Microwave-assisted periselective annulation of triarylphosphenes with aldehydes and ketones

Construction of 4-Vinyl-1,2-oxaphospholane 2-Oxides from Vinyloxiranes and Phosphoryl Diazomethanes

Various 4-vinyl-1,2-oxaphospholane 2-oxides are prepared in good to excellent yields from vinyloxiranes and in situ-generated phosphenes from phosphoryl diazomethanes via the phosphene-induced ring expansion of oxiranes. The reaction is a novel and expeditious strategy for the synthesis of 1,2-oxaphospholane 2-oxide derivatives, featuring ring expansion of readily available starting materials, high atom economy, no catalyst, a fast reaction rate, broad functional group tolerance, high yields, and separable diastereomers.

31P Nuclear Magnetic Resonance Spectroscopy for Monitoring Organic Reactions and Organic Compounds

31P NMR spectroscopy is a consolidated tool for the characterization of organophosphorus compounds and, more recently, for reaction monitoring. The evolution of organic synthesis, mainly due to the combination of elaborated building blocks with enabling technologies, generated great challenges to understand and to optimize the synthetic methodologies. In this sense, 31P NMR experiments also became a routine technique for reaction monitoring, accessing products and side products yields, chiral recognition, kinetic data, intermediates, as well as basic organic parameters, such as acid-base and hydrogen-bonding. This review deals with these aspects demonstrating the essential role of the 31P NMR spectroscopy. The recent publications (the last ten years) will be explored, discussing the experiments of 31P NMR and the strategies accomplished to detect and/or quantify distinct organophosphorus molecules, approaching reaction mechanism, stability, stereochemistry, and the utility as a probe.

Efficient Synthesis of Novel Phostone and Phostam Derivatives via Regioselective Intramolecular Heck Cyclizations of (2-Iodobenzyl)buta-1,3-dienylphosphonates, (2-Iodophenyl)buta-1,3-dienylphosphonates, and N-(2-Iodophenyl)-P-buta-1,3-dienylphosphonamidates

Here, we report the intramolecular Heck cross-coupling of 1,3-dienylphosphonates, affording unique and regioselective access to unprecedented benzofused phostone and phostam derivatives. The reactions proceeded under operationally simple and mild conditions with a wide substrate scope.

Stereoselective Synthesis of trans-1,2,4-Trihydrobenzo[d][1,2]azaphosphinine 3-Oxides from In Situ Formed Phosphenes and Formaldimines

Various trans-1,2,4-trihydrobenzo[d][1,2]azaphosphinine 3-oxides are synthesized highly stereoselectively from in situ generated phosphenes and formaldimines under microwave irradiation. Aryl(diazo)methyl(diaryl)phosphine oxides first undergo the Wolff rearrangement to generate phosphenes. Imines, in situ generated from 1,3,5-triazinanes or paraformaldehyde and primary amines, nucleophilically attack the phosphenes followed by a tandem stereoelectronic effect-controlled intramolecular nucleophilic addition and aromatization to give final trans-1,2,4-trihydrobenzo[d][1,2]azaphosphinine 3-oxides, exhibiting completely different annuloselectivity from linear nonformaldimines.

(Diazomethyl)dimethylphosphine Oxide - A Diazoalkane Reagent for [3+2] Cycloadditions

A safe and efficient method for the in-situ preparation of (diazomethyl)dimethylphosphine oxide - a hereto unexplored diazoalkane reagent - is developed. The method is based on the diazotization of the corresponding P(O)Me2-substituted amine (readily available in multigram quantities) in non-aqueous media. The protocol provides the target product as ca. 1.5 M CHCl3 solution which is stable at -18 °C. The utility of the synthesized diazoalkane is illustrated by its [3+2] cycloaddition with electron-poor alkynes and alkenes providing the corresponding P(O)Me2-substituted pyrazoles and pyrazolines with moderate to good efficiency. In this view, the title compound represents and an important extension of medicinally relevant phosphine oxide reagents.

Synthesis of medium and large phostams, phostones, and phostines

Phostams, phostones, and phostines are a series of 1,2-azaphosphaheterocycle and 1,2-oxaphosphaheterocycle 2-oxide derivatives. They are phosphorus analogues of lactams and lactones and important biologically active compounds. The strategies for the synthesis of medium and large phostams, phostones, and phostines are summarized. They include cyclizations and annulations. Cyclizations achieve ring construction through the formations of C-C, C-O, P-C, and P-O bonds in the rings, while annulations build the rings via [5 + 2], [6 + 1], and [7 + 1] fashions with the stepwise formation of two ring bonds. This review includes the recent syntheses of seven to fourteen-membered phostam, phostone, and phostine derivatives.

Microwave-mediated stereocontrolled annulations of diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates

Chemoselective annulations of phosphoryl carbenes generated from diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates were performed under microwave irradiation, affording 1-diarylphosphoryl-1H-benzo[c]thiopyran derivatives via [3+3] annulation and indolizine derivatives via ([1+5]-1) annulation with P-Cope elimination as the key step. The annuloselectivity was controlled by the steric hindrance of pyridiniums in pyridinium 1,4-zwitterionic thiolates.

Visible-Light-Induced [1+5] Annulation of Phosphoryl Diazomethylarenes and Pyridinium 1,4-Zwitterionic Thiolates

Visible-light-induced [1+5] annulation of phosphoryl diazomethylarenes and pyridinium 1,4-zwitterionic thiolates generates various trifunctionalized dialkyl 1-phosphoryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-3,4-dicarboxylates in good to excellent yields and diastereoselectivities. The annulation involves the nucleophilic attack of thiolates on diazomethylarene-generated carbenes followed by an intramolecular cyclization, is free of catalysts, is atom-economical, and has mild reaction conditions.

Synthetic strategies for the preparation of γ-phostams: 1,2-azaphospholidine 2-oxides and 1,2-azaphospholine 2-oxides

γ-Phostams include γ-phosphonolactams and γ-phosphinolactams and their fused derivatives, phosphorus analogues of γ-lactams. They are 1,2-azaphospholidine 2-oxides and 1,2-azaphospholine 2-oxides and important biological five-membered azaphosphaheterocycles. They have been prepared through two major strategies of cyclizations and annulations. Cyclizations achieve ring construction through the formation of any bond in the ring, while annulations build the ring via [4 + 1] and [3 + 2] fashions with the simultaneous formation of two bonds. The review includes the synthesis of 1,2-azaphospholidine and 1,2-azaphospholine 2-oxides/sulfides and their fused derivatives.

Direct oxidation of N-ynylsulfonamides into N-sulfonyloxoacetamides with DMSO as a nucleophilic oxidant

N-Arylethynylsulfonamides are oxidized into N-sulfonyl-2-aryloxoacetamides directly and efficiently with dimethyl sulfoxide (DMSO) as both an oxidant and solvent with microwave assistance. DFT calculations indicate that DMSO nucleophilically attacks the ethylic triple bond and transfers its oxygen atom to the triple bond to form zwitterionic anionic N-sulfonyliminiums to trigger the reaction. Then it nucleophilically attacks the generated iminium intermediates to accomplish the oxidation via the second oxygen atom transfer. The current method provides a straightforward and efficient strategy to transform various N-arylethynylsulfonamides into N-sulfonyl-2-aryloxoacetamides, sulfonyl oxoacetimides, without any other electrophilic activators or oxidants.

Synthesis of β-Phosphinolactams from Phosphenes and Imines

Various cis-β-phosphinolactams are synthesized stereoselectively for the first time from imines and diazo(aryl)methyl(diaryl)phosphine oxides under microwave irradiation. Diazo(aryl)methyl(diaryl)phosphine oxides first undergo the Wolf rearrangement to generate phosphenes. Imines nucleophilically attack the phosphenes followed by an intramolecular nucleophilic addition via less steric transition states to give final cis-β-phosphinolactams. C-Styrylimines generally give rise to β-phosphinolactams in higher yields than C-arylimines. The stereoselectivity and proposed mechanism are rationalized by DFT theoretical calculation.

Microwave-accelerated and efficient synthesis of structurally diverse N-(2,2-diphenylvinyl)-β-oxoamides

N-(2,2-Diphenylvinyl)-β-oxoamides are both the structural moiety of biologically active compounds and important synthetic intermediates. Structurally diverse N-(2,2-diphenylvinyl)-β-oxoamides are prepared efficiently from 2-diazo-1,3-dicarbonyl compounds and N-alkyl-2,2-diphenylaziridines via an electrophilic ring opening reaction under two different reaction conditions of reflux and microwave irradiation. 2-Diazo-1,3-dicarbonyl compounds undergo the Wolff rearrangement under heating to generate α-oxoketenes, which electrophilically react with N-alkylaziridines to directly produce structurally diverse N-(2,2-diphenylvinyl)-β-oxoamides in good to excellent yields under microwave irradiation. Microwave irradiation accelerates the reaction obviously and efficiently. Both 2-diazo-1,3-diketones and alkyl 2-diazo-3-oxoalkanoates work well. The reaction is catalyst-free and highly atom economical, involves only loss of nitrogen and does not require additives. The products are useful synthons for the convenient preparation of multisubstituted β-lactam derivatives.