Systematic synthetic study of four diastereomerically distinct limonene-1,2-diols and their corresponding cyclic carbonates

Article abstract of DOI:10.3762/bjoc.15.13

In order to produce versatile and potentially functional terpene-based compounds, a (R)-limonene-derived diol and its corresponding five-membered cyclic carbonate were prepared. The diol (cyclic carbonate) comprises four diastereomers based on the stereochemical configuration of the diol (and cyclic carbonate) moiety. By choosing the appropriate starting compounds (trans- and cis-limonene oxide) and conditions, the desired diastereomers were synthesised in moderate to high yields with, in most cases, high stereoselectivity. Comparison of the NMR data of the obtained diols and carbonates revealed that the four different diastereomers of each compound could be distinguished by reference to their characteristic signals.

Full text of DOI:10.3762/bjoc.15.13

Systematic synthetic study of four diastereomerically distinct
limonene-1,2-diols and their corresponding cyclic carbonates
Hiroshi Morikawa*1, Jun-ichi Yamaguchi1, Shun-ichi Sugimura1, Masato Minamoto1,
Yuuta Gorou1, Hisatoyo Morinaga2 and Suguru Motokucho3
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2019, 15, 130–136.
1
Department of Applied Chemistry, Kanagawa Institute of
Technology, 1030, Shimo-ogino, Atsugi, Kanagawa 243-0292, Japan,
Faculty of Education, Graduate Faculty of Interdisciplinary Research,
University of Yamanashi, 4-4-37, Takeda, Kofu, Yamanashi
00-8510, Japan and 3Graduate School of Engineering, Nagasaki
doi:10.3762/bjoc.15.13
2
Received: 08 October 2018
Accepted: 17 December 2018
Published: 14 January 2019
4
University, 1-14, Bunkyo-machi, Nagasaki-city 852-8521, Japan
Associate Editor: J. S. Dickschat
Email:
Hiroshi Morikawa* - morikawa@chem.kanagawa-it.ac.jp
© 2019 Morikawa et al.; licensee Beilstein-Institut.
License and terms: see end of document.
*
Corresponding author
Keywords:
cyclic carbonate; diastereomer; diol; limonene; NMR
Abstract
In order to produce versatile and potentially functional terpene-based compounds, a (R)-limonene-derived diol and its correspond-
ing five-membered cyclic carbonate were prepared. The diol (cyclic carbonate) comprises four diastereomers based on the stereo-
chemical configuration of the diol (and cyclic carbonate) moiety. By choosing the appropriate starting compounds (trans- and cis-
limonene oxide) and conditions, the desired diastereomers were synthesised in moderate to high yields with, in most cases, high
stereoselectivity. Comparison of the NMR data of the obtained diols and carbonates revealed that the four different diastereomers of
each compound could be distinguished by reference to their characteristic signals.
Introduction
(
R)-Limonene (LM) is a naturally occurring terpene, and there- chemicals such as oxazolizin-2-ones [8] and polyurethanes [9].
fore a very attractive and renewable resource [1]. Its deriva- For (R)-limonene-derived 5CC (LM5CC), four diastereomers
tives have versatilely and widely been studied [1-4].
are considered from the different stereochemical configurations
at the 1- and 2-positions of LM (Figure 1). A few studies on 1a
Otherwise, syntheses of five-membered cyclic carbonates and 1d have been recently reported [10,11], whereas 1b and 1c
5CCs) have been intensively investigated [5-7] in terms of util- have never been synthesised. Consequently, the systematic and
isation of CO2 and the further reactions to produce functional stereoselective syntheses of these four LM5CCs are of deep
(
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Beilstein J. Org. Chem. 2019, 15, 130–136.
Figure 1: Diastereomers of LM5CCs, 1a–d.
Scheme 1: Dihydroxylation of (a) (R)-limonene and (b) (R)-dihy-
drolimonene.
significance, largely because LM derivatives with their versa-
tile functionality can be effectively utilised in organic and
polymer chemistry.
further reports on the systematic synthesis and comparison of
the four LMdiols have been published. The stereochemical
(
4R)-Limonene-1,2-diols (LMdiols) are some of the most im- structures of LMdiols are not depicted in several reports [26]
portant LM derivatives because they act as precursors of bioac- presumably due to a lack of reliable characterisation data for the
tive molecules [12-14]. Furthermore, LMdiol is detected as four LMdiols. Therefore, reliable characterisation data of
metabolite in vivo in biochemistry [15], and is known to react in LMdiols and LM5CCs are required, particularly if the confu-
the atmosphere to afford the secondary organic aerosol as air sion surrounding LMdiols should be resolved.
pollutants [16]. Among the four diastereomers of LMdiols
(
Figure 2), 2b and 2c have already been reported [14,17-20]. Herein, we focus on two compounds, LMdiol and LM5CC, as
Conversely, the distinct characterisations of 2a and 2d remain versatile and functional LM derivatives, and report the system-
unreported.
atic synthesis of each of their four diastereomers and their char-
acterisation using spectroscopic methods, mainly NMR.
Comparing the data, unambiguous distinction of the four dia-
stereomers is achieved in both cases.
Results and Discussion
Syntheses of LM5CC 1a and 1d and LMdiol
2a and 2d
Facile syntheses of two LM5CCs 1a and 1d and one LMdiol 2d
have been preliminarily reported in our previous study [27]. Of
these, 1a has already been synthesised by other groups [10,11]
as well as our group. Particularly, Kleij et al. revealed the
Figure 2: Diastereomers of LMdiols, 2a–d.
Very recently, Wang et al. synthesised 2a and 2d using OsO4, solid-state structure of 1a via X-ray analysis [11], but the isola-
and exclusively 2d using Sharpless AD-mix-β [21] as a catalyst tion and characterisation of 1d has only been reported by our
(
Scheme 1a) [16]. In contrast to that, Mori reported that (R)- group.
dihydrolimonene, the structure of which is similar to LM, was
oxidised using Sharpless AD-mix-β to afford a 2a-type main Herein, we report the synthesis of 1a from the trans-isomer of
product (Scheme 1b) [22]. Hao et al. also reported the synthesis (R)-limonene oxide (LO) and 1d from cis-LO using CO2 and
of 2a and 2d using OsO4 (Scheme 1a) [23]. However, the NMR tetrabutylammonium chloride (TBAC) as a catalyst. Both reac-
data of 2a and 2d were not consistent with those [16] reported tions proceeded without any side reactions and produced no
by Wang. Moreover, they referred to a published paper [24] for unwanted isomers, such as 1c. Though the CO2 pressure em-
the assignment of 2d. However, the reaction mechanism in the ployed in our previous study was 3 MPa [27], 5 MPa CO2 was
referred paper indicates the formation of 2b. A rational explana- applied in the present study to promote a higher consumption of
tion for the syntheses of 2a and 2d is not available at the present LO. The result showed the isolated yields were improved to
stage.
84% yield for 1a and 30% yield for 1d.
Since Royals et al. presented a pioneering study despite insuffi- In our previous report, 1d was reduced by lithium aluminium
cient data for three diastereomers of LMdiol in 1966 [25], no hydride (LAH) to obtain the corresponding LMdiol 2d [27].
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Beilstein J. Org. Chem. 2019, 15, 130–136.
Notably, the structure of 2d was confirmed by X-ray analysis. It which was obtained in 70% yield after purification. These
has been reported that reduction of the 5CC moiety with LAH results are in good agreement with those of previous reports
gives the corresponding diol with the same stereochemical con- [18,20,32].
figuration at the carbon atoms as of the original 5CC moiety
[
28,29]. Such a reduction with LAH was initially applied in this Similarly to the aforementioned carbonation of 2a (Scheme 2),
study to 1a (Scheme 2) as an analogy to the reaction of 1d. The 2b and 2c were also reacted with triphosgene. Neither of the
reaction proceeded smoothly giving the corresponding LMdiol desired products 1b and 1c have been synthesised until now.
2
a in an excellent yield (Scheme 3).
When 2c was used, the carbonation proceeded smoothly to
afford the corresponding carbonate 1c exclusively. The isolated
yield after purification was moderate (58%). Conversely, the
reaction of 2b was accompanied by side reactions. Although the
starting material 2b was completely consumed, two major prod-
ucts were detected by thin-layer chromatography. After purifi-
cation, the desired 1b was obtained in a relatively low yield of
2
4%.
Two conformations (A and B in Scheme 4) are possible for the
intermediate when 2b is reacted with triphosgene. The confor-
mation A is expected to be more stable because the isopropenyl
group remains in the equatorial position on the cyclohexane
ring. In this conformation, the remaining hydroxy group is lo-
cated in the axial position and away from the carbonyl group of
the chloroformate moiety. This conformation makes the forma-
tion of the five-membered cyclic structure by ring-closing very
difficult, leading to the low yield. However, although the yield
of 1b was low, both 1b and 1c were successfully synthesised for
the first time in the present study.
Scheme 2: Reduction of LM5CC (1a) and carbonation of LMdiol (2a).
Scheme 3: Overall synthetic routes to LM5CCs and LMdiols. The
9
3% value (standing for *) from 1d to 2d was cited from ref [27].
Reagents and conditions: (a) 5 MPa CO2, 10 mol % TBAC, 100 °C,
2 h; (b) LAH, rt, 2 h; (c) triphosgene, rt, 2 h; (d) H2O/dioxane
1:1, v/v), 120 °C, 72 h; (e) H2O, 90 °C, 12 h.
7
(
It is also possible to synthesise 5CCs from diols by reaction
with triphosgene (Scheme 2). It is well known that this carbona-
tion reaction maintains the stereochemical configuration of the
original diol [30,31]. Accordingly, the reactions of 2a and 2d
Scheme 4: Plausible conformations of the intermediate in the reaction
of LMdiol (2b) with triphosgene.
with triphosgene successfully afforded 1a and 1d, respectively, The carbonates 1b and 1c were also reacted with LAH in the
in this study (Scheme 3). The two carbonates obtained from the same manner as 1a (Scheme 2). After reaction and purification,
diols and triphosgene were spectroscopically identical to those 2b and 2c were afforded in high yields (Scheme 3). The two
synthesised from LO and CO2, as confirmed by 1H and resultant compounds were characterised by 1H and 13C NMR
1
3C NMR analyses.
analyses, and the spectroscopic data were identical to those of
b and 2c obtained from LO and water. Therefore, these results
2
Syntheses of LM5CC 1b and 1c and LMdiol
b and 2c
confirm the formation of the two carbonates 1b and 1c.
2
Overview of synthetic routes to the LM5CCs
The reaction of trans-LO and water in dioxane afforded a mix-
ture of two LMdiols 2b/2c. After purification, 2b and 2c were and LMdiols
isolated in 58% and 19% yields, respectively (Scheme 3). Con- The overall results for the syntheses of the four LM5CCs and
versely, the reaction of cis-LO with water afforded only 2b, the four LMdiols are shown in Scheme 3. All the reactions do
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Beilstein J. Org. Chem. 2019, 15, 130–136.
not lead to the formation of other diastereomers as byproducts
except for the reaction of trans-LO with water (Scheme 3,
conditions (d)). The reduction under conditions (b) and carbon-
ation under conditions (a) and (c) retain the diastereomeric con-
formations around the epoxy, 5CC and diol moieties.
Table 1: Chemical shift values (ppm) of four LM5CCs with the assign-
mentsa.
In all the reactions, the yields for the reduction of LM5CC with
LAH were high at 84–94%. Conversely, the yields of the
carbonations to LM5CC differ depending on both the starting
material and reaction conditions, i.e., (a) and (c) in Scheme 3.
Thus, all the LM5CCs and LMdiols can be synthesised by
choosing the appropriate starting LO and reaction conditions
with high diastereomeric stereoselectivity and, in most cases,
moderate to high yields.
1
a
1b
1c
1d
1
1
54.6 (C11) 155.1 (C11) 155.2 (C11) 154.4 (C11)
47.2 (C7)
145.7 (C7)
111.9 (C8)
86.2 (C1)
81.6 (C2)
38.5 (C4)
31.7 (C6)
25.8 (C3)
25.1 (C5)
22.5 (C9)
16.8 (C10)
146.4 (C7)
110.7 (C8)
85.4 (C1)
84.8 (C2)
43.0 (C4)
33.0 (C6)
28.9 (C3)
27.9 (C5)
20.8 (C9)
16.9 (C10)
147.3 (C7)
109.8 (C8)
82.6 (C1)
81.7 (C2)
37.3 (C4)
34.1 (C6)
30.5 (C3)
26.2 (C5)
22.2 (C10)
20.8 (C9)
110.0 (C8)
2.0 (C1)
80.4 (C2)
8
To compare the four LMdiols and the four LM5CCs, a set of
the characteristic analytical data such as melting points, optical
rotation values and Kovats retention index values in gas chro-
matography was listed in Tables S1 and S2 in Supporting Infor-
mation File 1.
3
3
3
2
2
2
9.8 (C4)
3.9 (C3)
2.9 (C6)
6.1 (C10)
5.6 (C5)
0.5 (C9)
Analysis and comparison of the four LM5CCs
aIn CDCl3.
In our previous study, the assignments of the NMR signals for
1
a and 1d were not adequate [27]. Table 1 lists the 13C NMR
chemical shift values for all LM5CCs, showing the assign-
ments for each of the carbon atoms. The multiplicities were
ascertained using DEPT135 analysis (Supporting Information
File 1, pages S13, S18, S23, and S28).
As characteristic signals, the C9 values are observed at higher
magnetic fields than the C10 values for 1a and 1d. However,
the relationship is reversed for 1b and 1c. In addition, the values
for C10 in 1b and 1c are observed at the higher magnetic fields
(
16.8 and 16.9 ppm, respectively) compared with those for 1a
and 1d. The order of C3, C6 and C5 signals for 1a is also differ-
ent from that (C6, C3, C5) of the other three LM5CCs.
1
H NMR spectra of the four LM5CCs are shown in Figure 3
(
(
selected range) and Supporting Information File 1, page S32
full range) with the assignments of signals a–h. Three charac-
teristic signals f, a and c are clearly observed at 5.0–4.7, 4.4–4.2
and 2.4–1.9 ppm, respectively. Obviously, the respective dia-
stereomers can be distinguished by comparison of the character-
istic signals. The determination of all the signals in 1H and
Figure 3: 1H NMR spectra of LM5CCs 1a–d in CDCl3.
1
3C NMR is also supported by 1H,1H COSY and HETCOR
(
Supporting Information File 1).
rather similar values for all the signals. In the 28–24 ppm
Analysis and comparison for the four LMdiols region, two characteristic signals ascribed to C5 and C10, which
Table 2 lists the chemical shifts in the 13C NMR spectra with are clearly distinguishable by DEPT 135, are observed. The two
the assignments for all LMdiols. The listed values for 2a and 2c values are approximately 4 ppm apart for 2d, but less than
are close, but distinguishable. Conversely, 2b and 2d present 1 ppm apart for 2b. Furthermore, the order is reversed for the
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Beilstein J. Org. Chem. 2019, 15, 130–136.
two samples; the signal of C10 appears at higher field than that
for C5 in case of 2d. This demonstrates that 2b and 2d are simi-
lar but can be differentiated by their characteristic NMR signals.
Table 2: Chemical shift values (ppm) of four LMdiols with the assign-
mentsa.
2a
2b
2c
2d
1
49.0 (C7)
08.8 (C8)
149.1 (C7)
109.0 (C8)
73.8 (C2)
71.4 (C1)
37.4 (C4)
33.9 (C3)
33.7 (C6)
26.5 (C10)
26.1 (C5)
21.1 (C9)
148.4 (C7)
109.1 (C8)
77.2 (C2)
74.0 (C1)
43.6 (C4)
38.5 (C6)
36.1 (C3)
28.7 (C5)
20.9 (C9)
18.9 (C10)
149.0 (C7)
108.9 (C8)
73.7 (C2)
71.9 (C1)
37.5 (C4)
34.5 (C3)
34.1 (C6)
28.2 (C5)
24.4 (C10)
21.2 (C9)
1
7
7
4
3
3
2
2
2
5.1 (C2)
0.8 (C1)
3.7 (C4)
7.3 (C6)
5.5 (C3)
7.1 (C10)
6.1 (C5)
0.8 (C9)
Figure 4: 1H NMR spectra of LMdiols 2a–d in CDCl3.
neighbouring proton b. Conversely, for 1d, the proton locates at
the equatorial position; thus, the interaction with proton b is
weak. These interactions support the structures shown in
Figure 5. For 1b, two oxygen atoms located at the equatorial
positions form a 5CC cyclic structure; then, the isopropenyl
group is located at the axial position. This speculation is also
supported by the low 24% yield in the synthesis of 1b from 2b,
aIn CDCl3.
In 1H NMR spectra of the four LMdiols (Figure 4 and Support- as shown in Scheme 3 and Scheme 4.
ing Information File 1, page S61), characteristic signals a are
observed at 3.41 for 2a and 3.58 ppm for 2c, demonstrating that In these conformations, proton c is expected to be located in the
they are different. However, signals a and c as well as others axial position for 1a, 1c and 1d, and in the equatorial position
show similar values for 2b and 2d. The most significant differ- for 1b. In fact, the coupling constants match well the conforma-
ence is observed for the signal at 1.3 ppm of 2d (Supporting tions in Figure 5 although the signal c for 1d unfortunately
Information File 1, page S55), allowing the two samples to be overlaps with other signals. The structure of 1a is in good
distinguished.
agreement with the solid-state structure reported previously
11].
[
The assignments in the 1H and 13C NMR signals were sup-
ported by DEPT135, 1H,1H COSY, HETCOR and HMBC Conformations of the four LMdiols were also considered in the
heteronuclear multiple bond correlation) analyses. Two sam- same manner as those of LM5CCs by reference to the a and c
ples of 2a and 2b were also subjected to 1,1-ADEQUATE signals in Figure 4. The coupling constants for the signal a
(
(
adequate double quantum transfer experiment) analysis.
support the structures shown in Figure 5. Indeed, the equatorial
position of the isopropenyl group for 2c and 2d in the solid state
was confirmed by X-ray diffraction analysis, as reported previ-
Structures of four LMdiols and four LM5CCs
Plausible conformations for the LM5CCs and LMdiols in ously [20,27]. The c protons are expected to stay in the axial po-
CDCl3 are proposed in Figure 5. In Figure 3, large coupling sitions for all the LMdiols. These considerations are consistent
constants (J > ca. 10 Hz) for the signal a are observed for 1a–c. with the fact that the signals exhibit large coupling constants for
Conversely, the signal for 1d exhibits a small coupling constant 2a, 2c and 2d. For 2b in CDCl3, the coupling constants could
(
J < ca. 3 Hz), showing a largely singlet shape. For the former not be estimated because of the multiplet shape; however, a
three LM5CCs, this means that the proton a locates at the axial large coupling constant was clearly observed in CD3OD and in
position on the cyclohexane ring and interacts strongly with the benzene-d6 (Supporting Information File 1, page S42).
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Beilstein J. Org. Chem. 2019, 15, 130–136.
Figure 5: Plausible conformations of LM5CCs and LMdiols in CDCl3.
Conclusion
ORCID® iDs
Four diastereomers of (R)-limonene-derived diols (LMdiols)
Hiroshi Morikawa - https://orcid.org/0000-0001-9942-3369
Jun-ichi Yamaguchi - https://orcid.org/0000-0003-0230-1678
Hisatoyo Morinaga - https://orcid.org/0000-0002-0350-4728
Suguru Motokucho - https://orcid.org/0000-0002-6627-2194
and the corresponding five-membered cyclic carbonates
(
LM5CCs) were synthesised and characterised by NMR analy-
sis. In particular, the NMR data for 2b and 2d exhibit rather
similar values. The assignments of 1H and 13C NMR signals
were found to provide a means of differentiating the respective References
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