POCl 3 Chlorination of 4-Quinazolones

The reaction of quinazolones with POCl(3) to form the corresponding chloroquinazolines occurs in two distinct stages, which can be separated through appropriate temperature control. An initial phosphorylation reaction occurs readily under basic conditions (R(3)N, aq pK(a) > 9) at t < 25 °C to give a variety of phosphorylated intermediates. Pseudodimer formation, arising from reaction between phosphorylated intermediates and unreacted quinazolone, is completely suppressed at these temperatures, provided the system remains basic throughout the POCl(3)addition. Clean turnover of phosphorylated quinazolones to the corresponding chloroquinazoline is then achieved by heating to 70-90 °C. (N)- and (O)-phosphorylated intermediates, involving multiple substitution at phosphorus, have been identified and their reactions monitored using a combination of (1)H, (31)P, and (19)F NMR. Kinetic analysis of the reaction profiles suggest that the various intermediates react with both Cl(-) and Cl(2)P(O)O(-), but product formation arises exclusively from reaction of (O)-phosphorylated intermediates with Cl(-). (O)- and (N)-phosphorylated intermediates equilibrate rapidly on the time scale of the reaction. A minimum of 1 molar equiv of POCl(3) is required for efficient conversion of the intermediates to product.