. This method is characterized by its mild and sustainable conditions, ease of operation, scalability, and excellent functional group compatibility. The synthesized compounds exhibit promising photophysical properties, including significant Stokes shifts and quantum yields, making them potential candidates for innovative fluorescent probes.

Solvent-Switchable Remote C-H Activation via 1,4-Palladium Migration Enables Site-Selective C-P Bond Formation: A Tool for the Synthesis of P-Chiral Phosphinyl Imidazoles

Solvent-switchable and site-selective phosphorylation of imidazoles at the C2 or C5 position of the imidazole ring was achieved via 1,4-palladium migration. P-Chiral tert-butyl(aryl)phosphine oxides were cross-coupled to 1-(2-bromophenyl)-1H-imidazoles with high enantiospecificity, thereby leading to a novel class of chiral imidazole-based phosphine oxides. As proof of concept, reduction of an analogue yielded the corresponding P-chiral 2-phosphinyl imidazole ligand, which was shown to induce high enantioselectivity in the formation of axially chiral molecules synthesized via Pd-catalyzed Suzuki-Miyaura cross-coupling.

TEMPO/PhI(OAc)2 promotes the α-aminophosphinoylation of alcohols with amines and H-phosphine oxides in aqueous medium

A novel method for synthesizing α-aminoalkyl phosphine oxides in aqueous medium, using Ar2P(O)-H reagents, alcohols and amines, is described. This method: (i) allows for the smooth aminophosphinoylation of alcohols with amines and H-phosphine oxides under mild conditions; (ii) provides an efficient and alternative approach to access various α-aminoalkylphosphine oxides. Although various amines exhibited remarkable versatility and tolerance for functional groups in this reaction, alcohols and H-phosphine oxides demonstrated limited applicability as reactants. Hence, further investigation using a wider range of substrates is crucial. The postulated mechanism indicated that the three-component reaction followed the imine pathway due to the in situ oxidation of alcohol to aldehyde.

Visible light-enabled synthesis of phosphorylated indolizine and pyridoindole derivatives via HAT-mediated radical cascade cyclization

A visible light-enabled cascade cyclization strategy is disclosed with concomitant phosphorylation and heterocycle construction. It provides a novel and environmentally benign approach for accessing tetrahydroindolizine-containing phosphonates under metal-free conditions. Mechanistic studies revealed that phosphinoyl radicals were generated from H-phosphonates via a HAT process.

Organocatalytic Diastereoselective (4 + 1) Cycloaddition of o-Hydroxyphenyl-Substituted Secondary Phosphine Oxides

The first organocatalytic diastereoselective (4 + 1) cycloaddition of o-hydroxyphenyl-substituted secondary phosphine oxides (SPOs) has been established, which makes use of o-hydroxyphenyl substituted SPOs as suitable four-atom phosphorus-containing 1,4-dinucleophiles and 3-indolylformaldehydes as competent 1,1-dielectrophiles under Bro̷nsted acid catalysis. The reaction mechanism was suggested to involve the formation of 3-indolylmethanol intermediates and vinyliminium intermediates, which played an important role in controlling the reactivity and diastereoselectivity of the (4 + 1) cycloaddition under Bro̷nsted acid catalysis. By this approach, a series of benzo oxaphospholes bearing P- and C-stereocenters were synthesized in moderate to good yields (50%-95% yields) with excellent diastereoselectivities (all >95:5 dr). This reaction not only represents the first organocatalytic diastereoselective (4 + 1) cycloaddition of o-hydroxyphenyl-substituted SPOs but also provides an efficient and diastereoselective method for the construction of phosphorus-containing benzo five-membered heterocyclic skeletons bearing both P-stereocenter and C-stereocenter.

Tandem addition of nucleophilic and electrophilic reagents to vinyl phosphinates: the stereoselective formation of organophosphorus compounds with congested tertiary carbons

Carbon anions formed via the addition of Grignard reagents to SP-vinyl phosphinates were modified with electrophilic reagents to afford organophosphorus compounds with diverse carbon skeletons. The electrophiles included acids, aldehydes, epoxy groups, chalcogens and alkyl halides. When alkyl halides were used, bis-alkylated products were afforded. Substitution reactions or polymerization occurred when the reaction was applied to vinyl phosphine oxides.

Regioselective Direct C-H Phosphorylation of Benzofulvenes

A practical and straightforward protocol to access site-selective C-3 phosphorylated benzofulvenes by means of cross-dehydrogenative coupling of two nucleophilic moieties, employing silver as a promoter, is described here. Remarkably, this protocol provides a broad, structurally diverse phosphorylated benzofulvene. Initial mechanistic studies shed light on its radical coupling nature, and late-stage transformations offer highly diversified benzofulvenes core.

Direct phosphorylation of benzylic C-H bonds under transition metal-free conditions forming sp3C-P bonds

Direct phosphorylation of benzylic C-H bonds was achieved in a biphasic system under transition metal-free conditions. A selective radical/radical sp3C-H/P(O)-H cross coupling was proposed, and various substituted toluenes were applicable. The transformation provided a promising method for constructing sp3C-P bonds.