The Synthesis of 3-pyrazinyl-pyrazolo [1,5-a] pyridines from an enol ether

The synthesis of 3-pyrazinyl-pyrazolo[1,5-a]pyridines from an enol ether and 4-substitued 1- aminopyridinium iodides via a 3+2 cycloaddition is presented. A high throughput reaction screen was used to optimize the yield of the cycloaddition. This protocol is operationally simple, scalable, proceeds at room temperature and the reaction profiles are very clean.