Asymmetric Synthesis of Serricornin via Boronic Esters

Highly stereoselective boronic ester chemistry has been used for the synthesis of (4S,6S,7S)-7-hydroxy-4,6-dimethylnonanone (1), the pheromone of the cigarette beetle. 2-Bromo-1-butene (8) was made from 1-butyne via bromoboration and protodeboronation, and was converted to 1-ethylethenylmagnesium bromide. (R,R)-1,2-Dicyclohexyl-1,2-ethanediol [“(R)-DICHED”] methylboronate was treated with (dichloromethyl)lithium to yield (R)-DICHED (S)-1-chloroethylboronate (9), which with 1-ethylethenylmagnesium bromide yielded (R)-DICHED (R)−(2-ethyl-1-methyl-2-propenyl)boronate (10). Further chain extensions with (chloromethyl)lithium, (dichloromethyl)lithium followed by methylmagnesium bromide, and (dichloromethyl)lithium followed by ethylmagnesium bromide completed assembly of the carbon skeleton. Deboronation with hydrogen peroxide yielded (3S,5S,6S)-2-ethyl-3,5-dimethylocten-6-ol (14), which with osmium tetraoxide and sodium periodate yielded 1.