Solvent selection in synthesis of 4-(1-arylfluoroethoxy)quinazolines and thienopyrimidines

The nucleophilic aromatic substitution of 4-chloroquinazoline and 6-bromo-4-chlorothieno[2,3-d]pyrimidine with 1-aryl-2-fluoroethanols as nucleophilies has been studied focusing on the use of carbonate bases in combination of environmental acceptable solvents. The conversion rate depended on the solvent properties, the acidity of the nucleophile and the nature of the base. By using acetonitrile as reaction medium and K2CO3 as base, 2,2,2-trifluoro-, 2,2-difluoro-, and 2-fluoro-1-phenylethanol could efficiently be coupled to 4-chloropyrimidines. Alternatively, employing Cs2CO3, allowed for shorter reaction time for these substrates, and also couplings of the non-fluorinated alcohols proceeded well. tert-Butanol was also found to be a suitable reaction medium in transformation of the fluoro alcohols. Testing of hydrolytic stability of the 4-alkoxypyrimidines revealed that the fluorinated and non-fluorinated derivatives were labile under acidic conditions, whereas in basic media the fluoroalkoxy derivatives were more stable than their non-fluorinated counterparts.