Regio- and Diastereoselective Samarium-Mediated Allylic Benzoate Reductions

Article abstract of DOI:10.1055/s-0036-1590831

A regio- and diastereoselective samarium(II)-mediated reduction of allylic benzoates is described. Yields for the reactions are generally high with diastereoselectivities up to 90:10 and in some cases only a single regioisomer was obtained. The stereoselectivity of the reaction is proposed to arise from chelation of a hydroxyl-stereocenter and starting alkene geometry, with protonation occurring intramolecularly by samarium-bound water.

Full text of DOI:10.1055/s-0036-1590831

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
©
Georg Thieme Verlag Stuttgart · New York
2017, 28, A–E
letter
A
en
Synlett
T. F. Stockdale, G. W. O’Neil
Letter
Regio- and Diastereoselective Samarium-Mediated Allylic Benzo-
ate Reductions
Trevor F. Stockdale
Gregory W. O’Neil*
non-stereospecific to
OBz stereochemistry
-
R2
R2
OBz
SmI2, H2O
isolated yields >70%
d.r. up to 90:10
complete regioselectivity
( )n
( )n
Department of Chemistry, Western Washington University,
Bellingham, WA, USA
oneilg@wwu.edu
R1
R1
OH
OH
CH3 n = 0,1
CH3
stereospecific to
alkene geometry
Received: 01.06.2017
Accepted after revision: 19.06.2017
Published online: 20.07.2017
OBz
R'
O
Ph
Ph
R
SmI2
R'OH Ph
SmLn
H
SmLn
DOI: 10.1055/s-0036-1590831; Art ID: st-2017-r0421-l
or
OBz
R
Ph
R
Ph
R
2
1
Abstract A regio- and diastereoselective samarium(II)-mediated re-
duction of allylic benzoates is described. Yields for the reactions are
generally high with diastereoselectivities up to 90:10 and in some cases
only a single regioisomer was obtained. The stereoselectivity of the re-
action is proposed to arise from chelation of a hydroxyl-stereocenter
and starting alkene geometry, with protonation occurring intramolecu-
larly by samarium-bound water.
R
OP
OP
OP
OP
SmI2, MeOH
98%)
(
OBz
honokiol; P = H
OBz
Key words samarium, reduction, stereoselective synthesis, regiose-
Scheme 1 Regioselective SmI allyl benzoate reductions
2
lectivity, diastereoselectivity
this general strategy into a stereoselective process. Herein
we report the development of a regio- and diastereoselec-
tive samarium-mediated allylic benzoate reduction using
both Roche ester and lactate derived substrates. The reac-
tion appears to be quite general, affording both aryl and al-
kyl products containing methyl or ethyl stereocenters in
comparable yield and selectivities. Importantly, diastereo-
selectivities were independent of the initial benzoylated
hydroxyl stereochemistry yet stereospecific with regard to
the trisubstituted alkene geometry.
Samarium diiodide (SmI ) has emerged as one of the
2
8
more useful and versatile reductants available to synthetic
1
chemists, capable of controllable (e.g. through the use of
2
additives like HMPA or H O) and selective reductions of a
2
3
wide variety of functional groups. Our group recently re-
ported a SmI -mediated reductive removal of allylic benzo-
2
ates leading selectively to non-conjugated olefin products of
4
type 1 (Scheme 1). The reaction is proposed to proceed via
an organosamarium intermediate 2, with regioselectivity
controlled by sterics and intramolecular proton delivery
from a samarium-coordinated proton donor (e.g. water or
SmI , MeOH
2
5
OBz
*
MeOH). This method then featured as part of our synthesis
+
(90%)
3
(not detected)
of the biologically-relevant natural product honokiol, used
to simultaneously install both allyl substituents found in
Scheme 2 Reduction of a trisubstituted alkene allylic benzoate and
formation of a new stereocenter (*)
6
the target compound.
As an extension of that work, we began investigating the
reaction applied to trisubstituted alkene substrates. For in-
Our initial investigations began with the PMB-protected
7
stance, treatment of allyl benzoate 3 with SmI /MeOH led
trans-phenyl compound 4, prepared by zirconium-cata-
2
9
to its rapid and clean conversion to 3-phenyl-1-butene with
lyzed carboalumination of phenylacetylene and trapping
1
10
complete regioselectivity by H NMR analysis (Scheme 2).
of the resulting vinylalane with aldehyde (S)-5 (Scheme
We recognized that this reaction generated a new stereo-
center, and were intrigued about the possibility of adapting
3). The stereochemistry of the newly formed hydroxyl in 6
for the major isomer is assumed to be S arising from chela-
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

B
Synlett
T. F. Stockdale, G. W. O’Neil
Letter
tion control,11 but was not rigorously determined as this
stereocenter proved unimportant for the subsequent elimi-
nations (vide infra). Benzoylation and treatment with
SmI /ROH or SmI /DMPU (followed by quenching with H O)
Table 1 Regio- and Diastereoselective Reduction of Alcohol 9
OBz OH
OH
OH
SmI2
+
Ph
Ph
Ph
2
2
2
conditions
9
10
11
at room temperature led to rapid elimination, affording a
mixture of alkene regioisomers generally in favor of the
non-conjugated product 7 (up to 5:1). Careful analysis of
Entry
Additivea
10:11b
Compound 10 d.r.b
1
the H NMR spectra, however, revealed no appreciable lev-
1
2
3
4
5
DMPU
t-BuOH
i-PrOH
MeOH
2:1
1:0
75:25
67:33
67:33
60:40
76:24
75:25
els of diastereoselectivity for any of the reactions.12 The
highest diastereomeric ratio (d.r.) was obtained when using
tert-butanol (t-BuOH), however, this reaction proceeded
with only modest regioselectivity and produced what we
have tentatively characterized as dimerization products
presumably due to a slower protonation event (similar
products were also observed for the anhydrous DMPU en-
c
2.3:1
1:0C
H
2
2
O
15:1
5:1
6
H
Od
a
Reactions were performed by adding the additive (16 equiv DMPU or
(7 equiv) followed by the substrate and stirring for
13
1400 equiv ROH) to SmI
2
try). The SmI /H O reaction was much cleaner in this re-
2
2
3
0 min.
Determined by NMR.
b
gard (i.e. 5:1 regioselectivity and no dimerization), howev-
er, it was non-diastereoselective (d.r. 1:1).
c
Compound 11 was not detected by NMR.
d
The reaction was performed at 0 °C.
OH
AlMe3, Cp2ZrCl2
OHC
BzCl, pyr.
Ph
Ph
OPMB
In order to determine if the stereochemistry of the OBz
(quant.)
OPMB
6
stereocenter might impact the stereoselectivity of the reac-
tion, we prepared compound 9 as a ca. 1:1 mixture of dias-
tereomers (compared to the originally obtained ca. 2:1 mix-
ture) using an oxidation/reduction sequence (Scheme 4). As
shown, treatment of this 1:1 mixture with SmI /H O gave
then
OBz OPMB
(85%, d.r. 70:30)
5
OPMB
OPMB
SmI2
+
Ph
Ph
Ph
(
see Table)
4
7
8
2
2
Entry
Additivea 7:8b
7 d.r.b
Notes:
a
product 10 in the same diastereomeric ratio as that ob-
tained when 9 was used as a 70:30 mixture of diastereo-
mers, meaning that there is no memory of chirality associ-
1
.
DMPU
t-BuOH
1.3:1
3:1
60:40
69:31
60:40
50:50
Reactions were performed by adding the
additive (16 equiv DMPU or 1400 equiv ROH)
to SmI2 (7 equiv) followed by the substrate at
room temperature.
2
.
3
4
.
.
MeOH
H2O
3:1
5:1
17
b
Determined by NMR
ated with the OBz stereocenter. This is attractive from a
synthetic standpoint, in that the stereochemistry of this po-
sition need not be controlled when preparing substrates for
this reaction.
Scheme 3 Initial screening of compound 4 reductions with SmI2
We surmised that removal of the PMB-protecting group
and performing the reaction with a free hydroxyl at this po-
sition might impart better diastereoselectivity through en-
14
hanced samarium chelation. Indeed after deprotection
with DDQ, samarium reduction of the primary alcohol
compound 9 now proceeded with not only improved regio-
selectivity but also enhanced diastereoselectively (up to
76:24). Table 1 presents results from our investigations into
the impact of different proton sources on the outcome of
the reaction with 9. Interestingly, the highest (and nearly
identical) diastereoselectivities were obtained using either
anhydrous conditions followed by quenching (DMPU, entry
1
) or in the presence of water (entry 5),15 suggestive against
16
an internal protonation by the hydroxyl group per se.
These reactions produced compound 10 as a 3:1 mixture of
diastereomers and exclusively as the trans isomer. However,
regioselectivity for the DMPU reaction was much lower (2:1
Scheme 4 Examining the impact of compound 9-OBz stereochemistry
on the stereoselectivity of SmI -reductions
2
vs 15:1 for H O). In an attempt to improve the diastereose-
2
lectivity the reaction was also performed at 0 °C, however
the colder conditions gave the same d.r. and an erosion of
regioselectivity (entry 6).
Table 2 shows optimizations with respect to the equiva-
lents of H O for the SmI /H O reduction of 9. Interestingly,
2
2
2
the d.r. for all of the reactions remained essentially the
same, which is in contrast to an earlier report from Keck de-
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

C
Synlett
T. F. Stockdale, G. W. O’Neil
Letter
scribing diastereoselective reductions of β-hydroxyketones
ate 13,22 involving hydroxyl chelation of samarium23 fol-
lowed by intramolecular protonation by a coordinated wa-
ter molecule.
by SmI wherein higher equivalents of H O leads to a loss of
2
2
18
diastereoselectivity. Our results suggest that irrespective
of H O equivalents, the hydroxyl group in 9 is able to effec-
tively chelate to samarium. This is consistent with other
The reaction is not limited only to aryl substrates like 9.
For instance, the TBS-protected compound 14 could be ob-
tained with complete regioselectivity and identical diaste-
reoselectivity to that obtained for the phenyl product 10
(ca. 3:1, Scheme 6). At this stage, the stereochemistry of the
newly generated methyl stereocenter is assumed to be anal-
ogous to compound 10 (ref. Scheme 5). Ethyl stereocenters
could also be prepared by this protocol using a similar car-
2
studies showing that even high concentrations of H O do
2
19
not lead to complete saturation of Sm(II). Regioselectivity
improved at fewer equivalents of H O, perhaps due to mini-
2
mizing competing intermolecular protonation (ref. Scheme
1
). Yields also tended to increase with decreased H O with
2
the exception of one equivalent, where side products (e.g.
possible dimers) were observed leading to a lower isolated
yield of 10 (66% with 1 equiv).
9
boalumination (in this case with triethylaluminum) fol-
lowed by aldehyde addition for substrate preparation. In
this way, compounds 15 and 16 ultimately were obtained in
81% and 80% yield, respectively and 4:1 d.r.
Table 2 Impact of Water Equivalents on Regioselectivity, Diastereose-
2
0
lectivity, and Isolated Yield from the SmI Reduction of Compound 9
2
X
OBz
X
SmI2 (7 equiv)
OBz OH
OH
OH
SmI2
R
OH
R
OH
H2O (350 equiv)
+
Ph
Ph
Ph
conditions
9
10
11
Et
Et
TBSO
( )3
OH Ph
15 (81%, d.r. 80:20)
OH n-Bu
16 (80%, d.r. 80:20)
OH
b
c
H
2
O (equiv)a
10:11b
d.r. of 10
Yield of 10
1
4 (85%, d.r. 76:24)
2
00
00
86:14
86:14
86:14
91:9
75:25
76:24
75:25
75:25
75:25
76:24
72:28
72:28
30%
60%
75%
82%
90%
76%
86%
66%
1
Scheme 6 Regio- and diastereoselective SmI /H O reductions to pro-
duce non-aryl and/or non-methyl products 14–16
2
2
5
0
5
5
0
2
1
1
In order to examine the role (if any) of alkene geometry
on the stereochemistry of the newly formed stereocenter,
we set out to prepare a mixture of (E)- and (Z)-isomeric
substrates. This was accomplished through first an Evans’
aldol reaction24 with citral (mixture of cis- and trans-iso-
mers) giving E/Z-17 (Scheme 7). Reduction with LiBH4,
monoprotection of the resulting diol, benzoylation, and re-
moval of the TBS protecting group then produced a mixture
of 18 and 19.
97:3
98:2
5
98:2
1
100:0
a
b
c
2
Relative to SmI .
Determined by NMR.
Isolated yield.
The stereochemistry of the newly formed stereocenter
was determined by ozonolysis of 10 giving aldehyde 12
Scheme 5). A comparison of the optical activity of 12 to
that previously reported revealed that this compound was
enriched in the S-enantiomer, indicating that the major di-
astereomer of 10 had the (2R,5R)-configuration. A potential
model that would explain this outcome is given in Scheme
OH
O
O
TiCl4, Et3N, NMP
CHO
(
O
O
N
21
citral
(
mixture of E- and
Et
17 (87%)
N
Bn
Z-isomers)
Bn
1
2
. LiBH4 (65%)
. TBSCl, imid. (69%)
OBz OH
OBz OH
+
5, based on the energetics of a fused 5,6-bicyclic intermedi-
3. BzCl, pyr. then
HF•pyr. (70%)
18
19
Scheme 7 Synthesis of citral-derived isomers trans-18 and cis-19
OH
O3 then Me2S
O
Ph
Ph
1
0
(+)–12
Compounds 18 and 19 were partially separable by chro-
matography on silica allowing for the isolation of three
roughly equal mass fractions: (1) a sample enriched in the
trans-isomer 18 (87:13 18:19), (2) a sample enriched in the
cis-isomer 19 (16:84 18:19), and (3) a closer to equimolar
mixture of 18 and 19 (42:58 18:19). Each of these mixtures
was then taken separately into the reaction with SmI /H O
H
H
OBz OH
CH3
Ph
H
CH3
OH
SmI2
H O
O
Sm
O
Ph
Ph
2
H
H
(2R,5R)-10
CH3
13
Scheme 5 Determination of absolute stereochemistry of the major
stereoisomer of 10 by ozonolysis
2
2
1
(Scheme 8). As can be seen from the crude H NMR spectra,
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

D
Synlett
T. F. Stockdale, G. W. O’Neil
Letter
the cis- and trans-isomers gave opposing selectivities (i.e.
major = 20 from 18; major = 21 from 19). Using the starting
OH
1
. AlMe3, Cp2ZrCl2
1. BzCl, pyr.
OPMB
R
R
OHC
then 22
OPMB
2. SmI /H O Ph
18:19 ratio and anticipated diastereoselectivity based on
2
2
those previously observed for products 10 and 14 (i.e. 3:1),
we could calculate an expected ratio of products 20:21
from each of the three samples assuming that the reaction
is stereospecific with respect to alkene geometry. As
shown, the actual values obtained were very close to those
predicted.
R = Ph, 23; 82% (d.r. 58:42)
R = n-Bu, 24; 58% (d.r. 56:44)
1
2
. BzCl, pyr.
. DDQ
H2O
(equiv) d.r.
Isolated
yield
R
OBz
SmI2/H2O
Ph
Ph
Ph
5
86:14
84:16
84:16
90:10
88:12
53
60
60
50
55
OH
OH
R
R
100
200
n-Bu 50
n-Bu 100
see Table
R = Ph, 25, 80%
R = n-Bu, 26, 82%
R = Ph, 27
R = n-Bu, 28
Scheme 9 Synthesis and elimination of lactate-derived compounds
3–26
2
O3
OH
O
Ph
Ph
(S)-(+)–12
then DMS
27
H
OBz
H
O
SmI2
H2O
H
CH3
OH
OH
Sm
Ph
H
O
Ph
Ph
25
(
2R,5R)-27
Scheme 10 Ozonolysis and determination of the stereochemistry of
the major isomer of compound 27
Scheme 8 Alkene stereospecificity experiments using differentially en-
riched mixtures of 18 and 19. Colored lines are signals for the same col-
ored hydrogens.
In sum, SmI /H O reductions of allylic benzoates adja-
2
2
We also prepared and investigated the reductive cleav-
cent to trisubstituted alkenes and flanked by an alcohol ste-
reocenter occur with high regioselectivity and good diaste-
reoselectivity. The method appears to be quite general in
terms of the types of stereocenters (e.g. methyl, ethyl, etc.)
that may be installed. Selectivity is proposed to arise
through chelation of the hydroxyl group to samarium fol-
lowed by intramolecular protonation by samarium-coordi-
nated water, with stereochemistry controlled by ring-con-
formation considerations and starting alkene geometry.
Current efforts are aimed at further understanding the
mechanism and selectivity of this reaction, as well as ex-
ploring alternative auxiliary groups that may afford better
diastereoselectivities.
25
age of lactate aldehyde 22 -derived benzoate esters 23–26
26
(
Scheme 9). Perhaps unsurprisingly, treatment of PMB-
protected compound 23 with SmI /H O led exclusively to β-
2
2
elimination. Removal of the PMB protecting group sup-
pressed this competing process to some extent, allowing for
7 to be obtained in 53% yield from 25 when using five
2
equivalents of water. It was hypothesized that increasing
the amount of water might increase the rate of protonation
relative to elimination thus improving the yields. Indeed,
the use of 100 equivalents of water gave a higher yield (60%
20
vs 53%). Further increasing the amount of water equiva-
lents to 200 equivalents, however, resulted in no additional
yield enhancement. The diastereomeric ratios for com-
pounds 27 and 28 were slightly higher (86:14 and 90:10,
respectively) than those obtained from the related Roche
ester derived compounds (ca. 75:25, see Table 2).
Funding Information
Financial support from the National Science Foundation (CHE-
Ozonolysis of product 27 again gave primarily (S)-(+)-
1151492) is gratefully acknowledged.Dvsoin
of
C
h
e
mstiry
C(
H
E-1
1
5
1
4
9
2)
12, indicating that the absolute stereochemistry of the ma-
jor isomer of 27 was (2R,5R) (Scheme 10). A possible model
for this selectivity is given, similar to that previously pro-
posed for the one-carbon homologated samarium interme-
Supporting Information
Supporting informations for this article is available online at
https://doi.org/10.1055/s-0036-1590831.
3
27
diate 13 but as an η -complex. At this stage, however, ex-
S
u
p
p
ortioIgnfmr oaitn
S
u
p
p
o
nrtogI
i
f
rm oaitn
tended hydrogen bonded networks involving multiple wa-
28
29
ter molecules and/or multiple samariums need also be
considered.
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

E
Synlett
T. F. Stockdale, G. W. O’Neil
Letter
References and Notes
(17) For a recent review, see: Alezra, V.; Kawabata, T. Synthesis 2016,
4
8, 2997.
18) Keck, G. E.; Wager, C. A.; Sell, T.; Wager, T. T. J. Org. Chem. 1999,
4, 2172.
19) Sadasivam, D. V.; Teprovich, J. A. Jr.; Procter, D. A.; Flowers, R. A.
Org. Lett. 2010, 12, 4140.
(
1) (a) Nicolaou, K. C.; Ellery, S. P.; Chen, J. S. Angew. Chem. Int. Ed.
009, 48, 7140. (b) Edmonds, D. J.; Johnston, D.; Procter, D. J.
(
(
(
2
6
Chem. Rev. 2004, 104, 3371. (c) Molander, G. A.; Harris, C. R.
Chem. Rev. 1996, 96, 843.
(2) (a) Hasegawa, E.; Curran, D. P. J. Org. Chem. 1993, 58, 5008.
20) General Procedure for SmI /H O Reductions: To a solution of
2
2
(
(
b) Amiel-Levy, M.; Hoz, S. J. Am. Chem. Soc. 2009, 131, 8280.
c) Szostak, M.; Spain, M.; Parmar, D.; Procter, D. J. Chem.
SmI in THF (0.1 M, 11.2 mL) was added degassed H O (2.0 mL)
2
2
and the resulting red solution was stirred for 5 min before
adding the substrate (0.16 mmol). The solution was stirred for
Commun. 2012, 48, 330. (d) Szostak, M.; Spain, M.; Parmar, D.;
Procter, D. J. Chem. Soc. Rev. 2013, 42, 9155. (e) Szostak, M.;
Spain, M.; Eberhart, A. J.; Procter, D. J. J. Org. Chem. 2014, 79,
3
0 min before quenching with aq NaHCO (20 mL) and extract-
3
ing with EtOAc (2 × 20 mL). The combined organic extracts were
11988.
dried over MgSO , filtered, and concentrated in vacuo. The
4
(
(
(
3) Procter, D. J.; Flowers, R. A. II.; Skrydstrup, T. Organic Synthesis
using Samarium Diiodide; RSC Publishing: Cambridge, UK, 2010.
4) Schaefer, S. L.; Roberts, C. L.; Volz, E. O.; Grasso, M. R.; O’Neil, G.
W. Tetrahedron Lett. 2013, 54, 6125.
5) Yoshida, A.; Hanamoto, T.; Inanaga, J.; Mikami, K. Tetrahedron
Lett. 1998, 39, 1777.
residue was then purified by flash column chromatography on
silica to yield:
Compound 10: 20 mg (60%). Spectral data for the major isomer:
IR (ATR): 3360, 3083, 3061, 3025, 2961, 2925, 2871, 1950, 1876,
1
803, 1716, 1601, 1492, 1415, 1373, 1272, 1029, 971, 760, 698
–1
1
cm . H NMR (500 MHz, CDCl ): δ = 7.38 (t, J = 4.7 Hz, 1 H), 7.30
3
(
(
6) Wright, A. M.; O’Neil, G. W. Tetrahedron Lett. 2016, 57, 3441.
7) Takeda, M.; Takatsu, K.; Shintani, R.; Hayashi, T. J. Org. Chem.
(t, J = 6.9 Hz, 2 H), 7.20 (d, J = 8.0 Hz, 2 H), 5.74 (ddd, J = 15.5, 6.8,
1.1 Hz, 1 H), 5.33 (ddd, J = 15.5, 7.9, 1.4 Hz, 1 H), 3.47 (m, 2 H),
2
014, 79, 2354.
8) Marko, I. E.; Murphy, F.; Dolan, S. Tetrahedron Lett. 1996, 37,
089.
9) Wipf, P.; Lim, S. Angew. Chem. Int. Ed. 1993, 32, 1068.
3
.38 (dd, J =10.6, 8.1 Hz, 1 H), 2.36 (hept, J = 7.0 Hz, 1 H), 1.36 (d,
(
13
J = 7.0 Hz, 3 H), 1.01 (d, J = 6.9 Hz, 3 H). C NMR (125 MHz,
2
CDCl ): δ = 146.04, 136.89, 131.00, 128.43, 127.07, 126.06,
3
(
+
+
6
7.35, 42.27, 39.66, 21.48, 16.60. HRMS (ESI ): m/z [M] calcd
for C13H18O : 190.1358; found: 190.1358.
(
(
10) Mulzer, J.; Mantoulidis, A.; Öhler, E. J. Org. Chem. 2000, 65, 7456.
11) (a) Cram, D. J.; Kopecky, K. R. J. Am. Chem. Soc. 1959, 81, 2748.
+
Compound 27: 27 mg (60%). Spectral data for major diastereo-
mer: IR (ATR): 3328, 3083, 3060, 3026, 2967, 2925, 2871, 1601,
(b) Reetz, M. T. Acc. Chem. Res. 1993, 26, 462.
(
12) See Supporting Information.
–1 1
1
493, 1451, 1370, 1274, 1060, 970, 760, 699 cm . H NMR (500
(
13) For another report of SmI2 dimerization, see: Doisneau, G.;
Beau, J.-M. Tetrahedron Lett. 1998, 39, 3477.
MHz, CDCl ): δ = 7.30 (t, J = 7.6 Hz, 2 H), 7.18–7.22 (m, 3 H), 5.82
3
(ddd, J = 15.4, 6.7, 1.1 Hz, 1 H), 5.56 (ddd, J = 15.5, 6.6, 1.4 Hz, 1
(14) Kawatsura, M.; Hosaka, K.; Matsuda, F.; Shirahama, H. Synlett
H), 4.30 (p, J = 6.4 Hz, 1 H), 3.46 (p, J = 7.0, 6.4 Hz, 1 H), 1.36 (d,
1995, 729.
13
J = 7.0 Hz, 3 H), 1.28 (d, J = 6.4 Hz, 3 H). C NMR (125 MHz,
(15) The reaction was also performed using DMPU and H O together
2
CDCl ): δ = 145.56, 135.41, 132.87, 128.44, 127.16, 126.16,
3
and gave the same d.r. (75:25) as that obtained when using
+
+
6
8.87, 41.83, 23.42, 21.17. HRMS (ESI ): m/z [M – OH] calcd for
C12H15: 159.1174; found: 159.1175.
(21) Corey, E. J.; Hannon, F. J.; Boaz, N. W. Tetrahedron 1989, 45, 545.
DMPU (entry 1) or H O (entry 5).
2
(16) Performing the reaction in D O resulted in deuterium incorpo-
2
ration at C5 (Scheme 11):
(
22) Eleil, E. L.; Pillar, C. J. Am. Chem. Soc. 1955, 77, 3600.
(23) Prasad, E.; Flowers, R. A. II. J. Am. Chem. Soc. 2002, 124, 6357.
OBz OH
D
CH3
OH
(24) Evans, D. A.; Ennis, M. D.; Mathre, D. J. J. Am. Chem. Soc. 1982,
04, 1737.
SmI2
D2O
1
Ph
Ph
(25) Yu, W.; Zhang, Y.; Jin, Z. Org. Lett. 2001, 3, 1447.
(26) Qi, W.; McIntosh, M. C. Org. Lett. 2008, 10, 357.
(27) Bied, C.; Kagan, H. B. Tetrahedron 1992, 48, 3877.
(28) Chciuk, T. V.; Anderson, W. R. Jr; Flowers, R. A. J. Am. Chem. Soc.
9
Scheme 11
2016, 138, 8738.
(29) Prasad, E.; Flowers, R. A. J. Org. Chem. 2005, 127, 18093.
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E