Starting with dibenzyl phosphonate, I added LiN(TMS)2 at -75 °C, then TMSCl at 0 °C. At this point I have an impure mixture by P-31 NMR that includes (PhCH2O)2P(OSiMe3), which is a tervalent phosphorus compound that is my nucleophile. I usually observe a mixture at this point with related compounds, but sometimes it is a little cleaner. So far this is all very close to published protocols. Then I add para-formaldehyde that was dried using a vacuum pump, and not much seems to happen, or it is happening very slowly, again monitoring by P-31 NMR. I do see an increase in area of a peak near 0 ppm that could be my desired product, but after 5 hours the reaction is less than half complete. The desired compound at this point is (PhCH2O)2P(O)CH2OSiMe3). Next would come removal of the TMS group to provide the alcohol.
When we do this with tert-butylphosphonate, we run the last reaction at 45 °C for a few hours. We have tried making the dibenzyl version only twice before, and it was a long time ago. The first trial was around the same temperature, and the second trial, the temp was not recorded. I just checked the student's notebook from 13 years ago to refresh my memory. My recollection is that the first trial did not go well, but then I thought that we dropped the temperature of the PFA reaction to room temp. That is why I tried room temperature today. I am going to let it stir overnight, but then raise the temperature. I was thinking that I might add more PFA. However, PFA does not look completely soluble in THF, my solvent. It occurs to me that raising the temperature may make it more soluble. Any thoughts?