SHORT COMMUNICATIONSIn our preceding publication [1] a simple procedure was described for the preparation of both enantiomers of monoterpene alcohol ipsdienol 1, an actual pheromone component of bark beetle of genus Ips. The key synthesis stage was the resolution of the direct precursor of the ipsdienol, (±)-6-methyl-2-(2-chloroethyl)hepta-1,5-dien-4-ol by its conversion into acid phthalate and the crystallization of the acid phthalate as salt with (+)-or (-)-1-phenylethylamine. Then the optically active acid phthalates (S)-2 and (R)-2 were treated with potassium tert-butylate in tertbutyl alcohol. By the dehydrochlorination and the simultaneous alcoholysis of the ester moiety in one stage (S)-or (R)-ipsdienol was obtained in a 55% yield.The necessity of preparation of a large amount of optically active ipsdienol (S)-1 required a detailed study of the reaction between acid phthalate (S)-2 and potassium tert-butylate, since the reaction proceeded with a reproducible yield about 50%. In the initial procedure [1] a large amount of solvent and an essential excess of the base were required. In the reaction mixture a large quantity of unreacted acid phthalate of ipsdienol was present. The increase in the reaction dura-tion from 1 to 3 h and the use of more concentrated 20% solution of potassium tert-butylate not only did not increase the yield of ipsdienol (S)-1, but even resulted in a consi-derable decrease in its enantiomeric purity. In various expe-riments we observed unexpected and undesirable decrease in the enantiomeric excess of ipsdienol (S)-1 to 75-80% (Scheme 1).The heterolysis of esters of the optically active allylic alcohols at the O-R bond ( where R is the residue of the allylic alcohol) and the accompanying rearrangements with the migration of the double bond and the racemization along the S N 1 mechanism are studied in sufficient detail and have been discussed before [2][3][4][5]. These transformations were mostly studied by an example of acid phthalates which were used for resolution of the corresponding allylic alcohols into individual enantiomers. It was established by this research that the heterolysis of esters with the formation of allylic carbocations is sharply accelerated at higher temperature, but the optically active allylic alcohols proper do not suffer
(2S,3S,7S)-3,7-Dimethyl-2-pentadecyl acetate (ac-1), the sex pheromone of the pine sawfly Neodiprion sertifer, has been newly synthesized by the transformation of the corresponding esters 8 and 12 into 2-oxyalkyl-substituted allyl bromides 4 and 5 via tertiary cyclopropanols 6 and 7.
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