2,4-Diaminothieno[2,3-d]pyrimidines as antifolates and antimalarials. 2. Synthesis of 2,4-diaminopyrido[4',3':4,5]thieno[2,3-d]pyrimidines and 2,4-diamino-8H-thiopyrano[4',3':4,5]thieno[2,3-d]pyrimidines