Annulation of O-silyl N,O-ketene acetals with alkynes for the synthesis of dihydropyridinones and its application in concise total synthesis of phenanthroindolizidine alkaloids.

The formation of N-heterocycles with multiple substituents is important in organic synthesis. Herein, we report a novel method for the construction of functionalized dihydropyridinone rings through the annulation of an amide α-carbon with a tethered alkyne moiety. The reaction of the amide with the alkyne was achieved via O-silyl N,O-ketene acetal formation and silver-mediated addition. Furthermore, the developed method was applied for the total synthesis of phenanthroindolizidine and phenanthroquinolizidine alkaloids. By varying the coupling partners, a concise and collective total synthesis of these alkaloids was achieved.

Facile One-Pot Synthesis of Polysubstituted Pyridinium Salts by Annulation of Enamines with Alkynes.

An efficient and facile synthesis of highly substituted pyridinium salts through the annulation of enamines with alkynes is reported herein. A Ag2 CO3 /HNTf2 synergistically acting catalyst system was developed and used in a condensation reaction between carbonyl substrates and propargylamine to afford structurally diverse pyridinium salts. A mechanistic investigation shows that this one-pot transformation proceeded via selective 6-endo-dig cyclization of the in situ generated propargylenamine and protonolysis of the resulting vinyl-silver intermediate. The reaction conditions are mild, and the substrate scope is broad. During the cyclization, an unusual inversion of the normal reactivity of α,ß-unsaturated carbonyl systems was observed.

Calix[n]triazolium based turn-on fluorescent sensing ensemble for selective adenosine monophosphate (AMP) detection.

A novel calix[n]triazolium was synthesized and exhibited excellent selectivity for AMP. The binding between calix[n]triazolium and chromenolate anions forms a non-fluorescent complex and the resulting supramolecular ensemble selectively detects AMP in water and induces "turn-on" fluorescence. The sensing platform is the first macrocyclic system to discriminate AMP from ADP and ATP through fluorescence changes.