Synthesis of aggregation pheromone components of longhorn beetles through α-hydroxylation of alkylketones

Semiochemical lures attract a significant number of longhorn beetles and can be used to monitoring these pests. Several cerambycid species produce male aggregation pheromones consisting of 3-hydroxy-2-hexanone, 3-hydroxy-2-octanone and 2,3-hexanediol. With the aim of developing a synthetic strategy for these compounds to use them in monitoring these pests in citrus, a methodology for the α-hydroxylation of alkylketones was envisioned. The synthesis of 3-hydroxy-2-hexanone and 2,3-hexanediol, is achieved starting from 2-hexanone, through an α-hydroxylation using (diacetoxyiodo)benzene. Further reduction of 3-hydroxy-2-hexanone, gives 2,3-hexanediol in excellent yield. A study of the α-hydroxylation reaction of several alkylketones using hypervalent iodine chemistry is also disclosed. The synthesis of optically active (R)- and (S)-3-hydroxy-2-hexanone was achieved starting from 2-hexanone with nitrosobenzene and L- and D-proline respectively. This reaction renders intermediate aminooxyketone, and upon standing at room temperature for 24 hs. affords the product with excellent ee. The same strategy was employed for the synthesis of (R)-3-hydroxy-2-octanone.