Rhenium-catalyzed regioselective synthesis of 1,2-disubstituted naphthalenes

November 30, 2012, 10:40 am

≫ Next: Chirality induction by E–Z photoisomerization in [2,2]paracyclophane-bridged azobenzene dimer

≪ Previous: Facile route to highly functionalized 2H-chromene-2-thiones via ring annulations of β-oxodithioesters with phenols catalyzed by AlCl3 under solvent-free conditions

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Rui Umeda, Satoru Nishi, Aya Kojima, Kenta Kaiba, Yutaka Nishiyama

Rhenium-catalyzed coupling reaction of alkynes with phenylacetaldehyde dimethylacetal in the presence of H2O regioselectively afforded the corresponding 1,2-disubstituted naphthalenes.

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Chirality induction by E–Z photoisomerization in [2,2]paracyclophane-bridged azobenzene dimer

November 30, 2012, 10:40 am

≫ Next: Palladium-catalyzed oxidative arylation of trisubstituted olefin: an efficient synthesis of 3-(disubstituted)alkylidene-oxindoles

≪ Previous: Rhenium-catalyzed regioselective synthesis of 1,2-disubstituted naphthalenes

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
P.K. Hashim, Meethale C. Basheer, Nobuyuki Tamaoki

We designed and synthesized a new prochiral molecule in which two azobenzene moieties were embedded in [2,2]paracyclophane and showed the chirality induction by E–Z photoisomerization. We also demonstrated the on/off switching of asymmetry by irradiation and reflux respectively.

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Palladium-catalyzed oxidative arylation of trisubstituted olefin: an efficient synthesis of 3-(disubstituted)alkylidene-oxindoles

November 30, 2012, 10:40 am

≫ Next: Syntheses of (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)arenes through Pd-catalyzed borylation of arylbromides with the successive use of 2,2′-bis(1,3,2-benzodioxaborole) and pinacol

≪ Previous: Chirality induction by E–Z photoisomerization in [2,2]paracyclophane-bridged azobenzene dimer

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Hyun Ju Lee, Ko Hoon Kim, Se Hee Kim, Jae Nyoung Kim

A palladium-catalyzed oxidative arylation of 3-(monosubstituted)alkylidene-oxindoles with arenes afforded 3-(disubstituted)alkylidene-oxindoles in good to moderate yields.

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Syntheses of (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)arenes through Pd-catalyzed borylation of arylbromides with the successive use of 2,2′-bis(1,3,2-benzodioxaborole) and pinacol

November 30, 2012, 10:40 am

≫ Next: Efficient generation of hydrogen peroxide by aerobic photooxidation of 2-propanol using anthraquinone-2-carboxylic acid and one-pot epoxidation of α,β-unsaturated ketones

≪ Previous: Palladium-catalyzed oxidative arylation of trisubstituted olefin: an efficient synthesis of 3-(disubstituted)alkylidene-oxindoles

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Jun Takagi, Tetsu Yamakawa

Syntheses of (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)arenes through the Pd-catalyzed borylation of arylbromides with the successive use of 2,2′-bis(1,3,2-benzodioxaborole) and pinacol were investigated. PdCl2(dppf) and AcOK in EtOH or DMSO successfully provided (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)arenes. In particular, this method was more effective in the borylation of arylbromides bearing sulfonyl groups than the conventional Pd-catalyzed borylation using pinacolborane or bis(pinacolato)diboron.

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Efficient generation of hydrogen peroxide by aerobic photooxidation of 2-propanol using anthraquinone-2-carboxylic acid and one-pot epoxidation of α,β-unsaturated ketones

November 30, 2012, 10:40 am

≫ Next: Synthesis of a protected derivative of (2R,3R)-β-hydroxyaspartic acid suitable for Fmoc-based solid phase synthesis

≪ Previous: Syntheses of (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)arenes through Pd-catalyzed borylation of arylbromides with the successive use of 2,2′-bis(1,3,2-benzodioxaborole) and pinacol

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Lei Cui, Sohei Furuhashi, Yuma Tachikawa, Norihiro Tada, Tsuyoshi Miura, Akichika Itoh

We developed an efficient method for the generation of hydrogen peroxide by aerobic photooxidation of 2-propanol using anthraquinone-2-carboxylic acid and molecular oxygen in air and visible light from fluorescent lamps. One-pot epoxidation of α,β-unsaturated ketones using the generated hydrogen peroxide is also reported.

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Synthesis of a protected derivative of (2R,3R)-β-hydroxyaspartic acid suitable for Fmoc-based solid phase synthesis

November 30, 2012, 10:40 am

≫ Next: Cyclometallated Pd(II) thiosemicarbazone complexes: new catalyst precursors for Suzuki-coupling reactions

≪ Previous: Efficient generation of hydrogen peroxide by aerobic photooxidation of 2-propanol using anthraquinone-2-carboxylic acid and one-pot epoxidation of α,β-unsaturated ketones

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Boyaud France, Viguier Bruno, Inguimbert Nicolas

Synthesis of d-threo-hydroxyaspartic acid, orthogonally protected and compatible with an Fmoc solid-phase peptide synthesis strategy is reported. This synthetic procedure starting from (2R,3R)-dimethyltartrate is adaptable to a multi-gram scale. 2,2-Dimethyl-5-oxo-1,3-dioxazolane formation between the β-hydroxy alcohol and the β-carboxylic functions constitutes a key step of the differentiation of the two acidic functions allowing the preparation of (2R,3R)-Fmoc-β-hydroxyaspartic α-allyl ester.

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Cyclometallated Pd(II) thiosemicarbazone complexes: new catalyst precursors for Suzuki-coupling reactions

November 30, 2012, 10:40 am

≫ Next: Solid phase synthesis of hydroxamate peptides for histone deacetylase inhibition

≪ Previous: Synthesis of a protected derivative of (2R,3R)-β-hydroxyaspartic acid suitable for Fmoc-based solid phase synthesis

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Hong Yan, Prinessa Chellan, Tingyi Li, Jincheng Mao, Kelly Chibale, Gregory S. Smith

Four tridentate [C,N,S] thiosemicarbazone Pd(II) complexes were applied as catalyst precursors for the Suzuki–Miyaura coupling of a variety of aryl halides and aryl boronic acids. After screening various catalytic conditions, it was found that one dinuclear complex IV containing the bis(diphenylphosphino) ferrocene spacer was able to efficiently catalyze these reactions with yields up to 99% irrespective of the type of aryl substituent on the substrate.

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Solid phase synthesis of hydroxamate peptides for histone deacetylase inhibition

November 30, 2012, 10:40 am

≫ Next: Attempted Simmon–Smith reaction on β-alkylthio-α,β-unsaturated ketones: a regiospecific synthesis of 2,4-disubstituted thiophenes

≪ Previous: Cyclometallated Pd(II) thiosemicarbazone complexes: new catalyst precursors for Suzuki-coupling reactions

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
David M. Wilson, Lisa N. Silverman, Markus Bergauer, Kayvan R. Keshari

An orthogonal protecting group strategy was devised to synthesize hydroxamic acid containing peptides for biomimetic histone deacetylase (HDAC) inhibition. The basic building block was a protected aminosuberic acid (Asu) derivative bearing a protected hydroxamate in the side-chain, related closely to HDAC inhibitors that are transition-state analogs of acetyllysine. These inhibitors include suberoylanilide hydroxamic acid (SAHA), currently being used to treat a variety of human cancers. This strategy was employed to synthesize a series of nonameric peptides related to actual HDAC substrates, derived from known sites of acetylation/deacetylation on the N-terminal tails of the histone core proteins H2A, H2B, H3, and H4. In each case the lysine residue was replaced by a hydroxamate-bearing side chain, to mimic the endogenous site of deacetylation. Mass spectrometry and high performance liquid chromatography (HPLC) confirmed the success of automated solid-phase synthesis. These results suggest facile synthesis of a new class of HDAC inhibitors that may have enhanced selectivity for specific HDAC isoforms.

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Attempted Simmon–Smith reaction on β-alkylthio-α,β-unsaturated ketones: a regiospecific synthesis of 2,4-disubstituted thiophenes

November 30, 2012, 10:40 am

≫ Next: Triethynylmethane: a molecular unit inducing excimer-like emission in aggregated states of hydrocarbon fluorophores

≪ Previous: Solid phase synthesis of hydroxamate peptides for histone deacetylase inhibition

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Toreshettahally R. Swaroop, Rangaswamy Roopashree, Hiriyakkanavar Ila, Kanchugarakoppal S. Rangappa

A new regiospecific route to 2,4-disubstituted thiophenes has been developed through Simmon–Smith reaction on β-methylthio-α,β-unsaturated ketones. Extension of the reaction to β-ethyl/benzylthio-α,β-unsaturated ketones also gave the corresponding 2,4-disubstituted thiophenes in a regiospecific manner. A probable mechanism involving a carbenoid methylene insertion to divalent sulfur followed by intramolecular aldol condensation has been suggested.

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Triethynylmethane: a molecular unit inducing excimer-like emission in aggregated states of hydrocarbon fluorophores

November 30, 2012, 10:40 am

≫ Next: Light induced synthesis of symmetrical and unsymmetrical dihydropyridines in ethyl lactate–water under tunable conditions

≪ Previous: Attempted Simmon–Smith reaction on β-alkylthio-α,β-unsaturated ketones: a regiospecific synthesis of 2,4-disubstituted thiophenes

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Takahiro Otabe, Saki Matsumoto, Hiroki Nakagawa, Changfeng Hong, Chikara Dohno, Kazuhiko Nakatani

We report the synthesis of triethynylmethane (TEM) derivatives substituted with fluorescent aromatic hydrocarbons and the fluorescence properties in dilute aqueous solution and in spin-coated film. Pyrene-tethered TEM derivatives showed excimer-like fluorescence in 80% water in THF and spin-coated film. UV and ¹H NMR analyses showed the aggregation of TEM derivatives. Phenanthrene-tethered TEM also showed excimer-like fluorescence in high water content in THF. These data showed that TEM is a novel molecular unit inducing excimer-like emission in the aggregated states of aromatic hydrocarbon fluorophores.

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Light induced synthesis of symmetrical and unsymmetrical dihydropyridines in ethyl lactate–water under tunable conditions

November 30, 2012, 10:40 am

≫ Next: A convenient one-pot synthesis of (R)-2-amino-3,3,3-trifluoro-2-methyl-N-phenylpropanamide derivatives

≪ Previous: Triethynylmethane: a molecular unit inducing excimer-like emission in aggregated states of hydrocarbon fluorophores

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Partha Pratim Ghosh, Sanjay Paul, Asish R. Das

A highly efficient environment-friendly one-pot green methodology has been developed for the synthesis of symmetrical and unsymmetrical 1,4-dihydropyridines and polyhydroquinolines following the multicomponent Hantzsch synthesis under visible light irradiation in ethyl-l-lactate–water solution at room temperature. The present methodology offers several advantages such as simple procedure, greener condition, excellent yields and short reaction time sans any catalyst, support or promoter. The developed protocol has been materialized with the involvement of a household compact tungsten lamp as the visible light source, and the manifested high selectivity of the reaction performed in ethyl lactate–water solvent mixture under tunable conditions. The Ca²⁺ channel blocker nitrendipine and nemadipine B were also successfully synthesized applying the developed methodology in high yields.

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A convenient one-pot synthesis of (R)-2-amino-3,3,3-trifluoro-2-methyl-N-phenylpropanamide derivatives

November 30, 2012, 10:40 am

≫ Next: Identification of amino acid derivatives as condensation products between glyceraldehyde and guanine nucleoside

≪ Previous: Light induced synthesis of symmetrical and unsymmetrical dihydropyridines in ethyl lactate–water under tunable conditions

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Tian-Wen Li, Pei-Hua Shang, Chang-Mei Cheng, Yu-Fen Zhao

A convenient one-pot synthesis of enantiopure (R)-2-amino-3,3,3-trifluoro-2-methyl-N-phenylpropanamide derivatives has been developed. The key step in this synthetic methodology turned out to be the amide formation in which (R)-2-amino-3,3,3-trifluoro-2-methylpropanoic acid hydrochloride was simultaneously protected and activated by Vilsmeier reagent.

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Identification of amino acid derivatives as condensation products between glyceraldehyde and guanine nucleoside

November 30, 2012, 10:40 am

≫ Next: Synthesis of isomeric angularly fused dihydroquinazolinoquinazolinones and an unusual oxidative rearrangement

≪ Previous: A convenient one-pot synthesis of (R)-2-amino-3,3,3-trifluoro-2-methyl-N-phenylpropanamide derivatives

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Charles Pathirana, Yande Huang, Mark Bolgar, Danping Li, Russell Suda, Divyakant Desai, Ming Yang, Siva J. Prasad, Venkatapuram Palaniswamy

Two degradants observed in a drug formulation of the hepatitis B drug entecavir (Baraclude®), 1 were shown to be identical to the products resulting from the condensation between glyceraldehyde and the guanine nucleoside. The reaction products, 2a and 2b were identified by the analysis of comprehensive NMR data to be two diastereomeric derivatives of alanine implying a novel rearrangement in the reaction between glyceraldehyde and 1.

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Synthesis of isomeric angularly fused dihydroquinazolinoquinazolinones and an unusual oxidative rearrangement

November 30, 2012, 10:40 am

≫ Next: Regiodirecting effects in difunctionalised tricarbonyl[(1,2,3,4,5-η)-cyclohexadienyl]iron(1+) salts: building blocks for alkaloids

≪ Previous: Identification of amino acid derivatives as condensation products between glyceraldehyde and guanine nucleoside

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
Somepalli Venkateswarlu, Meka Satyanarayana, Kolla Srinivas, Kodumuri N.V.V. Aadisudhakar

Cyclization of 2-(2-aminophenyl)-2,3-dihydroquinazolin-4(1H)-ones onto N1-nitrogen and onto N3-nitrogen leading to 11b,12-dihydro-(13H)-quinazolino[3,4-a]quinazolin-13-ones and 13,13a-dihydro-(8H)-quinazolino[4,3-b]quinazolin-8-ones, respectively, is described for the first time. An unusual dehydrogenative rearrangement of 11b,12-dihydro-(13H)-quinazolino[3,4-a]quinazolin-13-one to (8H)-quinazolino[4,3-b]quinazolin-8-one is also described.

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Regiodirecting effects in difunctionalised tricarbonyl[(1,2,3,4,5-η)-cyclohexadienyl]iron(1+) salts: building blocks for alkaloids

November 30, 2012, 10:40 am

≫ Next: Graphical contents list

≪ Previous: Synthesis of isomeric angularly fused dihydroquinazolinoquinazolinones and an unusual oxidative rearrangement

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2
G. Richard Stephenson, Ian M. Palotai

Electrophilic tricarbonyl[(1,2,3,4,5-η)-cyclohexadienyl]iron(1+) salts that incorporate methoxy and 2-ethanoyl ester substituents have been prepared, and the regiochemistry of their reactions with nucleophiles in arylation reactions has been examined using the model nucleophile diphenylzinc. The 1-carbomethoxymethyl-2-methoxy salt 1 reacts selectively by the ω addition pathway, but the 2-carbomethoxymethyl-3-methoxy salt 9 gave a 6:1 mixture of ω and α addition products. The 1-carbomethoxymethyl-2-methoxy regioisomer 1 was prepared in >95% purity without recourse to chromatography and shows the correct regiocontrol for use as a starting material in organoiron-mediated routes to alkaloids such as lycorine and parkacine.

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Graphical contents list

November 30, 2012, 10:40 am

≫ Next: Editorial board

≪ Previous: Regiodirecting effects in difunctionalised tricarbonyl[(1,2,3,4,5-η)-cyclohexadienyl]iron(1+) salts: building blocks for alkaloids

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2

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Editorial board

November 30, 2012, 10:40 am

≫ Next: Silver catalyzed C–C and C–S coupling of aryl halides and thiols with boronic acids

≪ Previous: Graphical contents list

Publication year: 2013
Source:Tetrahedron Letters, Volume 54, Issue 2

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Silver catalyzed C–C and C–S coupling of aryl halides and thiols with boronic acids

December 1, 2012, 10:25 am

≫ Next: Graphical contents list

≪ Previous: Editorial board

26 December 2012
Publication year: 2012
Source:Tetrahedron Letters, Volume 53, Issue 52

An efficient Ag(I) catalyzed carbon–carbon and carbon–sulfur bond formation reaction of aryl halides and thiols with boronic acids has been demonstrated. Using this protocol, substrates with a wide range of functional group including electron-rich, and electron deficient substituents have been explored. These reactions are particularly useful to prepare symmetrical and unsymmetrical biphenyls and thioethers. These products were isolated in high yield.