PHEROMONES OF INSECTS AND THEIR ANALOGS. XX. METHYL-BRANCHED PHEROMONES BASED ON 4-METHYLTETRAHYDROPYRAN. I. SYNTHESIS OF RACEMIC 4,8-DIMETHYLDECANAL - THE PHEROMONE OF THE FLOUR BEETLES Tribolium confusum AND Tribolium castaneum

Article abstract of DOI:10.1007/BF00598420

A synthesis is proposed of 4,8-dimethyldecanal (VIII) - a pheromone of the flour beetles Tribolium confusum and T. castaneum.By heating 71.2 g of 4-methyltetrahydropyran (I), 83.2 g of AcBr and 1.57 g ZnCl2 (45 deg C , then 120 deg C, 2h), 1-acetoxy-5-bromo-3-methylpentane (II) was obtained.The hydrolysis of 19.8 g of (II) ( MeOH-H2O, TsOH, 20 deg C, 15h) 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 deg C, 20h) 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 deg C, 4 h, Ar).The interaction of 1.42 g of (V) with Et3Al (hexane, 20 deg C, Cp2ZrCl2, Ar) gave 3,7-dimethylnonan-1-ol (VI), boiling which with 48percent 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 deg C, 1 h; 20 deg C, 2h; Ar).The characteristics of the compounds - yield (percent), n_D (deg 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 the compounds (II) - (VII) are given.