Enantioselective synthesis and absolute configurations of aculeatins A and B

The two naturally occuring, bioactive spiroacetals aculeatins A and B have been synthesized for the first time in enantiopure form using an asymmetric allylation as the only chirality source. A further key step was a stereoselective aldol reaction with remote induction. The absolute configurations of the natural products have been established and the previously assigned relative configurations have been corrected.     

Enantioselective synthesis of cyclopropyl δ-lactonealdehydes and dodecyl-5-ene-1-yne-3-ol: advanced intermediates of solandelactone A and B

A stereocontrolled synthesis of cyclopropyl δ-lactonealdehydes and dodecyl-5-ene-1-yne-3-ol is accomplished with predictable absolute stereochemistry via organocatalytic and catalytic asymmetric transfer hydrogenation reactions. The salient feature of this protocol is the genesis of chirality through an organocatalytic reaction and utilized for installing a critical bifunctional trans-cyclopropane motif, which is a key segment of every representative member of the oxylipin class of natural products such as solandelactone A and B.     

Blue light photoredox decarboxylation and tin-free Barton-McCombie reactions in the stereoselective synthesis of (+)-muscarine

Starting from a 1,2-O-isopropylidene-α-d-xylofuranose derivative, a non-toxic free-radical approach for the synthesis of (+)-muscarine is reported. To this end, a stereoselective allylation reaction at the anomeric position of a respective xylofuranose derivative was employed as a new synthetic strategy for the installation of the methyl group at the C-5 position of (+)-muscarine. Accordingly, the allyl group was transformed into the methyl group in three sequential steps highlighting a blue-light photoredox decarboxylation reaction. Additionally, a tin-free Barton-McCombie deoxygenation reaction of the respective C-methyl glycoside allowed the completion of this free-radical approach to (+)-muscarine.     

Enantioselective synthesis of attenols A and B

[reaction: see text] Enantioselective synthesis of attenols A and B was accomplished by using diastereoselective hydroboration, Lindlar reduction, and acid-catalyzed acetal formation.     

Selective preparation of key intermediates for the synthesis of key intermediates for the synthesis of gemini surfactants by phase-transfer catalysis

A comparison of liquid-liquid and solid-liquid PTC for the selective synthesis of diglycidyl ether from protected pentaerythritol and epichlorohydrin is presented. Solid-liquid PTC was found to be more useful than liquid-liquid PTC because the use of water or other solvents can be avoided and higher yields and selectivity are achieved. It was proved that etherification takes place in the solid phase-organic phase system even in the absence of the phase-transfer catalyst. However, the use of tetrabutylammonium bisulfate as catalyst is essential due to its crucial effect on the enhancement of the rate of etherification and on the improvement of the selectivity to diglycidyl ether, which is higher than 98%.     

First total synthesis of two new heterocyclic compounds:Bretschneiderazines A and B

Facile synthesis of the two new natural heterocyclic compounds bretschneiderazines A（2） and B（3）,isolated from an extract of the stems of Bretschneidera sinensis,is reported.We employed the cyclization reaction of benzamide by directed lithiation and sequential treatment with sulfur and phosgene as key steps.All new compounds have been fully characterized by means of IR,¹H NMR,¹³C NMR,and HRMS.     

The synthesis of key intermediates in cembranolides

Two key intermediates of cembranolides- (2E,6E,10E)-3,7,11,15-tetramethyl-9-phenylsulfonyl-2,6,10,14-tetraen-1-hexadecanol (1) and (2E,6E,10E,14E)-2,6,10,14-tetramethyl-8-phenylsulfonyl-2,6,10,14-tetraen-1,16-hexadecanediol (2) were synthesized starting from geraniol and linalool and some improved synthetic methods were used.     

A novel synthesis of coumarin derivatives

The chemical behaviors of 3-ethynylcoumarin towards benzyl bromide,diazonium chic ride,hydrogen chloride,ethyl magnesium bromide and its self-coupling are reported.     

Enantioselective total synthesis of litseaverticillols A and B

[reaction: see text] The first enantioselective total synthesis of the (1R,5S)-stereoisomer of litseaverticillols A and B, anti-HIV monocyclic sesquiterpenoids isolated from a perennial shrub found in Vietnam, was accomplished in six steps from homogeranic acid by employing the Evans asymmetric aldol reaction and a microwave-promoted cyclization of a stannylated thiol ester intermediate as the C-C bond-forming steps.     

Regioselective ring cleavage of chiral β-trichloromethyl-β-propiolactone with organoaluminum compounds for the synthesis of optically active intermediates

A novel alkylating ring cleavage reaction of enantiomerically pure β-trichloromethyl-β-propiolactone as a chiral building block with organoaluminum compounds provided ring-opened products with a chiral trichloromethyl carbinol moiety. A product was demonstrated to be used as an effective chiral synthon for the synthesis of chiral bioactive derivatives such as ipsdienol and sodium cilastatin.     

Deoxynucleoside phosphoramidites—A new class of key intermediates for deoxypolynucleotide synthesis

The development of a new class of nucleoside phosphites is described. These compounds are stable to normal laboratory conditions, are activated by mild acid treatment, and are observed to react essentially quantitatively with protected nucleosides.     

Total synthesis of pachastrissamine (jaspine B) enantiomers from d-glucose

Synthesis of both enantiomers of pachastrissamine is described from a common chiral template. The stereoselective construction of the central tetrahydrofuran units was based on the pseudodesymmetrization of a pentodialdo-1,4-furanose derivative taking advantage of the latent symmetry present.     

合成2—芳氧基—5—氟—3H—4—嘧啶酮的新方法

由２－氰－５－氟－３Ｈ－４－嘧啶酮和取代苯酚钠在常压下反应，合成了７个未见文献报道的２－芳氧基－５－氟－３Ｈ－４－嘧啶酮化合物，产率７０￣８７％，结构经ＩＲ、＾１Ｈ ＮＭＲ和ＭＳ证实。     

An efficient synthesis of 4-chromanones

A two step efficient and practical synthesis of a variety of 4-chromanones is described. Phenols undergo a Michael addition to acrylonitriles in the presence of catalytic amounts of potassium carbonate and tert-butanol to generate the corresponding 3-aryloxypropanenitriles in 50-93% yields. Treatment of the resulting aryloxypropionitriles with 1.5 equiv of TfOH and 5 equiv of TFA, followed by an aqueous work up afforded 4-chromanones in moderate to excellent yields.     

Total synthesis of tryprostatins A and B

Three distinct synthetic routes to the 2-prenyl tryptophan core skeleton of tryprostatins and their total syntheses are described. The strategies include a traditional gramine-mediated coupling reaction, Fürstner indole synthesis, and our radical-mediated indole synthesis from o-alkenylphenyl isocyanide. The establishment of reliable conditions for the radical-mediated construction of indoles via a low-temperature radical initiator V-70 (2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile)) led to the highly efficient syntheses of tryprostatins A and B.     

Enantioselective synthesis of 3-substituted-4-aryl piperidines useful for the preparation of paroxetine

The asymmetric conjugate addition reaction between 4-fluorophenylmagnesium bromide and various chiral α,β-unsaturated esters and enoylsultam substrates was explored to prepare a key intermediate useful in the preparation of paroxetine. The most selective auxiliary was found to be Oppolzer's (1S)-(−)-camphorsultam. Interestingly, the diastereoselection was opposite to that reported for acyclic enoylsultams.     

A Coupling Reaction of 4-Amino-5-mercapto- 3-substituted-1,2,4-triazoles to Generate Symmetrically Substituted Hydrazines

Summary. A novel coupling reaction of 4-amino-5-mercapto-3-substituted-1,2,4-triazoles to generate symmetrically substituted hydrazines, N,N′-bis(5-mercapto-3-substituted-1,2,4-triazol-4-yl)hydrazines was unexpectedly observed. Five examples are presented to demonstrate this reaction. All isolated products were unambiguously characterized.     

Enantioselective total synthesis of (+)-sarcandralactone A

An enantioselective total synthesis of the lindenane sesquiterpene (+)-sarcandralactone A has been accomplished for the first time. The synthesis features a SeO₂-mediated [2,3]-sigmatropic rearrangement for the facile construction of the tertiary allylic alcohol as a single diastereoisomer.     

Intercepted-Knoevenagel condensation for the synthesis of unsymmetrical fused-tricyclic 4H-pyrans

4H-Pyrans (4H-Pys) and 1,4-dihydropyridines (1,4-DHPs) are important classes of heterocyclic scaffolds in medicinal chemistry. Herein, an indium(III)-catalyzed one-pot domino reaction for the synthesis of highly functionalized 4H-Pys, and a model of 1,4-DHP is reported. This alternative approach to the challenging Hantzsch 4-component reaction enables the synthesis of fused-tricyclic heterocycles, and the mechanistic studies underline the importance of an intercepted-Knoevenagel adduct to achieve higher chemoselectivity towards these types of unsymmetrical heterocycles.