Semiochemistry of Pentatomoidea 697
attractive to conspecific males and females, was identified as methyl (2E,4E,6Z)-2,4,6-decatrienoate ( 66 )
(Sugie et al. 1996). Because of the pest status of this bug, the synthesis of ester 66 as an attractant for P.
stali was patented in Japan (Yamashita et al. 1997) using controlled hydrogenation of methyl (2E,4E)-
2,4-decadien-6-ynoate with Lindlar catalyst in a key step. However, this intermediate took several steps
to make, and the reported yield of 65 from the reduction step was only 12%. Because 65 has been devel-
oped for commercial use in Japan, it seems likely that a better synthesis has been developed but has not
been disclosed.
Khrimian (2005) reported syntheses of all eight geometric isomers of methyl 2,4,6-decatrienoate
including the aggregation pheromone of P. stali, compound 66 (Figure 15.13) and a component of the
sex pheromone of several Thyanta spp., compound 73 (Figure 15.14).
Syntheses of the four (4E)-isomers (Figure 15.13) were accomplished from the same precursor, (E)-4,4-
dimethoxy-2-butenal ( 67 ), by fully exploiting Wittig-type olefinations, and taking advantage of an easy
separation of (2E)- and (2Z)-unsaturated esters by silica gel chromatography. The starting aldehyde 67
can be prepared readily by a controlled deacetalization of fumaraldehyde bis(dimethylacetal), which is
commercially available or can be prepared from furan (Gree et al. 1986). The Plautia stali pheromone
66 was prepared expeditiously in 55% overall yield and 96:4 EEZ/EEE ratio from 67 using consecutive
cis-Wittig olefination to acetal 68 followed by acid-catalyzed hydrolysis and trans-Horner–Wadsworth–
Emmons olefination of the (2E,4Z)-2,4-octadienal formed to give a 96:4 mixture of 66 : 71. The method
has been adopted by several semiochemical companies for commercial production of the P. stali phero-
mone (A.K., pers. comm.). trans-Wittig olefination of 67 yielded a diene acetal intermediate 70 , which
was converted to the all-E stereoisomer 71 analogous to the synthesis of 66. cis-Horner-Wadsworth-
Emmons olefination with strongly electrophilic (CF 3 CH 2 O) 2 P(O)CH 2 COOCH 3 and a highly dissociated
base, KN(TMS) 2 /18-crown-6 (Still and Gennari 1983) was utilized to make stereoisomers 69 and 72 in
good stereoisomeric purities from acetals 68 and 70 , respectively (Figure 15.13) (Khrimian 2005).
All four (4Z)-isomers of methyl 2,4,6-decatrienoate ( 73 , 76 , 79 , and 80 ) were synthesized by combining
Horner–Wadsworth–Emmons olefinations and controlled stereoselective reductions of carbon- carbon
triple bonds to introduce the required Z-double bonds (Figure 15.14) and, as previously mentioned,
exploiting the easy separation of 2E- and 2Z-unsaturated esters on silica gel (Khrimian 2005). The ther-
mally and chemically unstable (2E,4Z,6Z)-isomer 73 , the sex pheromone of several Thyanta spp. (Millar
1997, McBrien et al. 2002, Moraes et al. 2005a), was assembled by a one-pot oxidation of dienol 75 with
CO 2 CH 371 ( 71 / 66 , 95:5)70 ( 70 / 68 , 94:6) 68 ( 68 / 70 , 96:4)72 ( 72 / 69 , 95:5) 69 ( 69 / 72 , 93:7)66 ( 66 / 71 , 96:4)67CO 2 CH 3 CO 2 CH 3OCH (^3) OCH OCH 3
3
OCH 3
H
O
b, c b, c
b, d b, d
ea
OCH 3 OCH 3
CO 2 CH 3
FIGURE 15.13 Syntheses of four methyl (4E)-2,4,6-decatrienoates including Plautia stali pheromone 66. a) Ph 3 PC 4 H 9 Br/
[(CH 3 ) 3 Si] 2 NNa; b) PTSA, acetone-H 2 O; c) (CH 3 O) 2 P(O)CH 2 CO 2 CH 3 , K 2 CO 3 -H 2 O; d) (CF 3 CH 2 O) 2 P(O)CH 2 CO 2 CH 3 /
[(CH 3 ) 3 Si] 2 NK, 18-crown-6; e) Ph 3 PC 4 H 9 Br/ 2 BuLi, THF.