Chiral N-alkyl-2,4,6-triphenylpyridiniums as enantioselective triplet photosensitizers. laser flash photolysis and preparative studies

Three N-alkylpyridinium photosensitizers having chiral alkyl groups have been prepared by reacting 2,4,6-triphenylpyrylium tetrafluoroborate ion with (1R,2S)-(-)-norephedrine, (S)-(+)-2-(aminomethyl)pyrrolidine, and (R)-(-)-1-cyclohexylethylamine. Laser flash photolysis allows detection of the corresponding triplet excited states that are quenched by hydrogen atom donors and electron donors. Asymmetric quenching of the chiral triplet excited state was observed using enantiomerically pure 1,2-diamino cyclohexane as quencher. Low enantiomeric excess values (up to 7%) were measured for the photochemical cyclization of 5-methyl-4-hexenoic acid to its corresponding gamma-lactone using these chiral N-alkylpyridinium as photosensitizers.     

Structural and coordination properties of 1,2-bis(cyclopropyl)-3,4-bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidenecyclobutene prepared by dehydrogenative homocoupling of 3-cyclopropyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaallene

According to a protocol for the synthesis of phosphaallenes we recently established, 3-cyclopropyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphallene was obtained from (Z)-2-bromo-3-cyclopropyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphapropene. A novel bidentate ligand, 1,2-bis(cyclopropyl)-3,4-bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidenecyclobutene, was prepared by oxidative homocoupling of 3-cyclopropyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaallene in the presence of butyllithium, together with the generation of hydrogen gas. The 1,2-bis(cyclopropyl)-3,4-diphosphinidenecyclobutene was allowed to react with (tht)AuCl (tht = tetrahydrothiophene) to afford the corresponding digold(I) complex of a six-membered metallacycle containing the P=C-C=P skeleton. The molecular structures of the 2-bromo-3-cyclopropyl-1-phosphapropene, 1,2-bis(cyclopropyl)-3,4-diphosphinidenecyclobutene and the digold complex were unambiguously determined by X-ray crystallography and are discussed from the point of view of the cyclopropyl conjugation.     

Preparation and coordination properties including catalytic activities of a bulky 2-methyl-3-thioxo-1,3-diphosphapropene

[reaction: see text] 2-Methyl-3,3-diphenyl-3-thioxo-1-(2,4,6-tri-tert-butylphenyl)-1,3-diphosphapropene, which bears a P=C-P=S skeleton, was prepared and used as a ligand of transition-metal complexes. The palladium complexes containing the ligated 3-thioxo-1,3-diphophapropene were stable and used for catalytic reactions such as cross-couplings and direct conversion of allyl alcohol to allylaniline.     

Phospha-S-triazines. IX. Chloro-substituted monophospha-S-triazines and derivatives

1-Dichlorophospha-3,5-bis(perfluoro-n-heptyl)-2,4,6- triazine and one of its perfluoroalkylether analogues were synthesized by interaction of phosphorus pentachloride with the respective imidoylamidines; subsequent replacement of the chloro- by azido groups proceeded readily. 1-Chloro(phenyl)- phospha-3,5-bis(perfluoro-n-heptyl)-2,4,6-triazine was prepared by a parallel process using tetrachlorophenylphosphorane instead of phosphorus pentachloride; phenoxy and stearyloxy derivatives were formed without difficulty. All the compounds, with the exception of 1-stearyloxy(phenyl)phospha-3,5-bis(perfluoro- n-heptyl)-2,4,6-triazine, exhibited the characteristic mass spectral fragmentation patterns associated with the monophospha- s-triazine ring system.     

4(R)-(2,4,6-三甲基苄氧基)-(S)-脯氨酸促进的直接不对称羟醛反应

方便地合成了一种新的不对称羟醛反应的手性催化剂4(R)-(2,4,6-三甲基苄氧基)-(S)-脯氨酸. 以过量的丙酮作溶剂, 使用5 mol%该催化剂, 有效地催化了多种取代苯甲醛与丙酮间的不对称羟醛反应, 产率最高达91.0%, ee最高达84.3%.     

Synthesis and polymerization of 1-(2,4,6-tricyanophenylthio)-3-[3,5-bis(n,n-dimethylamino)phenoxy]-2-propyl methacrylate; polymer effect on intramolecular charge–transfer interaction

1-[3,5-Bis(N,N-dimethylamino)phenoxy]-ω-(2,4,6-tricyanophenylthio)alkanes ( 1a–c ), where an electron-accepting 2,4,6-tricyanophenylthio group and an electron-donating 3,5-bis(N,N-dimethylamino)phenoxy one are linked with a spacer such as ethylene, trimethylene, and tetramethylene, were prepared in order to examine an effect of the spacer chain length on intramolecular charge–transfer interaction between the 2,4,6-tricyanophenylthio and 3,5-bis(N,N-dimethylamino)phenoxy groups. From the UV-vis spectra measurements of 1a–c , 1-[3,5-bis(N,N-dimethylamino)phenoxy]-3-(2,4,6-tricyanophenylthio)Propane ( 1b ) carrying the trimethylene chain as a spacer was found to have the strongest intramolecular charge–transfer interaction. A new methacrylate-type monomer carrying the 1b unit as a side chain, 1-(2,4,6-tricyanophenylthio)-3-[3,5-bis(N,N-dimethylamino)phenoxy]-2-propyl methacrylate ( 2 ), was prepared successfully in 9.2% total yield in seven steps. The monomer 2 homopolymerized in benzene, tetrahydrofuran, acetone, and dimethyl sulfoxide in the presence of 2,2′-azobis(isobutyronitrile) at 60°C to give polymers [poly( 2 )] with molecular weights of 6,000 to 98,000. An intramolecular charge–transfer interaction in the poly( 2 ) was found to be larger than that in the monomer 2 and to increase with an increase in the degree of polymerization of the poly( 2 ), suggesting that there is an existence of polymer effect other than the polymer effect due to the high local concentration of the donor-acceptor pair. © 1995 John Wiley & Sons, Inc.     

Organoantimony Derivatives of 2,4,6-Tribromophenol

2,4,6-Tribromophenoxytetraphenylantimony was prepared in 93% yield by the reaction of pentaphenylantimony with bis(2,4,6-tribromophenoxy)triphenylantimony Ph₃Sb(OC₆H₂Br₃-2,4,6)₂ in toluene at 90°C (1 h). Bis(2,4,6-tribromophenoxy)triphenylantimony, in turn, was prepared by oxidation of triphenyl- stibine with hydrogen peroxide in the presence of 2,4,6-tribromophenol in ether at 20°C (12 h) in 47% yield, with the second reaction product being -oxobis[(2,4,6-tribromophenoxy)triphenylantimony] in which the antimony atom, according to single crystal X-ray diffraction, has a trigonal bipyramidal surrounding with the bridging oxygen atom and 2,4,6-tribromophenoxy substituents in the axial positions.     

Enhanced photodecarboxylation of an aryl ester in polyethylene films

[reaction: see text] Photodecarboxylation is the exclusive photoreaction of 2,4,6-trimethylphenyl (S)-2-methylbutanoate in unstretched high-density polyethylene films. The sole product, (S)-1-(2-methylpropyl)-2,4,6-trimethylbenzene, is formed with complete retention of stereochemistry. In other polyethylene films, organic solvents, and beta-cyclodextrin cavities, cage-escaped products derived from Fries-type bond scission are obtained as well. The results indicate the importance of the media in controlling the conformations of aryl esters and, thereby, their photoreactions.     

Synthesis and structure of tetra- and triphenylantimony 2,4,6-trichlorophenoxides

The reaction of pentaphenylantimony with 2,4,6-trichlorophenol or bis(2,4,6-trichlorophenoxy)- triphenylantimony in toluene afforded (2,4,6-trichlorophenoxy)tetraphenylantimony. The reaction of triphenylantimony with tert-butyl hydroperoxide and 2,4,6-trichlorophenol led to the formation of bis(2,4,6-trichlorophenoxy) triphenylantimony; further reaction of the latter with triphenylantimony dichloride provided (2,4,6-trichlorophenoxy)triphenylantimony chloride. According to the XRD data, the antimony atoms in the prepared compounds had distorted trigonal-bipyramidal coordination with electronegative ligands in axial positions.     

Exceptionally Persistent Nitrogen-Centered Free Radicals. Syntheses, ESR Spectra, Isolation, and X-ray Crystallographic Structures of N-(Arylthio)-2-tert-butyl-4,6-diarylphenylaminyl and N-(Arylthio)-4-tert-butyl-2,6-diarylphenylaminyl Radicals(1)

The preparation, ESR spectra, isolation, and X-ray crystallographic structure of N-(arylthio)-2-tert-butyl-4,6-diarylphenylaminyls (1) and N-(arylthio)-4-tert-butyl-2,6-diarylphenylaminyls (2) are described. The aminyls are generated by PbO(2) oxidation of N-(arylthio)-2-tert-butyl-4,6-diarylanilines and N-(arylthio)-4-tert-butyl-2,6-diarylanilines. The kinetic ESR study shows that the aminyls are quite persistent, even in the presence of oxygen, and exist in the individual radical forms. Among the seventeen aminyls prepared, N-[(4-nitrophenyl)thio]-2-tert-butyl-4,6-diphenylphenylaminyl (1b), N-[(4-nitrophenyl)thio]-2-tert-butyl-4,6-bis(4-chlorophenyl)phenylaminyl (1f), N-[(4-nitrophenyl)thio]-4-tert-butyl-2,6-diphenylphenylaminyl (2b), N-[(4-nitrophenyl)thio]-4-tert-butyl-2,6-bis(4-chlorophenyl)phenylaminyl (2h), and N-[(3,5-dichlorophenyl)thio]-4-tert-butyl-2,6-bis(4-chlorophenyl)phenylaminyl (2j) are isolated as radical crystals. The crystallographic structures of 1b and 2b are determined by the X-ray crystallographic analyses. Aminyls 1 and 2 give similar ESR spectra consisting of 1:1:1 triplets with the a(N) values of 0.921-0.948 mT. Deuteration of the phenyl groups on the anilino benzene ring gives rise to a further splitting of the nitrogen 1:1:1 triplet by the anilino meta (0.126-0.138) and phenylthiyl ortho and para protons (0.077-0.096 mT). Upon recording at high gain, one of the partly deuterated aminyls gives satellite lines due to (33)S isotopes at natural abundance from which a(33)(S) is determined to be 0.51 mT. The ESR parameters for 1 and 2 are compared with those for structurally close N-(arylthio)-2,4,6-triarylphenylaminyl and N-(arylthio)-2,4,6-tri-tert-butylphenylaminyl.     

Complete stereochemistry of neamphamide A and absolute configuration of the beta-methoxytyrosine residue in papuamide B

The absolute stereochemistry of the three unresolved structural components in neamphamide A (1) was determined to be (R)-beta-methoxy-L-tyrosine, (2R,3R,4S)-4-amino-7-guanidino-2,3-dihydroxyheptanoic acid, and (2R,3R,4R)-3-hydroxy-2,4,6-trimethylheptanoic acid. Stereochemical assignments were made by chemical degradation of 1, derivatization of the resulting products, and then spectroscopic and chromatographic comparison of the derivatives with synthetically prepared standards. Using the same analytical protocol developed for 1, the beta-methoxytyrosine residue in papuamide B (2) was found to be (R)-beta-methoxy-D-tyrosine. This represents a rare example of divergent stereochemistry in an unusual amino acid residue that is present in two closely related classes of peptides.     

Monodithiolene molybdenum(V, VI) complexes: a structural analogue of the oxidized active site of the sulfite oxidase enzyme family

The active sites of the xanthine oxidase and sulfite oxidase enzyme families contain one pterin-dithiolene cofactor ligand bound to a molybdenum atom. Consequently, monodithiolene molybdenum complexes have been sought by exploratory synthesis for structural and reactivity studies. Reaction of [MoO(S(2)C(2)Me(2))(2)](1-) or [MoO(bdt)(2)](1-) with PhSeCl results in removal of one dithiolate ligand and formation of [MoOCl(2)(S(2)C(2)Me(2))](1-) (1) or [MoOCl(2)(bdt)](1-) (2), which undergoes ligand substitution reactions to form other monodithiolene complexes [MoO(2-AdS)(2)(S(2)C(2)Me(2))](1-) (3), [MoO(SR)(2)(bdt)](1-) (R = 2-Ad (4), 2,4,6-Pr(i)(3)C(6)H(2) (5)), and [MoOCl(SC(6)H(2)-2,4,6-Pr(i)(3))(bdt)](1-) (6) (Ad = 2-adamantyl, bdt = benzene-1,2-dithiolate). These complexes have square pyramidal structures with apical oxo ligands, exhibit rhombic EPR spectra, and 3-5 are electrochemically reducible to Mo(IV)O species. Complexes 1-6 constitute the first examples of five-coordinate monodithiolene Mo(V)O complexes; 6 approaches the proposed structure of the high-pH form of sulfite oxidase. Treatment of [MoO(2)(OSiPh(3))(2)] with Li(2)(bdt) in THF affords [MoO(2)(OSiPh(3))(bdt)](1-) (8). Reaction of 8 with 2,4,6-Pr(i)(3)C(6)H(2)SH in acetonitrile gives [MoO(2)(SC(6)H(2)-2,4,6-Pr(i)(3))(bdt)](1-) (9, 55%). Complexes 8 and 9 are square pyramidal with apical and basal oxo ligands. With one dithiolene and one thiolate ligand of a square pyramidal Mo(VI)O(2)S(3) coordination unit, 9 closely resembles the oxidized sites in sulfite oxidase and assimilatory nitrate reductase as deduced from crystallography (sulfite oxidase) and Mo EXAFS. The complex is the first structural analogue of the active sites in fully oxidized members of the sulfite oxidase family. This work provides a starting point for the development of both structural and reactivity analogues of members of this family.     

In situ encapsulation of laccase in nanofibers by electrospinning for development of enzyme biosensors for chlorophenol monitoring

A biosensor based on Trametes versicolor laccase (Lac) was developed for the determination of phenolic compounds. The biosensor was prepared by in situ electrospinning of a mixture of polyvinyl alcohol (PVA), Lac, PEO-PPO-PEO (F108) and gold nanoparticles (Au NPs), where F108 was used as an enzyme stabilizing additive and Au NPs was used to enhance the conductivity of the biosensor. Laser confocal scanning microscopy and electrochemical impedance spectroscopy proved that the enzyme was successfully encapsulated into the electrospun nanofibers. Under the optimal conditions, the lowest detection limit was found to be 0.04 μM (S/N = 3) for 2,4-DCP and the highest detection limit was found to be 12.10 μM for 4-CP. The sensitivity of the biosensor obtained in the linear range for chlorophenols followed the sequence 2,4-dichlorophenol (2,4-DCP) > 2,4,6-trichlorophenol (2,4,6-TCP) > 4-chlorophenol (4-CP). The sensing performance for chlorophenols was attributed to the suitable electrochemical interface of PVA/F108/Au NPs/Lac, resulting from biocompatibility, a high surface area-to-volume ratio (10.42 m(2) g(-1)) and superior mechanical properties of the electrospun nanofibers. The biosensor exhibited good repeatabilities of 7.6%, 2.8% and 9.0% (R.S.D.) and reproducibilities of 14.9%, 10.4% and 13.7% (R.S.D.) for 4-CP, 2,4-DCP and 2,4,6-TCP, respectively. Lac retained 65.8% of its initial activity after a 30-day storage period.     

Reaction systems related to dissimilatory nitrate reductase: nitrate reduction mediated by bis(dithiolene)tungsten complexes

Kinetics of the oxygen atom transfer reactions [M(IV)(QC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- + XO --> [M(VI)O(QC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- + X in acetonitrile with substrates XO = NO3- and (CH2)4SO have been determined. The reactants are bis(dithiolene) complexes with M = Mo, W and sterically encumbered axial ligands with Q = O, S to stabilize mononuclear square pyramidal structures. The complex [MoIV(SC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- is an analogue of the active site of dissimilatory nitrate reductase which in the reduced state contains a molybdenum atom bound by two pyranopterindithiolene ligands and a cysteinate residue. Nitrate reduction was studied with tungsten complexes because of unfavorable stability properties of the molybdenum complexes. Product nitrite was detected by a colorimetric method. All reactions with both substrates are second-order with associative transition states (deltaS approximately -20 eu). Variation of atoms M and Q, together with data from prior work, allows certain kinetics comparisons to be made. Among them, k2W/k2Mo = 25 for (CH2)4SO reduction (Q = S), an expression of the kinetic metal effect. Further, k2S/k2O = 28 and approximately 10(4) for nitrate and (CH2)4SO reduction, respectively, effects attributed to relatively more steric congestion in achieving the transition state with hindered phenolate vs thiolate ligands. The effect is more pronounced with the larger substrate. These results demonstrate the feasibility of tungsten-mediated nitrate reduction by direct atom transfer using molecules with both axial thiolate and phenolate ligands. Complexes of the type [M(IV)(OR)(S2C2Me2)2] are capable of reducing biological N-oxide, S-oxide, and nitrate substrates and thus constitute functional analogue reaction systems of enzymic transformations.     

Catalytic enantioselective Diels-Alder reactions using titanium complexes of cis-N-sulfonyl-2-amino-1-indanols

A titanium complex derived from (1R, 2S)-N-(2,4,6-trimethylbenzenesulfonyl)-2-amino-1-indanol catalyzes the Diels-Alder reaction of 2-bromoacrolein and cyclopentadiene with 96.5:3.5 enantioselectivity. A new and efficient synthesis of 2-amino-1-indanol (6) contributes to the potential of this methodology.     

SGLT2抑制剂——3-羰基达格列净的合成新方法

以4-甲氧基苯基-β-D-吡喃葡萄糖苷为原料,经9步反应制得新型关键中间体2,4,6-三-O-苄基-3-羰基-D-葡萄糖酸内酯乙二硫醇缩酮（10）; 10与5-溴-2-氯-4′-乙氧基二苯甲烷经亲核加成反应制得甲基糖苷（12）; 12在BF₃·Et₂O催化下经Et₃SiH还原、AlCl₃脱去苄基、再经PhI(CF₃CO₂)₂氧化脱除乙二硫醇保护基合成了SGLT2抑制剂3-羰基达格列净,共13步反应,总收率9%,该合成路线包含了11个新化合物的合成,其结构经¹H NMR, ¹³C NMR, IR和HR-ESI-MS表征。     

Reaction of dichlorocarbene with 1-(2,4,6-tri-t-butylphenyl)-1-phosphaallenes

1-(2,4,6-Tri-t-butylphenyl)-1-phosphaallene reacted with dichlorocarbene to give 2-dichloromethylene-1-(2,4,6-tri-t-butylphenyl)-1-phosphirane. The structure was confirmed by X-ray crystal structure analysis. A similar isomerization product was obtained in the reaction of dichlorocarbene with 3-phenyl-1-(2,4,6-tri-t-butylphenyl)-1-phosphaallene.     

Improved asymmetric synthesis of aziridine 2-phosphonates using (S)-(+)-2,4,6-trimethylphenylsulfinamide

The aza-Darzens reaction of lithium diethyl iodomethylphosphonate with enantiopure N-(2,4,6-trimethylphenylsulfinyl)imines affords a single diastereomeric N-sulfinylaziridine 2-phosphonate which, on treatment with MeMgBr, gives the corresponding NH-aziridine 2-phosphonate chiral building blocks. An improved asymmetric synthesis of (S)-(+)-2,4,6-trimethylphenylsulfinamide is also given.     

Pi-pi stacking versus steric effects in stereoselectivity control: highly diastereoselective synthesis of syn-1,2-diarylpropylamines

N-Arylarylideneamines react with sulfinylbenzyl carbanions derived from 2-(p-tolylsulfinyl)toluenes (S)-1 and (S)-2, affording epimeric mixtures at C1 of 1,2-diarylethyl- and 1,2-diarylpropylamine derivatives. The sulfinyl group completely controls the configuration at C2 in the reactions of (S)-2. The configuration at C1 depends on the electron density of the ring adjacent to the iminic carbon atom which is modulated by pi-pi stacking interactions with the ring joined to the carbanionic centre. The stereoselectivity was controlled by modifying the acceptor character of the arylideneamine ring with appropriate substituents, the formation of the highly selective (R) configuration at C1 being made possible by electron-donating groups. N-(2,4,6-Trimethoxyphenyl)arylideneamines have been shown to be suitable starting materials for the preparation of (R)-1,2-diarylethyl- and (1R,2S)-1,2-diarylpropylamines (syn epimers) in a highly stereoselective manner.     

The 1,2,4-triazolyl cation: thermolytic and photolytic studies

The generation of the 1,2,4-triazolyl cation (1) has been attempted by the thermolysis and photolysis of 1-(1,2,4-triazol-4-yl)-2,4,6-trimethylpyridinium tetrafluoroborate (2) and the thermolysis of 1- and 4-diazonium-1,2,4-triazoles, using mainly mesitylene as the trapping agent. Thermolysis of 2 gave mostly 1,2,4-triazole, together with 3-(1,2,4-triazol-4-yl)-2,4,6-trimethylpyridine, 4-(1,2,4-triazol-4-ylmethyl)-2,6-dimethylpyridine, and 4-(2,4,6-trimethylbenzyl)-2,6-dimethylpyridine. Thermolysis of each of the diazonium salts in the presence of mesitylene again gave mainly triazole together with very low yields of 1-(1,2,4-triazol-1-yl)-2,4,6-trimethylbenzene and the corresponding -4-yl isomer in about the same ratio. On the other hand, photolysis of 2 in mesitylene gave mainly 1-(1,2,4-triazol-1-yl)-2,4,6-trimethylbenzene. A photoinduced electron transfer from mesitylene to 2 has been observed and preliminary laser flash photolyses of 2 and the corresponding 2,4,6-triphenylpyridinium salt have been carried out. The observed transients are explained as arising from the first excited states of the pyridinium salts rather than from 1. Ab initio MO calculations are reported and indicate that the predicted electronic ground-state of the triazolyl cation is a triplet state of B1 symmetry with five pi electrons, which corresponds to a diradical cation (1c). Possible mechanisms for the formation of the various products are proposed.