Synthesis of the racemic dibutyroxynonane, a sex pheromone

Rahmani, Niloofar 2026. Synthesis of the racemic dibutyroxynonane, a sex pheromone. MPhil Thesis, Cardiff University. Item availability restricted.

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Abstract

The orange wheat blossom midge (Sitodiplosis mosellana) is a significant agricultural pest whose larvae feed on developing wheat grains, resulting in substantial losses in crop yield and quality. The sex pheromone of this species has been identified as (2S,7S) dibutyroxynonane, and commercial monitoring traps containing a racemic mixture of this compound are widely used for population monitoring and pest management. The aim of this study was to develop a synthetic route to racemic dibutyroxynonane using batch chemistry and to investigate the applicability of continuous-flow chemistry to selected stages of the synthesis. The batch synthesis involved silylation of 5-hexen-2-ol and 1,4-pentadien-3-ol using di-tert-butylsilyl bis(trifluoromethanesulfonate), followed by ring-closing metathesis, deprotection, alkene reduction, and esterification to afford the target molecule. Under continuous-flow conditions, two nucleophilic substitution steps involved in the silicon-tethering sequence were investigated: the reaction of di-tert butylsilyl bis(trifluoromethanesulfonate) with 5-hexen-2-ol, and the subsequent reaction of di-tert-butyl(hex-5-en-2-yloxy)silyl trifluoromethanesulfonate with 1,4-pentadien-3-ol. The first substitution was investigated under continuous-flow conditions across a range of flow rates and residence times, although quantitative comparison of reaction efficiency was limited by the use of crude products, while prolonged low-temperature operation caused freezing and reactor blockage. The second substitution was also investigated under continuous-flow conditions, with formation of the desired silicon-tethered product supported by ¹H and ¹³C NMR spectroscopy. Reaction progress and product formation were monitored and characterized by ¹H and ¹³C NMR spectroscopy throughout the synthesis. The batch route successfully delivered the key cyclic intermediate by ring-closing metathesis in up to 70% calculated crude yield, followed by TBAF-mediated deprotection to give the dienediol in 63% isolated yield and hydrogenation to afford 56 mg of nonane-2,7-diol. Final esterification afforded racemic dibutyroxynonane, with its formation supported by both ¹H and ¹³C NMR spectroscopy. The ¹H NMR spectrum showed characteristic signals for the butyrate α-methylene protons at δ 2.16–2.22 ppm and terminal methyl protons at δ 0.85–0.91 ppm, while the ¹³C NMR spectrum showed the characteristic ester carbonyl resonances at δ 173.4 and 173.6 ppm, consistent with incorporation of the two butyrate ester groups.

Item Type:	Thesis (MPhil)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry
Date of First Compliant Deposit:	28 September 2026
Last Modified:	28 Sep 2026 14:59
URI:	https://orca.cardiff.ac.uk/id/eprint/189827

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