New Flexible Synthesis of Pyrazoles with Different, Functionalized Substituents at C3 and C5

Grotjahn, Douglas B.; Van, Sang; Combs, David J.; Lev, Daniel A.; Schneider, Christian; Rideout, Marc C.; Meyer, Christoph; Hernandez, Genaro; Mejorado, Lupe

doi:10.1021/jo026083e

Cited by 104 publications

(40 citation statements)

References 56 publications

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“…[22] Grotjahn and co-workers synthesized a series of chelate ligands bearing soft phosphorous and sulfur donor tethers and reported their ligation to a square planar Pd II center (11 and 12). [23,24] The NÀH stretching band of 11 (L = SMe, R = tBu) is observed at 3342 cm À1 in the IR spectrum, which is shifted to 2498 cm À1 upon deuteriation (n NH /n ND = 1.338). [23] We have recently demonstrated that cyclometalation of 3,5-diphenylpyrazole leads to the formation of the C-N chelate pyrazole complex 13 as shown in Scheme 5.…”

Section: Protic Pyrazole Complexesmentioning

confidence: 99%

β‐Protic Pyrazole and N‐Heterocyclic Carbene Complexes: Synthesis, Properties, and Metal–Ligand Cooperative Bifunctional Catalysis

Kuwata

Ikariya

2011

Chemistry A European J

130

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This Minireview provides an overview of the chemistry of pyrazole and N-heterocyclic carbene (NHC) complexes bearing an NH group at the β-position to the metal. The synthesis and structures as well as the Brønsted acidic nature of the β-NH group are described in detail. These complexes are attractive candidates for novel metal-ligand cooperative bifunctional catalysts, which would benefit highly effective molecular and energy transformations.

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Section: Protic Pyrazole Complexesmentioning

confidence: 99%

β‐Protic Pyrazole and N‐Heterocyclic Carbene Complexes: Synthesis, Properties, and Metal–Ligand Cooperative Bifunctional Catalysis

Kuwata

Ikariya

2011

Chemistry A European J

130

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“…[1][2][3][4][5][6][7][8] Also, THP-protected alcohols are generally stable under a wide range of reaction conditions and reagents, such as metal hydrides, alkyllithiums, Grignard reagents, and catalytic hydrogenation. [9][10][11][12][13] For the THP ethers, a number of deprotecting methods have been introduced. 14) Various acids, including AcOH, 15) pyridinium para-toluenesulfonate (PPTS), 1) boric acid, 16) and TsOH, 17) can cleave THP ethers to regenerate free alcohols with high efficacy.…”

Section: Notesmentioning

confidence: 99%

One-Step Transformation of Tetrahydropyranyl Ethers Using Indium(III) Triflate as the Catalyst

Mineno

Nikaido

Kansui

2009

CHEMICAL & PHARMACEUTICAL BULLETIN

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NotesTetrahydropyranyl (THP) group is a well-utilized moiety, mainly as a tool to protect alcohol units due to its feasibility of installation and low cost. Stirring the free alcohols with 3,4-dihydro-2H-pyran (DHP) under acidic conditions can easily produce THP-protected alcohols.1-8) Also, THP-protected alcohols are generally stable under a wide range of reaction conditions and reagents, such as metal hydrides, alkyllithiums, Grignard reagents, and catalytic hydrogenation. O, 19,20) and CuSO 4 · 5H 2 O, 21) has also been reported.Previously, we have reported a couple of convenient reaction methods using indium or indium-related reagents. [22][23][24][25] The authors have recently developed a practical approach to tetrahydropyranylation and depyranylation of various alcohols using indium(III) triflate.26) It is worth noting that with the same catalyst, the reactions proceed in directions of both protection and deprotection. In the presence of a catalytic amount of indium(III) triflate, protection of alcohols is carried out using CH 2 Cl 2 as the solvent, whereas deprotection uses MeOH/H 2 O as the solvent. Kamal et al. also reported that tetrahydropyranylation can be controlled using catalytic aluminum(III) triflate. 27) Another report has shown the cleavage of THP ethers using titanium(III) triflate in good yields.28) According to our earlier experiments, indium(III) triflate was revealed to be an efficient catalyst for the transformation of THP ethers into their corresponding acetates. In further intensive work, we have developed a useful transforming reaction of THP ethers using various anhydride moieties with indium(III) triflate as the catalyst. Herein, we report the details of this one-step transformation. Results and DiscussionTHP-protected benzyl alcohol and N-(2-hydroxyethyl)-phthalimide were used as the starting materials. First, the suitability of the catalysts was examined by reactions with acetic anhydride (Chart 1). In both cases, the reaction proceeded and produced excellent yields in a shorter time when indium(III) triflate was employed as the catalyst (Table 1, entries 1 and 3), as compared with indium(III) chloride (Table 1, entries 2 and 4). Giving the satisfactory results with indium(III) triflate, we then expanded our investigation to the other types of anhydrides. The reactions were carried out with THP-protected benzyl alcohol, N-(2-hydroxyethyl)phthalimide, and a wide range of anhydrides (Chart 2).As expected, the reactions with another aliphatic anhydride of isobutyric anhydride generated similar satisfactory results (Table 2, entries 1 and 7). In the case of benzoic anhydride, the reaction required an extended period of time, although acceptable results were obtained (Table 2, entries 2 and 8). With the exception of entry 5, these conditions were then applied to the cyclic anhydrides, and the reactions produced entirely poor yields. These results were presumably due to the low reaction temperature. When reactions were resumed at reflux using THF as the solvent, good to excellent out...

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“…4a, 16 However, either the regioselectivity issue has not been studied in detail or the occurrence of mixtures of regioisomers was reported. 17 Despite of very few examples, 18 the regioselective formation of N-substituted pyrazoles by the alkynone pathway has remained unexplored. With respect to the interesting pharmacological and electronic properties of pyrazoles, in particular as fluorophores, and the increasing quest for tailor-made functional π-electron systems by diversity-oriented strategies, we have developed regioselective one-pot syntheses of substituted pyrazoles.…”

Section: Pyrazolesmentioning

confidence: 99%

Consecutive multi-component syntheses of heterocycles via palladium-copper catalyzed generation of alkynones

Willy¹,

Müller²

2008

Arkivoc

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New Flexible Synthesis of Pyrazoles with Different, Functionalized Substituents at C3 and C5

Cited by 104 publications

References 56 publications

β‐Protic Pyrazole and N‐Heterocyclic Carbene Complexes: Synthesis, Properties, and Metal–Ligand Cooperative Bifunctional Catalysis

β‐Protic Pyrazole and N‐Heterocyclic Carbene Complexes: Synthesis, Properties, and Metal–Ligand Cooperative Bifunctional Catalysis

One-Step Transformation of Tetrahydropyranyl Ethers Using Indium(III) Triflate as the Catalyst

Consecutive multi-component syntheses of heterocycles via palladium-copper catalyzed generation of alkynones

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