Insect pheromones and their analogues. XVI. Practical synthesis of hexadec-9Z-enal — A component of the sex pheromone of the cotton bollwormHeliothis armigera

Abstract

A synthesis of hexadec-9Z-enal — a component of the sex pheromone of the cotton boll-wormHeliothis armigera (Hübner) — based on cyclooctene (I) is proposed. Through a solution of 22 g of (I), 250 ml of cyclohexane, and 40 ml of MeOH is passed (at 5°C) 0.2 M O₃/O₂, the solution is decanted off, and the precipitated ozonide is dissolved in 200 ml of MeOH and is reduced with 19 g of NaBH₄ (40°C) with the isolation, after the usual working up, of 23.4 g of octane-1,8-diol (II). From 0.5 mole of (II) and 0.6 mole of 45% HBr 8-bromooctan-1-ol (III) is obtained and this is converted into 1-(2-THPL)oxy)-8-bromooctane (IV). The condensation of (IV) with oct-1-yne (Ar, LiNH₂, HMPTA, 10°C, 1 h, and then 55°C, 10 h) leads to 1-(2-THPL-oxy)hexadec-9-yne (V) the hydrolysis of which (MeOH, H₂O, p-TsOH, 20°C for 20 h) yields hexadec-9-yn-ol (VI). The reduction of (VI) (Et₂O, iso-BuMgBr, Cp₂TiCl₂, 0°C, 15 min, then 20°C, 1 h) yieldshexadec-9Z-en-l-ol (VII). The oxidation of (VII) (PyHCrO ⁺₃ Cl⁻, CH₂Cl₂, 20°C, 2 h) gives hexadex-9Z-enal (VIII). Characteristics of the compounds (yield (%), n ²⁰_D ⁽²⁵⁾: (II) − 80, mp 61–62°C; (III) − 75, 1.4807; (IV) − 99, —; (V) − 52, 1,4650; (VI) − 85, 1.4657; (VII) − 99, 1.4650; (VIII) − 98, 1.4600. Characteristics of the IR and PMR spectra of compounds (V–VII) are given.