Dual Citizenship Travel in Europe For Extended Stay [duplicate]

I'm trying to figure out the best way to have an extended stay in Europe and was wondering if this was possible with dual citizenship.

If I had a US and Singaporean passport, and traveled to a country in the Schengen area, either passport would give me a 90 day visa in a 6 month period.

Would this loophole be considered "legal" if say I travel to Spain using my Singaporean passport for 90 days, then went to UK or Ireland using my US passport, and reentered the Schengen area using my US passport. This would technically be me renewing my 90 day visa without needing to wait 90 days before doing so.