16 Synthesis of Insect Juvenile Hormones

Abstract

Synthetic approaches to the insect juvenile hormones (JH, I and II) ard their analogs are discussed in detail with a brief summary of structure-activity relationship and possible use of JH for silkworm rearing. Stereoselective synthesis of the cis-double bond portion of JH. Three new routes were developed for this purpose: (i) Mevalonolactone (IV) was converted to a C_6-alcohol (VIII). (ii) A C_7-alcohol (XVII) was prepared from methyl cyclopropyl ketone (XII). (iii) Methyl vinyl ketone (XX) was converted to VIII. Synthesis of dl-C_<17>-Cecropia JH. This was accomplished non-stereoselectively (XIX→XXVIII). Stereoselective synthesis of 6-ethyl-10-methyldodeca-5-trans, 9-cis-dien-2-one (XXIX). The stereoselective ring fission of XXXIII to XXXIV enabled us to prepare XXIX stereoselectively (IX→XXIX). This was further transformed into dl-C_<18>-Cecropia JH. in the usual manner. Stereoselective synthesis of dl-C_<17>-Cecropia JH. Coupling and subsequent modification of the two structural units, XLIII and XLIV, afforded dl-C_<17>-JH. XLIII was prepared stereoselectively from geraniol. Conversion of farnesol into the 10-trans-isomer of dl-C_<17>-JH. A stereoselective homologetion of the trans-terminal methyl group of farnesol (XLVIII) to an ethyl group yielded the 10-trans-C_<17>-JH (LIV). Structure-activity relationship. Two alkyls at C-11 are essential for high JH activity. An alkyl at C-7 was less important. An alkyl at C-3 was unnecessary. Practical use of JH. JH application on the silkworm, Bombyx mori, remarkably increased the yield of silk.