A series of 2-oxo-2-(p-nitrophenoxy)-1, 3-dioxa-2-phosphacyclmtane derivatives (1-5) having either a nitrogen or a sulfur atom placed transannularly in the ring were synthesized, and their rates of hydrolysis were examined. The pH-rate profile shows that while 1 undergoes hydrolysis over a wide pH range, others are hydrolyzed at a significant rate only in basic medium, thus implicating the amino function for rate enhancement. By ...