Synthesis of 2H-1,2-Oxaphosphorin 2-Oxides via Ag2CO3-Catalyzed Cyclization of (Z)-2-Alken-4-ynylphosphonic Monoesters

Transition-Metal-Free Electrochemical Selenylative Cyclization of Alkynyl Phosphonates

Unprecedented regioselective electrochemical tandem selenation/cyclization of alkynyl phosphonates with diselenide is described here. These obtained selenoether products can be chemo-selectively converted into halogen-functionalized cyclic enol phosphonates under our electrochemical conditions. These protocols provide straightforward access to valuable cyclic enol phosphonate or phosphaisocoumarins under the electrochemical and transition-metal-free conditions. The robustness of these transformations was illustrated by their compatibility with various complex natural products and bioactive molecules. The selenoether and halogen functional groups allow the further diversification of the phosphorus heterocycles thus obtained.

Recent Progress in the Selective Functionalization of P(O)-OH Bonds

As we all know, organic phosphorus compounds have high application values in chemical industries. Compared with traditional compounds with P-X (X = Cl, Br, I) and P-H bonds, phosphorylation reagents containing P(O)-OH bonds are stable, environmentally friendly, and inexpensive. However, in recent years, there have been few studies on the selective functionalization of P(O)-OH bonds for the fabrication of P-C and P-Z bonds. In general, four-coordinated P(O)-OH compounds have reached coordination saturation due to the phosphorus atom center, but cannot evolve the phosphorus coordination center through intra-molecular tautomerization; however, the weak coordination effects between the P=O bond and transition metals can be utilized to activate P(O)-OH bonds. This review highlights the most important recent contributions toward the selective functionalization of P(O)-OH bonds via cyclization/cross coupling/esterification reactions using transition metals or small organic molecules as the catalyst.

Recent Organic Transformations with Silver Carbonate as a Key External Base and Oxidant

Silver carbonate (Ag2CO3), a common transition metal-based inorganic carbonate, is widely utilized in palladium-catalyzed C–H activations as an oxidant in the redox cycle. Silver carbonate can also act as an external base in the reaction medium, especially in organic solvents with acidic protons. Its superior alkynophilicity and basicity make silver carbonate an ideal catalyst for organic reactions with alkynes, carboxylic acids, and related compounds. This review describes recent reports of silver carbonate-catalyzed and silver carbonate-mediated organic transformations, including cyclizations, cross-couplings, and decarboxylations.

Synthesis of polycyclic phosphonates via an intramolecular Diels-Alder reaction of 2-benzoylbenzalaldehyde and alkenyl phosphites

In this paper, we present a Lewis-acid-promoted reaction of 2-benzoylbenzaldehyde and trialkenyl phosphites, which resulted in the formation of polycyclic phosphonates. The reaction proceeded via nucleophilic attack of trialkenyl phosphite on the carbonyl carbon of 2-benzoylbenzaldehyde. The subsequent intramolecular Diels-Alder reaction led to the formation of the cyclic phosphonate.

Copper-Catalyzed Oxidative Alkylation (Methylation) of Phosphonamides and Phosphinamides Using Dicumyl Peroxide

An effective and practical CuI-catalyzed methodology toward N-alkyl or N-methyl phosphonamides and phosphinamides was herein demonstrated. The transformation took place readily under the oxidative conditions, and plenty of N-alkylated (methylated) amides (30 examples) were successfully furnished in high efficiency (up to 92% yields). Dicumyl peroxide was considered to act either as the oxidant for the alkylation reaction or as methyl donator for the methylation protocol.

Rhodium(iii)-catalyzed ortho-alkenylation using a cyclic N-phosphoryl ketimine as the directing group

A novel cyclic N-phosphoryl ketimine structure can efficiently react with olefins as useful directing groups to construct a myriad of phosphate scaffolds via rhodium(iii)-catalyzed ortho-alkenylation.

Copper-mediated reaction of oxazirconacyclopentenes with dichlorophenylphosphine: a new pathway for the formation of 1,2-oxaphosphole derivatives

CuCl-mediated reaction of oxazirconacyclopentenes with dichlorophenylphosphine afforded dihydrooxaphospholes in high yields, in which the reaction was performed conveniently in one-pot from an alkyne, carbonyl compound and dichlorophosphine.

Regioselective synthesis of fused imidazo[1,2-a]pyrimidines via intramolecular C-N bond formation/6-endo-dig cycloisomerization

An efficient regioselective cascade synthesis of N-fused imidazo heterocycles has been developed. This cascade transformation proceeds via a transition-metal (copper/silver) catalyzed coupling reaction between 2-aminobenzimidazole, aldehydes, and alkynes leading to the formation of propargylamine intermediate, which regioselectively undergoes 6-endo-dig cyclization through intramolecular N-H bond activation interceded C-N bond formation leading to highly functionalized imidazo[1,2-a]pyrimidines in good to excellent yields.

Rhodium-catalyzed oxidative C-H activation/cyclization for the synthesis of phosphaisocoumarins and phosphorous 2-pyrones

Rhodium-catalyzed cyclization of phosphinic acids and phosphonic monoesters with alkynes has been developed. The oxidative annulation proceeds with complete conversion of phosphinic acid derivatives and allowed the atom-economic preparation of useful phosphaisocoumarins with high yield and selectivity. The reaction is tolerant of extensive substitution on the phosphinic acid, phosphonic monoester and alkyne, including halides, ketone, and hydroxyl groups as substituents. Furthermore, we found that alkenylphosphonic monoesters proceed to give a wide range of phosphorus 2-pyrones through oxidative annulation with alkynes. Mechanistic studies revealed that C-H bond metalation was the rate-limiting step.

Cationic dirhodium carboxylate-catalyzed synthesis of dihydropyrimidones from propargyl ureas

Cationic Rh(II) complexes are able to catalyze the regioselective hydroamination of propargyl ureas in a 6-endo fashion. This transformation permits access to interesting substitution patterns of dihydropyrimidines which have found use as nucleotide exchange factor inhibitors.

Synthesis of phosphaisocoumarins through rhodium-catalyzed cyclization using alkynes and arylphosphonic acid monoesters

A rhodium-catalyzed cyclization using alkynes and arylphosphonic acid monoesters for the synthesis of phosphaisocoumarins is reported. A number of arylphosphonic acid monoesters were selectively cyclized in high yields with functional group tolerance. In addition, unsymmetrical alkynes are applied in high regioselectivity.

A remarkable accelerating effect of Ag-salt on intramolecular cyclization of o-(1-alkynyl)benzenesulfonamides

Herein, we report transition metal-catalyzed intramolecular cyclization of o-(1-alkynyl)benzenesulfonamides to afford 3-substituted benzothiazines regioselectively via a C-N bond forming reaction and Cu-catalyzed sequential C-N and C-C bond formation leading to the corresponding 3,4-disubstituted derivatives.

Selective Synthesis of 2,3-Disubstituted-2H-isoindol-1-ylphosphonate and 2,3-Disubstituted-1,2-dihydroiso- quinolin-1-ylphosphonate via Metal-Tuned Reaction of α-Amino (2-Alkynylphenyl)methylphosphonate

Palladium(II)-catalyzed reaction of alpha-amino (2-alkynylphenyl)methylphosphonate provides a novel and efficient route to 2,3-disubstituted-2H-isoindol-1-ylphosphonate via 5-exo-cyclization and [1,5]-H shift; while 2,3-disubstituted-1,2-dihydroisoquinolin-1-ylphosphonate is afforded through 6-endo-cyclization utilizing silver triflate as catalyst.