3433-80-5Relevant articles and documents
Preparation of 1,5-Dihydropyrazolo[3′,4′:5,6]pyrano[3,4- b]pyridines via a Microwave-Assisted, Palladium-Catalyzed Regioselective C-H Heteroarylation of Electron-Rich Pyrazoles
Garrison, Aaron T.,Childress, Elizabeth S.,Davis, Dexter C.,Lindsley, Craig W.
, p. 5855 - 5862 (2019)
Here we report the first synthesis of a family of novel heterocyclic compounds based on a 5-dihydropyrazolo[3′,4′:5,6]pyrano[3,4-b]pyridine core. In the course of our drug discovery programs, we had need to access the previously unknown 5-dihydropyrazolo[3′,4′:5,6]pyrano[3,4-b]pyridine core. Initial attempts required long reaction times, which led to degradation and side products. Reaction optimization identified a Pd-catalyzed, microwave-assisted C-H heteroarylation protocol for the rapid, general, and high yielding synthesis of this tricyclic core (as well as related analogs) suitable to drive optimization efforts.
Thiourea-Catalyzed C?F Bond Activation: Amination of Benzylic Fluorides
Houle, Camille,Savoie, Paul R.,Davies, Clotilde,Jardel, Damien,Champagne, Pier Alexandre,Bibal, Brigitte,Paquin, Jean-Fran?ois
supporting information, p. 10620 - 10625 (2020/07/24)
We describe the first thiourea-catalyzed C?F bond activation. The use of a thiourea catalyst and Ti(OiPr)4 as a fluoride scavenger allows the amination of benzylic fluorides to proceed in moderate to excellent yields. Preliminary results with S- and O-based nucleophiles are also presented. DFT calculations reveal the importance of hydrogen bonds between the catalyst and the fluorine atom of the substrate to lower the activation energy during the transition state.
Carbocation Catalyzed Bromination of Alkyl Arenes, a Chemoselective sp3 vs. sp2 C?H functionalization.
Ni, Shengjun,El Remaily, Mahmoud Abd El Aleem Ali Ali,Franzén, Johan
supporting information, p. 4197 - 4204 (2018/09/25)
The versatility of the trityl cation (TrBF4) as a highly efficient Lewis acid organocatalyst is demonstrated in a light induced benzylic brominaion of alkyl-arenes under mild conditions. The reaction was conducted at ambient temperature under common hood light (55 W fluorescent light) with catalyst loadings down to 2.0 mol% using N-bromosuccinimide (NBS) as the brominating agent. The protocol is applicable to an extensive number of substrates to give benzyl bromides in good to excellent yields. In contrast to most previously reported strategies, this protocol does not require any radical initiator or extensive heating. For electron-rich alkyl-arenes, the trityl ion catalyzed bromination could be easily switched between benzylic sp3 C?H functionalization and arene sp2 C?H functionalization by simply alternating the solvent. This chemoselective switch allows for high substrate control and easy preparation of benzyl bromides and bromoarenes, respectively. The chemoselective switch was also applied in a one-pot reaction of 1-methylnaphthalene for direct introduction of both sp3 C?Br and sp2 C?Br functionality. (Figure presented.).
