Biomimetic total synthesis of cruentaren A via aromatization of diketodioxinones

The total synthesis of cruentaren A, a biologically active resorcylate natural product, is reported. The aromatic unit was constructed via late-stage cyclization and aromatization from a diketodioxinone intermediate and macrocyclization using Fürstner ring-closing alkyne metathesis.     

1,4-二氢吡啶衍生物合成方法的改进和芳构化研究

改进了Hantzsch合成法,通过一锅煮合成1,4-二氢吡啶衍生物,大大缩短了反应时间,操作简便,发现氯化铁是一个较好的1,4-二氢吡啶衍生物芳构化的氧化剂。     

Application of microwave heating to the determination of free, combined and total sulphur in rubber

An atomic absorption spectrometry (AAS) method for the determination of total and combined sulphur in rubber and a catalytic method for the determination of free sulphur in rubber are described. The catalytic method is based on the iodine-azide reaction and is followed by an extraction of free sulphur with benzene, toluene or acetone. The catalytic determination, with the aid of gas chromatography, was performed in N,N-dimethylformamide after expelling the more volatile solvents used in the extraction. The calibration is linear over the range 2 × 10⁻⁶ – 3 × 10⁻⁴ M. Before the determination of total and combined sulphur, the rubber samples were decomposed by microwave assisted heating (5 min, 110 W) in a Teflon closed vessel. After microwave heating the solution was clear and homogenous and all sulphur compounds contained in the rubber were quantitatively oxidized to sulphate. The sulphates were then precipitated as BaSO₄ and an excess of barium was determined by AAS. From the difference in the results of the determinations of total and free sulphur the amount of combined sulphur can be calculated, and from the difference in the determinations of total and combined sulphur the amount of free sulphur can be calculated. In the latter case the catalytic analysis is not needed.     

Solid-phase total synthesis of the pentacyclic system lamellarins U and L

[reaction: see text] A total solid-phase synthesis of lamellarins U and L has been achieved. The conversion of an aldehyde group into a formate by a Baeyer-Villiger reaction and a intramolecular [3 + 2] cycloaddition of a 3,4-dihydroisoquinolinium salt over a triple bond comprise the key steps of the process. Each transformation has been controlled with the proper spectroscopic and analytical methods.     

金属蒸气合成在金属有机合成中的应用

本文简要地介绍了金属蒸气合成法的基本原理、仪器和实验技术, 并按金属原子分别与炔、单烯、多烯、环烯、芳烃体系、卤代烃、有机混和物的反应及有机金属硼化合物的合成, 对金属蒸气合成法在金属有机合成中的应用进行了讨论。     

Application of a catalytic palladium biaryl synthesis reaction, via C-H functionalization, to the total synthesis of Amaryllidaceae alkaloids

The total synthesis of the Amaryllidaceae alkaloids dehydroanhydrolycorine, hippadine, pratosine, anhydrolycorine, assoanine, anhydrolycorin-7-one and oxoassoanine was achieved from the appropriate N-benzylisatin precursors using an intramolecular, palladium catalyzed, dehydrohalogenation, biaryl synthesis reaction to establish the carbon skeleton of the natural products. In order to avoid the formation of regioisomers in the cyclization reactions it was found necessary to incorporate the halogen on the benzyl group. Borane reduction of the 7H-pyrrolo[3,2,1-de]phenanthridine-4,5-dione derivatives gave 7H-pyrrolo[3,2,1-de]- and 4,5-dihydro-7H-pyrrolo[3,2,1-de]-phenanthridines (dehydroanhydrolycorine, dehydroassoanine, anhydrolycorine and assoanine). The former were readily reduced to the latter with NaCNBH₃ to give anhydrolycorine and assoanine. These compounds were then oxidized to anhydrolycorin-7-one and oxoassoanine whilst the same mixtures of borane reduction products could be oxidized to give hippadine and pratosine.     

Application of vicarious nucleophilic substitution to the total synthesis of dl-physostigmine

A concise, highly efficient formal total synthesis of dl-physostigmine is described, using a relatively simple method that should be adaptable to the synthesis of homologous members of this type of alkaloid. The key step in the synthesis is a new vicarious nucleophilic substitution reaction between p-nitroanisole and a C-silylated derivative of N-methylpyrrolidinone. Subsequent conversion of the initial adduct to the tricyclic framework of physostigmine follows a well-established protocol and provides the key intermediate 8 in high yield. The vicarious nucleophilic substitution reaction has also been extended to six-membered lactams, with encouraging results.     

Iminophosphorane-mediated synthesis of 1-acyl-β-carbolines: A new access to the alkaloids eudistomin T, S and xestomanzamine A of marine origin

New syntheses of the alkaloids eudistomin T and S are described. The key step, formation of the 1-phenylacetyl β- carboline, involves a tandem aza Wittig / electrocyclic ring closure process. The first synthesis of the alkaloid xestomanzamine A is achieved by coupling of a N-protected harmane, now available via aza Wittig / electrocyclic ring closure process, with a 5-lithioimidazole derivative.     

Stereoselective synthesis of E,Z-configured 1,3-dienes by ring-closing metathesis. Application to the total synthesis of lactimidomycin

Strategic positioning of a silyl group on the diene unit of a diene-ene substrate allows rigorous regio- and stereocontrol to be exerted during metathesis-based macrocyclization reactions. The versatility of this concise approach to E,Z-configured 1,3-dienes of ring sizes of 12 or larger is demonstrated by an application to the total synthesis of lactimidomycin, a potent translation and cell-migration inhibitor.     

The novel transition metal free synthesis of 1,1′-biazulene

Reaction of 1-azulenyl methyl sulfoxide (1) under acidic conditions gave the 1,1′-biazulene derivative 3. Methylmercapt groups of 3 were readily converted to formyl groups by Vilsmeier reaction to afford 3,3′-diformyl-1,1′-biazulene (4), which reacted with pyrrole in the presence of acetic acid to give the parent 1,1′-biazulene (5). Reaction of 5 with pyridine in the presence of Tf₂O gave 3,3′-dihydropyridyl-1,1′-biazulene derivative 6. 3,3′-(4-Pyridyl)-1,1′-biazulene (7) was obtained by the reaction of 3 with KOH in EtOH at room temperature in good yield.     

One-pot synthesis of carbazoles from indoles via a metal free benzannulation

We report a simple, one-pot, and metal free benzannulation protocol to carbazoles starting with indoles, carbonyl compounds and an appropriate dienophiles. Mechanistically, this strategy generates an in situ diene by condensation between indole and carbonyl compound succeed and subsequent dehydration. Later, Diels–Alder reaction of this diene with a suitable dienophile followed by oxidation delivers the carbazole derivative. This methodology provide an easy access to carbazoles containing 1,4-naphthoquinone moiety.     

TFA-mediated intramolecular Friedel-Crafts reaction. An efficient metal and halogen free route to stereoselective synthesis of benzocycles

6-Acetoxy-4-alkenyl arenes undergo regio- and stereoselective intramolecular Friedel-Crafts reaction affording benzocycles in moderate to excellent yields in TFA/HOAc (3:1). It was observed that introduction of alkyls or phenyl group to the allylic acetate moiety facilitates the cyclization reaction. The optically active tricyclic (4bR,8aS)-4b,7,8,8a,9,10-hexahydrophenanthrene skeleton could also be easily obtained in excellent yields.     

Application of iron carbonyl complexation to the selective total synthesis of sanshools

We focused on the iron-complexes of sanshools (hydroxyl-α-sanshool, hydroxyl-β-sanshool, and γ-sanshool) as the key intermediates for the selective synthesis of these structurally unstable compounds. Consequently, we developed a concise and selective method for the total synthesis of sanshools in 5-6 steps (26-45% overall yield), including complexation of dienes with iron tricarbonyl group.     

Intramolecular phosphine-directed hydroformylation. Application to the total synthesis of (+)-phyllanthocin

The temporary incorporation of a coordinating phosphine residue [m-(Ph₂P)C₆H₄CO] into the tetracyclic phyllanthocin precursor1a directed the [(COD)RhOAc]₂-catalyzed hydroformylation of1d largely to the desired C(3) position. This “intramolecular hydroformylation” strategy substantially improves a key transformation in the total synthesis of (+)-phyllanthocin.     

Combined coinage metal catalysis in natural product synthesis: total synthesis of (+)-varitriol and seven analogs

A modular total synthesis of the natural product (+)-varitriol (1) and seven analogs was achieved by using combined coinage metal catalysis. Starting from enynol 13, reagent-controlled introduction of stereogenic centers and efficient center-to-axis-to-center chirality transfer viaα-hydroxyallene 5 afforded (+)-varitriol with 6.4% yield over 10 steps.     

Ring-closing alkyne metathesis. Application to the total synthesis of sophorolipid lactone

The first total synthesis of a major component of the microbial biosurfactant sophorolipid has been achieved. This approach to the 26-membered macrolide 1 containing a Z-configured alkene group in its lipidic tether spanning the sophorose backbone is based on a ring-closing metathesis reaction of diyne 21 catalyzed by Mo[N(t-Bu)(Ar)](3) (5; Ar = 3,5-dimethylphenyl) activated in situ by CH(2)Cl(2), followed by Lindlar reduction of the resulting cycloalkyne 22. The two beta-glycosidic linkages of compound 21 were installed by means of the glucal epoxide method and a modified Koenigs-Knorr reaction promoted by AgOTf/lutidine, respectively.     

Transition metal free intramolecular S-arylation: one-pot synthesis of thiochromen-4-ones

A convenient one-pot method for the synthesis of thiochromen-4-ones by the condensation of 2′-haloacetophenone and dithioesters at room temperature in the presence of NaH in DMF in moderate to good yields has been developed. The method involves unusual intramolecular S-arylation. The reaction is operationally facile, readily scalable and offers rapid entry into substituted chromene-4-ones.     

Application of Prins cyclization to the total synthesis of (+)-decytospolides A and B

(+)-Decytospolides A and B, natural products containing the tetrahydropyran skeleton, were synthesized via Prins cyclization as the key step.