Room Temperature DBN Initiated Phospha‐Brook Rearrangement of α‐Hydroxyphosphonates to Phosphates

A series of substituted aryl phosphate esters have been synthesized from their α‐hydroxyphosphonates substrates, using DBN (1,5 diazabicyclo(4.3.0)non‐5‐ene) at room temperature, via a phospha‐Brook rearrangement. The aryl‐substrate dependence of the rearrangement was explored, and excellent yields of the phosphate esters were achieved irrespective of whether the aryl moiety was activated or unactivated. A plausible mechanism for the rearrangement has been proposed. Based on the low temperature 31P‐NMR, the mechanism of the phospha‐Brook rearrangement is proposed to take place via an oxaphosphirane intermediate. Organophosphates are very important in physiological processes. The phospha‐Brook rearrangement from α‐hydroxyphosphonates has been optimized producing a range of benzyl phosphate esters in excellent yields by using 1,5‐diazabicyclo(4.3.0)non‐5‐ene at room temperature. Mechanistic studies, using low temperature 31P‐NMR, evidence possible formation of an oxaphosphirane intermediate, supporting previous chemical calculations reported.