Semiochemistry of Pentatomoidea 687
methanesulfonyl chloride to give chloride 28 via the intermediate mesylate (Figure 15.5). Reaction of
the Grignard reagent from 28 with (R)-epichlorohydrin in the presence of CuI gave the key intermediate
29. Hodgson’s intramolecular cyclopropanation of 29 triggered by lithium 2,2,6,6- tetramethylpiperidide
afforded exo-alcohol ent- 25 as a single stereoisomer. Oxidation of ent- 25 with TPAP and
N-methylmorpholine N-oxide furnished ketone 20 , a late-stage intermediate of the E. lewisi pheromone
in the previous synthesis (Figure 15.3). The yield of ketone 20 from (R)-citronellal in this six-step syn-
thesis was 31% versus 11% in the previous 11-step synthesis (Figure 15.3).
The third synthesis of 10 was based on two key steps (Figure 15.6): asymmetric addition of allyl-
zinc to an alkynyl carbonyl intermediate and diastereoselective, gold-catalyzed cycloisomerization of
CHO
(S)-citronellalent- 17
endo-alcohols, not separated on SiO 2exo-alcohols, separated on SiO 2ent- 16ent- 20 ent- 192425 26HOminormajorHOO OHOHOO++abccFIGURE 15.4 Diastereomeric resolution of ketone 24 via LiB(sec-Bu) 3 H reduction, chromatographic separation, and
oxidation. a) Mori (2007); b) LiB(sec-Bu) 3 H; c) PhI(OAc) 2 /TEMPO.
CHO a27 2829 ent-^25(R)-citronellal20 10bc dfCI eOH CIHOOHOOHFIGURE 15.5 Asymmetric synthesis of Eysarcoris lewisi pheromone 10. a) Mori (2007); b) MsCl/Py; c) 1. Mg,
2. (R)-epichlorohydrin/CuI; d) n-BuLi, 2,2,6,6-tetramethylpiperidine; e) TPAP/NMO; f) Tashiro and Mori (2008).