TERMITE TRAIL ATTRACTANTS - NEW SYNTHESES OF RACEMIC (E)-ALPHA-BISABOLENE, (Z)-ALPHA-BISABOLENE AND BETA-BISABOLENE

Racemic (E)-alpha-bisabolene (E)(1) was synthetized starting from 4-me thyl-3-cyclohexenecarboxylic acid (3) by a reaction sequence involving the Pd(0)-catalyzed cross-coupling reaction between the (E)-2-methyl- 1-alkenyltrimethylstannane 8 and 3-methyl-2-buten-1-yl acetate (9). Th ree different procedures, in which a common precursor was used as key intermediate, were tested for the synthesis of racemic (Z)-alpha-bisab olene (Z)(1). The best one, which involved the reaction between bromid e 18 and lithium dialkenylcuprate 19, afforded a mixture of (Z)- and ( E)-1 in a 93:7 molar ratio, respectively. Finally, racemic beta-bisabo lene (2) was synthetized by a simple reaction sequence involving the Z r-promoted methylenation of ketone 22 prepared from 3.