Biprorulus bibax

2 Determination of absolute configuration (2). hemiacetal pheromone of Biprorulus bibax 

Chemical Synthesis of Hormones, Pheromones and Other Bioregulators 

Accordingly, ( )-alcohol A was oxidized to give B. Asymmetric reduction of B with Corey s CBS reagent gave (5)-A (79% ee). The 5-configuration of A was confirmed by its conversion to the known lactone (5)-C. Then, the ester (5)-D prepared from (5)-A was subjected to the Claisen rearrangement to 

Bioassays of 74 and 74 in Australia showed them to be equally active as the pheromone. However, B. bibax produces only (3R,4S)-74 as revealed by GC analysis.24 Thus, spined citrus bugs in Australia do not discriminate between the enantiomers of their aggregation pheromone. This is similar to the fact that even a perfumer cannot discriminate between camphor enantiomers. 

Selective protection of the primary alcohol gave 138 (P=TBDMS), which was then esterified with ( )-3-hexenoic acid to produce the key intermediate 139 for cyclization. Ireland ester-enolate Claisen rearrangement and hydrolysis produced a protected hydroxyacid, which, after reduction of the acid and deprotection of the alcohol, yielded meso diol 128 more quickly and efficiently than in the previous synthesis. The meso diol was then converted to the racemate of the lactol pheromone 130 as previously described. 

The authors then used a modification of their Lipase-AK route to produce the natural enantiomer, as described in detail in the chapter by Kenji Mori in this volume. Instead of using the enzyme to execute a stereoselective monohydrolysis of meso diacetate 140, the enzyme was used to esterify selectively one of the hydroxy groups of meso diol 128, resulting in the antipodal hydroxyester. After oxidation of the free hydroxyl to the acid, and recrystallization of its salt with (JR)-l-naphthylethylamine, the purified acid was then carried through the remaining steps to furnish the chiral pheromone compound (see the chapter by Kenji Mori in this volume). 

In one final improvement to the synthesis of the racemate, after it had been shown that even the unnatural enantiomer of the pheromone attracted bugs, the Z-isomer of diene ester 139 was used in the ester-enolate Claisen rearrangement, resulting in a slightly higher yield, and avoiding the use of HMPA as a solvent in that step [113]. 

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Hemiacetal 25 [(3 ,4S,l E)-3,4-bis(r-butenyl)tetrahydro-2-furanol] is the male pheromone of the spined citrus bug (Biprorulus bibax). Scheme 38 summarizes Mori s synthesis of 25 [61]. Claisen rearrangement (A B) and lipase-catalyzed asymmetric acetylation [meso-C >(5S,6R)-D] were the two key steps of the synthesis. Further purification of D was executed at the stage of its crystalline derivative E. In this particular case, the unnatural (3S,4R,l E)-25 was as active as the natural (3R,4S,VE)-25. Accordingly, a more efficient synthesis of ( )-25 was achieved by the rearrangement of F, avoiding the use of toxic HMPA [62]. 

Scheme 20 Synthesis of racemic lactol pheromone component from Biprorulus bibax [108]...

Scheme 21 Syntheses of racemic and chiral forms of the lactol pheromone of Biprorulus bibax [111]...

The spined citrus bug (Biprorulus bibax) is a pest of citrus in southern Australia. The major component (74, Figure 4.5) of the male-produced pheromone of B. bibax was isolated and identified by the joint work of James in Australia and Oliver et al. in the USA. Oliver found by chiral GC analysis that the insect produces a single enantiomer of 74. In 1992 I became interested in clarifying the absolute configuration of this pheromone, because Dr. Oliver requested me to do so. 

Figure 4.5 Synthesis of the pheromone of Biprorulus bibax employing Diels-Alder reaction. Modified by permission of Shokabo Publishing Co., Ltd...

Figure 4.10 Efficient synthesis of the racemic pheromone of Biprorulus bibax...

Suzuki T, Morita K, Ikemiyagi H, Watanabe K, Hiroi K, Katoh T (2006) Synthesis of the hemiacetal pheromone of the spined citrus bug biprorulus bibax utilizing an iridium catalyzed oxidative lactonization. Heterocycles 69 457-461... 

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