Thereupon rhymes with:
whereupon, upon, whereupon, dainippon, nippon, pon, spahn, spawn, spohn, upon, whereupon
Thereupon sounds like:
tarpon, tarvin, terrebonne, trapani, trevino, tribune, tropeano, trupiano, trupin, tryphena, turban, turben, turbin, turbine, turbinen, turbofan, turpen, turpin