Bench-Stable 2-Halopyridinium Ketene Hemiaminals as Reagents for the Synthesis of 2-Aminopyridine Derivatives.

2-Chloro-1-(1-ethoxyvinyl)pyridinium triflate and several other bench-stable -(1-alkoxyvinyl) 2-halopyridinium triflates have been developed as reagents for the synthesis of valuable 2-aminopyridine scaffolds via unusually mild SAr substitutions with amine nucleophiles. Advantages of this approach include an operationally simple mix-and-stir procedure at room temperature or mild heat and ambient atmosphere and without the need for transition metal catalysts, coupling reagents, or high-boiling solvents. The stable -(1-ethoxyvinyl) moiety serves as a dual SAr-activating group and pyridine -protecting group that can be cleaved under thermal, acidic, or oxidative conditions.

Synthesis and crystal structure of a bench-stable pyridinium ketene hemiaminal: 1-(1-eth-oxy-ethen-yl)-2-[meth-yl(phen-yl)amino]-pyridin-1-ium tri-fluoro-methane-sulfonate.

The novel bench-stable -quaternized ketene ,-acetal, CHNO·CFOS, was synthesized and its structure determined. The title compound is a rare example of a pyridinium ketene hemiaminal for which a crystal structure has been determined, joining the 2-chloro-1-(1-ethyoxyethen-yl)pyridin-1-ium tri-fluoro-methane-sulfonate salt from which it was synthesized. The cationic species of the title compound can be defined by three individually planar fragments assembling into a non-coplanar cation.

Synthesis of Bench-Stable Quaternized Ketene ,-Acetals and Preliminary Evaluation as Reagents in Organic Synthesis.

-Quaternized ketene ,-acetals are typically an unstable, transient class of compounds most commonly observed as reactive intermediates. In this report, we describe a general synthetic approach to a variety of bench-stable -quaternized ketene ,-acetals via treatment of pyridine or aniline bases with acetylenic ethers and an appropriate Brønsted or Lewis acid (triflic acid, triflimide, or scandium(III) triflate). The resulting pyridinium and anilinium salts can be used as reagents or synthetic intermediates in multiple reaction types.