You are probably referring to Lysimachia punctata - that's
the only plant I've ever heard called "circle flower" - but
common names are notoriously regional, not to mention
multiple. . .which is a perfect example of why botanical
names are so valuable. . .only ONE name per plant!

By the way, I've also heard L. punctata commonly called
whorled loosestrife. . .

Depending upon which region you live in, Circle Flower (Lysimachia punctata) is also known as Dotted Loosestrife, Garden Loosestrife, Large Yellow Loosestrife, Yellow Loosestrife, Whorled Loosestrife and various other unprintable names! It is an Introduced species, from Central & South Europe, and has spread from coast to coast across the northern tier of states, especially in wetlands, a habitat that it prefers. It is commonly available with a cultivar name; 'Alexander'
Some gardeners report that it is well behaved and not at all invasive. I can't verify, as I have no Lysimachia species or cultivars.
Rb

That's it thanks!!