Insect pheromones synthesis

Another insect pheromone synthesis illustrates one of the drawbacks of chiral pool approaches. The ambrosia beetle aggregation pheromone is called sulcatol and is a simple secondary alcohol. This pheromone poses a rather unusual synthetic problem the beetles produce it as a 65 35 mixture of enantiomers so, in order to mimic the pheromone s effect, the chemist has to synthesize both enantiomers separately and mix them together in the right proportion. 

The Baeyer-Villiger reaction is regioselective — the more substituted group migrates—and stereospecific — it does so with retention. Hydroxy ketone (22) was needed for insect pheromone synthesis and is a 1,6-difunctionalised compound. It could be made by nucleophilic displacement by an organo-metallic reagent (R ) on lactone (23), the Baeyer-Villiger product from (24) which can be made from aromatic (26). 

R. Rossi, Insect Pheromones 1. Synthesis of Achiral Components of Insect Pheromones , Synthesis, 1977, 817. 

The remainder of this section is devoted to a survey of novel syntheses and is organized alphabetically by Order and Family. Certain aspects of insect pheromone synthesis have been recently reviewed (83 a, 89, 90). 

Rossi, R., and A. Carpita Insect pheromones — synthesis of chiral sex pheromone components of several species of Trogoderma (Coleoptera Dermestidae). Tetrahedron 33,2447—2450(1977). 

Rossi, R. Insect pheromones. II. Synthesis of chiral components of insect pheromones. Synthesis (Stuttgart) 1978, 413—434. 

Enantiomerically enriched formyl irimclhyleiiemethane -irontricarbonyl complexes add to allylzinc bromides with high stereoselectivity. This was used, after photochemical deprotection, in an enantioselcctive synthesis of the insect pheromone (-)-ipsdienol4s. 

Both chiral lactones and ketones have been utilized in asymmetric synthesis of bioactive compounds like lipoic acid [175[ and natural products like various insect pheromones [176[. 

Figure 10.33 Complementary, backbone-inverting approaches for the asymmetric synthesis of the insect pheromone (-l-)-exo-brevicomin.

Four new or improved methods useful in the synthesis of aliphatic insect pheromones were reported. co-Bromo-l-alkanols are important building blocks in pheromone synthesis. Chong found that a,co-diols gave good yield of co-bromo-l-alkanols when heated with hydrobromic acid and toluene at reflux (Scheme 1) [10]. 

Mori K (1981) The synthesis of insect pheromones. In ApSimon J (ed) The total synthesis of natural products, vol 4. Wiley, New York, p 1... 

Trost and coworkers have devised a stereocontrolled 1,3-diene synthesis employing a palladium-catalysed decarboxylative elimination procedure from allylic acetates carrying carboxylic acid functionality ji- to the acetate group (equation 18)48. This decarboxylative elimination strategy has been applied to the synthesis of an insect pheromone, codlemone48a and the ethyl ester of vitamin A carboxylic acid (Table 5)48b. 

The optically active propargylic and allylic alcohols thus obtained are important synthetic intermediates in the enantioselective synthesis of insect pheromones, prostaglandins, prostacyclins, and many other bioactive compounds (Scheme 6-26).53... 

Scheme 18.5 Synthesis of the insect pheromone 12 from chiral sulfoxide 13 (pTol = p-tolyl) [23].

Scheme 18.6 Synthesis ofthe insect pheromone 12 from the manganese complex 14 (mCPBA=m-chloroperbenzoic acid) [24],...

Scheme 18.7 Synthesis ofthe insect pheromone 12 by palladium-catalyzed SN2 -substitution (dba = dibenzylideneacetone).

Mori K (1992) The synthesis of insect pheromones. In ApSimon J (ed) The total synthesis of natural products, vol 9. Wiley, New York, p 1 Mori K (1997) Chem Commun 1153 Mori K (1998) Eur J Org Chem 1479 Mori K (2000) Acc Chem Res 33 102 Mori K (1996) Biosci Biotechnol Biochem 60 1925 Mori K (1998) Chirality 10 578... 

Intermolecular addition of radicals, generated by photo-electrochemical catalysis, to activated alkenes can also be brought about. The reaction of 66 is used as a key step in one synthesis of the insect pheromone, brevicomin [219]. The reaction of a secondary radical from 67 occurs at low cathode potentials and without photochemical assistance [219]. This illustrates the equiibrium between a secondary al-kylcobalt(m) species and the radical - cobalt(ii) pair. The carbon radical is eventually captured by reaction with the alkene. Further steps in the synthesis lead to four isomers of the pheromone, multistriatin, each of which is a pure enantiomer since... 

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