Enantioselective synthesis of hydroxylated pyrrolidines via Sharpless epoxidation and olefin metathesis

The enantioselective synthesis of polyhydroxylated pyrrolidines from enantiomerically pure 2,3-epoxy-pent-4-en-1-ol 5 is described herein. The epoxy alcohol, readily available in any configuration by Sharpless epoxidation, was submitted to regioselective C-3 ring-opening with allyl amine, Boc-protection and ring-closing metathesis to yield dehydropyrrole derivative 7. From this key intermediate, 1,4-dideoxy-1,4-imino-d-ribitol (+)-3 and 1,4-dideoxy-1,4-imino-d-allitol (+)-4 were prepared in high yields. The enantiomers of these compounds can be obtained by the same sequence starting from an epoxy alcohol with the opposite configuration.     

Hydroboration-oxidation of ricinoleic acid derivatives

The regioselectivity in the hydroboration-oxidation of ricinoleic acid derivatives only slightly depends on the configuration of the optically active center: the fraction of the resulting 1,3-diol is larger by 6–10% than that of the 1,4-isomer. The new asymmetric center has preferentially S configuration, as follows from the formation of the corresponding stereoisomeric 1,3-dioxane from the 1,3-diol and of 2,5-dialkyltetrahydrofuran from the 1,4-diol.     

Hydrogen bond formation between aliphatic alcohols and tertiary amines

Hydrogen bond formation between tertiary amines and long chain and branched chain alcohols has been studied in order to understand the influence of chain length and the steric effect on the complex formation between tertiary amines and alcohols. On the addition of the amine to the alcohol the intensity of the monomeric OH band decreases and the new band appears corresponding to the alcohol—amine complex. The equilibrium constants of the complex formation are correlated by a two parameter equation. The three correlation equations obtained for three tertiary amines are: log K = 3.41 + 10.01σ* + 0.02χ (for triethylamine-alcohol) log K = 0.97 + 2.54σ* + 0.21χ (for tributylamine-alcohol) log K = 1.01 + 1.81σ* + 0.26χ (for trioctylamine-alcohol), where σ* is Taft's polar constant and χ the molecular connectivity index of the R skeleton of the alcohol.     

Hydrogénolyse en phase liquide sur Pd/C des époxydes du carvomenthène et du limonène

Hydrogenolysis over Pd/C of cis and trans epoxides of carvomenthene and limonene give a mixture of hydrocarbons, secondary and tertiary alcohols, and ketones in proportions dependent upon the nature of the starting material. In the limonene epoxides, the extracyclic double bond plays an important role in the opening of the oxirane ring through a common unsaturated tertiary alcohol intermediate by double bond migration, hydrogenation of which leads to the products. For the carvomenthene epoxides the results are similar to those found in the 4-t-butyl series with competition between cis addition and trans addition of hydrogen. The presence of the isopropenyl group leads to slower reaction rates in comparison with t-butyl analogues.     

Rhodium‐Catalyzed Allylation of Aldehydes with Homoallylic Alcohols by Retroallylation and Isomerization to Saturated Ketones with Conventional or Microwave Heating

The treatment of an aldehyde with a tertiary homoallylic alcohol at 100–250 °C in the presence of cesium carbonate and a rhodium catalyst leads to allyl transfer from the homoallylic alcohol to the aldehyde. The process includes Rh‐mediated retroallylation to form an allyl rhodium species as the key intermediate. The homoallylic alcohol formed initially through allyl transfer is converted under the reaction conditions into the corresponding saturated ketone when bulky ligands are used. Microwave heating at 250 °C accelerates the reaction significantly.     

Photochemical reaction of alcohols—II : Irradiation of aromatic alcohols

The UV irradiation of aromatic alcohols leads to the formation of several products: carbonyl compounds, ethers, α-glycols and tetra-aryl-1,4-dioxanes.The photoformation of α-glycols is qualitatively and quantitatively compared to the photoreduction of the carbonyl compounds. It is noteworthy that the glycols are formed with a stereochemistry very different depending upon whether the substrate is an alcohol or a carbonyl compound.The structure, configuration and conformation of the 1-4-dixoanes obtained are studies as well as their origin.Other aspects of the photochemistry of the alcohols are analyzed using hydroperoxides as model substrates.     

Oxidation of secondary amines by molecular oxygen and cyclohexanone monooxygenase

Cyclohexanone monooxygenase from Acinetobacter calcoaceticus catalyzed the oxidation of tertiary and secondary amines to N-oxides and nitrones, respectively. The formation of a hydroxylamine intermediate was involved with secondary amines as starting substrates.     

Total Synthesis and Structure Revision of Halioxepine

The first total synthesis of halioxepine is accomplished using a 1,4-addition for constructing the quaternary center at C10 and a halo etherification for the generation of the tertiary ether at C7. The correct structure of halioxepine was determined by assembling different enantiomeric building blocks and by changing the relative configuration between C10 and C15.     

Reductive cleavage of C-OH bonds in allyl position-formation of gaseous products in the course of the cathodic reduction of some simple unsaturated alcohols

The problem of the reductive cleavage of C?OH bonds in allyl position has been considered starting from the literature data concerning the behaviour of allyl alcohol. The formation of hydrocarbons has been shown in the case of the electroreduction of crotyl alcohol, 2-butene-1,4-diol, propargyl alcohol, 2-butyne-1,4-diol and 1-butyne-3-ol. The composition of the gaseous products was analyzed, current efficiency values with respect to the hydrocarbon formation were calculated. Schemes for the reduction path were given.     

Five-component synthesis of dihydropyridines based on diketene

A novel five-component strategy involving commercially available diketene, primary amines, malononitrile and various benzaldehydes for the synthesis of densely functionalized 1,4-dihydropyridines in good yields was achieved. The reaction pathway involves a sequential ring-opening of diketene/enamine formation/Knoevenagel-condensation/Michael addition and 6-exo-tet cyclization, resulting in multiple bond-formation events including two C–C and three C–N bonds ultimately leading to the formation of the respective 1,4-dihydropyridines.     

Kinetics and Mechanism of Reaction between N-Polyfluorophenylcarbonimidoyl Dichlorides and Tertiary Amines in Acetonitrile

The reaction of N-polyfluorophenylcarbonimidoyl dichlorides with tertiary amines in acetonitrile afforded chloroamidines R²NC(Cl) = NAr_F and alkyl chloride. The precursor of the products is the corresponding quaternary ammonium salt [R³N+C(Cl) = NAr_F]-Cl^-. The rate of the salt formation is described by a second order equation; however with some amines a saturation effect was observed for the reaction rate with the growing amine concentration. This fact and also the influence of the amine and the substrate structure on the reaction rate suggests that reaction proceeds by addition-elimination mechanism with formation of a tetrahedral intermediate. The latter in the rate-limiting stage undergoes a stereomutation into an intermediate of a configuration favorable for conversion into a quaternary salt.     

One-pot synthesis of 4-substituted 4-alkoxy-1,4-dihydro-3,1-benzoxazine-2-thiones by the reaction of 2-isothiocyanatobenzoates with organolithiums

An efficient one-pot procedure for the preparation of 4-substituted 4-alkoxy-1,4-dihydro-3,1-benzoxazine-2-thiones from 2-isothiocyanatobenzoates has been developed. Thus, 2-isothiocyanatobenzoates were reacted with organolithiums including lithium enolates of acetates and tertiary acetamides in THF at −78 °C to give the desired products in generally good yields.     

Synthesis of 1,4-polyisoprene support of 2-chloroethylphosphonic acid (ethephon), a stimulating compound for the latex production by the Hevea brasiliensis

2-Chloroethylphosphonic acid (ethephon) is a well known stimulating product used to improve the latex production by the rubber tree (Hevea brasiliensis). Its chemical fixation in side position of 1,4-polyisoprene chains by weak chemical bond was considered in order to prepare new derivatives having prolonged stimulating activity. The synthesis was considered by using a chemical modification procedure according to a two-step process. Firstly, an epoxidized 1,4-polyisoprene intermediate was prepared by partial epoxidation of 1,4-polyisoprene. Secondly, the grafting of 2-chloroethylphosphonic acid was achieved by using the reactivity of the P-OH acidic function (or a P-OSiMe₃ derived from P-OH) of the reagent toward oxirane rings of epoxidized 1,4-polyisoprene. It was noted that grafting yields are improved when the reaction is carried out in bulk or in a non-polar solvent, and more especially in neutral conditions, that is by replacing ethephon with its trimethylsilylated derivatives [monotrimethylsilyl 2-chloroethylphosphonic acid or, more especially, di(trimethysilyl) 2-chloroethylphosphonate]. With this latter, the addition occurs by the intermediate of the P-OSiMe₃ bond, and the formation of 2-oxo-l,3,2-dioxaphospholane structures is highly favored.     

Oxidation of aromatic amines with chromyl chloride-II : Studies on the intermediate solid adducts

Oxidation of aromatic primary amines with chromyl chloride results in the formation of intermediate solid Etard adducts (C. Nallaiah and J.A. Strickson, Tetrahedron 42,4083 ( 1986)). Elemental analysis of the adducts indicates that the anilines, which give 1,4-benzoquinone anils in good yields, form adducts close to a 1:1 stoichiometry with the oxidant while those forming 1,4-benzoquinones in substantial yields form 1:2 adducts. Magnetic measurements on the adducts reveal that chromium atoms are mainly present m the oxidation state chromium(IV). IR studies indicate that the adducts comprise of 1,4-benzoquinone imines and di-imines as ligands and that giant molecules are formed by chloro and hydroxy bridges.     

Concise approach to the syntheses of (±)-gliocladin C and related diketopiperazine alkaloids

A unique approach to the diketopiperazine indole alkaloid (±)-gliocladin C was developed and applied to formal syntheses of the related alkaloids (±)-gliocladine C and (±)-T988C. The key features of the strategy include an unprecedented nucleophilic addition of a diketopiperazine to an isatin derivative followed by a Friedel-Crafts alkylation of the resultant tertiary alcohol with indole to establish the critical quaternary center. Subsequent reduction of the intermediate oxindole moiety and cyclization then delivered a pivotal hexahydropyrrolo[2,3-b]indole diketopiperazine intermediate that was readily converted into (±)-gliocladin C as well as racemic versions of key intermediates in the Overman syntheses of (+)-gliocladine C and (+)-T988C.     

An efficient synthesis of γ-amino β-ketoester by cross-Claisen condensation with α-amino acid derivatives

Cross-ester condensation between N-protected amino acid ester and the lithium enolate prepared from alkyl acetate gave the corresponding β-ketoester in high yield without the formation of the tertiary alcohol that is commonly seen as by-product. This interesting reaction is applicable to the amino acid derivatives with suitable N-protecting groups, which can help to stabilize the reaction intermediates.     

Metal salt catalyzed carbenoid—XIII: On the mechanisms of cyclopropanation and allylic CH insertions by diazo esters in the presence of olefins and homogeneous copper catalysts

Evidence is presented demonstrating the existence of two paths to the title processes which arise from a common intermediate. A rationale involving catalyzed addition of the diazo compound to the olefin and carbenoid addition to the olefin is proposed. The penultimate intermediate has one new CC bond formed. It is partitioned between products by forming the second CC bond or formation of a hydrocarbenoid allyl complex which collapses to the allylic CH insertion products. Cyclopropanation occurs stereospecifically. The proposed mechanism accounts for the stereospecificity of cyclopropanation, the variance of syn/anti ratios with catalyst concentration when diazoacetic ester is employed and optical inductions with chiral catalysts. The question of whether the alleged carbenoid and/or the penultimate intermediate contain N₂ is not answered although it is felt that a cupro-cyclobutane intermediate is the most probable intermediate before product partitioning.     

Tetrazine Assists Reduction of Water by Phosphines: Application in the Mitsunobu Reaction

Reaction of 3,6‐disubstituted‐1,2,4,5‐tetrazines with water and PEt₃ forms the corresponding 1,4‐dihydrotetrazine and OPEt₃. Thus PEt₃, as a stoichiometric reductant, reduces water, and the resulting two reducing equivalents serve to doubly hydrogenate the tetrazine. A variety of possible initial interactions between electron‐deficient tetrazine and electron‐rich PR₃, including a charge transfer complex, were evaluated by density functional calculations which revealed that the energy of all these make them spectroscopically undetectable at equilibrium, but one of these is nevertheless suggested as the intermediate in the observed redox reaction. The relationship of this to the Mitsunobu reaction, which absorbs the components of water evolved in the conversion of alcohol and carboxylic acid to ester, with desirable inversion at the alcohol carbon, is discussed. This enables a modified Mitsunobu reaction, with tetrazine replacing EtO₂CN=NCO₂Et (DEAD), which has the advantage that dihydrotetrazine can be recycled to tetrazine by oxidation with O₂, something impossible with the hydrogenated DEAD. For this tetrazine version, a betaine‐like intermediate is undetectable, but its protonated form is characterized, including by X‐ray structure and NMR spectroscopy.     

Studies of the reactions between indole-2,3-diones (isatins) and 2-aminobenzylamine

Reflux of equimolecular amounts 2-aminobenzylamine and isatins in acetic acid produced indolo[3,2-c]quinolin-6-ones in good yields. A proposed mechanism involving initial formation of a spiro compound is given. This isolable intermediate subsequently rearranges via a sequential isocyanate ring opening and a cyclisation process to a urea derivative which finally cyclized to the indolo[3,2-c]quinolin-6-ones. The urea derivative could be prepared separately and cyclized selectively to indolo[3,2-c]quinolin-6-one. Reaction of N-acetylisatin with 2-aminobenzylamine at room temperature yielded the 1,4-benzodiazepinone 3-(2-acetamidophenyl)-1,5-dihydro-1,4-benzodiazepin-2-one whereas its isomer 2(2-acetamidophenyl)-4,5-dihydro-1,4-benzodiazepin-3-one was obtained from 2-(2-acetylaminophenyl)-N-(2-aminobenzyl)-2-oxoacetamide in acetic acid at room temperature.The previously unknown linear isomer of indolo[3,2-c]quinolin-6-one, i.e. indolo[2,3-b]quinolin-11-one, has been prepared by thermal (260°C) cyclization of methyl 2-phenylamino indole-3-carboxylate, which in turn was prepared in two steps from methyl indole-3-carboxylate.     

Approach to the synthesis of cladiell-11-ene-3,6,7-triol

[reaction: see text] The synthesis of an advanced intermediate in the synthesis of the title compound has been achieved. Key steps include an Ireland-Claisen rearrangement to install the C7 tertiary alcohol stereocenter, an SN2' reaction of an alkoxymethyl Cu reagent, and a diastereoselective Re-catalyzed allylic alcohol transposition.