33993-35-0Relevant articles and documents
Gold-Catalyzed Bicyclic and [3+2]-Annulations of Internal Propargyl Alcohols with Nitrones and Imines To Yield to Two Distinct Heterocycles
More, Sayaji Arjun,Chao, Tzu-Hsuan,Cheng, Mu-Jeng,Liu, Rai-Shung
supporting information, p. 525 - 531 (2020/12/01)
A gold-catalyzed synthesis of 1,3-dihydrooxazolo[3,4-a]indoles from 1-oxo-3-yn-4-ols and nitrones is described; this new bicyclic annulation presents the first examples that internal alkynes can react with nitrones to undergo an oxoarylation route. DFT calculations indicate a [3,3]-sigmatropic shift of initial alkenylgold intermediates to elude the intermediacy of gold carbenes. We also developed new [3+2]-annulations of the same 1-oxo-3-yn-4-ols with imines, yielding oxazolidin-4-ylidene derivatives efficiently. The tethered alcohols of these 1-oxo-3-ynes allow trapping of their metastable 2-azadienium intermediates to enable a novel annulation. Our mechanistic analysis indicates that the two products, despite their structural relevance, are produced from two independent systems. (Figure presented.).
Synthesis of chromeno[3,4-b]piperazines by an enol-ugi/reduction/cyclization sequence
Bornadiego, Ana,Neo, Ana G.,Marcos, Carlos F.
supporting information, (2021/05/31)
Keto piperazines and aminocoumarins are privileged building blocks for the construction of geometrically constrained peptides and therefore valuable structures in drug discovery. Combining these two heterocycles provides unique rigid polycyclic peptidomimetics with drug-like properties including many points of diversity that could be modulated to interact with different biological receptors. This work describes an efficient multicomponent approach to condensed chromenopiperazines based on the novel enol-Ugi reaction. Importantly, this strategy involves the first reported post-condensation transformation of an enol-Ugi adduct.
Insight into the Modes of Activation of Pyridinium and Bipyridinium Salts in Non-Covalent Organocatalysis
Weiss, Robin,Golisano, Tamara,Pale, Patrick,Mamane, Victor
supporting information, p. 4779 - 4788 (2021/09/06)
A series of pyridinium and bipyridinium salts were prepared and their catalytic properties were evaluated in the aza-Diels-Alder reaction between imines and Danishefsky diene. Depending on the substituents of the pyridinium/bipyridinium rings and on the nature of the counterion, two mechanisms of activation were demonstrated. In case of non-substituted rings, the substrate is activated through charge transfer involving the aryl ring on the C-side of the imine. When halogen atoms were introduced on the catalysts, the activation mode switched to halogen bond involving the imine nitrogen lone pair. Moreover, alternative activation modes based on hydrogen bonding and radical cation were ruled out. This work allowed us to develop two families of catalysts whose potential was demonstrated in the cycloaddition of various imines with Danishefsky diene. The first family is composed of the simple methyl pyridinium triflate and dioctyl bipyridinium triflate. The former is active only with imines bearing a p-methoxyphenyl group on the C-side and the latter was found to be efficient with imines bearing different substituents on both the N- and C-sides of the imines. The second family is based on halogenated pyridinium salts which proved active with almost all considered imines. (Figure presented.).
