Spiroacetal pheromones synthesis

This process has found occasional use in the synthesis of heterocycles. The major product resulting from the reaction of MeLi on the dibromocarbene adduct (51) is the tetrahydrofuran (52), as shown in equation (105).189 In a novel approach to the synthesis of spiroacetal pheromones, caibene insertion into an acetal C—H bond was studied (equation 106).252 Unfortunately, the reaction proceeds in low yield and the approach is further hampered by the lack of stereocontrol in the ring opening of the cyclopropane. Carbene insertions into N—H and C—H bonds adjacent to nitrogen have been shown to give azabicyclo systems, as shown in equations (107) and (108).188... 

Figure 4.35 Synthesis of the spiroacetal pheromone of Andrena wilkella (I). Modified by permission of Shokabo Publishing Co., Ltd...

The synthesis of (2 5, 6R, 8 S)-2,8-dimethyl-l,7-dioxaspiro[5,5]undecane (868), one of the spiroacetal components of the pheromone isolated from the olive fruit fly, hinges on a dialkylation of tolylmethyl isocyanide with bromide 866. The bromide is obtained from 845b by sequential reduction of the olefin and ester followed by conversion of the resulting alcohol to bromide. Acidic hydrolysis of dialkylated product 867 provides the pheromone 868 directly... 

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