RESUMEN
Three-substituted 4H-quinolizin-4-ones were obtained via a facile method with good selectivity and high efficiency. On the basis of alkyne substrate control, the mild and cost-efficient reaction has a broad substrate scope (20 examples, up to 93% yield) and is also easy to scale up. Active sites on the products allow for further modifications. The alkyne substrate control strategy could be further extended to achieve more complex three-substituted 4H-quinolizin-4-one skeletons.
Asunto(s)
Alquinos , Estructura MolecularRESUMEN
C-H arylation of arenes without the use of directing groups is a challenge, even for simple molecules, such as benzene. We describe spatial anion control as a concept for the design of catalytic sites for C-H bond activation, thereby enabling nondirected C-H arylation of arenes at ambient temperature. The mild conditions enable late-stage structural diversification of biologically relevant small molecules, and site-selectivity complementary to that obtained with other methods of arene functionalization can be achieved. These results reveal the potential of spatial anion control in transition-metal catalysis for the functionalization of C-H bonds under mild conditions.
RESUMEN
A new approach to anion sensing that involves excimer disaggregation induced emission (EDIE) is reported. It involves the anion-mediated disaggregation of the excimer formed from a cationic macrocycle. This leads to an increase in the observed fluorescence intensity. The macrocycle in question, cyclo[1] N2, N6-dimethyl- N2, N6-bis(6-(1 H-imidazolium-1-yl)pyridin-2-yl)pyridine-2,6-diamine[1]1,4-dimethylbenzene (12+; prepared as its PF6- salt), is obtained in ca. 70% yield via a simple cyclization. X-ray diffraction analyses of single crystals revealed that, as prepared, this macrocycle exists in a supramolecular polymeric form in the solid state. Macrocycle 12+ is weakly fluorescent in acetonitrile. The emission intensity is concentration dependent, with the maximum intensity being observed at [12+] ≈ 0.020 mM. This finding is ascribed to formation of an excimer, followed possibly by higher order aggregates as the concentration of 12+ is increased. Addition of tetrabutylammonium pyrophosphate (HP2O73-) to 12+ (0.020 mM in acetonitrile) produces a ca. 200-fold enhancement in the emission intensity (λex = 334 nm; λem = 390-650 nm). These findings are rationalized in terms of the HP2O73- serving to break up essentially non-fluorescent excited-state dimers of 12+ through formation of a highly fluorescent anion-bound monomeric complex, 12+·HP2O73-. A turn-on in the fluorescence intensity is also seen for H2PO4- and, to a lesser extent, HCO3-. Little (HSO4-, NO3-) or essentially no (N3-, SCN-, F-, Cl-, Br- and I-) response is seen for other anions. Solid-state structural analysis of single crystals obtained after treating 12+ with HP2O73- in the presence of water revealed a salt form wherein a H2P2O72- anion sits above the cone-like macrocycle.
RESUMEN
Using carbon dioxide as a C1 precursor, here we report relatively simple and cost-effective orthogonal tandem catalysis, namely Ag2O in conjunction with Cs2CO3 serves to promote a multicomponent tandem reaction forming two new C-C and one new C-N bonds. 4 H-Quinolizin-4-ones, key skeletal components in a variety of biologically active molecules, were obtained with yields up to 99%. The present approach features a broad substrate scope and mild reaction conditions and benefits from using cost-effective reaction and catalysts.