Yes, sir, but, there is no official media (comics, games, or animation) that depicts Sonic moving so fast in his base form that Reverse Flash (or any Flash) didn't notice him steal a Chaos Emerald.
Here's why:
Separate Universes: Sonic the Hedgehog and The Flash (including Reverse Flash) exist in completely separate fictional universes. Sonic is primarily from Sega's video game franchise and its associated comic book lines (Archie Comics, IDW Publishing), while The Flash is a character from DC Comics. Crossovers between these two universes are virtually non-existent in official, canon media.
Feat Specificity: Even if a crossover did occur, the specific feat you're describing (stealing a Chaos Emerald from an unnoticing Reverse Flash while in base form) would be an extraordinary and almost impossible feat for base Sonic.
Base Sonic's Speed: While incredibly fast, base Sonic is typically depicted as having speeds ranging from supersonic to light-speed in bursts.
Reverse Flash's Speed & Perception: Characters like Eobard Thawne (Reverse Flash) are consistently portrayed as having speed and reaction times on par with or exceeding the fastest Flashes (like Wally West). They can perceive events in femtoseconds (quadrillionths of a second), move faster than light by orders of magnitude, and interact with the world at speeds that make regular light seem frozen. They can also steal speed. For base Sonic to move faster than Reverse Flash's perception, let alone steal an object from him without being noticed, would contradict the established power levels of both characters in their respective canons. Super Sonic, with the Chaos Emeralds, is a different story, but even then, a direct comparison is highly speculative.