Synthesis of (+)-Methyl Dihydropalustramate and of the Pyrido[1,2- a ]azepine Core of Stemona Alkaloids

Article abstract of DOI:10.1055/s-0034-1380685

Starting from a readily available, enantiomerically pure 2,6-disubstituted piperidine the synthesis of pyrido[1,2-a]azepines was accomplished. Key reactions for the ring closure were a photochemically induced acyl radical addition or a SmI₂-pro

Full text of DOI:10.1055/s-0034-1380685

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
©
Georg Thieme Verlag Stuttgart · New York
2015, 26, 1505–1509
1505
letter
Synlett
C. Mayer et al.
Letter
Synthesis of (+)-Methyl Dihydropalustramate and of the Pyrido-
1,2-a]azepine Core of Stemona Alkaloids
[
Camilla Mayer
Alexandra Romek
Thorsten Bach*
AcO
OH (>95% ee)
N
Z
H
H
Department Chemie and Catalysis Research Center (CRC),
Technische Universität München, 85747 Garching, Germany
thorsten.bach@ch.tum.de
O
O
N
MeO
N
H
H
Dedicated to Professor K. Peter C. Vollhardt
O
H
H
H
OMEM
OH
O
Received: 05.03.2015
Accepted after revision: 09.04.2015
Published online: 30.04.2015
1
4
AcO
OH
DOI: 10.1055/s-0034-1380685; Art ID: st-2015-b0149-l
N
ROOC
N
N
Z
9
X
H
H
H
H
OPG
Abstract Starting from a readily available, enantiomerically pure 2,6-
disubstituted piperidine the synthesis of pyrido[1,2-a]azepines was ac-
complished. Key reactions for the ring closure were a photochemically
Y
A
B (X = OH, Y = H; X,Y = O)
1
Figure 1 General structure A of the pyrido[1,2-a]azepine core in Ste-
mona alkaloids, general structure B (PG = protecting group) of target
compounds, and structure of enantiomerically pure alcohol 1 (Z = ben-
zyloxycarbonyl)
induced acyl radical addition or a SmI -promoted ketyl radical addition
2
to an α,β-unsaturated ester. En route to the cyclization precursor an ep-
oxidiation/ring opening sequence led to an undesired oxazolidinone
which turned out to be useful for the configuration assignment. The
compound was successfully converted into (+)-methyl dihydropalustra-
mate.
an enantioselective lipase-catalyzed acetylation of the re-
8
Key words alkaloids, cyclization, piperidines, radical reaction, total
synthesis
spective meso-diol. It was attempted to close the azepine
ring by a reductive cyclization reaction upon installation of
the appropriate substituents on the piperidine core. In this
communication, we present the preliminary results of our
synthetic studies, including the enantioselective prepara-
tion of dihydropalustramic acid, a key degradation product
of palustrine.
While Stemona alkaloids with a pyrrolo[1,2-a]azepine
1,2
core have received wide synthetic attention, the homolo-
gous alkaloids with a pyrido[1,2-a]azepine core (A, Figure
3
1
) have not been intensively investigated. Indeed, they are
smaller in number than the former compound class and
Due to 1,3-allylic strain, the carbon substituents of
piperidine 1 (AcOCH , CH OH) are likely forced in axial posi-
tions by the Z protecting group at the nitrogen. This ar-
rangement renders reactions at these substituents capri-
cious and leads to unexpected side reactions. The stereose-
represent only a fractional subset of known Stemona alka-
2
2
4
5
9
loids. According to a classification suggested by Pilli et al.,
only one out of eight Stemona alkaloid groups contains a
pyrido[1,2-a]azepine core. Still, the reported biological ac-
tivity of several naturally occurring pyrido[1,2-a]azepines
lective conversion of the primary hydroxymethyl (CH OH)
2
6
7
is remarkable and warrants synthetic studies. We have
been interested particularly in a possible route to Stemona
alkaloids, which could be derived from a potential interme-
diate B, in which the piperidine ring is not further oxygen-
ated but in which the stereogenic hydroxypropyl group is
properly attached to position C4 of the pyrido[1,2-a]aze-
pine core.
Our approach to target compounds of structure B was
planned to commence with chiral piperidine 1 (Figure 1),
which is readily available in enantiomerically pure form by
into the hydroxypropyl group has not yet proven feasible by
an oxidation/ethyl addition sequence. Despite literature
precedence for related pyrrolidine aldehydes,10 attempted
addition reactions to the intermediary formed piperidine
aldehyde gave low yields and produced, if at all, mainly the
undesired product diastereoisomer. An alternative route
was found to start with Wittig reaction of the aldehyde to
11
olefin 2, which could be oxidized with dimethyldioxirane
to a diastereomeric mixture (dr = 48:52) of epoxides, from
which product 3 was isolated in 41% yield (Scheme 1). Ring
opening with dimethyl cuprate12 and Swern oxidation de-
13
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1505–1509

1
506
Synlett
C. Mayer et al.
Letter
2.
O
O
1
. Swern oxidation;
H2C=PPh3
AcO
CH2
AcO
AcO
1
N
Z
N
89%
H
H
41%
H
H
H
H
O
Z
2
3
3
. Me2CuLi;
Swern oxidation
4. NaBH4
87%
AcO
N
N
Z
78%
H
H
Z
O
OH
4
5
Scheme 1 Preparation of secondary alcohol 5 from primary alcohol 1. Reagents and conditions: (1) (a) (COCl) (2.0 equiv), DMSO (3.0 equiv), Et N (4.0
2
3
®
equiv), CH Cl , −78 °C → r.t., 2 h; (b) t-BuOK (3.0 equiv), Ph PMeBr (3.0 equiv), toluene, r.t., 30 min, 89%; (2) Oxone (7.5 equiv), NaHCO (22 equiv),
2
2
3
3
acetone–H O = 2:1, r.t., 48 h, 3 (41%), epi-3 (45%); (3) (a) CuI (3.0 equiv), MeLi (6.0 equiv), Et O, −35 °C, 15 min; (b) (COCl) (2.0 equiv), DMSO (3.0
2
2
2
®
equiv), Et N (4.0 equiv), CH Cl , −78 °C → r.t., 2 h, 78%; (4) NaBH (1.5 equiv), THF–MeOH, 0 °C → r.t., 1 h, 87%; Oxone = KHSO ·0.5KHSO ·0.5K SO .
3
2
2
4
5
4
2
4
livered ketone 4, which underwent in the anticipated fash-
ion a diastereoselective reduction to secondary alcohol 5.
Following this route, we could obtain the desired product 5
in an overall yield of 25% from primary alcohol 1.
H
HO
1. Me2CuLi AcO
90%
7. KSeCN
85%
N
N
Z
2
H
H
H
O
O
O
6
epi-3
Attempts to convert the epimeric epoxide epi-3 into al-
cohol 5 failed because the intermediate of the dimethyl cu-
prate ring opening cyclized readily to oxazolidinone 6
3
. N2
PO(OMe)2
H
H
2
. Swern
oxidation
O
(
Scheme 2). The relative configuration of oxazolidinone 6
N
H
N
H
63%
H
14
was initially established by NMR data. We noted, however,
that the compound could be nicely employed for the syn-
thesis of dihydropalustramic acid, which in turn would un-
ambiguously prove its absolute and relative configuration.
To this end, Swern oxidation of the primary alcohol group
to aldehyde 7 was followed by alkynylation with the
Seyferth–Gilbert reagent. Although conversion of termi-
nal alkynes into aldehydes and carboxylic acids has been
described via hydroboration methods, we found the direct
O
O
O
O
7
8
O
5. Pinnick oxidation;
MeOH, H+
4
. H2O
[Ru]
O
H
N
MeO
N
8
6%
H
H
82%
15
O
O
O
O
9
10
16
6
. HBr, H2O;
MeOH, H+
O
anti-Markovnikov addition of water based on the Hinter-
(+)-methyl dihydro-
palustramate (11)
17
mann procedure superior. In the event, alkyne 8 was
MeO
N
H H
H
66%
treated in an acetone–water mixture with ruthenium cata-
OH
lyst CpRuCl(PPh3) ligated by 2-(diphenylphosphino)-6-
2
Scheme 2 Conversion of epoxide epi-3 into (+)-methyl dihydropalus-
tramate and into olefinic precursor 2. Reagents and conditions: (1) CuI
(2,4,6-triisopropylphenyl)pyridine yielding the desired al-
dehyde 9 in 86% yield. Further conversion into the known
ester 10 was performed by a Pinnick-Lindgren oxidation18
followed by esterification. Product 10 was in all scalar prop-
erties identical to its enantiomer ent-10, which has been
previously reported and which has been successfully con-
verted into (–)-dihydropalustramic acid and (–)-methyl di-
(6.0 equiv), MeLi (12 equiv), THF, 0 °C, 3 h, 90%; (2) (COCl)
2
(3.0 equiv),
DMSO (4.0 equiv), Et N (5.0 equiv), CH Cl , −78 °C → r.t., 2 h; (3) N CH-
3
2
2
2
PO(OMe) (2.0 equiv), t-BuOK (2.0 equiv), THF, −78 °C → r.t., 16 h, 63%,
2
two steps; (4) CpRuCl(PPh ) (0.05 equiv), (dpp)(tpp)py (0.05 equiv),
3
2
acetone–H O = 4:1, 65 °C, 43 h, 86%; (5) (a) NaClO (10 equiv), KH PO
2
2
2
4
(7.0 equiv), t-BuOH–2-methyl-2-butene–H O = 3:1:2, r.t., 16 h; (b) H -
2
2
SO
(1.5 equiv), MeOH, 65 °C, 3 h, 82%; (6) (a) HBr–H
O–DME = 2:1:1,
4
2
19
110 °C, 3 d; (b) H
2
SO (2.0 equiv), MeOH, 55 °C, 3 h, 66%; (7) KSeCN (3.0
hydropalustramate. In an analogous fashion we employed
equiv), t-BuOH–H O, r.t., 3 d, 85%; Cp = cyclopentadienyl, (dpp)(tpp)py
19a
2
the same set of reaction conditions to prepare the enan-
=
2-(diphenylphosphino)-6-(2,4,6-triisopropylphenyl)pyridine.
tiomeric product (+)-methyl dihydropalustramate (11) via
(+)-dihydropalustramic acid.
Gratifyingly, it was found that epoxide epi-3 could be
the desired alcohol 5 became available. The further conver-
sion of alcohol 5 into an appropriate precursor for reductive
cyclization turned out to proceed uneventfully (Scheme 3).
Protection of the hydroxyl group in 5 with MEM chloride
gave product 12, from which the Z group was removed hy-
drogenolytically. An acylation of the resulting piperidine
converted into the starting material 2 of the epoxidation by
20
treatment with KSeCN (Scheme 2). Based on this recycling
step, the overall yield of the transformation 2 → 5 (Scheme
) could be significantly improved and gram quantities of
1
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1505–1509

1
507
Synlett
C. Mayer et al.
Letter
with TBDPS-protected 4-hydroxybutanoyl chloride (13) de-
livered amide 14. Saponification of the acetate led to pri-
mary alcohol 15, which was oxidized to the respective alde-
hyde. A Wittig reaction delivered the α,β-unsaturated ester
catungstate was suggested to abstract a hydrogen atom
from the aldehyde and to transfer it back after Michael ad-
dition to the respective acceptor-substituted radical. While
yields for this reaction were reported to exceed 70%, if un-
functionalized aldehydes and simple Michael acceptors (e.g.
methyl acrylate) were employed,22 preliminary experi-
ments with tert-butyl 4-oxobutanoate and a piperidine-
substituted α,β-unsaturated ester resulted only in yields
below 40%. Likewise, the attempted cyclization of aldehyde
16, which was E-configured as expected. Removal of the
TBDPS protecting group was accomplished by treatment
with HF and the resulting alcohol was oxidized by Swern
oxidation. Overall, aldehyde 17 was obtained from alcohol 5
in six steps and 40% overall yield.
1
7 could not be optimized to a synthetically useful level.
2
3
. H2 [Pd/C]
TBDPSO
Both substrate (0.04–0.1 M) and catalyst (2–10 mol%) con-
centrations had little influence on the reaction outcome
with yields varying slightly between 26% and 30%. It ap-
pears likely that intramolecular hydrogen abstraction reac-
tions are competing reaction pathways, which lead to deg-
radation of the substrate. Remarkably, product 18 was iso-
.
COCl
AcO
1
. MEMCl
8%
1
3
N
Z
5
H
H
OMEM
9
66%
12
AcO
HO
lated as
a
single diastereoisomer but its relative
N
N
4
. K2CO3
H
H
O
H
H
O
configuration could not be unambiguously assigned. Given
the low yields of the cyclization, further work with product
18 was not performed, but rather other cyclization condi-
tions, which could be applicable to aldehyde 17, were eval-
uated.
OMEM
OMEM
97%
TBDPSO
TBDPSO
1
4
15
MeOOC
N
H
H
5
. Swern oxidation;
MeOOCCH=PPh3
H
H
6. HF;
Swern oxidation
O
O
OMEM
O
β
SmI2
N
N
H
H
O
O
H
H
O
+
O
17
OMEM
OMEM
8
0%
TBDPSO
79%
70%
H
H
1
6
19a
19b
MeOOC
Scheme 4 Reductive cyclization of aldehyde 16. Reagents and condi-
7
. hν
N
tions: SmI (5.0 equiv), HMPA (20 equiv), THF, r.t., 1 h, dr = 19a/19b =
2
MeOOC
N
H
H
O
[
TBADT]
O
H
H
OMEM
77/23, 70%; HMPA = hexamethylphosphoramide.
OMEM
O
29%
1
8
O
In this context, previous work by Honda et al. seemed
particularly promising.2b They had employed a SmI -pro-
1
7
2
moted reductive cyclization23 of an appropriate aldehyde to
an α,β-unsaturated ester as the key step in the total synthe-
sis of the pyrrolo[1,2-a]azepine alkaloid (–)-stemoamide.
The reaction was suggested to proceed by a ketyl radical
which adds intramolecularly to the Michael acceptor lead-
ing to formation of the pyrrolo[1,2-α]azepine skeleton. The
resulting γ-hydroxyester was found to form in situ the re-
spective γ-lactone. The vicinal stereogenic centers at the
pyrrolidine carbon atom and the lactone β-carbon atom
were found to be trans (60% yield) if the reaction was per-
formed in MeOH–THF but cis (55% yield) if performed in the
presence of hexamethylphosphoramide (HMPA). The effect
of the double bond configuration at the α,β-unsaturated es-
ter on the relative product configuration was found to be
marginal. Although it was clear that these results could not
be expected to apply similarly to a pyrido[1,2-a]azepine cy-
clization, we subjected aldehyde 17 to the reaction condi-
Scheme 3 Synthesis of cyclization precursor 17 and photocyclization
to product 18. Reagents and conditions: (1) MEMCl (3.0 equiv), NEti-Pr2
(
6.0 equiv), 1,2-DCE, 70 °C, 16 h, 98%; (2) H (1 atm), Pd(OH) /C (0.2
2
2
equiv), MeOH, r.t., 1 h, 83%; (3) ClOC(CH ) OTBDPS (2.0 equiv), DMAP
2
3
(
1.1 equiv), py–THF = 10:1, 80 °C, 3 d, 79%; (4) K CO (3.0 equiv),
2 3
MeOH–H O = 2:1, r.t., 97%; (5) (a) (COCl) (2.0 equiv), DMSO (3.0
2
2
equiv), Et N (4.0 equiv), CH Cl , −78 °C → r.t., 2 h; (b) Ph PCHCOOMe
3
2
2
3
(
2
3.0 equiv), toluene, 60 °C, 1 h, 80%; (6) (a) HFaq (18 equiv), MeCN, r.t.,
h, 82%; (b) (COCl) (2.0 equiv), DMSO (3.0 equiv), Et N (4.0 equiv),
2
3
CH Cl , −78 °C → r.t., 2 h, 96%; (7) hν (λ = 366 nm), TBADT (0.02 equiv),
2
2
MeCN, r.t., 13 h, 29%; MEM = 2-methoxyethoxymethyl, 1,2-DCE = 1,2-
dichloroethane, TBDPS = tert-butyldiphenylsilyl, DMAP = 4-dimethyl-
aminopyridine, TBADT = tetrabutylammonium decatungstate.
Our original plan to induce the desired azepine ring clo-
sure was to employ a method established by the group of A.
Albini and M. Fagnoni. They had found that tetrabutylam-
21
monium decatungstate, [NBu ] [W O ], was an excellent
4
4
10 32
catalyst for the photochemical generation of acyl radicals
from aldehydes, which in turn underwent smooth addition
to appropriate Michael acceptors. The photoactivated de-
tions of the SmI -promoted cyclization. No ring closure was
observed in the absence of HMPA and aldehyde 17 was in-
stead almost quantitatively reduced to the respective alco-
2
22
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1505–1509

1
508
Synlett
C. Mayer et al.
Letter
hol (90% yield). However, we were pleased to find that
HMPA conditions allowed for a smooth cyclization to the
desired azepine ring (Scheme 4). Addition of MeOH proved
in this case detrimental to the success of the reaction and
the cyclization was performed with 20 equivalents of
HMPA in THF under strict exclusion of air and moisture.
Products 19 were impossible to separate and turned out
to be oils, which were difficult to obtain completely pure
from solvent. Satisfactory NMR data could still be obtained
for the major diastereoisomer 19a. The relative configura-
tion was tentatively assigned to both diastereoisomers 19a
and 19b based on NOESY experiments. Although the rela-
tive configuration at the β-carbon atom of the γ-lactone
ring in 19a may need adjustment for further work, it is be-
lieved that compounds 19 hold great promise for further
synthetic work towards the synthesis of pyrido[1,2-a]aze-
pines.
In summary, it was shown that enantiomerically pure
piperidine 1 can serve as a useful building block for the
construction of the pyrido[1,2-a]azepine core of Stemona
alkaloids. While it turned out to be more problematic than
expected to establish the hydroxypropyl group at carbon C4
of the core, the further reaction sequence proceeded
smoothly and delivered with aldehyde 17 a suitable precur-
sor for subsequent cyclization reactions. Upon treatment
Primary Data
Primary data for this article are available online at http://www.thieme-
connect.com/products/ejournals/journal/ 10.1055/s-00000083 and can
be cited using the following DOI: 10.4125/pd0066th.
P
m
ri arDy at
P
m
ri arDy at
1
04.1
2
5
p/
d
0
0
6
6
htPmr.i ary
D
at
Z
a
heln
1
0
1
C
h
e
mstiry
References and Notes
(1) For a review, see: Alibés, R.; Figueredo, M. Eur. J. Org. Chem.
2009, 2421.
(2) For recently completed total syntheses, see: (a) Hoye, A. T.;
Wipf, P. Org. Lett. 2011, 13, 2634. (b) Honda, T.; Matsukawa, T.;
Takahashi, K. Org. Biomol. Chem. 2011, 9, 673. (c) Chen, Z.; Chen,
Z.; Zhang, Y.; Tu, Y.; Zhang, F. J. Org. Chem. 2011, 76, 10173.
(d) Chen, Z.; Zhang, Y.; Chen, Z.; Tu, Y.; Zhang, F. Chem. Commun.
2011, 47, 1836. (e) Fujioka, H.; Nakahara, K.; Kotoku, N.; Ohba,
Y.; Nagatomi, Y.; Wang, T.; Sawama, Y.; Murai, K.; Hirano, K.;
Oki, T.; Wakamatsu, S.; Kita, Y. Chem. Eur. J. 2012, 18, 13861.
(f) Bardaji, N.; Sánchez-Izquierdo, N.; Alibés, R.; Font, J.; Busqué,
F.; Figueredo, M. Org. Lett. 2012, 14, 4854. (g) Swamy, N. K.;
Pyne, S. G. Heterocycles 2012, 84, 473. (h) Schulte, M. L.;
Turlington, M. L.; Phatak, S. S.; Harp, J. M.; Stauffer, S. R.;
Lindsley, C. W. Chem. Eur. J. 2013, 19, 11847. (i) Kim, C.; Kang, S.;
Rhee, Y. H. J. Org. Chem. 2014, 79, 11119. (j) Fu, J.; Shen, H.;
Chang, Y.; Li, C.; Gong, J.; Yang, Z. Chem. Eur. J. 2014, 20, 12881.
(3) For reviews, see: (a) Pyne, S. G.; Ung, A. T.; Jatisatienr, A.;
Mungkornasawakul, P. Mj. Int. J. Sci. Tech. 2007, 01, 157.
(b) Fischer, G. Adv. Heterocycl. Chem. 2011, 103, 61.
with SmI in HMPA/THF, the desired skeleton B could be ac-
2
(4) For recent reviews on Stemona alkaloids, see: (a) Pilli, R. A.;
Rosso, G. B.; de Oliveira, M. C. F. Nat. Prod. Rep. 2010, 27, 1908.
cessed, which seems to be a reasonable starting point for
further synthetic studies. It became obvious, though, that
those reactions, which proceed readily with pyrrolidines,
do not always work similarly with related piperidines. It is
therefore necessary to modify the existing protocols for the
construction of pyrrolo[1,2-a]azepines when applied to
pyrido[1,2-a]azepines or to develop completely new syn-
thetic strategies for the preparation of the latter.
(
b) Greger, H. Planta Med. 2006, 72, 99.
5) Pilli, R. A.; Rosso, G. B.; de Oliveira, M. C. F. Alkaloids Chem. Biol.
005, 62, 77.
(
2
(6) For examples, see: (a) Kaltenegger, E.; Brem, B.; Mereiter, K.;
Kalchhauser, H.; Kählig, H.; Hofer, O.; Vajrodaya, S.; Greger, H.
Phytochemistry 2003, 63, 803. (b) Mungkornasawakul, P.; Pyne,
S. G.; Jatisatienr, A.; Supyen, D.; Lie, W.; Ung, A. T.; Skelton, B.
W.; White, A. H. J. Nat. Prod. 2003, 66, 980.
(c) Mungkornasawakul, P.; Pyne, S. G.; Jatisatienr, A.; Supyen,
D.; Jatisatienr, C.; Lie, W.; Ung, A. T.; Skelton, B. W.; White, A. H.
J. Nat. Prod. 2004, 67, 675. (d) Lin, L.-G.; Tang, C.-P.; Dien, P.-H.;
Xu, R.-S.; Ye, Y. Tetrahedron Lett. 2007, 48, 1559. (e) Wang, Y.-Z.;
Tang, C.-P.; Dien, P.-H.; Ye, Y. J. Nat. Prod. 2007, 70, 1356.
Acknowledgment
This work was supported by the Deutsche Forschungsgemeinschaft
(Ba 1372/16-1) and by the TUM Graduate School. We gratefully ac-
(
7) For previous synthetic studies, see: (a) Fozard, A.; Jones, G.
J. Org. Chem. 1965, 30, 1523. (b) Tietze, L. F.; Wünsch, J. R.;
Noltemeyer, M. Tetrahedron 1992, 48, 2081. (c) Marx, K.;
Eberbach, W. Tetrahedron 1997, 53, 14687. (d) Chou, S.-S. P.;
Liang, C.-F.; Lee, T.-M.; Liu, C.-F. Tetrahedron 2007, 63, 8267.
knowledge Prof. Klaus Ditrich (BASF SE, GVF/B) for a generous dona-
tion of immobilized Candida antarctica lipase (Novozyme® 435) as
well as Profs. Angelo Albini and Maurizio Fagnoni (Università di Pavia)
for a sample of TBADT. Prof. Lukas Hintermann (TU München) is ac-
knowledged for helpful discussions and for donation of the alkyne hy-
dration catalyst.
(e) De la Funeta, M. C.; Dominguez, D. J. Org. Chem. 2007, 72,
8804. (f) Chaiyong, S.; Jatisatienr, A.; Mungkornasawakul, P.;
Sastraruji, T.; Pyne, S. G.; Ung, A. T.; Urathamakul, T.; Lie, W.
J. Nat. Prod. 2010, 73, 1833. (g) Shengule, S. R.; Willis, A. C.;
Pyne, S. G. Tetrahedron 2013, 69, 8042.
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1380685. Included are procedures
and analytical data for all new compounds.
(8) (a) Chênevert, R.; Dickman, M. J. Org. Chem. 1996, 61, 3332.
(b) Chênevert, R.; Ziarani, G. M.; Morin, M. P.; Dasser, M. Tetra-
hedron: Asymmetry 1999, 10, 3117.
S
u
p
p
ortioIgnfrm oaitn
S
u
p
p
ortioIgnfrm oaitn
(
9) (a) Paulsen, H.; Todt, K. Angew. Chem. Int. Ed. 1966, 5, 899.
b) Sugg, E. E.; Griffin, J. F.; Portoghese, P. S. J. Org. Chem. 1985,
0, 5032.
(
5
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1505–1509

1
509
Synlett
C. Mayer et al.
Letter
(
10) (a) Toyooka, N.; Zhou, D.; Nemoto, H.; Tezuka, Y.; Kadota, S.;
Jones, T. H.; Garraffo, H. M.; Spande, T. F.; Daly, J. W. Synlett
008, 1894. (b) See also:Ookawa, A.; Soai, K. J. Chem. Soc., Perkin
(16) (a) Asao, N.; Ohishi, T.; Sato, K.; Yamamoto, Y. J. Am. Chem. Soc.
2001, 123, 6931. (b) Vintonyak, V. V.; Maier, M. E. Org. Lett.
2007, 9, 655.
2
Trans. 1 1987, 1465.
11) (a) Murray, R. W.; Jeyaraman, R. J. Org. Chem. 1985, 50, 2847.
(17) (a) Labonne, A.; Kribber, T.; Hintermann, L. Org. Lett. 2006, 8,
5853. (b) Boeck, F.; Kribber, T.; Xiao, L.; Hintermann, L. J. Am.
Chem. Soc. 2011, 133, 8138.
(18) (a) Lindgren, B. O.; Nilsson, T. Acta Chem. Scand. 1973, 27, 888.
(b) Kraus, G. A.; Roth, B. J. Org. Chem. 1980, 45, 4825. (c) Bal, B.
S.; Childers, W. E. Jr.; Pinnick, H. W. Tetrahedron 1981, 2091.
(19) (a) Muraoka, O.; Zheng, B.; Okumura, K.; Tanabe, G.; Momose,
T.; Eugster, C. H. J. Chem. Soc., Perkin Trans. 1 1996, 1567.
(b) Mayer, C.; Trueb, W.; Wilson, J.; Eugster, C. H. Helv. Chim.
Acta 1968, 51, 661.
(
(
b) Murray, R. W.; Singh, M. Org. Synth. 1997, 74, 91. (c) Bach, R.
D.; Dmitrenko, O.; Adam, W.; Schambony, S. J. Am. Chem. Soc.
003, 125, 924.
12) (a) Gilman, H.; Jones, R. G.; Woods, L. A. J. Org. Chem. 1952, 17,
630. (b) Badorrey, R.; Porteña, E.; Diaz-de-Villegas, M. D.;
2
(
(
(
1
Galvez, J. A. Org. Biomol. Chem. 2009, 7, 2912.
13) (a) Omura, K.; Swern, D. Tetrahedron 1978, 34, 1651. (b) Lesma,
G.; Colombo, A.; Landoni, N.; Sacchetti, A.; Silvani, A. Tetrahe-
dron: Asymmetry 2007, 18, 1948.
14) (a) Nader, B.; Bailey, T. R.; Franck, R. W.; Weinreb, S. M. J. Am.
Chem. Soc. 1981, 103, 7573. (b) Angle, S. R.; Henry, R. M. J. Org.
Chem. 1998, 63, 7490. (c) Schützenmeister, N.; Müller, M.;
Reinscheid, U. M.; Griesinger, C.; Leonov, A. Chem. Eur. J. 2013,
(20) Behan, J. M.; Johnstone, R. A. W.; Wright, M. J. J. Chem. Soc.,
Perkin. Trans. 1 1975, 1216.
(21) For reviews, see: (a) Tzirakis, M. D.; Lykakis, I. N.; Orfanopoulos,
M. Chem. Soc. Rev. 2009, 38, 2609. (b) Tanielian, C. Coord. Chem.
Rev. 1998, 178-180, 1165. (c) Hill, C. L. Synlett 1995, 127.
(22) (a) Dondi, D.; Fagnoni, M.; Albini, A. Chem. Eur. J. 2006, 12, 4153.
(b) Esposti, S.; Dondi, D.; Fagnoni, M.; Albini, A. Angew. Chem.
Int. Ed. 2007, 46, 2531.
(23) For reviews, see: (a) Nicolaou, K. C.; Ellery, S. P.; Chen, J. S.
Angew. Chem. Int. Ed. 2009, 48, 7140. (b) Edmonds, D. J.;
Johnston, D.; Procter, D. J. Chem. Rev. 2004, 104, 3371.
19, 17584.
(
15) (a) Seyferth, D.; Marmor, R. S.; Hilbert, P. J. Org. Chem. 1971, 36,
1
4
379. (b) Gilbert, J. C.; Weerasooriya, U. J. Org. Chem. 1979, 44,
997. (c) Maehr, H.; Schaffner, C. Synth. Commun. 2009, 39, 299.
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1505–1509