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The principal constituents of the pheromone of male rhinoceros beetles of the genus Oryctes are 4-methyloctanoic acid (1) and its ethyl ester [1]. Known methods for synthesizing racemic 1 are typically multi-step and in most instances use difficultly accessible compounds as starting materials [2, 3–6]. We developed a convenient and efficient synthetic pathway to 1 that was based on the catalytic carbomagnesiation of 1-alkenes using EtMgCl (Et2Mg) and TaCl5 catalyst that was recently discovered by us (Scheme 1) [7].

A synthesis is proposed of 4,8-dimethyldecanal (VIII) — a pheromone of the flour beetlesTribolium confusum andT. castaneum. By heating 71.2 g of 4-methyltetrahydropyran (I), 83.2 g of AcBr and 1.57 g of ZnCl2 (45°C), then 120°C, 2 h), 1-acetoxy-5-bromo-3-methylpentane (II) was obtained. The hydrolysis of 19.8 g of (II) (MeOH-H2O, TsOH, 20°C, 15 h) gave 5-bromo-3-methylpentan-1-ol (III). From 18.1 g of (III) and 38.9 ml of 2,3-dihydropyran (Et2O, TsOH, 20°C, 20 h) was obtained the 2-THPL ester of (III), (IV), which was converted into 3-methyloct-7-en-1-ol (V) by the treatment of the corresponding Grignard reagent with allyl bromide (THF, CuI-bi-2-pyridyl, 2°C, 4 h, Ar). The interaction of 1.42 g of (V) with Et3Al (hexane, 20°C, Cp2ZrCl2, Ar) gave 3,7-dimethylnonan-1-ol (VI), boiling which with 48% HBr in the presence of concentrated H2SO4 gave 1-bromo-3,7-dimethylnonane (VII) which was then converted into the desired (VIII) by the reaction of the corresponding Grignard reagent with DMFA (0–2°C, 1 h; 20°C, 2 h; Ar). The characteristics of the compounds — yield (%), nD (°C): (I), 79, 1.4340 (22); (III) 89, 1.4660 (23); (IV), 82, 1.4739 (23); (V), 85, —; (VI), 90, 1.4483 (20); (VII), 88, 1.4409 (22); (VIII), 88, 1.4589 (22). Details of the IR and PMR spectra of compounds (II)–(VII) are given.

A synthesis of hexadec-9Z-enal — a component of the sex pheromone of the cotton boll-wormHeliothis armigera (Hubner) — 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 D 20 (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.