The best results were obtained when the reducing agent was added in two portions, with an interval of one hour between the two (Table 3, entry 4). It should be taken into account that the DIBAL-H addition must be done necessarily in two portions (Table 3, entry 3 vs 4) in order to increase the yield of the reac- tion. We speculate that the free hydroxy group coordinates to the DIBAL-H, making compulsory the additional amount of reducing agent.