1-Oxo-2-oxa-1-phosphabicyclo(2.2.2)octane: a new mechanistic probe for the basic hydrolysis of phosphate esters

1-Oxo-2-oxa-1-phosphabicyclo(2.2.2)octane was synthesized in a multistep sequence starting from hypophosphorous acid. A rate enhancement is observed in strong base, with the bicyclic phosphinate 1-oxo-2-oxa-1-phosphabicyclo(2.2.2)octane hydrolyzing two orders of magnitude faster than the bicyclic phosphate OP(OCH2)3CCH3. Acceleration is entirely enthalpic. The greater ease with which OP(OCH2)3CCH3 achieves the five-coordinate transition state is credited for the rate enhancement. The molecular structure of 1-oxo-2-oxa-1-phosphabicyclo(2.2.2)octane, compared with OP(OCH2)3CCH3, shows no signs of strain within either bicyclic framework.