Pheromone synthesis Subject

The last decade has witnessed the application of 1-halogenoacetylenes as crucial intermediates for the synthesis of increasingly complex structures, especially in natural product chemistry. In pheromone synthesis it is essential to create double-bond systems diastereoselec-tively, and a route often taken consists in the preparation of a suitable alkyne precursor which is then converted into the final olefin by various addition reactions (catalytic hydrogenation, metalation, etc.). For the construction of the alkyne precursor to the pheromone, 1-bromo-(94) and 1-iodoalkynes (95) have been particularly valuable since they can easily be subjected to metal-catalyzed coupling reactions [105]. For ocample, the unsaturated ester 163, which is a sex attractant of Lepidoptera (moths and butterflies), has been prepared by first converting the terminal acetylene 160 into its 1-iodo derivative 161. This is subsequently hydrogenated... 

The goal of this chapter is to provide an overview of the occurrence of Type II polyene pheromones and their derivatives, and their chemistry, including their biosynthesis and synthesis. The older literature in this subject area was reviewed in Millar (2000), and summarized more recently in Ando et al. (2004). Thus, this chapter will provide a comprehensive summary of all known Type II pheromone structures and their occurrence in Tables 1 1, whereas the text will focus more on work over the past ten years. The interested reader is further directed to three useful online databases, two of which focus on lepidopteran pheromones (www.tuat.ac.jp/ antetsu/review/e-List.pdf Ando, 2003 www-pherolist.slu. se/pherolist.php Witzgall et al., 2004) and the third of which covers insect pheromones in general (www.pherobase.com El-Sayed, 2008). 

Asymmetric syntheses directed toward construction of enantiomers of the western and southern corn root-worm pheromones are described. A brief review of the subject of asymmetric synthesis as it is related to the synthesis of insect sex pheromones is presented. The laboratory s previous research with chiral pheromones is summarized (Japanese beetle, white peach scale, and lesser tea tortrix) before detailing synthetic work on the pheromones of the aforementioned rootworm species. Throughout the course of the synthetic effort, cholesteric stationary phases for GLC have found use. Their superior ability to separate crucial diastereomeric intermediates for synthesis is detailed. 

Since the synthesis of pheromones has been extensively reviewed,2-8 corresponding aspects will not be the subject of this chapter. 

To deduce the location of the double bond within the lipid backbone, the mixture (500 ng) was subjected to consecutive bisthiomethylation of the alkene85 and O-methyloxime formation (Equation 3). GC—MS study of the fragmentation of these derivatives (e.g., see 31, derived from 24) allowed simultaneous determination of the cleavage site (between C24 and C25) and of which portion contained the original ketone (i.e., the odd versus even mass fragments of 17 3 and 426 for 31). All of the monounsaturated lipid ketones had the alkene in the same downstream location in other words, they varied in the number of methylene units between the ketone and alkene functional groups but were constant in their -octyl terminal alkyl moiety. The four most major components (24, 25, 27, and 28) were prepared by chemical synthesis and used to confirm their identity in the natural pheromone and their pheromonal activity both alone and in admixtures. 

The protection of an a, p-unsaturated ketone by a conjugate addition strategy is the subject of our last example but it does not involve the use of an 0,0-acetal. During a synthesis of the cockroach pheromone Periplanone B. Still needed to perform a copper(I)-mediated Sn2 reaction on the allylic acetate 37.1 [Scheme 2.37], In order to prevent competing addition to the a, p-unsaturated ketone, it was protected temporarily by conjugate addition of trimethylstannyl-lithium and trapping of the intermediate enolate with chlorotrimethylsilane. The desired Sn2 reaction was then performed on the adduct 37.2 and the a.p-un-saturated ketone recovered by oxidation of the C-Sn bond to a C-OH using m-chloroperbenzoic acid. Concomitant destruction of the labile enol ether and -elimination of water returned the a, p-unsaturated ketone 373. 

A mixed di-f-butylsilylene has been prepared from (5)-5-hexen-2-ol and prochiral l,4-pentadiene-3-ol for synthesis of (25, 7S)-dibutyroxynonane, the sex pheromone of Sitodiplosis mosellana. The intermediate 43 was then subjected to ring closing metathesis to provide the diene 44 in 70% yield over two steps (eq 16). Deprotection of the nine-membered silylene was achieved using TBAF under refluxing condition in the presence of molecular sieves. Reduction with H2/Pt02 and diacetylation yielded the desired (25, 7S)-dibutyroxynonane in 22% overall yield. ... 

As an alternative to baker s yeast, the use of plant tissues (e.g., from apple, carrot, cucumber, onion, or potato) has been suggested [112,113]. It remains unclear, however, whether endophytic microorganisms are involved in these reductions [114]. Heterocyclic ketones [111, 115-117] as well as many a-hydroxy ketones [96,118-121] have been the subject of yeast-mediated reductions. For the latter compounds very high ee values have been obtained, albeit the yields were moderate. Monobenylated (S)-l,n-diols have been prepared using highly diluted yeast suspensions, and ee values up to 95% could be achieved [122]. Yeast-mediated reductions of acyclic ketones were key steps in the total synthesis of the pheromone sulcatol [123], brefeldin A [124], and endo-brevicomin [125]. 

Maruoka and coworkers [65] also reported the total synthesis of (+) mono-morine (127) using a phase-transfer-catalyzed conjugate addition of glycine ester 128 to Michael acceptor 129 as an early key step in the synthesis sequence. Monomorine (127) is a bicyclic amine, known to be the trail pheromone of Monomorium pharanois [66]. The conjugate addition product 131 was subjected to an intramolecular reductive amination and acetal hydrolysis in one pot reaction with Hantzsch ester 132 and trifluoroacetic acid in aqueous... 

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