Stereoselective construction of all-carbon quaternary stereocenters by allylboration of chiral aldehydes: synthesis of a fragment of (+)-vibsanin A

Article abstract of DOI:10.1016/j.tet.2016.07.030

Stereoselective construction of all-carbon quaternary stereocenters by allylboration of chiral aldehydes is described. Sugar-derived aldehydes were allylated with geranylboronate or nerylboronate to provide γ-adducts possessing quaternary stereocenters wi

Full text of DOI:10.1016/j.tet.2016.07.030

Tetrahedron xxx (2016) 1e7
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Stereoselective construction of all-carbon quaternary stereocenters
by allylboration of chiral aldehydes: synthesis of a fragment of
(þ)-vibsanin A
Akihiro Sakama, Yoshiyasu Nishimura, Yuko Motohashi, Keisuke Yoshida,
*
Ken-ichi Takao
Department of Applied Chemistry, Keio University, Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Stereoselective construction of all-carbon quaternary stereocenters by allylboration of chiral aldehydes is
Received 7 June 2016
Received in revised form 6 July 2016
Accepted 8 July 2016
Available online xxx
described. Sugar-derived aldehydes were allylated with geranylboronate or nerylboronate to provide g-
adducts possessing quaternary stereocenters with high diastereoselectivity. The reaction was applied to
the synthesis of a fragment of (þ)-vibsanin A.
Ó 2016 Elsevier Ltd. All rights reserved.
Keywords:
Allylation
Boronates
Carbohydrates
Diastereoselectivity
Quaternary stereocenter
1. Introduction
All-carbon quaternary stereocenters are found in many phar-
maceuticals and bioactive natural products. For example,
(þ)-hyperforin (1),1 (ꢀ)-hyphenrone A (2),2 and (þ)-vibsanin A (3)3
have a common structural motif including an asymmetric quater-
nary stereogenic center (Fig. 1). To synthesize such complex com-
pounds, it is essential to develop
a practical method for
constructing the quaternary stereocenter. However, this remains
a challenge due to steric factors and the difficulty of asymmetric
induction.4 One approach uses 3,30-disubstituted allylmetal re-
agents. Although much research has focused on developing ster-
eoselective carbonyl allylation reactions,5 the construction of an
asymmetric quaternary stereocenter by these reactions is still
challenging.6 Denmark and co-workers have reported a solution to
this problem using allylic trichlorosilanes.7 We also reported a zinc-
mediated Barbier-type allylation of sugar-derived aldehydes in
aqueous media (Scheme 1a).8
Thus, the reaction of
from
-mannitol in two steps)9 and geranyl chloride (5) in the
presence of zinc powder preferentially provides -adduct 6-C,
D
-glyceraldehyde acetonide 4 (prepared
D
Fig. 1. Structures of (þ)-hyperforin, (ꢀ)-hyphenrone A, and (þ)-vibsanin A.
g
which contains an all-carbon quaternary stereocenter with (R)-
configuration, in accordance with the b-chelation/six-membered
* Corresponding author. Fax: þ81 45 566 1551; e-mail address: takao@applc.keio.
ac.jp (K. Takao).
http://dx.doi.org/10.1016/j.tet.2016.07.030
0040-4020/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Sakama, A.; et al., Tetrahedron (2016), http://dx.doi.org/10.1016/j.tet.2016.07.030

2
A. Sakama et al. / Tetrahedron xxx (2016) 1e7
2. Results and discussion
The allylboration reaction was investigated with readily avail-
able sugar-derived aldehydes, also used in the Barbier-type allyla-
tion,8 and with pinacol allylboronic ester 8 or 9 as substrates.
Geranylboronate 8 was prepared from geraniol according to the
16
ꢀ
convenient procedure developed by Szabo and Aggarwal. Ner-
ylboronate 917 was also prepared from nerol by a similar method.18
These 3,30-disubstituted allylboronic esters were configurationally
stable, and equilibrium between E- and Z-isomers was not observed
at room temperature.
As shown in Table 1, the reaction of 4 with 8 in CH2Cl2 at 0 ꢁC to
room temperature provided
g-adducts 6-AeD with high stereo-
selectivity and complete regioselectivity (entry 1). The
g-adducts
were separated into (3R)-isomers 6-A/6-B (4R/4S¼9:1) and (3S)-
isomers 6-C/6-D (4R/4S¼1:5) by column chromatography in yields
of 5% and 71% from 8, respectively. In this case, (3S,4S)-isomer 6-D
was obtained as the major product.19 Thus, the synthesis of the
chiral building block with (4S)-configuration was achieved in three
steps from D-mannitol, which is a more concise route than Barbier-
type allylation of ent-4. By using 9 instead of 8, the reaction pref-
erentially produced (3S,4R)-isomer 6-C, which is the epimer of 6-D
at the quaternary stereocenter (entry 2). The stereoselectivity was
slightly lower than in the reaction with 8, but was still good. In both
cases (entries 1 and 2), the stereochemical outcomes were the
opposite of the Barbier-type allylation using the corresponding allyl
chlorides (Scheme 1).8 Products 6-D and 6-C possessing a quater-
nary carbon are inseparable, although the two diastereomers can
be separated at a later stage.10 Therefore, they are expected to be
useful chiral building blocks for natural product synthesis.
Table 1
Allylboration of D-glyceraldehyde derivative 4
Scheme 1. (a) Zinc-mediated Barbier-type allylation, (b) our total synthesis of
(þ)-vibsanin A, and (c) this work.
model. Recently, we achieved the first total synthesis of (þ)-vib-
sanin A (3) by using the Barbier-type allylation (Scheme 1b).10 In
our total synthesis, we needed to use ent-4 as a substrate for the
Barbier-type allylation because an (S)-configured quaternary
stereocenter was required for the natural enantiomer of 3. Com-
pound ent-4 was prepared from L
-ascorbic acid in five steps,11
taking more time and effort than preparation of 4. To achieve the
synthesis of 3 from 4, we aimed to develop a stereochemically
complementary method to the zinc-based Barbier-type allylation,
this time using the allylboration reaction where chelation of the
aldehyde would not be possible because of the limited co-
ordination shell of boron.12
There are only limited examples of allylboration in the syn-
thesis of optically active compounds bearing all-carbon quater-
ꢀ
nary stereocenters. Although Szabo and co-workers recently
reported catalytic asymmetric allylboration in the synthesis of
quaternary stereocenters,13,14 most methods use chiral allylboron
reagents as chiral sources.15 Herein, we describe the construction
of all-carbon quaternary stereocenters by allylboration of chiral
aldehydes with achiral 3,30-disubstituted allylboronic esters,
thereby extending the approach to lower fragment 7 of (þ)-vib-
sanin A (3) (Scheme 1c).
Entry
Allylboronate
AþB
CþD
Yielda
A/Bb
Yielda
C/Db
1
2
8
9
5%
6%
9:1
1:8
71%
66%
1:5
4:1
a
Yield from 8 or 9.
b
Ratio was determined by 1H NMR analysis.
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A. Sakama et al. / Tetrahedron xxx (2016) 1e7
3
To expand the scope of the substrates, we used
D
-threose de-
reaction was performed using 9, (4S,5R)-isomer 13-C was obtained
as the major product (entry 2). These results were analogous to
those shown in Table 1, although the stereoselectivity for the (4S)-
configuration was slightly lower.
rivative 10 prepared from
D
-galactose20 (Table 2). We have pre-
viously shown that aldehyde 10 stereoselectively generated
a quaternary stereocenter through the Barbier-type allylation.
However, the reaction of 10 with 8 produced (4R)-isomers 11-A/11-
B in low yield with moderate stereoselectivity, whereas (4S)-iso-
mers were not observed (entry 1).19 Using 9 did not improve the
result, but gave the opposite stereochemical outcome (entry 2).
Our proposed transition states for the reactions of aldehyde 4
are shown in Scheme 2. The allylboration of carbonyl compounds is
thought to proceed via a six-membered chair-like transition state
providing
FelkineAnh transition state, which results in the formation of
g
-adducts exclusively.23 In the reaction of 4 with 8, the
g-
Table 2
adduct 6-D, is plausible based on the stereoelectronic effect, al-
though steric destabilization by the syn-pentane interaction occurs
(Scheme 2a). The transition state leading to 6-A appears to be less
favorable because of the lack of stereoelectronic benefit as depicted
in the Newman projection. The other isomers (6-B and 6-C) are
presumably generated through unfavorable transition states, in
which the stronger steric interaction exists. Therefore, the reaction
between 4 and 8 produced 6-D stereoselectively.
Allylboration of
D
-threose derivative 10
Entry
Allylboronate
AþB
Yielda
A/Bb
1
2
8
9
34%
35%
3:1
1:3
a
Yield from 8 or 9.
b
Ratio was determined by 1H NMR analysis.
The reactions of
D
-erythrose derivative 12, prepared from D-
glucose,21 were examined next (Table 3). Good stereoselectivity
was achieved in the reaction with 8 (entry 1). In this reaction,
(4S,5S)-isomer 13-D was preferentially produced.22 When the
Table 3
Allylboration of D-erythrose derivative 12
Scheme 2. Plausible transition states for the allylborations of 4.
In the reaction of 4 with 9, the steric congestion is minimized
through the Cornforth-like transition state, which is analogous to
that for the reaction of 4 with (Z)-crotylboronates proposed by
Roush and co-workers24 (Scheme 2b). Hence, the reaction of 4 with
9 provided 6-C preferentially. The stereochemical outcomes of the
reactions of 12 can be explained by similar arguments.
We demonstrated the utility of the allylboration by using the
major product 6-D as a chiral building block in a synthesis of
fragment 7 of (þ)-vibsanin A (Scheme 3). Benzylation of 6-D/6-C
(d.r.¼5:1) followed by hydroboration with thexylborane and an
oxidative workup provided a diastereomerically pure diol 14-D
(43%) and a mixture of the corresponding 3-epimer of 14-D and
Entry
Allylboronate
AþB
CþD
Yielda
A/Bb
Yielda
C/Db
1
2
8
9
12%
11%
>20:1
1:>20
44%
53%
1:4
4:1
a
Yield from 8 or 9.
b
Ratio was determined by 1H NMR analysis.
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4
A. Sakama et al. / Tetrahedron xxx (2016) 1e7
(6R)-isomer 14-C (38%). The primary hydroxy group in 14-D was
selectively protected as a silyl ether, and the leftover secondary
alcohol was treated with Martin sulfurane (Ph2S[OC(CF3)2Ph]2)25 to
regenerate the trisubstituted olefin. Product 15 was subjected to
a selective hydrolysis26 to diol 16. We repeated the same steps,
starting from a mixture of 3-epi-14-D and 14-C to obtain additional
16 as a single isomer. Combined 16 was deprotected under Birch
conditions to afford triol 17. Oxidative cleavage of 17 provided al-
dehyde 18, whose transformation into fragment 7 has already been
reported in our previous paper.10
4. Experimental section
4.1. General remarks
1H NMR spectra were recorded at 500 MHz with tetrame-
thylsilane as an internal standard on
a JEOL JNM-ECA500
(500 MHz) spectrometer. 13C NMR spectra were recorded at
125 MHz. High-resolution mass spectra (HRMS) were measured
by the EI mode (70 eV) on a JEOL JMS-GCmate spectrometer or by
the ESI mode on a Waters LCT premier XE spectrometer. Thin-
layer chromatography (TLC) was performed on Merck Kieselgel
60 F254 plates. The crude reaction mixtures and extracted mate-
rials were purified by chromatography on Silica gel 60N (Kanto
Chemical) or Wakogel C-300 (Wako). Combined organic extracts
were dried over anhydrous Na2SO4. Solvents were removed from
the reaction mixture and the combined organic extracts by con-
centration under reduced pressure using an evaporator with bath
at 35e45 ꢁC.
4.2. Procedures
4.2.1. (2R,3R,4R)-1,2-(Isopropylidenedioxy)-4,8-dimethyl-4-
vinylnon-7-en-3-ol (6-A), (2R,3R,4S)-isomer (6-B), (2R,3S,4R)-isomer
(6-C), and (2R,3S,4S)-isomer (6-D). The following reaction was
carried out under Ar. To a cooled (0 ꢁC) stirred solution of 8 (2.77 g,
10.5 mmol) in CH2Cl2 (100 mL) was added 4 (2.93 g, 22.5 mmol).
The mixture was stirred at 0 ꢁC to room temperature for 72 h, and 4
(0.73 g, 5.6 mmol) was added at 0 ꢁC. After being stirred at 0 ꢁC to
room temperature for 16 h, the mixture was diluted with H2O
(150 mL) and extracted with EtOAc/hexane (1:1, 100 mLꢂ5). The
combined extracts were dried and concentrated under reduced
pressure. The residue was purified by column chromatography on
silica gel (EtOAc/hexane, 1:10) to provide 135 mg (5%) of 6-A/6-B
(d.r.¼9:1) and 2.02 g (71%) of 6-C/6-D (d.r.¼1:5). A mixture of 6-
A and 6-B was obtained as a colorless oil: TLC Rf 0.48 (EtOAc/
hexane, 1:2); IR (neat) 3545, 2980, 2920, 2880 cmꢀ1
;
1H NMR
(500 MHz, CDCl3) for 6-A 1.01 (s, 3H), 1.37 (s, 3H), 1.40e1.52 (m,
d
2H), 1.41 (s, 3H), 1.58 (s, 3H), 1.67 (s, 3H), 1.81e1.90 (m, 2H), 2.53 (d,
1H, J¼6.1 Hz, OH), 3.25 (dd, 1H, J¼6.1, 4.4 Hz), 3.72 (t, 1H, J¼7.8 Hz),
4.00 (dd, 1H, J¼7.8, 6.3 Hz), 4.16 (ddd, 1H, J¼7.8, 6.3, 4.4 Hz), 5.01
(dd, 1H, J¼17.7, 1.3 Hz), 5.10 (m, 1H), 5.14 (dd, 1H, J¼11.0, 1.3 Hz),
5.85 (dd, 1H, J¼17.7, 11.0 Hz); for 6-B
d 1.03 (s, 3H), 1.36 (s, 3H), 1.40
(s, 3H), 1.49e1.58 (m, 2H), 1.58 (s, 3H), 1.67 (s, 3H), 1.83e1.92 (m,
2H), 2.42 (br, 1H, OH), 3.24 (m, 1H), 3.69 (t, 1H, J¼8.0 Hz), 3.95 (dd,
1H, J¼8.0, 6.4 Hz), 4.16 (ddd, J¼8.0, 6.4, 3.4 Hz), 5.04 (dd, 1H, J¼17.5,
1.5 Hz), 5.09 (m, 1H), 5.15 (dd, 1H, J¼10.9, 1.5 Hz), 5.72 (dd, 1H,
Scheme 3. Synthesis of fragment 7. Reagents and conditions: a) NaH, BnBr, DMF, rt,
94%; b) thexylborane, THF, 0 ꢁC, then aq NaOH, aq H2O2, rt, 42% for 14-D and 38% for
a mixture of 3-epi-14-D and 14-C; c) iPr2NEt, DMAP, TBDPSCl, CH2Cl2, rt, 92%; d) Martin
sulfurane, CH2Cl2, rt, 97%; e) Zn(NO3)2$6H2O, MeCN, 50 ꢁC, 76% for 16 and 15% for
recovered 15; f) Li, liq. NH3/Et2O, e78 ꢁC, 77%; g) NaIO4, MeOH/H2O, rt, 91%.
J¼17.5, 10.9 Hz); 13C NMR (125 MHz, CDCl3) for 6-A
d 17.8, 19.1, 22.7,
25.8 (2C), 26.6, 36.6, 43.9, 68.1, 75.0, 76.9, 109.2, 114.3, 124.9, 131.5,
143.4; for 6-B
74.9, 76.0, 109.3, 114.9, 124.9, 131.4, 143.2; HRMS (EI) calcd for
16H28O3 (Mþ) m/z 268.2038, found 268.2033. A mixture of 6-C
and 6-D was obtained as a colorless oil: TLC Rf 0.35 (EtOAc/hex-
ane, 1:2); IR (neat) 3590, 2985, 2915 cmꢀ1 1H NMR (500 MHz,
CDCl3) for 6-C 0.98 (s, 3H), 1.33 (s, 3H), 1.40 (s, 3H), 1.44e1.49 (m,
d 16.9, 17.8, 22.6, 25.8, 26.0, 26.5, 38.4, 44.7, 68.1,
C
3. Conclusion
;
In conclusion, we have developed a method for diaster-
eoselective syntheses of homoallylic alcohols containing all-
carbon quaternary stereocenters by allylboration of sugar-
derived aldehydes. We applied this reaction to the synthesis of
a fragment of (þ)-vibsanin A, and thus demonstrated that the re-
action can be complementary to our previously reported Barbier-
type allylation. Because allylboration reactions proceed under
mild conditions just by mixing the substrates, this concise, con-
venient method could be applied widely to constructing chiral
building blocks bearing quaternary stereocenters.27 Further stud-
ies and applications in natural product synthesis are under way
and will be reported in due course.
d
2H), 1.57 (s, 3H), 1.66 (s, 3H), 1.86e1.93 (m, 2H), 2.06 (br, 1H, OH),
3.74 (d, 1H, J¼2.6 Hz), 3.81e3.91 (m, 2H), 4.14 (td, 1H. J¼7.1, 2.6 Hz),
5.02 (dd, 1H, J¼17.7, 1.4 Hz), 5.08 (m, 1H), 5.14 (dd, 1H, J¼10.9,
1.4 Hz), 5.85 (dd, 1H, J¼17.7, 10.9 Hz); for 6-D
d 1.02 (s, 3H), 1.36 (s,
3H), 1.40 (s, 3H), 1.40e1.56 (m, 2H), 1.58 (s, 3H), 1.67 (s, 3H),
1.79e1.97 (m, 2H), 2.03 (br, 1H, OH), 3.70 (br s, 1H), 3.80e3.91 (m,
2H), 4.16 (ddd, 1H, J¼7.8, 6.3, 3.4 Hz), 5.02 (dd, 1H, J¼17.7, 1.3 Hz),
5.09 (m, 1H), 5.13 (dd, 1H, J¼10.8, 1.3 Hz), 5.87 (dd, 1H, J¼17.7,
10.8 Hz); 13C NMR (125 MHz, CDCl3) for 6-C
d 17.7, 18.2, 22.6, 25.4,
25.8, 26.6, 38.1, 43.0, 64.4, 76.4, 76.9,107.6,114.4,124.7,131.5,143.1;
for 6-D 17.7, 18.2, 22.6, 25.7, 25.8, 26.6, 38.1, 43.3, 65.0, 76.5, 76.6,
d
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A. Sakama et al. / Tetrahedron xxx (2016) 1e7
5
107.7, 114.5, 124.7, 131.5, 143.0; HRMS (EI) calcd for C16H28O3 (Mþ)
m/z 268.2038, found 268.2027.
(12%) of 13-A and 19.4 mg (44%) of 13-C/13-D (d.r.¼1:4). Compound
13-A was obtained as a colorless oil: TLC Rf 0.36 (EtOAc/hexane,
1:2); IR (neat) 3408, 2969, 2925 cmꢀ1 1H NMR (500 MHz, CDCl3)
;
4.2.2. Synthesis of 6-AeD from 4 and 9. The following reaction was
carried out under Ar. To a cooled (0 ꢁC) stirred solution of 9
(72.4 mg, 0.274 mmol) in CH2Cl2 (3 mL) was added 4 (154 mg,
1.18 mmol). After being stirred at 0 ꢁC to room temperature for 40 h,
the mixture was diluted with H2O (15 mL) and extracted with
EtOAc/hexane (1:1, 15 mLꢂ2). The combined extracts were dried
and concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel (EtOAc/hexane, 1:10) to
provide 4.9 mg (6%) of 6-A/6-B (d.r.¼1:8) and 55.1 mg (66%) of 6-C/
6-D (d.r.¼4:1).
d 1.11 (s, 3H), 1.50e1.68 (m, 2H), 1.59 (s, 3H), 1.68 (s, 3H), 1.88e1.96
(m, 2H), 3.56e3.76 (m, 2H), 3.78 (d, 1H, J¼9.2 Hz), 4.00 (m,1H), 4.34
(dd, 1H, J¼10.8, 5.3 Hz), 5.04 (dd, 1H, J¼17.7, 1.4 Hz), 5.11 (m, 1H),
5.16 (dd, 1H, J¼10.8, 1.4 Hz), 5.56 (s, 1H), 5.88 (dd, 1H, J¼17.7,
10.8 Hz), 7.32e7.41 (m, 3H), 7.41e7.55 (m, 2H); 13C NMR (125 MHz,
CDCl3)
d 17.8, 19.7, 22.8, 25.8, 37.2, 44.3, 61.5, 71.5, 73.9, 79.9, 100.2,
113.9, 124.9, 126.0 (2C), 128.3 (2C), 129.0, 131.5, 137.6, 144.0; HRMS
(EI) calcd for C21H30O4 (Mþ) m/z 346.2144, found 346.2149. A
mixture of 13-C and 13-D was obtained as a colorless oil: TLC Rf 0.69
(EtOAc/hexane, 1:2); IR (neat) 3417, 2969, 2924 cmꢀ1 1H NMR
;
(500 MHz, CDCl3) for 13-C
d 1.12 (s, 3H), 1.50e1.63 (m, 2H), 1.57 (s,
4.2.3. (2R,3R,4R,5R)-1,3-[(S)-Benzylidenedioxy]-5,9-dimethyl-5-
vinyldec-8-ene-2,4-diol (11-A) and (2R,3R,4R,5S)-isomer (11-B). The
following reaction was carried out under Ar. To a cooled (ꢀ78 ꢁC) 8
(33.4 mg, 0.126 mmol) was added a solution of 10 (128 mg,
0.612 mmol) in CH2Cl2 (1 mL). After being stirred at room tem-
perature for 7 days, the mixture was diluted with saturated
aqueous NaHCO3 (10 mL) and extracted with CH2Cl2 (10 mLꢂ9).
The combined extracts were dried and concentrated under re-
duced pressure. The residue was purified by column chromatog-
raphy on silica gel (EtOAc/hexane, 1:3) to provide 14.8 mg (34%) of
11-A/11-B (d.r.¼3:1) as a colorless oil: TLC Rf 0.41 (EtOAc/hexane,
3H), 1.67 (s, 3H), 1.88e1.97 (m, 2H), 2.46 (br, 1H, OH), 3.60e3.77 (m,
3H), 3.94 (m, 1H), 4.35 (dd, 1H, J¼11.0, 5.3 Hz), 5.06 (m, 1H), 5.12
(dd,1H, J¼17.7,1.3 Hz), 5.24 (dd,1H, J¼10.9,1.3 Hz), 5.44 (s,1H), 5.88
(dd, 1H, J¼17.7, 10.9 Hz), 7.30e7.42 (m, 3H), 7.42e7.50 (m, 2H); for
13-D
d 1.13 (s, 3H), 1.42e1.65 (m, 2H), 1.54 (s, 3H), 1.66 (s, 3H),
1.80e1.97 (m, 2H), 2.33 (br, 1H, OH), 3.60e3.76 (m, 3H), 3.95 (m,
1H), 4.38 (dd, 1H, J¼10.9, 5.2 Hz), 5.07 (m, 1H), 5.17 (dd, 1H, J¼17.5,
1.2 Hz), 5.32 (dd, 1H, J¼10.9, 1.2 Hz), 5.48 (s, 1H), 5.86 (dd, 1H,
J¼17.5, 10.9 Hz), 7.31e7.41 (m, 3H), 7.42e7.48 (m, 2H); 13C NMR
(125 MHz, CDCl3) for 13-C
d 17.8, 18.9, 22.7, 25.8, 36.4, 44.9, 64.9,
70.7, 80.1, 80.5, 100.3, 115.1, 124.7, 126.1 (2C), 128.3 (2C), 128.9, 131.7,
137.8, 143.0; for 13-D 16.5, 17.7, 22.8, 25.8, 37.9, 45.6, 64.7, 70.7,
1:2); IR (neat) 3443, 2969, 2920 cmꢀ1
;
1H NMR (500 MHz, CDCl3)
1.09 (s, 3H), 1.46e1.62 (m, 2H), 1.57 (s, 3H), 1.67 (s, 3H),
d
for 11-A
d
79.3, 80.1, 100.3, 116.6, 124.6, 126.1 (2C), 128.3 (2C), 128.9, 131.7,
137.8, 143.6; HRMS (EI) calcd for C21H30O4 (Mþ) m/z 346.2144,
found 346.2127.
1.81e2.00 (m, 2H), 2.73 (br, 1H, OH), 3.15 (br, 1H, OH), 3.68 (d, 1H,
J¼6.8 Hz), 3.82 (m, 1H), 3.94 (dd, 1H, J¼6.8, 1.4 Hz), 4.07 (dd, 1H,
J¼12.1, 1.4 Hz), 4.24 (dd, 1H, J¼12.1, 1.8 Hz), 5.08 (m, 1H), 5.09 (dd,
1H, J¼17.8, 1.4 Hz), 5.21 (dd, 1H, J¼10.9, 1.4 Hz), 5.57 (s, 1H), 5.97
(dd, 1H, J¼17.8, 10.9 Hz), 7.32e7.41 (m, 3H), 7.45e7.51 (m, 2H); for
4.2.6. (2R,3S,4R,5S)-1,3-[(R)-Benzylidenedioxy]-5,9-dimethyl-5-
vinyldec-8-ene-2,4-diol (13-B), (2R,3S,4S,5R)-isomer (13-C), and
(2R,3S,4S,5S)-isomer (13-D). The following reaction was carried out
under Ar. To a cooled (ꢀ78 ꢁC) 9 (46.7 mg, 0.177 mmol) was added
a solution of 12 (84.3 mg, 0.405 mmol) in CH2Cl2 (2 mL). After being
stirred at room temperature for 6 days, the mixture was diluted
with saturated aqueous NaHCO3 (10 mL) and extracted with CH2Cl2
(10 mLꢂ7). The combined extracts were dried and concentrated
under reduced pressure. The residue was purified by column
chromatography on silica gel (EtOAc/hexane, 1:3) to provide 6.9 mg
(11%) of 13-B and 32.4 mg (53%) of 13-C/13-D (d.r.¼4:1). Compound
13-B was obtained as a colorless oil: TLC Rf 0.36 (EtOAc/hexane,
11-B
d 1.12 (s, 3H), 1.45e1.72 (m, 2H), 1.56 (s, 3H), 1.67 (s, 3H),
1.88e1.96 (m, 2H), 2.83 (br, 1H, OH), 3.16 (br, 1H, OH), 3.69 (d, 1H,
J¼6.6 Hz), 3.82 (m, 1H), 3.92 (dd, 1H, J¼6.6, 1.4 Hz), 4.07 (dd, 1H,
J¼12.0, 1.4 Hz), 4.24 (dd, 1H, J¼12.0, 1.7 Hz), 5.08 (m, 1H), 5.08 (dd,
1H, J¼17.7, 1.4 Hz), 5.16 (dd, 1H, J¼11.0, 1.4 Hz), 5.53 (s, 1H), 5.91
(dd, 1H, J¼17.7, 11.0 Hz), 7.34e7.42 (m, 3H), 7.46e7.51 (m, 2H); 13
C
NMR (125 MHz, CDCl3) for 11-A
d 17.7, 18.0, 22.7, 25.8, 38.2, 44.2,
64.9, 72.5, 76.1, 79.8, 100.8, 114.8, 124.9, 125.9 (2C), 128.4 (2C),
129.0, 131.5, 137.9, 143.3; for 11-B 17.7, 18.3, 22.7, 25.8, 37.6, 44.0,
d
65.1, 72.5, 76.7, 79.5, 100.8, 113.8, 124.9, 126.0 (2C), 128.3 (2C),
129.0, 131.5, 137.9, 143.5; HRMS (EI) calcd for C21H30O4 (Mþ) m/z
346.2144, found 346.2139.
1:2); IR (neat) 3408, 2969, 2925 cmꢀ1
;
1H NMR (500 MHz, CDCl3)
d
1.13 (s, 3H), 1.43e1.60 (m, 2H), 1.59 (s, 3H), 1.68 (s, 3H), 1.85e1.99
(m, 2H), 2.37 (br, 1H, OH), 2.46 (br, 1H, OH), 3.60e3.71 (m, 2H), 3.79
(d,1H, J¼9.5 Hz), 3.97 (m,1H), 4.33 (dd,1H, J¼10.8, 5.4 Hz), 5.09 (dd,
1H, J¼17.5, 1.5 Hz), 5.10 (m, 1H), 5.19 (dd, 1H, J¼10.9, 1.5 Hz), 5.55 (s,
1H), 5.88 (dd, 1H, J¼17.5, 10.9 Hz), 7.32e7.42 (m, 3H), 7.42e7.55 (m,
4.2.4. Synthesis of 11-A/11-B from 10 and 9. The following reaction
was carried out under Ar. To a cooled (ꢀ78 ꢁC) 9 (30.1 mg,
0.114 mmol) was added a solution of 10 (58.8 mg, 0.282 mmol) in
CH2Cl2 (1 mL). After being stirred at room temperature for 7 days,
the mixture was diluted with saturated aqueous NaHCO3 (10 mL)
and extracted with CH2Cl2 (10 mLꢂ9). The combined extracts were
dried and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel (EtOAc/hexane,
1:3) to provide 14.8 mg (35%) of 11-A/11-B (d.r.¼1:3) as a colorless
oil.
2H); 13C NMR (125 MHz, CDCl3)
d 17.8, 19.7, 22.8, 25.8, 37.2, 44.3,
61.5, 71.5, 73.9, 79.9, 100.2, 113.9, 124.9, 126.0 (2C), 128.3 (2C), 129.0,
131.5,137.6, 144.0; HRMS (EI) calcd for C21H30O4 (Mþ) m/z 346.2144,
found 346.2149.
4.2.7. (6S,7S,8R)-7-Benzyloxy-6-(2-hydroxyethyl)-8,9-(iso-
propylidenedioxy)-2,6-dimethylnonan-3-ol (14-D). To
a
cooled
(0 ꢁC) stirred solution of 6-D/6-C (d.r.¼5:1, 2.02 g, 7.53 mmol) in
DMF (40 mL) was added NaH (60% in oil, 1.2 g, 30 mmol). The
mixture was stirred at 0 ꢁC for 30 min, and BnBr (98%, 2.0 mL,
17 mmol) was added. After being stirred at room temperature for
2 h, the mixture was quenched with MeOH (25 mL) and K2CO3
(2.7 g), diluted with EtOAc/hexane (1:1, 100 mL), and washed with
saturated aqueous NH4Cl (80 mL) and saturated brine (40 mL),
respectively. The combined aqueous layers were extracted with
EtOAc (50 mLꢂ7). The combined organic layer and extracts were
dried and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel (toluene/hexane,
4.2.5. (2R,3S,4R,5R)-1,3-[(R)-Benzylidenedioxy]-5,9-dimethyl-5-
vinyldec-8-ene-2,4-diol (13-A), (2R,3S,4S,5R)-isomer (13-C), and
(2R,3S,4S,5S)-isomer (13-D). The following reaction was carried out
under Ar. To a cooled (ꢀ78 ꢁC) 8 (33.6 mg, 0.127 mmol) was added
a solution of 12 (89.2 mg, 0.428 mmol) in CH2Cl2 (2 mL). After being
stirred at room temperature for 4 days, the mixture was diluted
with saturated aqueous NaHCO3 (10 mL) and extracted with CH2Cl2
(10 mLꢂ7). The combined extracts were dried and concentrated
under reduced pressure. The residue was purified by column
chromatography on silica gel (EtOAc/hexane, 1:3) to provide 5.2 mg
Please cite this article in press as: Sakama, A.; et al., Tetrahedron (2016), http://dx.doi.org/10.1016/j.tet.2016.07.030

6
A. Sakama et al. / Tetrahedron xxx (2016) 1e7
1:1) to provide 2.50 g (94%) of benzyl ether (d.r.¼5:1) as a colorless
oil: TLC Rf 0.45 (EtOAc/hexane, 1:6).
(10 mLꢂ5). The combined organic layer and extracts were dried and
concentrated under reduced pressure. The residue was purified by
column chromatography on silica gel (EtOAc/hexane, 1:2) to pro-
vide 277 mg (76%) of 16 and 60.2 mg (15%) of 15 was recovered.
Compound 16 was obtained as a colorless oil: TLC Rf 0.64 (EtOAc/
The following reaction was carried our under Ar. To a cooled
(0 ꢁC) stirred solution of benzyl ether (d.r.¼5:1, 77.3 mg,
0.215 mmol) in THF (2 mL) was added thexylborane (0.5 M solution
in THF, 1.3 mL, 0.65 mmol). After being stirred at 0 ꢁC for 1 h, the
mixture was quenched with EtOH (2 mL). Then 1 M aqueous NaOH
(2.0 mL, 2.0 mmol) and 35 wt % aqueous H2O2 (0.35 mL, 4.0 mmol)
were added at 0 ꢁC. After being stirred at room temperature for 1 h,
the mixture was quenched with 20 wt % aqueous Na2S2O3 (20 mL),
diluted with H2O (20 mL), and extracted with EtOAc (15 mLꢂ5). The
combined extracts were dried and concentrated under reduced
pressure. The residue was purified by column chromatography on
silica gel (EtOAc/hexane, 1:3) to provide 35.9 mg (42%) of 14-D and
32.0 mg (38%) of a mixture of 3-epi-14-D and 14-C. Compound 14-D
hexane, 1:2); [
a
]
25 ꢀ2.9 (c 0.610, CHCl3); IR (neat) 3406, 2931 cmꢀ1
;
D
1H NMR (500 MHz, CDCl3)
d 0.93 (s, 3H), 1.06 (s, 9H), 1.25 (m, 1H),
1.43 (m, 1H), 1.54 (s, 3H), 1.65 (s, 3H), 1.73 (m, 1H), 1.82 (m, 1H),
1.87e1.93 (m, 2H), 2.05 (br, 1H, OH), 2.76 (br, 1H, OH), 3.47 (d, 1H,
J¼4.3 Hz), 3.64e3.87 (m, 5H), 4.54 (d, 1H, J¼11.3 Hz), 4.68 (d, 1H,
J¼11.3 Hz), 5.00 (br t, 1H, J¼7.0 Hz), 7.24e7.34 (m, 5H), 7.34e7.46
(m, 6H), 7.64e7.71 (m, 4H); 13C NMR (125 MHz, CDCl3)
d 17.6, 19.1,
22.0, 22.3, 25.7, 26.9 (3C), 36.5, 39.2, 40.0, 60.9, 64.7, 72.2, 75.6, 87.8,
124.7, 127.3 (2C), 127.5, 127.7 (4C), 128.3 (2C), 129.7 (2C), 131.2,
133.5, 133.6, 135.6 (4C), 138.4; HRMS (ESI) calcd for C36H51O4Si
(MþHþ) m/z 575.3557, found 575.3558.
was obtained as a colorless oil: TLC Rf 0.42 (EtOAc/hexane, 2:1);
[
a]
ꢀ7.3 (c 0.875, CHCl3); IR (neat) 3383, 2957 cmꢀ1
;
1H NMR
20
D
(500 MHz, CDCl3)
d
0.89 (d, 3H, J¼7.0 Hz), 0.91 (d, 3H, J¼7.0 Hz),
4.2.10. (2R,3S,4S)-4-[2-(tert-Butyldiphenylsilyloxy)ethyl]-4,8-
dimethylnon-7-ene-1,2,3-triol (17). To a cooled (ꢀ78 ꢁC) stirred
solution of lithium (8.6 mg, 1.2 mmol) in liquid NH3 (5 mL) was
added a solution of 16 (177 mg, 0.308 mmol) in Et2O (2 mL). The
mixture was stirred at ꢀ78 ꢁC for 10 min, and lithium (8.6 mg,
1.2 mmol) was added. After being stirred at ꢀ78 ꢁC for 10 min, the
mixture was quenched with solid NH4Cl (186 mg) and warmed to
room temperature. This was diluted with 20 wt % aqueous NH4Cl
(25 mL) and extracted with CH2Cl2 (10 mLꢂ5). The combined ex-
tracts were dried and concentrated under reduced pressure. The
residue was purified by column chromatography on silica gel
(EtOAc/hexane, 1:4) to provide 78.7 mg (53%) of 17 and 78.7 mg
(44%) of unreacted 16, which was treated by the same procedure to
0.96 (s, 3H), 1.24e1.74 (m, 7H), 1.37 (s, 3H), 1.47 (s, 3H), 3.27 (m, 1H),
3.56e3.71 (m, 3H), 4.02 (t, 1H, J¼7.7 Hz), 4.08 (t, 1H, J¼7.7 Hz), 4.38
(td, 1H, J¼7.7, 1.9 Hz), 4.62 (d, 1H, J¼11.1 Hz), 4.93 (d, 1H, J¼11.1 Hz),
7.25e7.39 (m, 5H); 13C NMR (125 MHz, CDCl3)
d 16.9, 18.9, 23.0,
25.0, 26.5, 27.8, 33.0, 33.5, 39.4 (2C), 58.8, 65.3, 75.6, 76.5, 77.2, 84.3,
107.6, 127.67, 127.70 (2C), 128.4 (2C), 138.3; HRMS (ESI) calcd for
C
23H39O5 (MþHþ) m/z 395.2797, found 395.2798.
4.2.8. (6S,7S,8R)-7-Benzyloxy-6-[2-(tert-butyldiphenylsilyloxy)-
ethyl]-8,9-(isopropylidenedioxy)-2,6-dimethylnon-2-ene (15). To
a cooled (0 ꢁC) stirred solution of 14-D (78.6 mg, 0.199 mmol) in
CH2Cl2 (1 mL) were added i-Pr2NEt (97%, 72 L, 0.41 mmol),
TBDPSCl (62 L, 0.24 mmol), and DMAP (2.0 mg, 16 mol). After
m
m
m
provide additional 17 (57.0 mg). In total, 136 mg (77%) of 17 was
28
being stirred at room temperature for 20 h, the mixture was
quenched with saturated aqueous NH4Cl (3 mL), diluted with H2O
(5 mL), and extracted with CH2Cl2 (5 mLꢂ4). The combined extracts
were dried and concentrated under reduced pressure. The residue
was purified by column chromatography on silica gel (EtOAc/hex-
ane, 1:15) to provide 116 mg (92%) of silyl ether as a colorless oil:
TLC Rf 0.36 (EtOAc/hexane, 1:4).
The following reaction was carried out under Ar. To a cooled
(0 ꢁC) stirred solution of silyl ether (440 mg, 0.694 mmol) in CH2Cl2
(0.5 mL) was added a solution of Martin sulfurane (96%, 658 mg,
0.939 mmol) in CH2Cl2 (3 mL). After being stirred at room tem-
perature for 4 h, the mixture was diluted with Et2O (15 mL) and
washed with 1 M aqueous NaOH (8 mLꢂ3). The organic layer was
dried and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel (EtOAc/hexane,
obtained as a colorless oil: TLC Rf 0.42 (EtOAc/hexane, 1:1); [a]
D
ꢀ0.4 (c 1.01, CHCl3); IR (neat) 3383, 2930 cmꢀ1; 1H NMR (500 MHz,
CDCl3) d 0.96 (s, 3H),1.05 (s, 9H), 1.20e1.62 (m, 4H), 1.53 (s, 3H), 1.65
(s, 3H), 1.74e1.95 (m, 2H), 2.73 (br, 2H, OHꢂ2), 3.66e3.89 (m, 6H),
4.34 (d, 1H, J¼3.8 Hz, OH), 5.03 (br t, 1H, J¼7.0 Hz), 7.38e7.49 (m,
6H), 7.63e7.70 (m, 4H); 13C NMR (125 MHz, CDCl3)
d 17.6, 19.0, 20.8,
22.0, 25.6, 26.7 (3C), 36.9, 39.1, 39.8, 60.9, 65.2, 71.3, 79.8, 124.5,
127.87 (2C), 127.89 (2C), 129.98, 130.04, 131.4, 132.3, 132.4, 135.5
(2C), 135.6 (2C); HRMS (ESI) calcd for C29H45O4Si (MþHþ) m/z
485.3087, found 485.3089.
4.2.11. (2S)-2-[2-(tert-Butyldiphenylsilyloxy)ethyl]-2,6-
dimethylhept-5-enal (18). To a cooled (0 ꢁC) stirred solution of 17
(23.6 mg, 48.7
(68.5 mg, 320
m
m
mol) in MeOH (1 mL) was added a solution of NaIO4
mol) in H2O (0.5 mL). After being stirred at room
1:60) to provide 413 mg (97%) of 15 as a yellow oil: TLC Rf 0.60
temperature for 4 h, the mixture was diluted with H2O (10 mL) and
extracted with CH2Cl2 (5 mLꢂ7). The combined extracts were dried
and concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel (EtOAc/hexane, 1:100) to
provide 18.7 mg (91%) of 18 as a colorless oil. The spectral data of
synthetic 18 was identical to those of our sample.10
25
(EtOAc/hexane, 1:4);
[
a
]
D
ꢀ2.0 (c 0.690, CHCl3); IR (neat)
2931 cmꢀ1
;
1H NMR (500 MHz, CDCl3)
d 0.83 (s, 3H), 1.03 (s, 9H),
1.13 (m, 1H), 1.33 (s, 3H), 1.40 (s, 3H), 1.51e1.60 (m, 2H), 1.52 (s, 3H),
1.65 (s, 3H), 1.74 (m, 1H), 1.83e1.91 (m, 2H), 3.61 (d, 1H, J¼1.6 Hz),
3.67e3.78 (m, 2H), 3.89 (t, 1H, J¼7.8 Hz), 4.00 (t, 1H, J¼7.8 Hz), 4.29
(td, 1H, J¼7.8, 1.6 Hz), 4.48 (d, 1H, J¼11.2 Hz), 4.89 (d, 1H, J¼11.2 Hz),
4.97 (br t, 1H, J¼7.0 Hz), 7.22e7.32 (m, 5H), 7.32e7.43 (m, 6H),
Acknowledgements
7.62e7.68 (m, 4H); 13C NMR (125 MHz, CDCl3)
d 17.6, 19.1, 22.0, 22.2,
24.9, 25.7, 26.4, 26.9 (3C), 36.8, 39.1, 39.2, 60.6, 64.8, 75.2, 76.7, 83.8,
107.2, 124.6, 127.2, 127.3 (2C), 127.6 (4C), 128.2 (2C), 129.5 (2C),
131.2, 133.9 (2C), 135.6 (4C), 139.0; HRMS (ESI) calcd for C39H55O4Si
(MþHþ) m/z 615.3870, found 615.3871.
This work was supported in part by the Ministry of Education,
Culture, Sports, Science, and Technology-Supported Program for
the Strategic Research Foundation at Private Universities,
2012e2016, and the Keio University Doctorate Student Grant-in-
Aid Program.
4.2.9. (2R,3S,4S)-3-Benzyloxy-4-[2-(tert-butyldiphenylsilyloxy)-
ethyl]-4,8-dimethylnon-7-ene-1,2-diol (16). To a stirred solution of
15 (389 mg, 0.633 mmol) in MeCN (3 mL) was added
Zn(NO3)2$6H2O (1.02 g, 3.43 mmol). After being stirred at 50 ꢁC for
24 h, the mixture was diluted with CH2Cl2 (10 mL) and washed with
H2O (10 mL). The aqueous layer was extracted with CH2Cl2
Supplementary data
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2016.07.030.
Please cite this article in press as: Sakama, A.; et al., Tetrahedron (2016), http://dx.doi.org/10.1016/j.tet.2016.07.030

A. Sakama et al. / Tetrahedron xxx (2016) 1e7
7
9. Schmid, C. R.; Bryant, J. D. Org. Synth. 1995, 72, 6e13 (Coll. Vol. IX, 1998,
450e453).
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Please cite this article in press as: Sakama, A.; et al., Tetrahedron (2016), http://dx.doi.org/10.1016/j.tet.2016.07.030