Fullerenyl boronic esters: ferric perchlorate-mediated synthesis and functionalization

Fullerenyl boronic esters have been prepared by a ferric perchlorate-promoted reaction of [60]fullerene with various arylboronic acids. The obtained fullerenyl boronic esters could undergo further functionalization with diols to afford C(60)-fused dioxane/dioxepane derivatives. A possible reaction mechanism for the formation of fullerenyl boronic esters has been proposed.     

Asymetric dihydroxylations via chiral oxazolidines

The title compounds, new chirally masked α,β unsaturated aldehydes, undergo diastereoselective dihydroxylation reactions with 45–60% diastereisomeric excesses; chromatographic purification of the major diols, di-O-protection and auxiliary removal afford optically pure α,β dialkoxy aldehydes.     

Regioselective transformation of alkynes into cyclic acetals and thioacetals with a gold(I) catalyst: comparison with Brønsted acid catalysts

Au(I) catalyzes the transformation of alkynes into cyclic acetals and thioacetals at much higher rate than Brønsted acids. The reaction appears to be general for a range of alkynes and diols or dithiols, which are efficiently transformed with high selectivities. One of the salient features of this reaction process is the high reactivity of the enol ether or enol thioether intermediates, which undergo a rapid isomerization reaction to afford the cyclic acetals or thioacetals, so that isolation or subsequent activation processes are not required. This type of reactions allows us to synthesize a series of fragrances.     

Direct Synthesis of Multi‐functional Pyrimidine,Pyrazine, and Pyridine Scaffolds via Inter‐ and Intramolecular Annulations of 3‐Amino‐thieno[2,3‐b]pyridine‐2‐carboxylate

The synthesis of a new series of annulated thieno[2,3‐b]pyridines was performed. Ester compound 1 underwent heterocyclization upon reaction with phenylisothiocyanate and formamide to afford pyrimidines 2 and 3 , respectively. Thienopyrimidine 5 was resulted via reaction of amino derivative 1 with triethyl orthoformate to afford the non‐isolable intermediate 4 , which allowed hydrazinolysis with hydrazine hydrate to afford the target compound. Pyrimidine type 5 was condensed with p‐nitrobenzaldehyde to afford Schiff base 6 . Refluxing of ester 1 with ethyl cyanoacetate and diethyl malonate followed by base‐mediated heterocyclization afforded condensed pyridines 8 and 9 , respectively. The tetracyclic pyrazine derivative 14 was obtained from the reaction of amino compound 1 with 2,5‐dimethoxytetrahydrofuran followed by hydrazinolysis to give carbohydrazide 11 , which undergo diazotization followed by Curtius rearrangement. The antibacterial results illustrated no significant results for the investigated compounds except compound 5 , which has moderate activity against Gram‐positive bacteria.     

C-H insertion approach to the synthesis of endo,exo-furofuranones: synthesis of (+/-)-asarinin, (+/-)-epimagnolin A, and (+/-)-fargesin

A series of novel 5-aryl-4-aryloxymethyl-3-diazotetrahydrofuran-2-ones (12, 24, and 35a/b) have been prepared and found to undergo regio- and stereoselective C-H insertion reactions to afford 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane-8-ones (18, 26, and 36a/b) with endo,exo stereochemistry. Subsequent reduction of the lactone ring and cyclization of the resulting diols 27 and 37a/b permitted the synthesis of three endo,exo-furofuran lignans: asarinin (2), fargesin (3), and epimagnolin A (4). En route to the key diazo compounds 24 and 35a/b, a modified procedure for the Ghosez keteniminium-olefin cyclization was developed, which was required to minimize the decomposition of acid-sensitive functional groups such as electron-rich benzylic ethers that were present in the target compounds 2-4.     

Use of an aminosilyllithium for the diastereoselective synthesis of diphenyl oxasilacyclopentane acetals and polyols

[reaction: see text] The conjugate addition reaction of a stable, in situ generated silyllithium gives a beta-hydroxysilyl ester with high diastereoselectivity. Conversion of the beta-hydroxysilyl ester to a beta-fluorosilyl ester affords the precursor to the oxasilacyclopentane acetal in high yields under mild conditions. A hydride reduction and subsequent intramolecular silylation lead to the acetal in excellent yields. Finally, highly selective nucleophilic substitution affords oxasilacyclopentanes, which undergo a mild oxidation to afford 1,3-trans diols with high selectivity.     

Application of a one-pot lipase resolution strategy for the synthesis of chiral γ- and δ-lactones

A successful one-pot reduction of γ-ketoesters, δ-ketoesters and lactones to the corresponding 1,4- and 1,5-diols followed by a lipase catalyzed kinetic resolution coupled with hydrolysis to afford optically active diols is described. The synthetic utility of this one-pot method was illustrated by the oxidation of these chiral diols to respective chiral γ-butyrolactone and δ-lactones. Lipase from Pseudomonas cepacia, immobilized on ceramic afforded the product with high enantiomeric excess in good yields under mild reaction conditions. This approach has been used to develop a convenient enantioselective route for several γ- and δ-lactones using achiral and corresponding racemic starting material.     

Palladium-catalyzed stereospecific epoxide-opening reaction of gamma,delta-epoxy-alpha,beta-unsaturated esters with an alkylboronic acid leading to gamma,delta-vicinal diols with double inversion of the configuration

A palladium-catalyzed stereospecific epoxide-opening reaction of gamma,delta-epoxy-alpha,beta-unsaturated esters with an alkylboronic acid leading to gamma,delta-vicinal diols is described, which proceeds with retention of the configuration, i.e., via two consecutive S(N)2 processes, to afford the corresponding gamma,delta-cyclic boronates in high yields.     

Suicide inhibition of alpha-oxamine synthases: structures of the covalent adducts of 8-amino-7-oxononanoate synthase with trifluoroalanine

The irreversible inhibition of 8-amino-7-oxononanoate synthase by trifluoroalanine involves decarboxylative defluorination of the inhibitor-PLP aldimine followed by attack of the conjugated imine by the amino group of the active site lysine to afford a covalently bound difluorinated intermediate which can subsequently undergo further HF losses and hydrolysis to afford a 2-(pyridoximine phosphate) acetoyl protein adduct.     

Regio-, Diastereo-, and Enantioselective Synthesis of Vicinal Diols via α-Silyl Ketones

A new versatile and efficient regio-, diastereo-, and enantioselective synthesis of vicinal diols s-trans- 4 , s-trans- 5 , and s-cis- 4 is described. Symmetrical ketones are converted into their SAMP-or RAMP-hydrazones which are then silylated with (isopropyloxy)dimethylsilyl chloride, followed by ozonolysis to afford the α-silyl ketones (R)- 2 of high enantiomeric purity (ee 90– ≥ 98%). On the other hand, methyl ketones, after conversion into the corresponding (?)–(S)-1-amino-2-(methoxymethyl) pyrrolidine (SAMP) hydrazones, are silylated and then alkylated with RI to afford unsymmetrical α-silyl ketones (S)- 3 of high enantiomeric purity (ee 90- ≥ 98%). The reduction of the above obtained α-silyl ketones with L -Selectride, followed by oxidative cleavage of the C? Si bond gives rise to s-trans-4, s-trans- 5 , and s-cis- 4 with high diastereoselectivity (de 95- ≥ 98%) and without racemization (ee ≥ 90– ≥ 98%).     

Synthesis of triazolo- and tetrazolo-tetrahydroisoquinolines and isoquinolines via temperature controlled palladium catalysed allene/azide incorporation/intramolecular 1,3-dipolar cycloaddition cascades

A novel palladium catalysed three-component process is described involving an allene, an aryl iodide containing an activated alkene and TMSN₃. The cascade proceeds via a (π-allyl)palladium species which is intercepted by azide anion followed by stereoselective intramolecular 1,3-dipolar cycloaddition of the organoazide to afford substituted triazolo- and tetrazolo-tetrahydroisoquinolines in good yield. These latter products undergo extrusion of nitrogen to afford isoquinolines at 100 °C.     

NaIO4/LiBr-mediated diastereoselective dihydroxylation of olefins: a catalytic approach to the Prevost-Woodward reaction

[reaction: see text] LiBr catalyzes efficiently the dihydroxylation of alkenes to afford syn and anti diols with excellent diastereoselectivity depending upon the use of NaIO(4) (30 mol %) or PhI(OAc)(2) (1 equiv), respectively, as the oxidants. The oxidation of non-benzylic halides has been achieved for the first time to afford the corresponding diols in excellent yields.     

A new method for the hydroxymethylation of carbonyl compounds

Benzyl chloromethyl ether reacts with carbonyl compounds in the presence of SmI₂ to afford alcohols (I), which are subsequently subjected to hydrogenolysis to yield diols (II).     

Synthesis of Peroxy Bond Containing Acetylene Alcohols,Ethers, and Esters,Derivatives of 2-Octanone

A synthesis was developed of 2,5-dimethyl-2-tert-alkylperoxy-5-lithiumoxy-3-undecynes by treating the corresponding peroxyalkynes with butyllithium followed by reaction of the arising lithium peroxyacetylides with 2-octanone. The lithium peroxyalcoholates undergo hydrolysis with water to furnish peroxy bond containing alcohols. They also react with methyl and ethyl iodides, alkyl and benzyl bromides in the presence of hexamethylphosphoramide to afford the corresponding 2,5-dimethyl-2-tert-alkylperoxy-5-alkyl(benzyl)oxy-3-undecynes, with benzoyl chloride they yield peroxy bond containing benzoates. The thermal stability of the peroxides obtained was estimated by derivatography.     

Oxidative Addition to Gold(I) by Photoredox Catalysis: Straightforward Access to Diverse (C,N)‐Cyclometalated Gold(III) Complexes

Herein, we report the oxidative addition of aryldiazonium salts to ligand‐supported gold(I) complexes under visible light photoredox conditions. This method provides experimental evidence for the involvement of such a process in dual gold/photoredox‐catalyzed reactions and delivers well‐defined (C,N)‐cyclometalated gold(III) species. The remarkably mild reaction conditions and the ability to widely vary the ancillary ligand make this method a potentially powerful synthetic tool to access diverse gold(III) complexes for systematic studies into their properties and reactivity. Initial studies show that these species can undergo chloride abstraction to afford Lewis acidic dicationic gold(III) species.     

Silenes as novel synthetic reagents: synthesis of diols and lactones from simple alkyldienes

Aryl substituted silenes can be generated by a modified Peterson olefination reaction and trapped in situ to afford silacycles with high diastereoselectivity. These silacycles can be elaborated by ‘Fleming-Tamao’ type oxidation to provide access to functionalized diols and lactones.     

Selective ring expansion alkylation of formyl[2.2.1]bicyclic carbinols with C-nucleophiles: a unique route to cyclopentane derivatives

Reactions of camphor-, and camphene-derived formyl [2.2.1]bicyclic carbinols with Grignard and organolithium reagents afford the corresponding regio- and stereospecific alkyl/aryl [3.2.1]bicyclic diols. Some of these bicyclic diols have been treated with lead tetraacetate to provide new chiral cyclopentane derivatives. A plausible mechanism of the ring expansion-alkylation reaction is proposed.     

CeCl3/Sm Promoted Pinacolic Coupling of Aromatic Aldehydes and Ketones

The pinacolic coupling of aromatic aldehydes and ketone was performed with cerium trichloride and samarium in THF at room temperature to afford the corresponding 1,2‐diols in good yields.     

Pd-catalyzed domino carbonylative-decarboxylative allylation: an easy and selective monoallylation of ketones

In the presence of an allyl alcohol, α-chloroacetophenones undergo an allyloxycarbonylation reaction followed by in situ decarboxylative allylation to selectively afford the corresponding monoallylated ketones via a Pd-catalyzed domino sequence. The scope of the reaction was extended to substituted α-chloroacetophenones as well as various allyl alcohols.     

A convenient synthesis of 1,2,4-trisubstituted azetidines by reductive cyclization of aza-Michael adducts of chalcones

Aza-Michael adducts of chalcones and diethyl N-arylphosphoramidates undergo reductive cyclization with sodium borohydride followed by sodium hydride to afford 1,2,4-trisubstituted azetidines diastereoselectively in a one-pot procedure and excellent yields.