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B(C6F5)3-catalyzed dehydrogenative cyclization of N-tosylhydrazones and anilines via a Lewis adduct: a combined experimental and computational investigation.

ABSTRACT: Tris(pentafluorophenyl)borane-catalyzed dehydrogenative-cyclization of N-tosylhydrazones with aromatic amines has been disclosed. This metal-free catalytic protocol is compatible with a range of functional groups to provide both symmetrical and unsymmetrical 3,4,5-triaryl-1,2,4-triazoles. Mechanistic experiments and density functional theory (DFT) studies suggest an initial Lewis adduct formation of N-tosylhydrazone with B(C6F5)3 followed by sequential intermolecular amination of the borane adduct with aniline, intramolecular cyclization and frustrated Lewis pair (FLP)-catalyzed dehydrogenation for the generation of substituted 1,2,4-triazoles.

PROVIDER: S-EPMC6839809 | BioStudies |

REPOSITORIES: biostudies

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Rapid Synthesis of N-Tosylhydrazones under Solvent-Free Conditions and Their Potential Application Against Human Triple-Negative Breast Cancer.

Project description:Some N-tosylhydrazone derivatives were effectively synthesized under solvent-free conditions by using a grinding method at room temperature. The short reaction time, clean and mild process with simple workup and easy purification of the target compounds were salient features of the present protocol, which enables straightforward access to N-tosylhydrazones. Among the tosylhydrazone derivatives evaluated, compound 3?l exhibits excellent apoptosis-promoting and anticancer potential against triple-negative breast cancer (TNBC) cell lines. This research shows that our synthesized compound 3?l may be a desirable and effective therapeutic drug against TNBC.

2018-01-01 | S-EPMC6276103 | BioStudies

[2 + 2 + 1] Cycloaddition of N-tosylhydrazones, tert-butyl nitrite and alkenes: a general and practical access to isoxazolines.

Project description:N-Tosylhydrazones have proven to be versatile synthons over the past several decades. However, to our knowledge, the construction of isoxazolines based on N-tosylhydrazones has not been examined. Herein, we report the first demonstrations of [2 + 2 + 1] cycloaddition reactions that allow the facile synthesis of isoxazolines, employing N-tosylhydrazones, tert-butyl nitrite (TBN) and alkenes as reactants. This process represents a new type of cycloaddition reaction with a distinct mechanism that does not involve the participation of nitrile oxides. This approach is both general and practical and exhibits a wide substrate scope, nearly universal functional group compatibility, tolerance of moisture and air, the potential for functionalization of complex bioactive molecules and is readily scaled up. Both control experiments and theoretical calculations indicate that this transformation proceeds via the in situ generation of a nitronate from the coupling of N-tosylhydrazone and TBN, followed by cycloaddition with an alkene and subsequent elimination of a tert-butyloxy group to give the desired isoxazoline.

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Reactivity of Amine/E(C6F5)3 (E = B, Al) Lewis Pairs toward Linear and Cyclic Acrylic Monomers: Hydrogenation vs. Polymerization.

Project description:This work reveals the contrasting reactivity of amine/E(C6F5)3 (E = B, Al) Lewis pairs toward linear and cyclic acrylic monomers, methyl methacrylate (MMA) and biorenewable ?-methyl-?-methylene-?-butyrolactone (?MMBL). While mixing of 2,2,6,6-tetramethylpiperidine (TMP) and B(C6F5)3 leads to a frustrated Lewis pair (FLP), Et3N reacts with B(C6F5)3 to form disproportionation products, ammonium hydridoborate ionic pair and iminium zwitterion. On the other hand, the stoichiometric reaction of either TMP or Et3N with Al(C6F5)3 leads to clean formation of a classic Lewis adduct (CLA). Neither TMP nor Et3N, when paired with E(C6F5)3, polymerizes MMA, but the Et3N/2B(C6F5)3 pair promotes transfer hydrogenation of MMA to form methyl isobutyrate. In contrast, the amine/E(C6F5)3 pairs promote rapid polymerization of ?MMBL carrying the more reactive exocyclic methylene moiety, achieving full conversion in less than 3 min even at a low catalyst loading of 0.0625 mol %. TMP is more effective than Et3N for the polymerization when paired with either the borane or the alane, while the alane exhibits higher polymerization activity than the borane when paired with Et3N. Overall, the TMP/Al(C6F5)3 system exhibits the highest polymerization activity, achieving a maximum turn-over frequency of 96,000 h-1 at 0.125 mol % of catalyst loading, producing high molecular weight P?MMBL with Mn = 1.29 × 105 g?mol-1.

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Borane-induced ring closure reaction of oligomethylene-linked bis-allenes† † Electronic supplementary information (ESI) available: Additional experimental details, further spectral and crystallographic data. CCDC deposition numbers are 1922906–1922913 and 1957134. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9sc03870a

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Rapid, Microwave Accelerated Synthesis of [1,2,4]Triazolo[3,4-b][1,3,4]oxadiazoles from 4-Acylamino-1,2,4-Triazoles.

Project description:1,2,4-Triazoles and 1,3,4-oxadiazoles are prevalent moieties in pharmaceutical agents, yet fused [1,2,4]-triazolo[3,4-b][1,3,4]oxadiazoles are surprisingly under-represented for both synthesis and biological application. We report a rapid, two-step synthesis of [1,2,4]-triazolo[3,4-b][1,3,4]oxadiazoles from commercial 4-amino-1,2,4-triazoles that is highlighted by a microwave accelerated intramolecular cyclization to generate the fused ring system. Our efforts to optimize reaction conditions and elucidate reaction mechanism are also described.

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I2/DMSO-Catalyzed Transformation of N-tosylhydrazones to 1,2,3-thiadiazoles.

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Construction of pyrazolo[3,4-b]pyridines and pyrazolo[4,3-c]pyridines by ring closure of 3-acylpyridine N-oxide tosylhydrazones.

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C-H bonds as ubiquitous functionality: preparation of multiple regioisomers of arylated 1,2,4-triazoles via C-H arylation.

Project description:We describe a general approach for the synthesis of complex aryl 1,2,4-triazoles. The electronic character of the C-H bonds and the triazole ring allows for the regioselective C-H arylation of 1-alkyl- and 4-alkyltriazoles under catalytic conditions. We have also developed the SEM and THP switch as well as trans-N-alkylation, which enable sequential arylation of the triazole ring to prepare 3,5-diaryltriazoles. This new strategy provides rapid access to a variety of arylated 1,2,4-triazoles and well complements existing cyclization methods.

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An Isolable Bis(Silanone-Borane) Adduct.

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