Moderate generation of sulfenylnitrenes from novel N-sulfenylsulfodiimides

N-Sulfenylated sulfodiimides were first prepared by the reaction of S,S-diphenyl-N-tosylsulfodiimide with arenesulfenyl chlorides under the basic conditions. Thermolysis of S,S-diphenyl-N-(2-nitrophenylsulfenyl)- and S,S-diphenyl-N-(2,4-dinitrophenylsulfenyl)sulfodiimides in the presence of olefins proceeded at 50-80 °C to give the corresponding deiminated S,S-diphenyl-N-tosylsulfimide and N-sulfenylaziridines in very good yields. 2,4-Dinitrophenyl-sulfenylnitrene was trapped by trans- and cis-1-phenylpropenes stereospecifically. The thermolysis temperature of the N-sulfenylsulfodiimides was found to be lower than N-sulfenylsulfoximide and higher than N-sulfenyliminosulfonium salt and very effective to trap the sulfenylnitrene to give the N-sulfenylaziridines in very good yields.     

[4+1] Cycloaddition of N-acylimine derivatives with isocyanides: efficient synthesis of 5-aminooxazoles and 5-aminothiazoles

[4+1] Cycloaddition reaction between isocyanides and N-acylimine derivatives generated from N-acyl N,O-acetals acting as isocyanophiles has been developed. These reactions proceeded smoothly and cleanly to afford the corresponding 5-aminooxazoles in high yields. This reaction was extended to the syntheses of 5-aminothiazoles by using N-thioacyl N,O-acetals. A wide range of N-acyl N,O-acetals, N-thioacyl N,O-acetals, and isocyanides were found to be applicable to this reaction.     

New investigation of Vilsmeier-type reaction using pyrazolones with various amides

New investigation of Vilsmeier-type reaction was evaluated to realize the solvent effect by using pyrazolones to react with various of amides, including formamide, N-methylformamide, N-propylformamide, N-tert-butylformamide, N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), N,N-dipropylformamide (DPF), N,N-diisopropylformamide, N,N-dibutylformamide, piperidine-1-carbaldehyde, and pyrrolidine-1-carbaldehyde, in the presence of phosphorous oxychloride POCl₃. The unexpected resulting products were observed in this work according to the difference chemoseletivities of substituted amides. The plausible reactive pathways were proposed to explain the experimental result.     

Conversion of a trans-syn-trans to a cis-syn-trans perhydrobenz[e]indenone triggered by intramolecular 1,5-hydrogen transfer

The conversion of a trans-syn-trans perhydroiodomethyltrimethylbenz[e]indenone to the corresponding cis-syn-trans perhydrobenz[e]indenone occurred during the reduction of the iodomethyl to a methyl group under radical conditions.     

Trans-selective γ-arylation of macrocyclic N-picolinoylcycloalkylamines through palladium-catalyzed methylene sp3 carbon–hydrogen bond activation

While numerous stereoselective methylene β- and γ-carbon–hydrogen activation reactions are reported, there are no examples of trans-selective γ-carbon–hydrogen activation of cyclic compounds. Herein I report the first trans-selective palladium-catalyzed γ-arylation of N-picolinoylcycloalkylamine with aryl iodides. Trans-arylation of macrocyclic N-picolinoylcyclododecylamine proceeded to give trans-3-aryl-N-picolinoylcyclododecylamine as a sole mono-arylated product in up to 85% yield. Other, larger substrates were also applicable to trans-arylation, albeit with lower efficiency. The picolinoyl group of the trans-arylated product was easily removed with zinc and diluted hydrochloric acid.     

Catalytic asymmetric Michael reactions of dibenzyl malonate to α,β-unsaturated N-acylpyrroles using a La(O-iPr)3/Ph-linked-BINOL complex

Catalytic asymmetric Michael reactions of a malonate to acyclic α,β-unsaturated N-acylpyrroles as ester equivalent acceptors are described. A La(O-iPr)₃/(S,S)-linked-BINOL complex, which is suitable for Michael addition to cyclic enones, is not suitable for acyclic α,β-unsaturated N-acylpyrroles. A new (S,S)-Ph-linked-BINOL chiral ligand was developed to improve enantioselectivity, and a La(O-iPr)₃/(S,S)-Ph-linked-BINOL complex with the addition of HFIP afforded Michael adducts in good yield and enantioselectivity (up to 96% ee).     

Suppression of Rice Cryptochrome 1b Decreases Both Melatonin and Expression of Brassinosteroid Biosynthetic Genes Resulting in Salt Tolerance

We investigated the relationship between the blue-light photoreceptor cryptochrome (CRY) and melatonin biosynthesis by generating RNA interference (RNAi) transgenic rice plants that suppress the cryptochrome 1b gene (CRY1b). The resulting CRY1b RNAi rice lines expressed less CRY1b mRNA, but not CRY1a or CRY2 mRNA, suggesting that the suppression is specific to CRY1b. The growth of CRY1b RNAi rice seedlings was enhanced under blue light compared to wild-type growth, providing phenotypic evidence for impaired CRY function. When these CRY1b RNAi rice plants were challenged with cadmium to induce melatonin, wild-type plants produced 100 ng/g fresh weight (FW) melatonin, whereas CRY1b RNAi lines produced 60 ng/g FW melatonin on average, indicating that melatonin biosynthesis requires the CRY photoreceptor. Due to possible feedback regulation, the expression of melatonin biosynthesis genes such as T5H, SNAT1, SNAT2, and COMT was elevated in the CRY1b RNAi lines compared to the wild-type plants. In addition, laminar angles decreased in the CRY1b RNAi lines via the suppression of brassinosteroid (BR) biosynthesis genes such as DWARF. The main cause of the BR decrease in the CRY1b RNAi lines seems to be the suppression of CRY rather than decreased melatonin because the melatonin decrease suppressed DWARF4 rather than DWARF.     

Reactivity of 1-phenylsulfinyl-2-phenylsulfanylethylene (SOSE) with O-nucleophiles generated by potassium tert-butoxide

E-1-Phenylsulfinyl-2-phenylsulfanylethylene (E-SOSE) reacts with O-nucleophiles generated by means of t-BuOK via an addition-elimination mechanism, thus affording the product of substitution of the phenylsulfanyl group in a stereo-conservative process. When used alone, the strongly basic and hindered tert-butoxide brings about elimination of either the phenylthiolate or phenylsulfinate groups. Z-SOSE is much more prone to elimination: either with t-BuOK alone or with other O-nucleophiles generated by t-BuOK, it always leads to products derived from elimination. Other alkaline tert-butoxides or other bases appear not as effective in generating species nucleophilic enough to react with E-SOSE.     

First straightforward synthesis of 2,4-disubstituted benz[g]isoquinoline-3,5,10(2H)-triones, 1,2,3,5-substituted naphtho[3,2,1-de]isoquinoline-4,7-diones, and 6-substituted benzo[h]pyrido[3,4,5-kl]-1,2,3,4-tetrahydroacridine-5,8-diones

Structural modifications to the benz[g]isoquinoline skeleton of N-substituted benz[g]isoquinoline-3,5,10(2H)-triones were envisaged in order to make future SAR studies possible for this type of bioactive compounds. Several N-substituted benz[g]isoquinoline-3,5,10(2H)-triones were converted to novel 2,4-substituted benz[g]isoquinoline-3,5,10(2H)-triones, new tetracyclic 1,2,3,5-substituted naphtho[3,2,1-de]isoquinoline-4,7-diones, and 6-substituted benzo[h]pyrido[3,4,5-kl]-1,2,3,4-tetrahydroacridine-5,8-diones. All the synthesized target compounds represent new heterocyclic systems, which were previously undescribed in the literature.     

Stereoselective synthesis and absolute configuration of the C33-C42 fragment of symbiodinolide

Cross-metathesis of methyl ester which was prepared from symbiodinolide with ethylene was performed to give the C33-C42 degraded fragment. This fragment was estimated to be (36S,40S)-diol by the modified Mosher method. Stereoselective synthesis of the (36S,40S)-diol and its diastereomer (36R,40S)-diol was achieved from l-aspartic acid. Synthetic bis-(S)- and (R)-MTPA esters which were derivatized from the (36S,40S)-diol exhibited spectroscopic data identical with those of bis-(S)- and (R)-MTPA esters derived from the degraded product. Thus, the absolute stereochemistry of the C33-C42 fragment was elucidated to be (36S,40S).     

Synthesis of p-amino-N,N′-dihydroxybenzamidine using a TBDMS protecting group protocol

A synthetic route to p-amino-N,N′-dihydroxybenzamidine is established using a TBDMS protecting group strategy starting with p-nitrobenzhydroxamic acid chloride, which is transformed to O,O′-bis(tert-butyldimethylsilyl)-N,N′-dihydroxybenzamidine. Reduction with sodium dithionite occurs without degradation of the dihydroxyamidine functional group. Deprotection with ammonium fluoride is fast and efficient. This is important because no other possibility to synthesize this derivative has been found up to now. Furthermore, TBDMS protecting group strategy is proved to be adaptable to other substituted N,N′-dihydroxybenzamidines.     

Synthesis and aromatic nucleophilic N-N, N-S and N-O exchange reactions of N,N-dimethyl-2-trifluoroacetyl-1-naphthylamine

We succeeded in the synthesis of N,N-dimethyl-2-trifluoroacetyl-1-naphthylamine (10) by the regioselective deacylation of N,N-dimethyl-2,4-bis(trifluoroacetyl)-1-naphthylamine with trifluoroacetic acid and water. The aromatic nucleophilic substitutions of 10 with various amines, thiols and alcohols proceeded cleanly to give the corresponding N-N, N-S and N-O exchanged products in moderate to excellent yields.     

Photoisomerization of octyl methoxycinnamate

The octyl-p-methoxy-trans-cinnamate (E-OMC) was exposed to sunlight to induce the E to Z transformation. Octyl-p-methoxy-cis-cinnamate (Z-OMC) was then purified from the mixture of the E- and the Z-OMC using C-18-semi-preparative HPLC. The UV absorption of the Z configuration at various concentrations in various solvents was measured. Molar absorption coefficient of the compound was then calculated. By using the obtained molar absorption coefficient of Z-OMC and of E-OMC, E to Z photoisomerization of octyl methoxycinnamate (OMC) in various solvents at various concentrations could be monitored by C-18 HPLC using UV detector. The result indicates that equilibrium of photoisomerization depends upon concentration and polarity of the solvent used.     

Highly stereoselective anti-aldol reactions catalyzed by simple chiral diamines and their unique application in configuration switch of aldol products

Chiral derivatives of trans-1,2-diaminocyclohexane with different N,N-dialkyl groups in well-defined orientations have been synthesized, and applied as catalysts for the asymmetric aldol reaction between a variety of aldehydes and ketones. Enantiomeric catalyst 1j catalyzed the reaction in ethanol and provided excellent diastereoselectivity and enantioselectivity. Significantly, simple replacement of organic solvents with water switched the products of the aldol reactions from anti to syn configuration. Such catalytic reactions led to the products with anti to syn diastereoselectivity up to 99:1 in ethanol, while in water gave the products with syn to anti diastereoselectivity up to 99:1.     

Rectangular source integral and recurrence relations

In this paper Hubbell's rectangular source integral H′(a,b), which is a double integral, is expressed as a series of many converging single integrals I_n (a,b). Recurrence relations relate these integrals. Once one integral I₁ is computed, recurrence relations are used to compute other integrals. I₁(a,b) can be computed analytically. H′(a,b) is approximated by considering the first seven terms in the series and the results are found to give good results for various values of a and b. Results are presented for the values of a and b (0.1 to 20 and to 2), respectively. The rate of convergence depends on the values of a and b.     

Use of Stille-type cross-coupling as a route to oligopyridylimines

The new tin reagents, 2-(n-Bu₃Sn)-6-{C(R)OCH₂CH₂O}-C₅H₃N, (R=H a, Me b), have been employed in Stille-type cross-coupling reactions with a range of oligopyridylbromides generating, following a facile deprotection step, a series of formyl- and acetyl-functionalised oligopyridines. Condensation reactions with 2,6-diisopropylaniline has allowed access to families of novel sterically bulky multidentate N,N,N,N (tetradentate), N,N,N,N,N (pentadentate), N,N,N,N,N,N (sexidentate) and N,N,N,N,N,N,N (heptadentate) nitrogen donor ligands. This work represents a straightforward and rapid synthetic route for the preparation of oligopyridylimines, which are expected to act as useful components for the self-assembly of polymetallic complexes.     

Engineering of Yeast Old Yellow Enzyme OYE3 Enables Its Capability Discriminating of (E)-Citral and (Z)-Citral

The importance of yeast old yellow enzymes is increasingly recognized for direct asymmetric reduction of (E/Z)-citral to (R)-citronellal. As one of the most performing old yellow enzymes, the enzyme OYE3 from Saccharomyces cerevisiae S288C exhibited complementary enantioselectivity for the reduction of (E)-citral and (Z)-citral, resulting in lower e.e. value of (R)-citronellal in the reduction of (E/Z)-citral. To develop a novel approach for the direct synthesis of enantio-pure (R)-citronellal from the reduction of (E/Z)-citral, the enzyme OYE3 was firstly modified by semi-rational design to improve its (R)-enantioselectivity. The OYE3 variants W116A and S296F showed strict (R)-enantioselectivity in the reduction of (E)-citral, and significantly reversed the (S)-enantioselectivity in the reduction of (Z)-citral. Next, the double substitution of OYE3 led to the unique variant S296F/W116G, which exhibited strict (R)-enantioselectivity in the reduction of (E)-citral and (E/Z)-citral, but was not active on (Z)-citral. Relying on its capability discriminating (E)-citral and (Z)-citral, a new cascade reaction catalyzed by the OYE3 variant S296F/W116G and glucose dehydrogenase was developed, providing the enantio-pure (R)-citronellal and the retained (Z)-citral after complete reduction of (E)-citral.     

Copolymerization of acrylic acid to nylon-6 by trapped radicals—I. Vapour phase grafting

Film of nylon-6 has been γ-irradiated in vacuo to various doses D. Grafting has been effected by subsequent exposure in vacuo to vapour at 50° of composition 9.1 wt% acrylic acid and 90.9 wt% water. Determinations have been made of total vapour uptake as well as the individual swellings due to monomer and water. For D ? ca. 2 Mrad, the initial rate of grafting R_g increased with D in accord with R_g ∝ D^β with β = 0.45 ± 0.05, thus suggesting bimolecular chain termination. However, for D ? ca. 2 Mrad, there is no further increase in R_g. This is attributed in part to the fact that the radical yield is proportional to dose only for D ? ca. 2.5 Mrad. Diffusion controlled grafting has been predicted elsewhere to be characterized by β = 0.67. Grafting proceeds from the surface and the initial stages are concluded to be essentially free from diffusion control, since (a) β ≠ 0.67, (b) the rate of uptake of monomer vapour >R_g and (c) a large change in film thickness yields only a very small change in R_g.     

Polymerization effects on molecular dynamics of n-ethylene glycol dimethacrylates followed by dielectric relaxation spectroscopy

A detailed dielectric characterization of n-ethylene glycol dimethacrylate monomers with n = 2 and 4 is provided. Besides the α relaxation associated to the glass transition, two secondary relaxation processes were detected: the γ process assigned to the twisting motions within the ethylene glycol moiety, and the β process related with hindered rotations of carboxylic groups. While the relaxation time of the γ process is independent of the size of the ethylene glycol group, the β process deviates to higher times with increasing n. Upon polymerization the α process goes to extinction, faster in the 4-ethylene monomer, with a concomitant depletion of the β process that remains at higher polymerization degrees relatively to the α process, thus acting as a more sensitive probe to evaluate conversion. The height decrease of α and β processes of monomers with the polymerization progress, occurs without significant changes of position. At intermediate states of polymerization, a new relaxation process evolves being only detectable in a narrow temperature range. In the end, the polymer networks show, in addition to the γ_pol relaxation identical to the γ relaxation of the monomer, a β_pol relaxation with similar features to the β relaxation found in poly n-alkyl methacrylates originated by a π flip of the ester unit accompanied by a restricted main chain rearrangement. The main dielectric relaxation corresponding to the swollen polymer network should appear at quite high temperatures already in early stages of the polymerization process because phase segregation occurs and only a limited amount of liquid monomer plasticizes the newly formed material.     

An efficient approach to d-threo-3-hydroxyaspartic acid for the synthesis of novel l-threo-oxazolines as selective blockers of glutamate reversed uptake

An efficient, stereoselective synthetic strategy to d-threo-3-hydroxyaspartic acid was developed. Starting from l-(2S,3S)-N-benzoyl-3-hydroxyaspartic acid dimethyl ester by a Deoxo-fluor-catalyzed cyclization reaction, an inversion of configuration at the β-center (erythro isomer), was observed. A base-induced epimerization reaction led to the d-trans-isomer, which was hydrolyzed to give d-threo-3-hydroxyaspartic acid with excellent stereoselectivity and overall yield. Starting from d-threo-3-hydroxyaspartic acid, l-threo-oxazolines can be stereoselectively synthesized.