Expanding available pyrazole substitution patterns by sydnone cycloaddition reactions

We report the use of alkynylsilanes for the regiocontrolled synthesis of pyrazoles from functionalised sydnones. The strategies outlined herein allow a range of pyrazoles to be accessed with substitution patterns that are otherwise not directly obtained with high selectivity by alkyne cycloadditions. Moreover, this study serendipitously highlighted a simple and convenient procedure for the synthesis of aryl monofluoromethyl ethers through the combination of TBAF and dichloromethane.