Fig. 1: Synthesis of compounds 10, 11, 12, 13 and 14.

(I) Acetylacetone, boron oxide, trimethyl borate, n-butylamine, DMF; (II) acetylacetone, boron oxide, trimethyl borate, n-butylamine, EtOAc; (III) boron oxide, trimethyl borate, n-butylamine, DMF; (IV) CuSO4, Na-ascorbate, t-BuOH/H2O/CH3CN 2:1:1; (V) CuSO4, Na-ascorbate, t-BuOH/H2O/CH3CN 2:1:1; (VI) diethylchlorophosphate, TEA, CH2Cl2.