erfumery. The natural oil is in short supply and, until recently, synthetic

Chapter 18, Problem 54

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erfumery. The natural oil is in short supply and, until recently, synthetic substituteshave been diffi cult to prepare. Polysantol (margin) is the most successful of these substitutes.Its synthesis in 1984 involved the aldol condensation shown below.O OHOKOH, H2O,CH3OH(a) This synthetic step, although usable, had a signifi cant drawback that was responsible for itsmodest yield (60%). Identify this problem in detail.(b) A solution that avoids conventional aldol condensation was published in 2004. A bromoketoneis prepared and, upon reaction with Mg metal, gives a magnesium enolate. This enolatethen reacts with the aldehyde selectively to give a hydroxyketone that may be dehydrated to thedesired product. Discuss how this approach solves the problem outlined in part (a).OOHO OBr2, CH3CO2H, CCl4 Mg, etherBrHOO MgBr