Phosphorus Analogues of Homoproline

Abstract

Aminophosphonic and aminophosphinic acid analogs of most of the natural amino acids have been synthesized recently (1). We describe here the synthesis of phosphonic and phosphinic analogs of the natural iminocarboxylic acid homoproline. The compounds were obtained by the iminoalkylation of P(O)H-containing organophosphorus compounds with the trimer of tetrahydropyridine. This trimer adds three equivalents of dialkyl phosphite or monoalkyl alkyl(ary1) phosphonite to form the esters of piperidine-2-phosphonic or piperidine-2-alkyl (ary1)phosphinic acids. Hydrolysis of the esters in acidic medium leads to the phosphorus analogs of homoproline.     

An indium-TMSCl promoted reaction of diphenyl diselenide and diorganyl disulfides with aldehydes: novel routes to selenoacetals, thioacetals and alkyl phenyl selenides

The reactions of diphenyl diselenide and dialkyl disulfides with aldehydes in the presence of In-TMSCl have been investigated. Aliphatic aldehydes provide the corresponding selenoacetals and aromatic aldehydes lead predominantly to benzyl phenyl selenides on reaction with diphenyl diselenide. However, the reaction of dimethyl disulfide and diphenyl disulfide with both aromatic and aliphatic aldehydes produce dithioacetals. This provides a novel route to the synthesis of selenoacetals, thioacetals and selenides from aldehydes.     

Insertion of Elemental Sulfur into the Se-Se Bond of Diorganyl Diselenides. Synthesis of Bis-alkyl(seleno) Polysulfides

Reaction of dialkyl diselenides R₂Se₂ (R = Me, n-Bu) with sulfur at room temperature in the presence of the catalytic system DMSO-Na₂S·9H₂O-triethylbenzylammonium chloride, as well as at 55-60°C in the presence or in the absence of catalysts leads to the insertion of from one to six atoms of sulfur into the Se-Se bond. Bis(methylseleno) polysulfides MeSeS_nSeMe with n = 5-6 gradually liberate sulfur on keeping. Dibutyl diselenide is less active than dimethyl diselenide, and diphenyl diselenide does not react with sulfur in boiling carbon disulfide. At 55-60°C a small portion of selenium in dialkyl diselenides passes into unreacted sulfur which is indicative of cleavage of the C-Se bonds in bis(methylseleno) polysulfides.     

Ti(O-isoPr)4 Catalyzed hydrophosphonylation of activated alkenes by diphenyl H-phosphonate

Diphenyl 2-(alkoxycarbonyl)alkylphosphonates were synthesized via a titanium alkoxide catalyzed Pudovik reaction under mild conditions. Methacrylates or acrylates were selectively hydrophosphonylated by diphenyl H-phosphonate even in the presence of a dialkyl phosphite.     

Dipotassium-Hydrogen-Phosphate-Powder-Catalyzed Stereoselective C-Vinylation of Diphenylacetonitril

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates by diphenylacetonitril, leads to the vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce the corresponding stabilized phosphorus ylides. Dipotassium hydrogen phosphate powder was found to catalyze the conversion of the stabilized phosphorus ylides to dialkyl(Z)-2-[cyano (diphenyl)methyl]-2-butenedioates under thermal and microwave conditions in a solventless system.     

Synthesis of β-Lactams by Palladium(0)-Catalyzed C(sp3)−H Carbamoylation

A general and user-friendly synthesis of β-lactams is reported that makes use of Pd⁰-catalyzed carbamoylation of C(sp³)−H bonds, and operates under stoichiometric carbon monoxide in a two-chamber reactor. This reaction is compatible with a range of primary, secondary and activated tertiary C−H bonds, in contrast to previous methods based on C(sp³)−H activation. In addition, the feasibility of an enantioselective version using a chiral phosphonite ligand is demonstrated. Finally, this method can be employed to synthesize valuable enantiopure free β-lactams and β-amino acids.     

Study of thermochemical properties of diphenyl[dialkyl(alkyl)carbamoylmethyl]phosphine oxides

The synthesis and the studies of properties of diphenyl[dialkyl(alkyl)carbamoylmethyl]phosphine oxides by differential scanning calorimetry, mass spectrometry and Knudsen effusion method were performed. The thermodynamic parameters of melting and vaporization were calculated.     

Synthesis of β‐Lactams by Palladium(0)‐Catalyzed C(sp3)−H Carbamoylation

A general and user‐friendly synthesis of β‐lactams is reported that makes use of Pd⁰‐catalyzed carbamoylation of C(sp³)−H bonds, and operates under stoichiometric carbon monoxide in a two‐chamber reactor. This reaction is compatible with a range of primary, secondary and activated tertiary C−H bonds, in contrast to previous methods based on C(sp³)−H activation. In addition, the feasibility of an enantioselective version using a chiral phosphonite ligand is demonstrated. Finally, this method can be employed to synthesize valuable enantiopure free β‐lactams and β‐amino acids.     

Mass spectra of phosphoramidic acid esters

The mass spectra of diphenyl, dibenzyl and six dialkyl phosphoramidates have been recorded and interpreted with the aid of high resolution measurements and the metastable defocusing technique.     

Eosin Y catalyzed visible light oxidative C-C and C-P bond formation

Eosin Y catalyzes efficiently the visible light mediated coupling of sp(3) C-H bonds adjacent to the nitrogen atom in tetrahydroisoquinoline derivatives in the absence of an external oxidant. Nitroalkanes, dialkyl malonates, malononitrile, and dialkyl phophonates were used as pronucleophiles in this metal-free, visible light oxidative coupling reaction.     

Cationic thiocarbonyl complexes of rhodium(I)

The syntheses are described of a range of cationic rhodium(I) thiocarbonyl complexes containing tertiary phosphine, phosphinite, phosphonite and phosphonite ligands.     

Palladium-catalyzed direct phosphonation of azoles with dialkyl phosphites

The first Pd-catalyzed direct phosphonation of azoles with dialkyl phosphites has been achieved without addition of base or acid. This method involves the oxidative cleavage of C-H and P(O)-H bonds and represents an atom-efficiency alternative to the classical phosphonation of Ar-X. A Pd(II)/Pd(IV) mechanism has been studied and proposed.     

Rhodium-catalyzed disulfide exchange reaction

A system of RhH(PPh3)4, trifluoromethanesulfonic acid, and (p-tol)3P catalyzes the disulfide exchange reaction. Treatment of two symmetrical dialkyl disulfides with the catalyst provides an equilibrium mixture of three disulfides within 15 min in refluxing acetone. The catalyst is active after reaching the equilibrium, and addition of a disulfide to the mixture changes the ratio of the products. The use of 4 mol equiv excess of one of the disulfides provides the unsymmetrical disulfide in a yield exceeding 80%. Disulfide-containing peptides also undergo an exchange reaction. The reactions of diaryl disulfides and dialkyl disulfides are even faster, and reach equilibrium within 5 min at room temperature in the presence of the rhodium complex and 1,2-bis(diphenylphosphino)ethane (dppe). This exchange reaction is considerably affected by the substituents on the disulfides. Treatment of diphenyl disulfide, di(p-tolyl) disulfide, and bis(sec-butyl) disulfide yields phenyl p-tolyl disulfide at room temperature with unchanged bis(sec-butyl) disulfide; random disproportionation occurs at reflux. The rhodium catalysis can be used for the exchange reaction of disulfides and diselenides giving selenosulfides as well as disulfides and ditellurides giving tellurinosulfides.     

Photosensitized oxygenation of sulfides within an amphiphilic dendrimer containing a benzophenone core

Photosensitized oxygenation of sulfides within amphiphilic dendrimers, Gn [n(generation) = 1-3], consisting of a benzophenone (BZP) sensitizing core, apolar interior based on n-undecane spacer, and polar dendron exterior based on 2,2-bis(hydroxymethyl)propionic acid, has been investigated in O(2)-saturated methanol. Sulfoxide formation occurring via reaction of O(2) with triplet excited-state sulfide ((3)sulfide), which is formed by a triplet energy transfer (TET) from photoformed (3)BZP to sulfide, was accelerated by the dendric sensitizers, where G2 showed the highest yields of alkylaryl and dialkyl sulfoxides. Laser photolysis studies revealed that enhanced access of sulfide to the (3)BZP core inside the apolar microenvironment accelerates the TET to sulfide, whereas prompt migration of polar sulfoxide to the polar outer shell of the dendrimer suppresses a competitive TET to sulfoxide, thus resulting in effective (3)sulfide formation. Another notable feature of the dendric sensitizer appears in oxygenation of diaryl sulfide, which is promoted by a persulfoxide intermediate formed by photooxygenation of dialkyl sulfide; photoirradiation of a mixture of diethyl sulfide (1a) and diphenyl sulfide (4a) with G2 gave 17-fold higher diphenyl sulfoxide (4b) yield than that obtained with unmodified BZP. The apolar microenvironment within the dendric sensitizer encapsulates a large quantity of 4a, which is oxidized effectively by the persulfoxide of 1a, thus resulting in high 4b yield. The BZP core within the dendric sensitizer is stable even by photoexcitation in protic solvent, suggesting potential utilities of this dendric system for effective and selective photosensitized oxygenation of sulfides.     

Synthesis and Ambiphilic Reactivity of Metalated Diorgano-Phosphonite Boranes

Unprecedented metalated phosphonite boranes were prepared from PH-substituted precursors and silyl amides. Although potassium derivatives were thermally stable and could even be isolated and structurally characterised, lithiated analogues proved to be unstable towards self-condensation under cleavage of LiOR at ambient temperature. Reaction studies revealed that the metalated phosphonite boranes exhibit ambiphilic character. Their synthetic potential as nucleophilic building blocks was demonstrated in the synthesis of the first stannylated phosphonite representing a new structural motif in phosphine chemistry.     

Concerted vs. Non‐Concerted 1,3‐Dipolar Cycloadditions of Azomethine Ylides to Electron‐Deficient Dialkyl 2,3‐Dicyanobut‐2‐enedioates

The quantum‐chemical calculations of the thermal ring opening of 1‐methyl‐2,3‐diphenyl‐ and 1,2,3‐triphenylaziridine with formation of the corresponding azomethine ylides of S‐, U‐, and W‐type as well as their cycloaddition to dimethyl acetylenedicarboxylate (DMAD) and dimethyl 2,3‐dicyanobut‐2‐enedioate, were performed at the DFT B3LYP/6‐31G(d) level of theory with the PCM solvation model. The calculations are in complete accordance with experimental results and explain the switch from the concerted to the non‐concerted pathway depending on substituents in the dipolarophile and the ylide. It was found that strong electron‐withdrawing substituents in dipolarophiles, such as in dialkyl dicyanobutenedioates, significantly reduce the barrier for the formation of zwitterionic intermediates in the reaction of azomethine ylides with such dipoles. This can render the stepwise cycloaddition competitive with the concerted one. However, the concertedness of the cycloaddition even to dipolarophiles with several electron‐withdrawing substituents is governed by a fine balance of electronic and steric effects in both ylide and dipolarophile counterparts. The hypothesis that introduction of substituents in the azomethine ylide that destabilize the positive charge in a corresponding zwitterion will favor the concerted cycloaddition even with dialkyl dicyanobutenedioates was tested theoretically and experimentally.     

Reaction of ethylN,N-(p-methoxybenzal)-p-aminobenzoate with dialkyl phosphonates

Abstact Interaction of ethylN,N-(p-methoxybenzal)-p-aminobenzoate with dialkyl phosphonates results in dialkyl (N-p-ethoxycarbonylphenylamino)-p-methoxybenzal phosphonates. In the resulting compounds hydrogen bonds are observed by IR spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1301–1303, May, 1996.     

Polyesters of phosphoric acid: Synthesis and kinetics of hydrolysis

Three major methods have been elaborated in our laboratory for preparation of polymers with poly(alkylene phosphates) backbones: ring-opening polymerization, poly-condensation and transesterification, and polyaddition. The second method is based on the reaction of the commercially available compounds, namely dialkyl (or diaryl)-H-phosphonates and glycols. Reaction of the aliphatic H-phosphonates with aliphatic glycols is a reversible process, whereas polycondensation of diphenyl H-phosphonates with aliphatic and cycloaliphatic diols is practically irreversible. This latter method has recently been developed and is described in this paper. Poly H-phosphonates with M̄_n up to 40–10³ were prepared. Polymers are easily oxidized and quantitatively converted into the relatively stable poly(alkylene phosphates). Some physical properties of these polymers and kinetics of their hydrolysis is discussed.     

Crystallization-induced light-emission enhancement of diphenylmethane derivatives

A family of diphenylmethane derivatives has been synthesized and their luminescence properties characterized. While in solution the compounds are weakly emissive, showing no aggregation-induced emission enhancement, the crystals of three dialkyl 5,5′-methylenebis(2-hydroxybenzoate) samples exhibit intense emission. This emission enhancement upon crystallization is ascribed to particular molecular packing, which stiffens the structure of the compounds via hydrogen bonds, preventing consecutive π–π interactions.     

Organoboron compounds,synthesis of allyl(dialkyl)boranes and diallyl(alkyl)boranes

Highly reactive allyl(dialkyl)-, crotyl(dialkyl)-, 3,3-dimethylallyl(dialkyl)-(= prenyl(dialkyl), and diallyl(alkyl)-boranes were prepared by allylation of esters R₂BOR′, RB(OR′)₂ or thioesters R₂BSR′ (R = alkyl) using allylic derivatives of aluminium, magnesium or boron in exchange reactions.The titled compounds are stable up to 100°C and do not symmetrize even on heating at 100°C for a long time. PMR spectroscopy data show that the characteristic feature of these compounds is a permanent allyl rearrangement, the rate of which increases with an increase in temperature. For allyl(diethyl)-borane at 100°C and 125°C the rates are equal to 2500 and 5000 sec^?1 respectively; activation energy of the rearrangement amounts to 11.8±0.2 kcal mol^?1.The boronallyl bonds in unsymmetrical allyl(alkyl)boranes readily split under the action of water and alcohols, protonolysis being accompanied by allyl rearrangement, crotyl and prenyl compounds are converted into 1-butene or 3-methyl-1-butene, respectively.