Fridkin Gil, Columbus Ishay, Saphier Sigal, Yehezkel Lea, Goldvaser Michael, Marciano Daniele, Ashkenazi Nissan, Zafrani Yossi
Department of Organic Chemistry, Israel Institute for Biological Research, Ness-Ziona 74100, Israel.
J Org Chem. 2015 May 15;80(10):5176-88. doi: 10.1021/acs.joc.5b00492. Epub 2015 May 1.
The effects solvents have on fluoride-promoted heterogeneous hydrolysis and alcoholysis of various organo-phosphorus (OP) compounds on the surface of KF/Al2O3 are described. Solid-state magic angle spinning NMR analyses and SEM microscopy have shown that not only is the identity of the solvent important in these reactions but also its quantity. That is, minimal solvent amounts are favored and much more effective in such solid-supported reactions (and maybe generally) than those featuring solvent-free or excess solvent (>50 wt %) conditions. The addition of a minute quantity of the correct solvent (3-10 wt %, molar equivalent scale) avoids reagents leaching from the matrix, permits mobility (mass transport) of the reaction components and ensures their very high local concentration in close proximity to the solid-support large porous surface area. Accordingly, significant acceleration of reactions rates by orders of magnitude is obtained. Fascinatingly, even challenging phosphoesters with poor leaving groups, which were found to be very stable in the presence of solvent-free KF/Al2O3 or wetted with excess water, were efficiently hydrolyzed with a minute amount of this solvent.