R. Sultanov, F. Khafizov, I. F. Khafizov
Sep 1, 2019
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Journal
Chemistry of Natural Compounds
Abstract
3-Ethyl-4-methylpentan-1-ol (1) was identified as the main component of the intrafamilial communication pheromone of Formica polyctena F. rufa ants (Hymenoptera: Formicidae) [1–4]. Both the enantiomer (R)-3-ethyl-4-methylpentan-1-ol and racemic analog 1 acted as pheromones [1, 2, 5, 6]. Known synthetic methods for 1 have several steps and require difficultly accessible starting compounds [5]. The present work proposes a new synthetic approach to racemic 1 that is based on reactions of 1-alkenes with Grignard reagents in the presence of Ta complexes that were discovered by us to give high yields of 2R′,3R-dialkyland 2R,3R-dialkyln-butylmagnesium halides (R′ = alkyl fragment from the 1-alkene, R = alkyl fragment from Grignard compound) [7, 8]. A search for catalysts capable of producing selectively only one of the aforementioned compounds showed that the two-component Ta-containing system TaCl5 + (i-PrO)3P (1:1 ratio) could produce 2R′,3R-dialkyl-n-butylmagnesium halides with 98% selectivity. The synthesis of 1 was used as an example to demonstrate the synthetic potential of this reaction using the modified catalyst. Thus, the reaction of propylene with n-BuMgBr in the presence of TaCl5–(i-PrO)3P [n-BuMgBr–C3H6–TaCl5– (i-PrO)3P, 125:100:5:5; THF–Et2O, 1:1; 20°C, 7 h] formed organomagnesium compound 2 (Scheme 1).