Pheromone synthesis. Part 262: Determination of the absolute configuration of the female sex pheromone [(1S,2S)-(?)-(1,2-dimethyl-3-methylenecyclopentyl) acetaldehyde] of the pineapple mealybug (Dysmicoccus brevipes) by synthesis coupled with X-ray analysis

Article abstract of DOI:10.1016/j.tet.2017.09.046

The enantiomers of (anti-1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde, one of which is the female sex pheromone of the pineapple mealybug (Dysmicoccus brevipes), were synthesized. Chirality was introduced by means of lipase-catalyzed asymmetric acetylation of (±)-2,3-dimethyl-2-cyclopenten-l-ol. X-ray analysis of (?)-camphanate ester of (1S,2S)-(?)-2-(1,2-dimethyl-3-methylenecyclopentyl)ethanol confirmed its (1S,2S)-absolute configuration. The natural pheromone was identified with the (1S,2S)-aldehyde by comparing the specific rotation, enantioselective GC retention time and pheromone activity.

Full text of DOI:10.1016/j.tet.2017.09.046

Accepted Manuscript
Pheromone synthesis. Part 262: Determination of the absolute configuration of
the female sex pheromone [(1S,2S)-(-)-(1,2-dimethyl-3-methylenecyclopentyl)
acetaldehyde] of the pineapple mealybug (Dysmicoccus brevipes) by synthesis
coupled with X-ray analysis
Kenji Mori, Jun Tabata
PII:
S0040-4020(17)30982-1
10.1016/j.tet.2017.09.046
TET 28997
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 2 August 2017
Revised Date: 12 September 2017
Accepted Date: 26 September 2017
Please cite this article as: Mori K, Tabata J, Pheromone synthesis. Part 262: Determination of the
absolute configuration of the female sex pheromone [(1S,2S)-(-)-(1,2-dimethyl-3-methylenecyclopentyl)
acetaldehyde] of the pineapple mealybug (Dysmicoccus brevipes) by synthesis coupled with X-ray
analysis, Tetrahedron (2017), doi: 10.1016/j.tet.2017.09.046.
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ACCEPTED MANUSCRIPT
Pheromone synthesis. Part 262: Determination of the absolute configuration of the
female sex pheromone [(1S,2S)-(-)-(1,2-dimethyl-3-methylenecyclopentyl)
acetaldehyde] of the pineapple mealybug (Dysmicoccus brevipes) by synthesis coupled
with X-ray analysis☆
Kenji Mori,a,*iD Jun Tabatab
a Photosensitive Materials Research Center, Toyo Gosei Co., Ltd, 4-2-1 Wakahagi,
Inzai-shi, Chiba 270-1609, Japan
b Division of Applied Entomology and Zoology, National Agriculture and Food
Research Organization, 3-1-3 Kannondai, Tsukuba-shi, Ibaraki 305-8604, Japan
ARTICLE INFO
Article history:
Received
Keywords:
Ireland-Claisen rearrangement
Lipase-catalyzed acetylation
Monoterpene aldehyde
Pheromone
Received in revised form
Accepted
Available on line
X-ray analysis
ABSTRACT
The enantiomers of (anti-1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde, one of
which is the female sex pheromone of the pineapple mealybug (Dysmicoccus brevipes),
were synthesized. Chirality was introduced by means of lipase-catalyzed asymmetric
acetylation of (±)-2,3-dimethyl-2-cyclopenten-l-ol. X-ray analysis of (-)-camphanate
ester of (1S,2S)-(-)-2-(1,2-dimethyl-3-methylenecyclopentyl)ethanol confirmed its
(1S,2S)-absolute configuration. The natural pheromone was identified with the
(1S,2S)-aldehyde by comparing the specific rotation, enantioselective GC retention time
and pheromone activity.
☆ For Part 261, see Ref.1. This work was orally reported by K.M. as his lecture at
International Chemical Ecology Conference 2017 (August 24, 2017) in Kyoto, Japan.
* Corresponding author.
E-mail address: kjk-mori@arion.ocn.ne.jp (K. Mori).
ORCID iD(Kenji Mori):0000-0003-2152-5167.
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1. Introduction
The pineapple mealybug [Dysmicoccus brevipes (Cockerell), Homoptera:
Pseudococcidae] is a pest infesting pineapples in Okinawa.2 Tabata et al. isolated 2.1 mg
of its female sex pheromone from 672,000 virgin females, and identified it as
(1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde (1, Fig.1).3 Synthesis of the
racemates of anti-1 with two methyl groups in anti-configuration and its syn-isomer
enabled the assignment of the anti-stereochemistry to the natural pheromone, because
anti-1 showed no NOE between the two methyl groups while syn-1 clearly showed
NOE.4 As to the absolute configuration of the natural pheromone, it remained
unknown to date.
Fig.1. Structure [(1S,2S)-1] of the pineapple mealybug pheromone and the previous
syntheses of its racemate.
The obvious way to solve the problem was to synthesize both (1S,2S)- and
(1R,2R)-1 and compare their physical and biological properties with those of the natural
pheromone. Our two syntheses of (±)-1 were based on either conjugate addition
[A→B, Fig.1 (a)] or Ireland-Claisen rearrangement (C →D →E) and ring-closing
metathesis [E →F, Fig.1 (b)].4 Unfortunately, these two routes were difficult to be
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modified to give pure enantiomers of anti-1. We therefore explored a different route,
which allowed us to assign (1S,2S)-absolute configuration to the natural pheromone.
The X-ray crystallographic analysis of a derivative of one of the synthetic intermediates
confirmed the configuration assigned to the natural pheromone. The present paper
describes in detail the synthesis of (1S,2S)-1 and its identification as the natural
pheromone.
2. Results and discussion
2.1. Retrosynthetic analysis of (1S,2S)-1
Fig.2 shows the retrosynthetic analysis of (1S,2S)-1. Since the stereoisomers at C-
2 were separable by SiO2 chromatography,4 introduction of chirality at C-1 was planned
by means of Ireland’s ester-enolate Claisen rearrangement [(S)-H → (S)-G].4,5
OTMS
O
CO2H
CHO
(1S,2S)-1
(S)-G
(S)-H
OAc
OH
OAc
+
(S)-I
(S)-J
(R)-I
OH
O
( )-J
A
Fig.2. Retrosynthetic analysis of (1S,2S)-1 basing on lipase-catalyzed asymmetric
acetylation of (±)-J.
The substrate (S)-I for the rearrangement would be prepared by acetylation of (S)-J,
whose preparation would be executed by lipase-catalyzed asymmetric acetylation of
(±)-J. Reduction of the known 2,3-dimethyl-2-cyclopenten-1-one (A)4 would afford
the racemic alcohol (±)-J. Another product (R)-I of the enzymatic acetylation would
eventually give (1R,2R)-1. The above plan enabled us the synthesis of (1S,2S)-1 in an
amount sufficient for its physical as well as biological identification with the natural
pheromone.
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2.2. Synthesis of (±)-2,3-dimethyl-2-cyclopenten-1-ol (6)
For the successful synthesis of (1S,2S)-1, it was necessary to secure at least over 20
g of (±)-6 (Scheme 1). Accordingly, a scalable synthesis of the parent ketone 5 was
explored at first. Although there exists a number of different syntheses of 5, none of
them is scalable, due to its multi-step nature or its use of expensive reagents.4
Gratifyingly, Prof. S. Kobayashi, a former student of Prof. Mukaiyama, suggested K.M.
to adopt Mukaiyama’s procedure for the conversion of levulinic acid (2) to
2,5-heptanedione (4) via mixed anhydride 3.6 Base-catalyzed aldol cyclization of 4 is
known to give the desired ketone 5.7
Scheme 1. Synthesis of (±)-6, the substrate for enzymatic acetylation. Reagents: (a)
t-BuCOCl, Et3N, Et2O (99%); (b) EtMgBr, THF, -60oC (54%); (c) NaOH, EtOH, H2O,
reflux (67%); (d) NaBH4, CeCl3·7H2O, MeOH, 10-15oC (81%); (e) Mg, THF;
5-hexen-2-one (56%); (f) Grubbs II, CH2Cl2 (N.R.).
Some modifications and scale-up of the Mukaiyama procedure afforded 10 g of 5 in
a single batch as follows (Scheme 1). Levulinic acie (2) was treated with pivaloyl
chloride in the presence of Et3N in Et2O to give mixed anhydride 3 in a quantitative
yield. Addition of 1 eq of EtMgBr in THF to 3 was executed at -60oC to keep the
ketone carbonyl of 3 intact, giving 4 in 54% yield after distillation. Cyclization of 4
with NaOH in aqueous EtOH according to Welch7 furnished 5 in 67% yield, whose GC
and spectral properties were identical with those of an authentic sample.4 Reduction of
5 with NaBH4 and CeCl3·7H2O in MeOH according to Luche8 afforded
(±)-2,3-dimethyl-2-cyclopenten-1-ol (6) in 81% yield. Nearly 40 g of (±)-6 could be
prepared from levulinic acid (2) through the present four-step synthesis in 29% overall
yield. The above route to 5 is superior to any other route examined previously.4
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An unsuccessful attempt was made to prepare 5 in a different manner.
1,2-Dimethyl-2-cyclopenten-1-ol (K) will give 5 by chromic acid oxidation
accompanied with allylic rearrangement. Synthesis of K seemed possible by
ring-closing metathesis of 8, which was synthesized from 5-hexen-2-one by treatment
with a Grignard reagent prepared from 7 and Mg in THF. Ring-closing metathesis of
8, however, was unsuccessful with second-generation Grubbs catalyst. No K could be
observed, and the starting 8 was recovered.
2.3. Lipase-catalyzed asymmetric acetylation of (±)-6 and (±)-10
Lipases and esterases are user-friendly biocatalysts in natural product synthesis to
secure enantiopure alcohols and esters.9,10 In 1991 Kazlauskas et al. proposed an
empirical rule to predict which enantiomer of a secondary alcohol reacts faster in
reactions catalyzed by lipase.11 For esters of secondary alcohols, the enantiomer
shown in L (Scheme 2) reacts faster than the other enantiomer. Crystallographic and
molecular-modeling studies of lipase B from Candida antarctica revealed a
stereospecificity pocket for secondary alcohols L.12 Accordingly, lipase-catalyzed
asymmetric acetylation of (±)-6 is expected to give (R)-acetate 9 and (S)-alcohol 6.
Earlier and published results supported the above assumption, because lipase-catalyzed
acetylation of (±)-i and (±)-iii yielded (R)-ii13 and (R)-iv.14
Prior to the large scale enzymatic acetylation of (±)-6, four 2-cyclopenten-1-ols
(±)-6, 10, 12 and 14 were subjected to asymmetric acetylation with lipase and vinyl
acetate so as to know the general feature of the reaction. Lipase AK (Amano) was
selected as the enzyme of choice, basing on our previous experience.13 The racemic
alcohol (±)-6 and vinyl acetate in (i-Pr)2O was stirred with lipase AK for 7 h at room
temperature. The resulting products were chromatographed over alumina (pH 9-11) to
give (R)-(+)-9 and (S)-(-)-6. The present relationship between absolute configuration
and sign of rotation was in accord with Hill’s result that (R)-2-cyclopenten-1-ol is
dextrorotatory.15
It must be emphasized that the separation of (R)-9 from (S)-6 was possible only over
slightly basic alumina. Chromatography over silica gel or neutral alumina resulted in
exothermic decomposition of the products giving dienes. The allylic system in 6 and 9
was very unstable due to the facile elimination under acidic conditions. The instability
of 6 and 9 under slightly acidic conditions also became apparent when (±)-6 was
subjected to Akai’s oxovanadium catalyst (VMPS)-catalyzed dynamic kinetic
resolution.16 Instead of dynamic kinetic resolution of (±)-6, its decomposition took
place to give a dark-colored suspension, affording useless dienes.
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Scheme 2. Asymmetric acetylation of (±)-6 and (±)-10. Reagents: (a) vinyl acetate,
lipase AK, (i-Pr)2O, room temp; (b) K2CO3,MeOH, room temp; (c) CH2(CO2Me)2,
Novozyme 435, KHCO3.
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After the separation, the enantiomeric purities of (R)-9 and (S)-6 were determined
by enantioselective GC, and found to be 77% ee for (R)-9 (56% yield) and 91% ee for
(S)-6 (44% yield). The result showed that nearly enantiopure (R)-9 and (S)-6 would be
obtained by repeating the enzymatic acetylation once more against (R)-6 derived from
(R)-9 of 77% ee and also against (S)-6 of 91% ee.
Asymmetric acetylation with lipase AK of (±)-2-methyl-2-cyclopenten-1-ol (10)
furnished (R)-11 (35% yield, 93% ee) and (S)-10 (47% yield, 76% ee). However,
when (±)-12 and (±)-14, both lacking the methyl group at C-2, were subjected to
asymmetric acetylation, the products were racemic acetates (±)-13 and (±)-15. It is
therefore concluded that the presence of a methyl group at C-2 of (±)-6 and (±)-10 is
crucial for the successful lipase-catalyzed asymmetric acetylation.
2.4. Preparative scale asymmetric acetylation of (±)-6 and chirality transfer by
Claisen rearrangement to give the enantiomers of 17 after methylation
The next stage of the synthesis was preparation of nearly enantiopure (R)- and (S)-9,
and their conversion to (R)- and (S)-16 by Ireland-Claisen rearrangement.
As shown in Scheme 3, lipase-catalyzed asymmetric acetylation of (±)-6 was
repeated twice to further increase the enantiomeric purities of the products. Eventually
it was possible to obtain 2.57 g of (R)-9 (94% ee) and 6.58 g of (S)-6 (94% ee) starting
from about 38 g of (±)-6. Chemical acetylation with Ac2O and pyridine of (S)-6 gave
5.50 g of (S)-9 (94% ee). It must be added that in the course of methanolysis of (R)-9
to give (R)-6 as well as in the course of chemical acetylation of (S)-6, partial elimination
of AcOH took place, decreasing the yields of (R)-6 and (S)-9. This also indicates the
ease of elimination of the acetoxy group at C-1 of 9.
Ireland-Claisen rearrangement of 9 to give (1,2-dimethyl-3-cyclopentenyl)acetic
acid (16) was the key step of the present synthesis, effecting the chirality transfer from
C-O to C-C bonds.5,17 As already noticed by Jäger,17 the rearrangement was
accompanied by elimination of AcOH, and the best yield of (S)-16 was 56%, while
(R)-16 was obtained in 30% yield. Methylation of 16 was executed with K2CO3 and
MeI in acetone/DMF to give 2.08 g of (S)-(-)-17 from 5.38 g of (S)-9. The amount
secured was sufficient for its conversion to (1S,2S)-1. Similarly, (R)-(+)-17 (988 mg)
was prepared from 2.30 g of (R)-9.
2.5. Improved synthesis of (±)-anti-1 starting from (±)-17
Considering the limited amount (2.08 g) of the secured (S)-17, it seemed appropriate
to modify and improve the existing synthetic steps4 necessary for the conversion of 17
to anti-1. Scheme 4 summarizes the result of such endeavor executed with more
accessible racemates.
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OH
OAc
OH
a
+
( )-6
(R)-9
(S)-6
(ca. 38 g)
(62%, 72% ee)
(32%, 75% ee)
b
a
(R)-9
(72% ee)
(R)-6
(R)-9
(94% ee)
(S)-6
(low ee)
+
(70% ee)
42%
61%
(2.57 g)
a
(S)-6
(R)-9
(S)-6
+
(77% ee)
(low ee)
(94% ee)
57%
(6.58 g)
OAc
c
d
(S)-6
(94% ee)
CO2R
(S)-9
(94% ee)
(S)-16 R = H
(S)-17 R = Me
e
OAc
d
CO2R
(R)-9
(94% ee)
(R)-16 R = H
(R)-17 R = Me
e
Scheme 3. Preparative scale asymmetric acetylation of (±)-6 and subsequent synthesis
of the enantiomers of 17. Reagents: (a) vinyl acetate, lipase AK, (i-Pr)2O, room temp;
(b) K2CO3,MeOH; (c) Ac2O, C5H5N (62%); (d) TMSCl, LiN(i-Pr)2, THF; then heat at
60oC [56% of (S)-16 and 30% of (R)-16]; (e) K2CO3,MeI, acetone, DMF [64% of (S)-17
and 68% of (R)-17].
The acyclic ester (±)-19 was prepared in 47% yield (5 steps) starting from 18 as
reported previously.4 Ring-closing metathesis of (±)-19 was conducted with 0.5 mol%
of Grubbs II catalyst to give (±)-17 in 84% yield. Conversion of (±)-17 to keto ester
(±)-21 was achieved by hydroboration-oxidation in 57% yield.4 However, an
alternative two-step process via epoxy ester (±)-20 was found to be experimentally less
demanding. Epoxidation of (±)-17 with m-chloroperbenzoic acid (MCPBA) gave
(±)-20, which was treated with BF3·OEt2 in CH2Cl2 to give (±)-21.14 The epoxidation
was non-stereoselective, and (±)-21 was obtained as a ca. 1:1 mixture of its two
diastereoisomers.
The next methylenation step was previously carried out with Tebbe, Petasis or Ando
reagents.4 Considering the compatibility with the ester group of (±)-21, methylenation
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in the present work was executed with Lombardo reagent18 or Yan reagent.19 When
Lombardo reagent (CH2Br2, Zn, TiCl4) was employed, (±)-21 furnished (±)-22 in 86%
yield, while the yield was 33% by using Yan reagent (CH2Cl2, Mg, TiCl4).
Scheme 4. Optimization of the synthetic steps employing racemic intermediates.
Reagents: (a) Grubbs II (0.5 mol%), CH2Cl2, reflux (84%); (b) MCPBA, CH2Cl2 (69%);
(c) BF3·OEt2, CH2Cl2 (83%); (d) BH3·SMe2, Et2O; then Jones CrO3, acetone (57%) (e)
CH2Br2, Zn, TiCl4, THF (86%); (f) CH2Cl2, Mg, TiCl4 (33%); (g) LiAlH4, Et2O
(82%-quant.); (h) SiO2 chromatog. (45% for anti-23); (i) DNBCl, DMAP, C5H5N
(74%); (j) NaOH, MeOH, H2O (77%).
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Reduction of (±)-22 with LiAlH4 gave (±)-23 in 82% yield. The diastereoisomers
of (±)-23 could be separated by silica gel chromatography, and (±)-anti-23 (anti/syn=
93:7-90:10) was secured in 27% yield (1.41 g) as the earlier eluting isomer. Owing to
the tailing of the earlier eluting (±)-anti-23, the later eluting (±)-syn-23 could not be
obtained pure in an amount sufficient for its further conversion to (±)-syn-1. This
causes no problem, because (±)-syn-1 is known to be biologically inactive.3,4
Oxidation of (±)-anti-23 will give (±)-anti-1 in good yield.4
An attempt was made to further purify (±)-anti-23 by converting it to crystalline
3,5-dinitrobenzoate (±)-anti-24. Treatment of (±)-anti-23 with 3,5-dinitrobenzoyl
chloride (DNBCl) and DMAP in pyridine gave (±)-anti-24, mp 62-64oC, in 74% yield
after recrystallization from EtOAc/hexane. It gave back (±)-23 upon alkaline
hydrolysis. The purity of the recovered alcohol was anti/syn = 100:7. Unfortunately
pure (±)-anti-23 could not be obtained via (±)-anti-24.
The above described efforts to improve the synthetic steps provided 1.15 g of
(±)-anti-23 and 7.15 g of a diastereomeric mixture of (±)-23 for further biological
studies.
2.6. Synthesis of (1S,2S)-1 and its identification with the natural pheromone
Basing on the experience obtained in the course of improving the synthetic steps
leading to (±)-23, (S)-17 was converted to the optically active pheromone (1S,2S)-1 as
shown in Scheme 5.
Epoxidation of (S)-17 with MCPBA gave 20 in 93% yield, which was treated with
BF3·OEt2 to furnish quantitatively (-)-keto ester (1S,2RS)-21. Lombardo reagent
converted 21 into (1S,2RS)-22 in 72% yield. Reduction of the ester 22 with LiAlH4
was followed by chromatographic separation to give 284 mg (30%) of (1S,2S)-(-)23,
[α]D26 -26.7 (c 0.52, hexane). Finally, oxidation of 23 with azadol20 and
diacetoxyiodobenzene (DAIB) in CH2Cl2, afforded (1S,2S)-1, [α]D25 -47.6 (c 0.50,
hexane), in 69% yield (87 mg). Since the specific rotation of the natural pheromone
was reported as [α]D26.3-39.45 (c 0.075, hexane), the absolution configuration of the
natural pheromone was determined as 1S,2S. Comparison of the enantioselective GC
retention time (tR) of the natural pheromone with that of (1S,2S)-1 also confirmed the
identity (see 4.26.3). The natural pheromone was enantiomerically pure (1S,2S)-1.
In the same manner, 1.00 g of (R)-17 yielded 90 mg of a mixture of (1R,2R)- and
(1R,2S)-1, [α]D24 +15.5 (c 0.61, hexane). This was used for the enantioselective GC
comparison with the natural pheromone, and a portion of it was further purified by
SiO2/AgNO3 chromatography to give (1R,2R)-1 in an amount sufficient for the field
bioassay.
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Scheme 5. Synthesis of the natural pheromone (1S,2S)-1 and preparation of a
crystalline derivative 25 for X-ray analysis. Reagents: (a) MCPBA,CH2Cl2 (93%); (b)
BF3·OEt2, CH2Cl2 (quant.); (c) CH2Br2, Zn, TiCl4, THF (72%); (d) LiAlH4, Et2O
(95%); then SiO2 chromatog. (30%); (e) DAIB, azadol, CH2Cl2 (69%); (f)
(-)-camphanic chloride, DMAP, CHCl3, C5H5N (98%).
2.7 Confirmation of the absolute configuration of (1S,2S)-(-)-1 by X-ray
crystallographic analysis of 25
The (1S,2S)-absolute configuration assigned to the naturally occurring (-)-1 was
based on the S-configuration of (-)-6, which was deduced on the basis of the empirical
rule on the stereochemical outcome of lipase-catalyzed asymmetric acetylation.11,12 In
order to confirm the stereochemical assignment, a crystalline ester 25 (Scheme 5) was
prepared by treatment of (1S,2S)-23 with (-)-camphanic chloride. The absolute
configuration of (1S)-(-)-camphanic chloride is known.21 Accordingly, solving the
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structure of 25 by X-ray analysis allows us to confirm the absolute configuration of
(1S,2S)-23. Fortunately, recrystallization of 25 from EtOAc furnished plates suitable
for X-ray analysis. Fig.3 shows the X-ray structure of 25.
Fig.3. X-ray structure of (-)-2-(anti-1,2-dimethyl-3-methylelnecyclopentyl)ethyl
camphanate (25). For details see CCDC 1516035.
As can be seen from Fig.3, (-)-23 possesses (1S,2S)-stereochemistry. The present
X-ray analysis, whose details are deposited as CDCC1560305, confirmed the absolute
configuration of (-)-23, and hence that of (-)-1 as (1S,2S).
2.8. Bioassay of the synthetic enantiomers (1S,2S)- and (1R,2R)-1
The attractiveness of each the enantiomer of anti-1 was tested by a trap bioassay at a
pineapple field in Okinawa. As shown in Fig.4, the naturally occurring (1S,2S)-1
attracted significantly greater number of males than its opposite enantiomer.
Fig.4. Numbers (mean + SEM; N=6) of Dysmicoccus brevipes males captured by field
traps baited with (1S,2S)- and (1R,2R)-1. An asterisk indicates a significant difference
according to ANOVA (P < 0.005).
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3. Conclusion
The stereostructure of the female-produced sex pheromone of the pineapple
mealybug, Dysmicoccus brevipes (Cockerell), was established as
(1S,2S)-(-)-(1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde (1) by
chemo-enzymatic synthesis employing lipase AK (Amano). The overall yield of
(1S,2S)-1 was 0.44% (13 steps) based on levulinic acid (2). X-ray analysis of 25
confirmed (1S,2S)-stereochemistry of the intermediate (1S,2S)-(-)-23. The natural
pheromone was seven times more bioactive than its opposite enantiomer.
4. Experimental
4.1. General
All bps and mp are uncorrected values. Refractive indices were measured on an
Atago DMT-1 refractometer. IR spectra were measured on a Jasco FT/IR-410
spectrometer. 1H NMR spectra (400 MHz, TMS at δ=0.00 as the internal standard)
and 13C NMR spectra (100 MHz, CDCl3 at δ=77.0 as the internal standard) were
recorded on a Jeol JNM-ECZ 400S/L1 spectrometer. GC-MS were measured on
Agilent Technologies 5975 inert XL. HRMS were recorded on Jeol JMS-T100GCV.
Silica gel column chromatography was carried out on Merck Kieselgel 60 Art 1.00734.
4.2. Levulinoyl pivaloyl anhydride (3)
A solution of pivaloyl chloride (6.00 g, 50 mmol) in dry Et2O (5 mL) was added
dropwise to a stirred and ice-cooled solution of levulinic acid (2, 5.80 g, 50 mmol) and
Et3N(5.0 g, 50 mmol) in dry Et2O (65 mL) at 5-10oC. The solution was stirred for 1.5
h at 5-10oC, and the precipitated Et3N·HCl was filtered off. The solid salt was washed
with Et2O. The combined filtrate and washings were dried (MgSO4), and concentrated
in vacuo to give 9.91 g (99%) of 3 as a colorless oil, νmax (film): 2979 (m), 2938 (w),
2876 (w), 1814 (s), 1744 (m), 1720 (s), 1366 (m), 1046 (s), 1015 (s), 684 (m). This oil
was used immediately in the next step.
4.3. 2,5-Heptanedione (4)
A solution of EtMgBr in THF (1M, 50 mL, 50 mmol) was added dropwise over 30
min to a stirred and cooled solution of 3 (9.91 g, 50 mmol) in dry THF (30 mL) at -60oC
under argon. After the addition, the mixture was stirred for further 30 min at -60oC.
Subsequently the cooling bath was removed, and the mixture was left to stand for 1 h
with stirring. The reaction was quenched by the addition of ice and NH4Cl solution,
and the mixture was extracted with Et2O. The Et2O solution was washed successively
with water and brine, dried (MgSO4), and concentrated in vacuo. The residues
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obtained from two runs were combined and distilled in vacuo to give 6.40 g (54% based
on 11.6 g of 3) of 4 as a colorless oil, bp 116-123oC/0.6 kPa; nD22=1.4264; νmax (film):
2978 (m), 2940 (m), 2909 (m), 1714 (s), 1414 (M), 1362 (m), 1166 (m), 1117 (m); δH
(CDCl3): 1.06 (3H, t, J=7.2 Hz), 2.18 (3H, s), 2.46-2.50 (2H, m), 2.65-2.74 (4H, m);
GC-MS [column: HP-5ms, 5% phenylmethylsiloxane, 0.25 mm x 30 m; carrier gas, He;
press. 61 kPa; temp: 70-230oC (+10oC/min)]: tR 5.13 min (88.1%); MS (70 eV, EI): m/z:
99 (100) [(M-C2H5)+] 85 (4), 71 (34), 57 (47), 43 (53). HRMS calc for C7H12O2:
128.0837, found: 128.0839.
4.4. 2,3-Dimethyl-2-cyclopenten-1-one (5)
A solution of 4 (9.52 g, 85 mmol) in 99% EtOH (30 mL) was added to a solution of
NaOH (2.0 g, 50 mmol) in water (100 mL). The mixture was stirred and heated under
reflux for 4.5 h. After cooling, the mixture was saturated with NaCl and extracted
with Et2O. The Et2O extract was washed with brine, dried (MgSO4), and concentrated
in vacuo. The residue was distilled to give 5.46 g (67%) of 5 as a colorless oil, bp
118-124oC/8.2 kPa (ref.4 bp 105-107oC/56 Torr); nD25=1.4844; νmax (film): 2919 (m),
2864 (w), 1698 (s), 1651 (m), 1442 (m), 1388 (m), 1330 (m), 1065 (m); δH (CDCl3):
1.66 (3H, s), 2.02 (3H, s), 2.34 (2H, m), 2.46 (2H, m); δC (CDCl3): 7.96, 17.27, 31.59,
34.26, 136.35, 170.02, 210.01; GC-MS (same conditions as those used for 4): tR 5.37
min (97.6%); MS (70 eV, EI): m/z: 110 (97) [M+], 95 (30), 81 (12), 67 (100), 54 (14), 53
(12), 39 (17). These spectral data were identical with those reported previously.4
4.5. (±)-2,3-Dimethyl-2-cyclopenten-1-ol (6)
Sodium borohydride (11.9 g, 314 mmol) was added portionwise over 15 min to a
stirred and ice-cooled solution of 5 (23.67 g, 215 mmol) and CeCl3·7H2O (120.0 g, 314
mmol) in MeOH (500 mL) at 10-15oC. After the addition, the mixture was stirred for
30 min at 5-10oC. It was then diluted with ice and brine and extracted with Et2O.
The Et2O extract was washed with water and brine, dried (MgSO4), and concentrated in
vacuo. The residue was distilled to give 19.53 g (81%) of (±)-6 as a colorless oil, bp
58-59oC/0.2 kPa; nD25=1.4731; νmax (film): 3326 (s), 2964 (s), 2914 (s), 2848 (s), 2737
(w), 1684 (w), 1442 (s), 1380 (m), 1330 (m), 1182 (m), 1063 (m), 1029 (m), 993 (m);
δH (CDCl3): 1.46-1.80 (2H, m), 1.65 (6H, s), 2.10-2.30 (2H, m), 2.32-2.45 (1H, m), 4.57
(1H, br. s); GC-MS (same conditions as those used for 4): tR 4.09 min (95.1%); MS (70
eV, EI): m/z: 112 (19) [M+], 111 (14), 97 (100), 79 (33), 77 (20), 55 (12), 43 (11), 41
(11). HRMS calc for C7H12O: 112.0888, found: 112.0880.
4.6. (±)-2,3-Dimethyl-1,6-heptadien-3-ol (8)
A solution of 2-bromopropene (7, 20 g, 165 mmol) in dry THF (50 mL) was added
dropwise to a stirred suspension of Mg turnings (4.1 g, 171 mmol) in dry THF (10 mL)
14

ACCEPTED MANUSCRIPT
containing a trace amount of I2 (10 mg). After adding 3 mL of the solution of 7, the
mixture was heated with a heat gun to initiate the reaction. Subsequently, the rest of
the solution was added slowly to maintain the refluxing of the mixture. The Grignard
reagent was then cooled with an ice-bath, and a solution of 5-hexen-2-one (15.0 g, 153
mmol) was added dropwise to the stirred and ice-cooled mixture. After the addition,
the mixture was stirred and heated at 40oC for 30 min. It was then cooled, poured onto
ice and dil HCl/NH4Cl solution, and extracted with Et2O. The Et2O solution was
washed successively with water, NaHCO3 solution and brine, dried (MgSO4), and
concentrated in vacuo. The residue was distilled to give 12.0 g (56%) of 8 as a
colorless oil, bp 57-59oC/0.4 kPa; nD26=1.4570; νmax (film): 3422 (br. s), 3079 (m),
2976 (s), 2944 (m), 1641 (m), 1446 (m), 1374 (m), 1110 (m), 997 (m), 905 (s);
(CDCl3): 1.32 (3H, s), 1.62 (1H, s), 1.64-1.70 (2H, m), 1.75 (3H, s), 1.90-2.15 (2H,
m), 4.82-5.10 (4H, m), 5.80-5.90 (1H, m); GC-MS (same conditions as those used for
4): tR 4.65 min (92.8%); MS (70 eV, EI): m/z: 125 (3) [(M-CH3)+], 107 (9), 97 (9), 86
(19), 85 (100), 69 (19), 57 (34), 43 (41). HRMS calc for C9H16O: 140.1201, found:
140.1205.
4.7. Lipase AK-catalyzed asymmetric acetylation of (±)-6 to give (R)-9 and (S)-6
Lipase AK Amano (400 mg) was added to a solution of (±)-6 (2.20 g, 20 mmol) and
vinyl acetate (4 mL, 3.7 g, 43 mmol) in (i-Pr)2O (40 mL). The mixture was stirred for
7 h at room temperature (22oC), and filtered to remove the enzyme, which was washed
thoroughly with Et2O. The combined filtrate and washings were concentrated in vacuo.
The residue (3.24 g) was chromatographed over Al2O3 (Wako Chemical 010-01525, 300
mesh, pH 9.0-11.0; 80 g). [CAUTION: Both (R)-9 and (S)-6 are very unstable against
acid. Use of silica gel or neutral alumina causes total decomposition of the products.]
Elution with pentane/EtOAc (100:1) gave (R)-9 (1.82 g, 56%). Further elution with
pentane/EtOAc (10:1) gave (S)-6 (1.05 g, 44%). These were purified by distillation to
give (R)-9 (482 mg) and (S)-6 (667 mg) both as colorless oils. They showed the
following properties. (R)-2,3-Dimethyl-2-cyclopentenyl acetate (9): bp 44oC/0.8 kPa;
nD22=1.4556; [α]D23 +53.4 (c 1.71, hexane); Chiral GC [Column: Chiramix®, 0.25 mm x
60 m; column temp: 40-180oC(+0.7oC/min); carrier gas, He; flow rate, 0.7 mL/min]: tR
98.3 min [11.4%, (S)-9], 98.7 min [88.6%, (R)-9], 77% ee; νmax (film): 2971 (m), 2917
(m), 2852 (m), 1734 (s), 1440 (m), 1371 (m), 1243 (s), 1015 (m), 990 (m), 968 (m), 876
(m); δH (CDCl3): 1.60 (3H, s), 1.68 (3H, s), 1.62-1.72 (1H, m), 2.04 (3H, s), 2.15-2.34
(2H, m), 2.38-2.48 (1H, m), 4.58 (1H, d-like, J=5.6 Hz); GC-MS (same conditions as
those used for 4): tR 6.42 min (86%); MS (70 eV, EI): m/z: 154 (<1) [M+], 97 (17), 95
(47), 94 (96), 93 (17), 91 (18), 79 (100), 77 (34), 67 (13), 43 (21), 39 (9). HRMS calc
15

ACCEPTED MANUSCRIPT
for C9H14O2: 154.0994, found: 154.1012. (S)-2,3-Dimethyl-2-cyclopenten-1-ol (6): bp
63-64oC/0.8 kPa; nD23=1.4742; [α]D23 -55.6 (c 1.61, hexane); Chiral GC (same
conditions as those used for 9 except that the column temp was increased at the rate of
+0.5oC/min): tR 118.0 min [95.5%, (S)-6], 119.90 min [4.5%, (R)-6], 91% ee; νmax
(film): 3230 (s), 2965 (s), 2914 (s), 2849 (s), 1684 (w), 1442 (m), 1063 (s), 1029 (m),
933 (s); δH (CDCl3): 1.640 (3H, s), 1.642 (3H, s), 1.52-1.70 (2H, m), 2.10-2.28 (2H, m),
2.38 (1H, m), 4.56 (1H, br s); GC-MS (same conditions as those used for 4): tR 4.09 min
(88.9%); MS (70 eV, EI): m/z: 112 (19) [M+], 111 (14), 97 (100), 94 (14), 91 (10), 79
(35), 77 (21), 55 (13), 43 (13), 41 (12). HRMS calc for C7H12O: 112.0888, found:
112.0879.
4.8. (±)-2-Methyl-2-cyclopenten-1-ol (10)
Sodium borohydride (1.80 g, 47 mmol) was added over 15 min to a stirred and
ice-cooled solution of commercially available 2-methyl-2-cyclopenten-1-one (TCI, 3.08
g, 32 mmol) and CeCl3·7H2O (17.5 g, 47 mmol) in MeOH (42 mL) at 5-10oC. The
mixture was stirred for 30 min at 5-10oC, and worked up as described for (±)-6 to give
(±)-10 (2.29 g, 73%) as a colorless oil, bp 60-61oC/1.6 kPa; nD23=1.4720; νmax (film):
3327 (s), 3039 (m), 2963 (s), 2939 (s), 2915 (s), 2855 (s), 1659 (w), 1449 (m), 1055 (s),
1031 (s), 973 (m), 823 (m); δH (CDCl3): 1.60-1.70 (2H, m), 1.76 (3H, s), 2.10-2.20 (1H,
m), 2.25-2.32 (1H, m), 2.32-2.46 (1H, m), 4.56 (1H, br. s), 5.50 (1H, s-like); GC-MS
[same conditions as those used for 4 except temp: 40-230oC (+6oC/min)]: tR 5.71 min
(99.0%); MS (70 eV, EI): m/z: 98 (53) [M+], 97 (46) [(M-H)+], 83 (100), 79 (29), 77
(12), 69 (16), 55 (30), 43 (18), 41 (22), 39 (20). HRMS calc for C6H10O: 98.0732,
found: 98.0722.
4.9. Lipase AK-catalyzed asymmetric acetylation of (±)-10 to give (R)-11 and
(S)-10
Lipase AK Amano (350 mg) was added to a solution of (±)-10 (2.29 g, 23 mmol)
and vinyl acetate (2 mL, 1.85 g, 21.5 mmol) in (i-Pr)2O (35 mL). The mixture was
stirred for 3 h at room temperature (22oC), and filtered to remove the enzyme, which
was washed thoroughly with Et2O. The combined organic solution was concentrated
in vacuo. The residue (2.72 g) was chromatographed over Al2O3 (Wako 010-01525, 40
g). Elution with pentane/EtOAc (100:1) gave (R)-11 (1.13 g, 35%). Further elution
with pentane/EtOAc (10:1) gave (S)-10 (1.07 g, 47%), both as colorless oils. They
showed the following properties. (R)-2-Methyl-2-cyclopentenyl acetate (11): bp
65-66oC/2.3 kPa; nD23=1.4490; [α]D21 +67.1 (c 4.77, hexane); Chiral GC [same
conditions as those used for (R)-9]: tR 81.4 min [96.4%, (R)-11], 89.6 min [3.6%, (S)-11],
93% ee; νmax (film): 3045 (w), 2970 (m), 2942 (m), 2920 (m), 2859 (m), 1735 (s),
16

ACCEPTED MANUSCRIPT
1438 (m), 1372 (m), 1243 (s), 1047 (m), 1027 (s), 974 (m), 833 (m), δH (CDCl3): 1.71
(3H, s), 1.70-1.79 (1H, m), 2.05 (3H, s), 2.20-2.30 (1H, m), 2.31-2.50 (2H, m), 5.58 (1H,
t, J=5.2 Hz), 5.65 (1H, s); GC [same conditions as those used for (±)-10]: tR 10.14 min
(99.0%); MS (70 eV, EI): m/z: 140 (<1) [M+], 97 (15), 83 (20), 81 (41), 80 (100), 79
(82), 77 (13), 53 (9), 43 (34), 41 (11), 39 (9). HRMS calc for C8H12O2: 140.0837,
found: 140.0853. (S)-2-Methyl-2-cyclopenten-1-ol (10): bp 67-68oC/2.7 kPa:
nD23=1.4710; [α]D22 -58.2 (c 3.02, hexane); Chiral GC [column:
heptakis-(2,3-di-O-acetyl-6-O-t-butyldimethylsilyl)-β-cyclodextrin, 0.25 mm x 30 m;
column temp: 40-180oC (+0.5oC/min); carrier gas, He; flow rate, 0.7 mL/min]: 61.2 min
[12.2%, (R)-10], 65.4 min [87.7%, (S)-10], 76% ee; νmax (film): 3327 (br. s), 3039 (m),
2963 (s), 2939 (s), 2915 (s), 2855 (s), 1659 (w), 1449 (m), 1055 (s), 1031 (s), 973 (m),
824 (s); δH (CDCl3): 1.60-1.70 (2H, m), 1.76 (3H, s), 2.10-2.20 (1H, m), 2.22-2.42 (2H,
m), 4.56 (1H, s), 5.50 (1H, s-like); GC-MS [same conditions as used for (S)-6]: tR 5.68
min (96.9%); MS (70 eV, EI): m/z: 98 (52) [M+], 97 (46), 83 (100), 79 (30), 77 (13), 69
(15), 55 (30), 43 (18), 41 (22), 39 (21). HRMS calc for C6H10O: 98.0732, found:
98.0725.
4.10. (R)-2,3-Dimethyl-2-cyclopenten-1-ol (6) via methanolysis of (R)-9
Potassium carbonate (700 mg, 4 mmol) was added to a solution of (R)-9 (92.8% ee,
348 mg, 2.3 mmol) in MeOH (5 mL). The mixture was stirred for 3 h at room
temperature (22oC). It was then concentrated in vacuo, diluted with water, and
extracted with Et2O. The extract was washed successively with water and brine, dried
(MgSO4), and concentrated in vacuo to give 202 mg (80%) of (R)-6 as a colorless oil,
[α]D22 +43.1 (c 1.98, hexane); Chiral GC [same conditions as those used for (S)-6]: tR
118.3 min [10.0%, (S)-6], 119.6 min [90.0%, (R)-6], 80% ee. Its spectral data were
identical to those of (S)-6. The reason was unclear why the unexpected partial
racemization took place in the present step.
4.11. (R)-2-Methyl-2-cyclopenten-l-ol (10) via methanolysis of (R)-11
In the same manner as described above for (R)-6, a mixture of (R)-11 (770 mg, 5
mmol) and K2CO3 (1.40 g, 9 mmol) in MeOH (10 mL) was stirred for 3 h at room
temperature (22oC). Subsequent work-up yielded 430 mg (80%) of (R)-11 as a
colorless oil, [α]D21 +68.9 (c 3.65, hexane); Chiral GC [same conditions as those used
for (S)-10]: tR 60.8 min [96.7%, (R)-11], 66.0 min [3.3%, (S)-11], 93% ee. Its spectral
data were identical to those of (S)-11.
4.12. Lipase AK-catalyzed asymmetric acetylation of (±)-6 in a preparative scale
to give (R)-9 and (S)-6
4.12.1. Asymmetric acetylation of (±)-6. Lipase AK Amano (3.0 g) was added to a
17

ACCEPTED MANUSCRIPT
solution of (±)-6 (19.5 g, 174 mmol) and vinyl acetate (30.0 g, 349 mmol) in (i-Pr)2O
(300 mL). The mixture was stirred for 4.5 h at room temperature (22oC), and filtered
to remove the enzyme, which was washed with Et2O. The combined filtrate and
washings were concentrated in vacuo. The residue was chromatographed over Al2O3
(Wako Chemial, 010-01525, 300 mesh, pH 9.0-11.0; 200 g). Elution with
pentane/EtOAc (100:1) gave 15.9 g (62%) of (R)-9 (ca. 75% ee) as a colorless oil.
Further elution with pentane/EtOAc (4:1) gave 6.24 g (32%) of (S)-6 (77% ee) as an oil.
4.12.2. Methanolysis of (R)-9 to give (R)-6. Potassium carbonate (50.0 g, 362 mmol)
was added to a solution of (R)-9 (ca. 75% ee, 15.9 g, 103 mmol) in MeOH (150 mL)
and H2O (10 mL). The mixture was stirred for 2 h at 35-40oC. Subsequent work-up
in the same manner as described in 4.10 gave 16.95 g of an oil. This was
chromatographed over Al2O3 (Wako Chemical, 010-01525, 170 g). Elution with
pentane gave hydrocarbon byproducts (7.09 g) obtained by elimination of AcOH from
(R)-9. Further elution with pentane/EtOAc (4:1) gave 7.12 g (61%) of (R)-6 (ca. 70%
ee).
4.12.3. Lipase AK-catalyzed asymmetric acetylation of (R)-6 of ca. 70% ee to give
(R)-9 of 94% ee. Lipase AK Amano (1.0 g) was added to a solution of (R)-6 (ca. 70%
ee, 6.34 g, 57 mmol) and vinyl acetate (6.0 g, 70 mmol) in (i-Pr)2O (100 mL). The
mixture was stirred for 3 h at room temperature (22oC). Further work-up in the same
manner as described in 4.9 gave 7.35 g of an oil. This was chromatographed over
Al2O3 (Wako Chemical, 010-01525, 150 g). Elution with pentane/EtOAc (100:1) gave
4.00 g (46%) of (R)-9, and further elution with pentane/EtOAc (3:1) gave 2.94 g of the
recovered impure 6. The acetate (R)-9 was distilled to give 2.57 g {42% recovery
based on the starting 6 or 9.6% based on (±)-6 [19% recovery of the existing (R)-6]} of
(R)-9, bp 63-65oC/0.8 kPa; nD23=1.4560; [α]D23 +68.4 (c 1.42, hexane); Chiral GC
[same conditions as used for (R)-9 in 4.7]: tR 102.2 [3.1%, (S)-9], 102.6 min [96.9%,
(R)-9], 94% ee; Chemical purity by GC [same conditions as used for (R)-9 in 4.7]: tR
6.37 min (88.1%). Its IR, 1H NMR and MS data were identical with those reported in
4.7. δC (CDCl3): 11.26, 14.27, 21.38, 29.43, 35.77, 84.25, 129.33, 138.94, 171.36.
HRMS calc for C9H14O2: 154.0994, found: 154.1007.
4.12.4. Lipase AK-catalyzed asymmetric acetylation of (S)-6 of ca. 77% ee to give
(S)-6 of 94% ee. Lipase AK Amano (2.0 g) was added to a solution of (S)-6 (ca. 77%
ee, 11.6 g, 103 mmol) and vinyl acetate (8.90 g, 103 mmol) in (i-Pr)2O (200 mL). The
mixture was stirred for 4 h at room temperature (22oC). Further work-up in the same
manner as described in 4.9 gave 12.7 g of an oil. This was chromatographed over
Al2O3 (Wako Chemical, 010-01525, 200 g). Elution with pentane/EtOAc (100:1) gave
18

ACCEPTED MANUSCRIPT
4.10 g of (S)-9 of low ee. Further elution with pentane/EtOAc (3:1) gave 6.58 g [57%
recovery based on the starting alcohol or 33.7% based on (±)-6 or 67% recovery of (S)-6
in the starting (±)-6] of (S)-6 of ca. 94% ee, [α]D24 -58.8 (c 1.87, hexane); Chemical
purity by GC [same conditions as those described for (S)-6 in 4.7]: tR 4.03 min (99.5%).
This was employed for the next step without distillation.
4.13. (S)-2,3-Dimethyl-2-cyclopentenyl acetate (9) by chemical acetylation of (S)-6
Acetic anhydride (15 mL) was added to a solution of the above described (S)-6 (6.49
g, 57.9 mmol) in dry C5H5N (40 mL). After the exothermic reaction, the mixture was
stirred for 2 h at 40oC. It was then cooled, poured into ice and water, and extracted
with Et2O. The Et2O solution was washed successively with water, CuSO4 solution,
NaHCO3 solution and brine, dried (MgSO4), and concentrated in vacuo. The residue
22
was distilled to give 5.50 g (62%) of (S)-9, bp 61-63oC/0.8 kPa; nD22=1.4572; [α]D
-59.1 (c 1.36, hexane); Chiral GC [same conditions as those used for (R)-9]: tR 102.1
[96.9%, (S)-9], 102.8 min [3.1%, (R)-9], 94% ee; δC (CDCl3): 11.26, 14.27, 21.39, 29.43,
35.77, 84.26, 129.32, 138.97, 171.38. Its IR, 1H NMR and MS data were identical
with those of (R)-9. Chemical purity by GC [same conditions as those used for (R)-9]:
tR 2.90 (11%), 4.03 (21%), 6.39 min [68%, (S)-9]. HRMS calc for C9H14O2: 154.0994,
found: 154.1003.
4.14. 2-(1,2-Dimethyl-2-cyclopentenyl)acetic acid (16)
4.14.1. (S)-Isomer. A solution of LiN(i-Pr)2 (TCI, 1.5 M in THF, PhEt and heptane, 36
mL, 54 mmol) was added dropwise over 15 min to a stirred and cooled solution of (S)-9
(5.38 g, 34.9 mmol) and TMSCl (18.3 mL=15.7 g, 145 mmol) in dry THF (25 mL) at
-78 to -60oC under argon. The mixture was stirred for 15 min at -78oC, and allowed to
reach room temperature. It was then stirred and heated at 60oC (bath temperature) for
3 h. After cooling, MeOH (22 mL) was added dropwise, keeping the inner
temperature below 40oC. The mixture was placed in a separatory funnel, and the acid
16 was extracted with 5% NaOH solution (35 mL x 3). The alkaline solution was
washed with Et2O, and the aqueous layer was acidified with dil HCl (containing 25 mL
of conc HCl) and ice. The separated acid was extracted with Et2O. The extract was
washed successively with water and brine, dried (MgSO4), and concentrated in vacuo to
give 3.00 g (56%) of crude (S)-16 as a slightly yellowish oil, [α]D21 -16.4 (c 1.79, Et2O);
νmax (film): 3040-2690 (br m), 1705 (s), 1439 (m), 1409 (m), 1287 (m), 1253 (m), 920
(m). This was used in the next step without further purification.
4.14.2. (R)-Isomer. In the same manner as described above (R)-9 (2.30 g, 14.9
mmol), 1.5 M LiN(i-Pr)2 (13.3 mL, 19.9 mmol) and TMSCl (7.6 mL, 60 mmol) in THF
(10 mL) gave 0.68 g (30%) of crude (R)-16, [α]D21 +16.9 (c 1.65, Et2O). Its IR
19

ACCEPTED MANUSCRIPT
spectrum was identical with those of (S)-16. This was used in the next step without
further purification.
4.15. Enantiomers of methyl 2-(1,2-dimethyl-2-cyclopentenyl)acetate (17)
4.15.1. (S)-Isomer. Potassium carbonate (7.0 g, 51 mmol) and MeI (12.0 g, 84.5
mmol) were added to a solution of crude (S)-16 (3.00 g, 19.5 mmol) in DMF (10 mL)
and acetone (30 mL). The mixture was stirred for 2 d at room temperature. After
removing acetone in vacuo, the mixture was diluted with water, and extracted with Et2O.
The Et2O solution was washed with brine, dried (MgSO4), and concentrated in vacuo.
The residue was distilled to give 2.08 g [64% or 35% based on (S)-9] of (S)-17 as a
colorless oil, bp 74-77oC/0.7 kPa: nD23=1.4552; [α]D23 -17.8 (c 1.36, hexane); νmax
(film): 3038 (w), 2954 (s), 2851 (m), 1739 (vs), 1437 (m), 1218 (s), 1165 (m), 1131 (m),
1018 (m), 846 (m); δH (CDCl3): 1.09 (3H, s), 1.62 (3H, s), 1.64-1.74 (1H, m), 2.06-2.14
(1H, m), 2.16-2.22 (2H, m), 2.27 (1H, d, J=13 Hz), 2.35 (1H, d, J=13 Hz), 3.64 (3H, s),
5.30 (1H, br s); δC (CDCl3): 12.41, 24.95, 29.23, 37.13, 43.28, 48.46, 51.33, 124.71,
145.44, 172.93; GC-MS (same conditions as those used for 4): tR 6.89 min (87.1%); MS
(70eV, EI): m/z: 168 (21) [M+], 96 (8), 95 (97), 94 (100), 93 (28), 91 (13), 79 (32), 77
(13), 67 (16), 55 (7). HRMS calc for C10H16O2: 168.1150, found: 168.1149.
4.15.2. (R)-Isomer. In the same manner as described above, (R)-16 (1.34 g, 8.7
mmol), K2CO3 (3.4 g, 25 mmol) and MeI (6.8 g, 48 mmol) gave 988 mg (68%) of
(R)-17 as a colorless oil, bp 70-72oC/0.7 kPa; nD22=1.4562; [α]D21 +16.7 (c 1.33,
hexane): Its IR, 1H NMR and MS data were identical with those of (S)-17. δC
(CDCl3): 12.42, 24.95, 29.23, 37.13, 43.28, 48.47, 51.33, 124.71, 145.44, 172.93;
GC-MS (same conditions as those used for 4): tR 6.88 min (81%). HRMS calc for
C10H16O2: 168.1150, found: 168.1149.
4.15.3. Racemate. Ring closing metatheses of (±)-19 gave (±)-17 as a colorless oil,
bp 78-80oC/1 kPa; δC (CDCl3): 12.41, 24.94, 29.22, 37.12, 43.27, 48.46, 51.31, 124.70,
145.42, 172.91. HRMS calc for C10H16O2: 168.1150, found: 168.1168.
4.16. (±)-Methyl (1,2-dimethyl-2,3-epoxycyclopentyl)acetate (20)
m-Chloroperbenzoic acid (MCPBA, 70% pure, 18.8 g, 76 mmol) was added
portionwise over 15 min to a stirred and cooled (ice-salt bath) solution of (±)-17 (10.6 g,
63.1 mmol) in CH2Cl2 (150 mL) at <15oC. The mixture was stirred for 45 min at
-10oC, and filtered. The filter cake was thoroughly washed with pentane. The
combined filtrate and washings were successively washed with NaHCO3 solution and
brine, dried (MgSO4), and concentrated in vacuo. The residue was chromatographed
over SiO2 (70 g). Elution with pentane/EtOAc (20:1) gave 8.01 g (69%) of (±)-20 as a
colorless oil, nD23=1.4532; νmax (film): 2955 (s), 2876 (m), 1738 (s), 1439 (s), 1199 (s),
20

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1097 (m), 1014 (m), 837 (m); δH (CDCl3): 1.03 (1.8H, s), 1.12 (1.2H, s), 1.31 (1.8H, s),
1.32 (1.2H, s), 1.20-1.42 (1H, m), 1.50-1.72 and 1.82-1.92 (total 2H, m), 2.24 (1H, s),
2.38-2.48 (2H, m), 3.26 (1H, s, J=14 Hz), 3.65 (3H, s); δC (CDCl3): 12.96, 13.04, 20.86,
21.87, 25.42, 25.82, 31.89, 32.78, 40.64, 41.49, 42.56, 42.86, 51.48, 51.62, 63.82, 64.63,
68.23, 68.37, 172.27, 172.86; GC-MS (same conditions as those used for 4): tR 8.60
(41.2%), 8.88 min (55.3%); MS of (±)-20 with tR=8.60 min (70 eV, EI): m/z: 184 (<1)
[M+], 169 (4), 153 (15), 125 (91), 111 (83), 110 (100), 109 (75), 95 (52), 81 (19), 67
(21), 55 (38), 43 (59), 41 (28); MS of (±)-20 with tR=8.88 min (70 eV, EI); m/z: 184
(<1) [M+], 169 (6), 153 (6), 125 (92), 111 (41), 110 (100), 109 (77), 95 (51), 81 (19), 67
(19), 55 (36), 43 (53), 41 (26). HRMS calc for C10H16O3: 184.1099, found: 184.1114
(short tR), 184.1115 (long tR).
4.17. (±)-Methyl (1,2-dimethyl-3-oxocylopentyl)acetate (21)
4.17.1. Rearrangement of (±)-20. A solution of (±)-20 (8.01 g, 43.5 mmol) in dry
CH2Cl2 (30 mL) was added dropwise over 15 min to a stirred and ice-cooled solution of
BF3·OEt2 (1.8 mL, 2.0 g, 14 mmol) in dry CH2Cl2 (120 mL) at 8-11oC under argon.
After the addition, the pale orange-colored solution was stirred for 5 min at 7oC, and
then quenched with sat. NaHCO3 solution (50 mL). The mixture was stirred for 1 h at
room temperature. The CH2Cl2 layer was separated, and the aqueous layer was
extracted with Et2O. The combined organic solution was washed with brine, dried
(MgSO4), and concentrated under atmospheric pressure with a Vigreux column. The
residue was distilled to give 6.62 g (83%) of (±)-21 as a colorless oil, bp 90-93oC/0.3
kPa; nD23=1.4610. Its IR, 1H NMR and MS spectra were identical with those reported
previously.4 δC (CDCl3): 7.89, 8.29, 19.76, 25.86, 32.14, 33.08, 34.84, 34.98, 38.68,
44.86, 51.56, 55.97, 171.97, 172.32, 219.44, 219.93; GC-MS (same conditions as those
used for 4): tR 9.88 (51.1%), 10.09 min (48.9%). HRMS calc for C10H16O3: 184.1099,
found: 184.1083 (short tR), 184.1087 (long tR).
4.17.2. Hydroboration-oxidation of (±)-17. A solution of BH3·THF (0.9 , 50 mL,
M
45 mmol) was added dropwise over 15 min to a stirred and ice-cooled solution of (±)-17
(12.9 g, 76.8 mmol) in dry Et2O (50 mL) at 5-10oC under argon. The mixture was
stirred for 3 h at room temperature (22oC). Water (15 mL) was added dropwise over 5
min to a stirred and ice-cooled mixture, which was further stirred for 5 min to destroy
excess BH3. The mixture was then concentrated in vacuo to remove Et2O and THF.
The residue was diluted with Et2O (100 mL), acetone (50 mL), and water (50 mL).
The mixture was stirred and cooled in an ice-bath. Jones CrO3 (45 mL, 360 mequiv)
was added dropwise over 20 min to the stirred and ice-cooled solution until red color
persisted. The mixture was further stirred for 10 min, and MeOH (20 mL) was added
21

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to destroy the excess CrO3. Then the mixture was diluted with water and extracted
with Et2O. The Et2O extract was washed successively with water, NaHCO3 solution
and brine, dried (MgSO4), and concentrated in vacuo. The residue was distilled to give
8.0 g (57%) of (±)-21 as a colorless oil, bp 78-85oC/0.2 kPa. Its spectral data
coincided with those reported previously.4 GC purity: 82.7% (tR 9.90 min/ tR 10.08
min =100:82). HRMS calc for C10H16O3: 184.1099, found: 184.1112 (short tR),
184.1107 (long tR).
4.18. (±)-Methyl (1,2-dimethyl-3-methylenecyclopentyl)acetate (±)-22
4.18.1. With Lombardo’s CH2Br2/Zn/TiCl4 reagent. (a) Activation of Zn. Zinc
powder (Wako Chemical, 25 g) was stirred with 2% HCl (60 mL) for 1 min, and
collected on a filter by vacuum filtration. The zinc powder was placed into a beaker,
and washed successively with 2% HCl (60 mL), pure water (60 mL), 99% EtOH (40
mL) and Et2O (40 mL). After removing Et2O by decantation, the remaining zinc
powder was dried in vacuo (0.13 kPa) for 2 d over blue silica. (b) Preparation of the
reagent. The activated and dried zinc powder (20.2 g, 310 mmol), CH2Br2 (7.1 mL,
100 mmol) and dry THF (175 mL) were placed in a 500 mL flask under argon. The
mixture was stirred and cooled at -40oC. Titanium tetrachloride (8.0 mL, 82 mmol)
was added dropwise to the stirred mixture at -40oC to give a dark slurry. The mixture
was stirred at -5oC for 3 d. It was then diluted with dry CH2Cl2 (35 mL) with cooling
in an ice-bath. (c) Reaction with (±)-21. A solution of (±)-21 (6.60 g, 35.9 mmol) in
dry CH2Cl2 (25 mL) was added to the stirred and ice-cooled slurry of the above reagent
over 10 min. The dark mixture was stirred for 1.5 h at room temperature (22oC), and
diluted with Et2O (200 mL). The mixture was added slowly to a stirred slurry of
NaHCO3 (75 g, 890 mmol) in water (40 mL) in a beaker. (CAUTION: Foaming !),
and the mixture was stirred for 1 h. Then the mixture was filtered through Celite, and
the Celite layer was washed with Et2O. The combined filtrate and washings were
washed with water and brine, dried (MgSO4), and concentrated under atmospheric
pressure with a Vigreux column. The residue was chromatographed over SiO2 (60 g).
Elution with pentane/EtOAc (20:1) gave 5.61 g (86%) of (±)-22 as a colorless oil. Its
spectral properties were identical with those reported previously. GC-MS (same
conditions as used for 4): tR 8.38 (52.1%), 8.50 min (31.4%). HRMS calc for
C11H18O2: 182.1307, found: 182.1322 (short tR), 182.1323 (long tR).
4.18.2. With Yan’s CH2Cl2/Mg/TiCl4 reagent. A solution of (±)-21 (4.27 g, 23.2
mmol) in dry CH2Cl2 (30 mL) and dry THF (20 mL) was added dropwise over 20 min
to a stirred and ice-cooled mixture of magnesium powder (Aldrich, 4.45 g, 186 mmol),
TiCl4 (4.9 mL, 46 mmol) and dry CH2Cl2 (50 mL) at 0-5oC under argon. The mixture
22

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was stirred for 30 min at 0-5oC and for another 30 min at room temperature to give a
dark green solution. The reaction was quenched by addition of a slurry of NaHCO3
(22 g, 297 mmol) and water (20 mL) under ice-cooling (CAUTION: Foaming !), and
diluted with Et2O (100 mL). The mixture was filtered through Celite, which was
washed with Et2O, and the filtrate was extracted with Et2O. The organic solution was
washed with water and brine, dried (MgSO4), and concentrated. The residue (ca. 5.82
g) was chromatographed over SiO2 (70 g). Elution with pentane/EtOAc (30:1) gave
1.41 g (33%) of (±)-22 as a colorless oil. Its spectral data were identical with those of
(±)-22.4
4.19. (±)-2-(1,2-Dimethyl-3-methylenecyclopentyl)ethanol (23).
A solution of (±)-22 (7.52 g, 41.3 mmol) in dry Et2O (50 mL) was added dropwise
over 15 min to a stirred and ice-cooled suspension of LiAlH4 (1.20 g, 31.6 mmol) in dry
Et2O (50 mL) at 5-15oC. The mixture was stirred for 10 min at 0-5oC and for 1 h at
room temperature (21oC). It was then ice-cooled, and the excess LiAlH4 was
destroyed by dropwise addition of water (20 mL). The mixture was acidified with dil
HCl and ice, and extracted with Et2O. The Et2O solution was washed successively
with water, NaHCO3 solution and brine, dried (MgSO4), and concentrated under
atmospheric pressure with a Vigreux column. The residue was distilled to give 5.21 g
(82%) of (±)-23 as a colorless oil, bp 105-110oC/1.2 kPa. Its spectral data were
identical with those reported previously.4 Its GC purity was ca. 100%
[(±)-anti-23/(±)-syn-23=1.2:1]. A sample (7.15 g) of (±)-23 was stored for further
biological use.
The oily (±)-23 (5.21 g) prepared similarly was chromatographed over SiO2 (70 g).
Elution with pentane/EtOAc (20:1) gave 0.95 g (18%) of (±)-anti-23 rich fraction
(anti/syn= 93:7-90:10 as judged by GC). The later eluting anti/syn mixture was
rechromatographed over SiO2 (60 g). Elution with pentane/EtOAc (20:1) gave 1.41 g
(27%) of anti rich fraction (anti/syn= 93:7). The (±)-anti-23-rich fractions were
combined (45%) and used for the next step.
4.20. (±)-2-(anti-1,2-Dimethyl-3-methylenecyclopentyl)ethyl 3,5-dinitrobenzoate
(24)
3,5-Dinitrobenzoyl chloride (4.60 g, 20 mmol) and DMAP (50 mg, 0.41 mmol) were
added to a stirred and ice-cooled solution of (±)-anti-23 (93% pure, 2.10 g, 13.6 mmol)
in dry C5H5N (25 mL). The mixture was stirred for 3 h at 0-5oC, diluted with ice and
water, and extracted with Et2O. The Et2O extract was washed successively with water,
dil HCl, NaHCO3 solution and brine, dried (MgSO4), and concentrated in vacuo to give
5.35 g (quant.) of a solid, which was recrystallized from EtOAc/hexane to give 1.61 g of
23

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the first crop of 24 as leaflets, 1.68 g of the second crop of 24 as fine leaflets, and 0.24 g
of the third crop of 24 as fine crystals. The yield of 24 was 3.53 g (74%). The first
crop melted at 62-64oC, and its IR, 1H and 13C NMR spectra were identical with those
reported previously.4
4.21. (±)-2-(anti-1,2-Dimethyl-3-methylenecyclopentyl)ethanol (23)
Crystalline (±)-anti-24 (3.35 g, 9.63 mmol) was added to a solution of NaOH (1.60
g, 40 mmol) in MeOH/H2O [1:1 (v/v), 15 mL]. The mixture was stirred and heated
under reflux for 30 min to give a dark red solution. This was diluted with water, and
extracted with Et2O. The Et2O solution was washed with water and brine, dried
(MgSO4), and concentrated under atmospheric pressure with a Vigreux column. The
residue was distilled in vacuo to give 1.15 g (77%) of (±)-anti-23 (anti/syn=100:7 by
GC analysis) as a colorless oil, bp 108-110oC/1.6 kPa; nD24=1.4782; νmax (film): 3328
(br s), 3072 (w), 2956 (s), 2871 (s), 1655 (m), 1454 (s), 1379 (m), 1054 (s), 1037 (s),
1000 (m), 878 (s); δH (CDCl3): 0.94 (3H, d, J= 7.2 Hz), 1.00 (3H, s), 1.20-1.39 (4H, m),
1.66-1.74 (1H, m), 1.96-2.06 (1H, br), 2.22-2.43 (2H, m), 3.63-3.80 (2H, t-like), 4.74
(1H, s), 4.82 (1H, s); δC (CDCl3): 12.16, 25.12, 29.24, 35.17, 36.13, 42.76, 50.66, 60.32,
104.82, 157.15; GC-MS (same conditions as those used for 4): tR 8.31 min (91.8%); MS
(70 eV, EI): m/z: 154 (<1) [M+], 121 (25), 110 (48), 109 (100), 108 (28), 107 (25), 95
(24), 93 (37), 79 (26), 67 (43), 41 (25). HRMS calc for C10H18O: 154.1358, found:
154.1344. A sample (1.09 g) of (±)-anti-23 was stored for further biological use.
4.22. Enantiomers of methyl (1,2-dimethyl-2,3-epoxycyclopentyl)acetate (20)
4.22.1. (1S,2RS,3SR)-Isomer. In the same manner as described in 4.16 for (±)-20,
(S)-17 (2.00 g, 11.9 mmol) in CH2Cl2 (30 mL) was epoxidized with MCPBA (3.20 g, 15
mmol) to give 2.04 g (93%) of (1S,2RS,3SR)-20 as a colorless oil. Its IR and MS data
were identical with those of (±)-20. GC-MS (same conditions as those used for 4): tR
8.56 (33.7%), 8.84 min (59.6%). HRMS calc for C10H16O3: 184.1099, found:
184.1103 (short tR), 184.1096 (long tR).
4.22.2. (1R,2SR,3RS)-Isomer. In the same manner as described in 4.16 for (±)-20,
(R)-17 (1.00 g, 0.59 mmol) in CH2Cl2 (15 mL) was epoxidized with MCPBA (1.60 g,
7.5 mmol) to give 0.99 g (90%) of (1R,2SR,3RS)-20 as a colorless oil. Its IR and MS
data were identical with those of (±)-20. GC-MS (same conditions as those used for
4): tR 8.56 (37.6%), 8.83 min (50.0%). HRMS calc for C10H16O3: 184.1099, found:
184.1100 (short tR), 184.1098 (long tR).
4.23. Enantiomers of methyl (1,2-dimethyl-3-oxocyclopentyl)acetate (21)
4.23.1. (1S,2RS)-Isomer. In the same manner as described in 4.17.1,
(1S,2RS,3SR)-20 (1.85 g, 10.1 mmol) in CH2Cl2 (10 mL) was treated with BF3·OEt3
24

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(0.6 mL, 0.67 g, 4.7 mmol) in CH2Cl2 (30 mL) to give 1.85 g (quant.) of (1S,2RS)-21 as
a colorless oil, [α]D24 -2.35 (c 1.67, hexane). Its IR and MS data were identical with
those of (±)-21. GC-MS (same conditions as those used for 4): tR 9.86 (47.9%), 10.07
min (46.0%). HRMS calc for C10H16O3: 184.1099, found: 184.1098 (short tR),
184.1096 (long tR).
4.23.2. (1R,2SR)-Isomer. In the same manner as described in 4.17.1,
(1R,2SR,3RS)-20 (0.99 g, 5.38 mmol) in CH2Cl2 (5 mL) was treated with BF3·OEt2 (0.3
mL, 0.33 g, 2.4 mmol) in CH2Cl2 (15 mL) to give 0.92 g (93%) of (1R,2SR)-21 as a
colorless oil, [α]D24 +1.30 (c 1.46, hexane). Its IR and MS data were identical with
those of (±)-21. GC-MS (same conditions as those used for 4): tR 9.82 (43.2%), 10.03
min (49.8%). HRMS calc for C10H16O3: 184.1099, found: 184.1097 (short tR),
184.1093 (long tR).
4.24. Enantiomers of methyl (1,2-dimethyl-3-methylenecyclopentyl)acetate (22)
4.24.1. (1S,2RS)-Isomer. In the same manner as described in 4.18.1, (1S,2RS)-21
(1.84 g, 10 mmol) in CH2Cl2 (10 mL) was added to the stirred and ice-cooled Lombardo
reagent (70 mL) under argon to give 1.33 g (72%) of (1S,2RS)-22 as a colorless oil,
[α]D23 -20.1 (c 1.50, hexane). Its IR and MS data were identical with those of (±)-22.
GC-MS (same conditions as those used for 4): tR 8.34 (49.8%), 8.51 min (41.8%).
HRMS calc for C11H18O2: 182.1307, found: 182.1305 (short tR), 182.1309 (long tR).
4.24.2. (1R,2SR)-Isomer. In the same manner as described in 4.18.1, (1R,2SR)-22
(0.91 g, 4.9 mmol) in CH2Cl2 (5 mL) was added to the stirred and ice-cooled Lombardo
reagent (35 mL) under argon to give 0.41 g (46%) of (1R,2SR)-22 as a colorless oil,
[α]D24 +17.6 (c 0.64, hexane). Its IR and MS data were identical with those of (±)-22.
GC-MS (same conditions as those used for 4): tR 8.34 (45.6%), 8.51 min (40.9%).
HRMS calc for C11H18O2: 182.1307, found: 182.1306 (short tR), 182.1308 (long tR).
4.25. Enantiomers of 2-(1,2-dimethyl-3-methylenecyclopentyl)ethanol (23)
4.25.1. (1S,2RS)-23 and its purification to give (1S,2S)-23. In the same manner as
described in 4.19, (1S,2RS)-22 (1.16 g, 6.37 mmol) in dry Et2O (10 mL) was added to a
stirred and ice-cooled suspension of LiAlH4 (250 mg, 6.6 mmol) in dry Et2O (10 mL) to
give 0.93 g (95%) of (1S,2RS)-23, [α]D22 +5.4 (c 1.40, hexane), as a colorless oil.
This was chromatographed over SiO2 (25 g). Elution with pentane/EtOAc (20:1) gave
(1S,2S)-23 (82 mg), a mixture of (1S,2S)- and (1S,2R)-23 (646 mg) and (1S,2R)-23 (93
mg). The mixture (646 mg) was rechromatographed over SiO2 (25 g). Elution with
pentane/EtOAc (20:1) gave (1S,2S)-23 (79 mg), a mixture of (1S,2S)- and (1S,2R)-23
(277 mg), and (1S,2R)-23 (215 mg). The mixture (277 mg) was further
rechromatographed over SiO2 (10 g). Elution with pentane/EtOAc (20:1) gave
25

ACCEPTED MANUSCRIPT
(1S,2S)-23 (123 mg). All the (1S,2S)-23 fractions were combined to give 284 mg
(30%) of (1S,2S)-23, nD24=1.4762; [α]D26 -26.7 (c 0.52, hexane); νmax (film): 3346 (br
m), 3072 (w), 2960 (s), 2871 (s), 1655 (m), 1455 (m), 1379 (m), 1125 (m), 1054 (m),
1036 (m), 877 (s); δC (CDCl3): 12.17, 25.13, 29.25, 35.18, 36.16, 42.78, 50.67, 60.36,
104.83, 157.16. Its 1H NMR and MS spectra were identical with those of (±)-anti-23.
GC-MS (same conditions as those used for 4): tR 8.28 min (91.6%). HRMS calc for
C10H18O2: 154.1358, found: 154.1365. (1S,2R)-23 was not purified further. Its
specific rotation was [α]D26 +45.4 (c 0.65, hexane) in one case and [α]D26 +37.8 (c 0.53,
hexane) in another case. νmax (film): 3853 (br m), 3073 (w), 2960 (s), 2937 (s), 2872
(m), 1655 (m), 1454 (m), 1379 (m), 1054 (m), 1037 (s), 1008 (m), 876 (s).
4.25.2. (1R,2SR)-23. In the same manner as described in 4.19, (1R,2SR)-21 (0.31 g,
1.7 mmol) in dry Et2O (5 mL) was added to a stirred and ice-cooled suspension of
LiAlH4 (100 mg, 2.6 mmol) in dry Et2O (5 mL) to give 0.23 g (88%) of (1R,2SR)-23,
23
[α]D -6.67 (c 0.58, hexane). Its spectral data were identical with those of
(1S,2RS)-23. Due to the scarcity of the material, (1R,2SR)-23 was not purified by SiO2
chromatography. GC-MS (same conditions as those used for 4): tR 8.27 (50.9%), 8.43
min (48.0%). HRMS calc for C10H18O: 154.1358, found: 154.1365 (short tR),
154.1364 (long tR).
4.26. Enantiomers of 2-(1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde (1).
4.26.1. (1S,2S)-Isomer. Diacetoxyiodobenzene (DAIB, 354 mg, 1.10 mmol) was
added to a stirred solution of (1S,2S)-23 (128 mg, 0.83 mmol) and azadol (15 mg, 0.1
mmol) in CH2Cl2 (5 mL). The mixture was stirred for 15 min at room temperature
(22oC), and diluted with Et2O. It was then washed successively with NaHCO3 solution
containing a small amount of Na2S2O3 and brine, dried (MgSO4), and concentrated in
vacuo to give an oil (420 mg). This was chromatographed over SiO2 (5 g). Elution
with pentane/EtOAc (50:1) gave 87 mg (69%) of (1S,2S)-1 as a colorless oil,
nD24=1.4710; [α]D25 -47.6 (c 0.50, hexane) {natural pheromone: [α]D26.3 -39.45 (c
0.0752, hexane)}; Chiral GC [column: Chiramix, 0.25 mm i.d. x 60 m; column temp:
40-180o (+0.7oC/min); carrier gas, He: flow rate 1.2 mL/min]: tR120.2 [97.3%,
(1S,2S)-1], 121.3 min [2.7%, (1R,2R)-1], 94.6% ee; νmax (film): 3074 (w), 2959 (s),
2872 (m), 2731 (w), 1721 (s), 1655 (w), 1455 (m), 1388 (m), 881 (m); δH (CDCl3): 0.95
(3H, d, J= 7.2 Hz), 1.18 (3H, s), 1.45-1.52 (1H, m), 1.80-1.90 (1H, m), 2.10 (2H, s),
2.09-2.16 (1H, m), 2.25-2.40 (1H, m), 2.40-2.55 (1H, m), 4.79 (1H, s-like), 4.88 (1H,
s-like), 9.83 (1H, t, J=2.8 Hz); δC (CDCl3): 12.06, 25.15, 28.95, 35.63, 43.64, 47.41,
50.42, 105.81, 155.67, 203.98; GC-MS (same conditions as those used for 4): tR 6.96
min (91.0%); MS (70 eV, EI): m/z: 152 (<1) [M+], 110 (10), 109 (100), 108 (50), 93 (19),
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91 (15), 81 (8), 79 (7), 77 (11), 67 (28), 41 (10). HRMS calc for C10H16O: 152.1201,
found: 152.1205.
4.26.2. (1R,2RS)-Isomer. In the same manner as described above, (1R,2RS)-23 (137
mg, 0.89 mmol) was oxidized with DAIB (354 mg, 1.10 mmol) and azadol (15 mg, 0.1
mmol) in CH2Cl2 (4 mL) to give 90 mg (67%) of a mixture of (1R,2R)- and (1R,2S)-1
(10:9 as analyzed by GC) as a colorless oil. Due to the scarcity, it was not further
separated by SiO2 chromatography. It showed the following properties: [α]D24 +15.5
(c 0.61, hexane)}; Chiral GC [same conditions as those used for (1S,2S)-1]: tR 120.4
[1.3%, (1S,2S)-1], 121.1 [51.6%, (1R,2R)-1], 92.5% ee; 123.2 [45.1%, (1R,2S)-1], 123.7
min [2.0%, (1S,2R)-1], 95.8% ee: νmax (film): 3074 (w), 2961 (s), 2872 (m), 2731 (w),
1721 (vs), 1655 (w), 1455 (w), 1382 (w), 879 (m); GC-MS (same conditions as those
used for 4): tR 6.95 (50.2%), 7.08 min (45.0%); MS of the mixture [(1S,2R)- and
(1R,2S)-1] was almost the same as that of (1S,2S)-1. HRMS calc for C10H16O:
152.1201, found: 152.1218 (short tR), 152.1211 (long tR).
4.26.3. Identification of the natural pheromone as (1S,2S)-1 by chiral GC. Chiral
GC analysis: [column, Supelco 24304, beta dex 120, 0.25 mm i.d. x 30 m; column temp,
100-180oC (+5oC/min); carrier gas, N2, flow rate 20 mL/min]: tR (1S,2S)-1=13.957;
natural 1=13.949; (1R,2R)-1=14.118, (1R,2S)-1=14.555 min. The natural 1 was
therefore (1S,2S)-1.
4.27. (-)-2-(1,2-Dimethyl-3-methylenecyclopentyl)ethyl camphanate (25)
(-)-Camphanic chloride (TCI, 100 mg, 0.46 mmol) was added to a solution of
(1S,2S)-23 (40 mg, 0.26 mmol) and DMAP (5 mg, 0.04 mmol) in CHCl3 (0.4 mL) and
dry C5H5N (1 mL). The mixture was left to stand overnight at room temperature. It
was then poured into iced water, and extracted with Et2O. The Et2O extract was
washed successively with dil HCl, NaHCO3 solution and brine, dried (MgSO4), and
concentrated in vacuo to give 85 mg (98%) of 25 as a solid. This was recrystallized
from EtOAc/hexane to give leaflets, mp 119-120oC (sinter at 85-86oC) (A sample for
25
X-ray crystallographic analysis was recrystallized from EtOAc to give plates). [α]D
-16.6 (c 0.07, Et2O); νmax (nujol): 3066 (w), 1784 (s), 1759 (w), 1720 (s), 1653 (w),
1402 (m), 1377 (m), 1346 (m), 1320 (m), 1271 (s), 1170 (m), 1099 (s), 1060 (m), 1022
(m), 931 (m), 919 (m), 882 (m); δH (CDCl3): 0.93 (3H, d, J=7.0 Hz), 0.95 (3H, s), 1.03
(3H, s), 1.05 (3H, s), 1.11 (3H, s), 1.46 (2H, t, J=7.2 Hz), 1.64-1.76 (2H, m), 1.86-2.12
(4H, m), 2.24-2.34 (1H, m), 2.35-2.52 (2H, m), 4.28 (2H, t, J=7.6 Hz), 4.78 (1H, s),
4.85 (1H, s); δC (CDCl3): 9.85, 12.18, 16.93, 24.86, 29.07, 29.12, 30.76, 31.66, 35.04,
42.76, 50.59, 54.30, 54.92, 63.68, 77.36, 91.24, 105.26, 156.53, 178.33. HRMS calc
for C20H30O4: 334.2144, found; 334.2133.
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4.28. X-ray crystal structure determination of 25
4.28.1. Instrument and softwares. The intensity data were collected on a Rigaku
R-Axis Rapid diffratometer. Rapid auto ver. 2.30 Rigaku and CrystalStructure Ver 4.2
Rigaku were used for control and analysis, respectively. GBX 100 was used as a
digital microscope.
4.28.2. Experimental conditions. X-ray source: Cu. Cu-Kα irradiation (λ=1.54187
Å) was used.
4.28.3. Crystal data. Empirical formula: C20H30O4, formula weight: 334.45; Crystal
color and habit: colorless, block; Crystal dimensions: 0.100 x 0.100 x 0.050 mm;
Crystal system: orthorhombic; Lattice type: primitive; Lattice parameters: a=6.26573
(17) Å, b=6.8852 (2) Å, c=44.5126 (13) Å, V=1920.70 (9) Å3; Space group: P212121
(#19); Z value:4; D calc: 1.157 g/cm3, F000: 728.000, µ(CuKα): 6.332 cm-1
4.28.4. Intensity measurements. No. of reflections measured: total: 22392; Unique:
3725 (Rint=0.0527); Friedel pairs: 1488; Corrections: Lorenz polarization absorption
(trans. factors: 0.639-0.969).
4.28.5. Structure solution and refinement. Solution: Direct methods (S1R 97);
Refinement: Full-matrix least-square on F; Function minimized: Σw(|Fo|-|Fc|)2; Least
2
2
squares weights: 1/[0.0010F0 +1.0000σ (F0 )]; 2Θmax cutoff: 143.7o; Anomalous
dispersion: All non-hydrogen atoms; No. of observations (all reflections): 3725; No. of
variables: 248; Reflection/Parameter ratio: 15.02; Residuals: R[I>2.00σ (I)]: 0.0916;
Residuals R (all reflections): 0.1301; Residuals: wR (all reflections) 0.1233; Goodness
of fit indicator: 1.755; Flack parameter (Friedel pairs=1488): 0.3 (6); Max shift/Error in
final cycle: 0.009; Maximum peak in final diff. map: 0.52 e-/Å3; Minimum peak in final
diff. map: -4.8e-/Å3. Crystallographic data for the structure 25 (Fig.8) have been
deposited with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 1560305. Copies of the data may be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax:
44(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.UK].
4.29. Bioassay of (1S,2S)- and (1R,2R)-1
Both the synthetic (1S,2S)-1 and a mixture of (1R,2R)- and (1R,2S)-1 were further
purified by SiO2/AgNO3 chromatography to give >99% pure (1S,2S)- and (1R,2R)-1.
Their enantiomeric purities were 94.6% ee for (1S,2S)-1 and 92.5% ee for (1R,2R)-1
(see 4.26.1 and 4.26.2). The attractiveness of each the enantiomer of anti-1 was tested
by a trap bioassay at a pineapple field (ca. 1200 m2) of the Okinawa Prefectural
Agricultural Research Center (26.6oN, 127.9oE; Nago-shi, Okinawa, Japan) from June
17 to July 3, 2017. Attractants (0.1 mg) dissolved in hexane (100 µL) were
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impregnated into red rubber septa (8 mm outside diameter 19 mm height; Wheaton;
Millville, NJ, USA) and incubated overnight at room temperature, while the solvent
evaporated. White delta-traps with 11 cm x 22 cm sticky boards (Sankei Chemical Co.,
Kagoshima, Japan) baited with the septa were placed 0.5 m above the ground at 5-m
intervals. Three blocks of traps with two sets of three attractant treatments including a
control (solvent only), in total six traps for each treatment, were prepared. Data were
log-transformed and analyzed by using analysis of variance, which was performed by
using the aov function of the R software v. 3. 2. 5. Both of the synthetic enantiomers
of anti-1 showed attractiveness to mealybug males in the field trap bioassay, while no
males were captured by the blank trap. The males showed significantly more
responses to (1S,2S)-1 than to the opposite enantiomer (1R,2R)-1 (ANOVA, F1,6=27.8,
P=0.00188; see Fig.4)
Acknowledgements
K.M. thanks Mr. M. Kimura (President, Toyo Gosei Co., Ltd) and Mr. Y. Kimura
(CEO, Toyo Gosei Co., Ltd) for their mental and financial support. X-ray analysis was
financially supported by Sumitomo Chemical Co. through Dr. E. Nagano (Health and
Crop Science Research Laboratory, Sumitomo Chemical Co., Ltd). Field bioassay and
comparison of the natural and synthetic pheromones were supported by National
Agriculture and Food Research Organization. K.M. thanks one of the reviewers for his
comments on configurational assignments. Prof. S. Kobayashi (ex. Tokyo University
of Science) advised K.M. concerning the preparation of 2,5-heptanedione. X-ray
analysis was executed by Mr. T. Kitagawa (Sumika Chemical Analysis Service). Dr. K.
Sakaguchi and Mr. Y. Shikichi (both Toyo Gosei Co., Ltd.) are thanked for NMR and
GC-MS measurements. Dr. T. Nakamura (RIKEN) kindly carried out the HRMS
analyses. Enantioselective GC analyses were executed by Dr. M. Amaike and Ms. M.
Kurosawa (both T. Hasegawa Co.). Mr. Y. Ohmine and Mr. M. Takeuchi (both
Okinawa Prefectural Agricultural Research Center) kindly helped the field bioassay of 1.
Dr. T. Tashiro (Niigata University of Pharmacy and Applied Life Sciences) and Mr. K.
Kikusato (RIKEN) helped K.M. in preparing the manuscript.
References
1. Mori K, Yang CY. Tetrahedron 2017; 73:4766-4769.
2. Tabata J. Ichiki RT, Tanaka H, Kageyama D. PLoS One 2016; 11:e0156587.
3. Tabata J. Ichiki RT, Moromizato C, Mori K. J R Soc Interface 2017; 14:20170027.
4. Mori K. Tetrahedron 2016; 72:6578-6588.
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