The decomposition of the title compound (DIMBOA, 1) in aprotic solvents was analysed in terms of linear solvation energy relationships using donor numbers. The results indicate rate-limiting cyclic hemiacetal opening in low donor number solvents and rate-limiting isocyanate formation in high donor number solvents. The addition of H 2O to DIMBOA decomposing in high donor number solvents had no effect upon the reaction rate, allowing one of the two proposed mechanisms to be rejected.