Abstract Photolysis of aryl??substituted 2, 5??dihydrophosphole oxides (5a–e and 8) in the presence of methanol afforded methyl aryl??H??phosphinates (2a–e) in good yields. In the case of 1??ethyl??, cyclohexyl??, or ethoxy??2, 5??dihydrophosphole oxides, the reaction was much slower (5f and 5h) or did not take place at all (5g). In such instances, the presence of an additional skeletal methyl group (7) or the use of the more strained 7?? ...