Asymmetric syntheses of 8-oxabicyclo[3,2,1]octane and 11-oxatricyclo[5.3.1.0]undecane from glycals

Article abstract of DOI:10.1039/c7sc02625k

Herein, we describe an efficient method to prepare enantiomerically pure 8-oxabicyclo[3.2.1]octanes via gold(i)-catalyzed tandem 1,3-acyloxy migration/Ferrier rearrangement of glycal derived 1,6-enyne bearing propargylic carboxylates. The resultant compou

Full text of DOI:10.1039/c7sc02625k

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Asymmetric syntheses of 8-oxabicyclo[3,2,1]octane
and 11-oxatricyclo[5.3.1.0]undecane from glycals†
Cite this: DOI: 10.1039/c7sc02625k
Hongze Liao, Wei-Lin Leng, Kim Le Mai Hoang, Hui Yao, Jingxi He,
*
Amanda Ying Hui Voo and Xue-Wei Liu
Received 12th June 2017
Accepted 31st July 2017
Herein, we describe an efficient method to prepare enantiomerically pure 8-oxabicyclo[3.2.1]octanes via
gold(I)-catalyzed tandem 1,3-acyloxy migration/Ferrier rearrangement of glycal derived 1,6-enyne
bearing propargylic carboxylates. The resultant compounds could then undergo interrupted Nazarov
cyclization to afford diastereomerically pure 11-oxatricyclo[5.3.1.0]undecanes.
DOI: 10.1039/c7sc02625k
rsc.li/chemical-science
Chiral 8-oxabicyclo[3.2.1]octane and 11-oxatricyclo[5.3.1.0]- catalysts, requiring installation of non-atom economical
undecane are common structural motifs featured in many auxiliaries and tedious chiral substrate synthesis. However, to
classes of natural products (Fig. 1), some of which show inter- our knowledge, there is still no report on the asymmetric
esting biological activities. Englerin A, a potential anti-tumor synthesis of 11-oxatricyclo[5.3.1.0]undecane.
reagent, is isolated from Phyllanthus engleri in Tanzania and
Tandem and sequential reactions are useful synthetic
shows selective activity to renal cancer cell lines at the nano- approaches as they offer the advantages of efficiency as well as
molar level.1 Balsamiferine J, isolated from Blumea balsamifera, reduction of cost and waste.8 Gold-catalyzed transformations
represents a novel type of sesquiterpenoids with NO inhibitory of 1,n-enyne bearing propargylic carboxylates to form complex
activity against murine microglial cell lines.2 Homalomenol C, molecules have progressed rapidly in the past decade and an
isolated from the roots of Homalomena aromatica, is reported as impressive series of transformations have been reported.9 It is
the bioactive component of the Vietnamese traditional medi- well established that the propargylic esters could undergo 1,2-
cine as an anti-inammatory agent.3
or 1,3-acyloxy migration to give the corresponding gold vinyl
Driven by their important bioactivities, many chemists are carbenoid or allene intermediates10 and these two intermedi-
interested in the synthesis of this type of natural products. ates could initiate further transformations depending on the
Attempts to gain access to this unique 8-oxabicyclo[3.2.1]- reaction conditions and properties of substrates.11 Hence, we
octane ring asymmetrically include [4 + 3],4 [5 + 2],5 [3 + 2]6 envisaged that the glycal linked 1,6-enyne bearing propargylic
cycloadditions and cascade reactions.7 Despite achieving carboxylates 1 could undergo the 1,3-acyloxy migration and
moderate to good diastereoselectivities, these methods suffer the resulting intermediate would be prone to subsequent
from the drawbacks of requiring expensive chiral metal Ferrier rearrangement, thus furnishing the enantiomerically
pure disubstituted 8-oxabicyclo[3.2.1]octanes 2. If successful,
this tandem 1,3-acyloxy migration/Ferrier rearrangement
would set the stage for a subsequent Nazarov cyclization12 to
form the 11-oxatricyclo[5.3.1.0]undecane derivatives
3
(Scheme 1). To the best of our knowledge, this mode of reac-
tivity is unprecedented in reactions involving 1,n-enyne
bearing propargylic carboxylates. Furthermore, this glycal
derived 1,6-enyne could be synthesized from readily available
glycals through simple steps, making this chirality source
cheap and atom economical.
Fig. 1 Selected natural products containing 8-oxabicyclo[3.2.1]octane
core structures.
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical
Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371.
E-mail: xuewei@ntu.edu.sg
† Electronic supplementary information (ESI) available: Experimental procedures
and characterisation data for all compounds are provided. CCDC 1436794 and
1520731. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c7sc02625k
Scheme 1 1,3-Acyloxy migration/Ferrier rearrangement and Nazarov
cyclization sequence.
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D-Glucal derived 1,6-enyne bearing propargylic carboxylates excellent yields. The stereochemistry was unambiguously
1a was selected as the starting material to commence the conrmed by X-ray analysis of compound 2b.14 A comparison of
investigation of this gold-catalyzed tandem reaction.13 To our the para-substituents of aryl substrates showed that those with
delight, the reaction could go smoothly with compound 1a as electron donating aryl substituents (2b, c) afforded higher yields
the starting material in the presence of AuCl3 to give the desired than those with electron withdrawing substituents (2d, e).
product 2a in 69% yield within 5 min (Table 1, entry 1). Other Replacing the aryl substituent at the alkyne position with less
commercially available gold catalysts could also promote this bulky alkyl substituents, such as cyclohexyl, n-butyl and methyl
reaction, further proving the feasibility of our strategy (Table 1, substituent (2f–h) furnished the corresponding products in
entries 2 and 3). Activated Ph3PAuSbF6 generated in situ from good yields. Alkene substituents were also tolerated (2i–m), but
Ph3PAuCl/AgSbF6 was found to be most suitable for this reac- the yield decreased when the reaction was carried out on
tion (Table 1, entry 4). Subsequently, the counter-ion effect was a larger scale (0.5 M). It should be noted that the reaction pro-
investigated through examining various silver salts and the ceeded readily to give the rearranged products when the benzyl
AgSbF6 presented the best performance (Table 1, entries 4–6). group was changed to methyl or methoxymethyl groups (2n–r).
Attempt to employ the Brønsted acid catalyst, p-TsOH resulted To the best of our knowledge, methoxy group has never been
in decomposition of the starting material (Table 1, entry 7). used as the leaving group for Ferrier rearrangement. When L-
Notably, Ph3PAuCl and AgSbF6 were found to be inactive when glycal derived propargylic acetates were tested for this reaction,
they were employed individually (Table 1, entries 8 and 9). similar results were obtained (ent-2a, 2b and 2g). As expected, D-
Solvent screening showed that CH2Cl2 was superior to other galactal derived substrate led to a diminished yield due to the
commonly used solvents (Table 1, entries 10–13). To demon- steric effect between benzyl group and propargylic ester (epi-2a).
strate the utility of this method, a reaction on a larger scale (0.5 Notably, complete diastereoselectivity was detected in all the
mmol) was carried out and 2a was afforded in 81% yield (Table examples (Table 2).
1, entry 14). Interestingly, when the propargylic ester group was
Based on the experimental results, a plausible mechanism
switched from acetyl group to pivaloyl or benzoyl groups, no for the formation of disubstituted 8-oxabicyclo[3.2.1]octane
signicant change was observed (Table 1, entries 15 and 16).
Using the optimal conditions, a range of the glycal derived
1,6-enyne bearing propargylic carboxylates were investigated to
demonstrate the wide application of this transformation. In
general, the desired products were rapidly obtained in good to
Table 2 Substrate scope of gold-catalyzed synthesis of 2
Table 1 Optimization of gold-catalyzed reaction of 1a
Entrya
Catalyst
Solvent
Time
Yieldb
1
2
3
4
5
6
7
8
AuCl3
AuCl
Ph3PAuNTf2
Ph3PAuCl/AgSbF6
Ph3PAuCl/AgClO4
Ph3PAuCl/AgOTf
p-TsOH
Ph3PAuCl
AgSbF6
Ph3PAuCl/AgSbF6
Ph3PAuCl/AgSbF6
Ph3PAuCl/AgSbF6
Ph3PAuCl/AgSbF6
Ph3PAuCl/AgSbF6
Ph3PAuCl/AgSbF6
Ph3PAuCl/AgSbF6
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DCE
Toluene
CH3NO2
CH3CN
CH2Cl2
CH2Cl2
CH2Cl2
5 min
5 min
5 min
5 min
5 min
5 min
—
—
—
5 min
2 h
5 min
1 h
69%
42%
72%
80%
62%
68%
Trace
n.r.
9
n.r.
10
11
12
13
14c
15d
16e
76%
52%
66%
48%
81%
79%
72%
5 min
5 min
5 min
a
Reaction conditions: propargylic ester 1 (0.1 M in CH2Cl2), 5 mol%
a
b
c
Reaction conditions: propargylic ester 1 (0.1 M in CH2Cl2), 5 mol%
PPh3AuCl, 10 mol% AgSbF6. Isolated yield. 53% yield based on
scale of 0.5 M of 1i. D-Galactal derived substrate. L-Glucal derived
b
c
d
e
gold catalyst, 10 mol% silver catalyst. Isolated yield. Reaction was
carried out on scale of 0.5 M of 1a. d Pivaloyl ester substrate. e Benzoyl
ester substrate. DCE ¼ ClCH2CH2Cl, n.r. ¼ no reaction.
substrate.
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Table 3 Optimization studies of the Nazarov cyclizationa
product is proposed with compound 1a (Scheme 2). The gold
catalyst is proposed to have dual role in this transformation.
Firstly, it helps to transform the propargylic ester motif of
compound 1a into the nucleophilic allenic intermediate C
through gold-catalyzed 1,3-acyloxy migration. Secondly, it
serves as Lewis acid to facilitate the intramolecular Ferrier
reaction by promoting the departure of benzyloxy group and
leading to the formation of allylic oxocarbenium ion E.15
Subsequently, electrophilic attack of the allylic oxocarbenium
motif to the allene generated oxa-bridged 7-membered ring
intermediate F. Finally, the leaving group of Ferrier rearrange-
ment attacks the oxonium species to generate the desired
disubstituted 8-oxabicyclo[3.2.1]octane product 2a with benzyl
acetate as the byproduct. The complete diastereoselectivity is
attributed to cis face attack of allenic ester at C-5 position of
glycal derived propargylic esters.
Entry
Acid
Additive
Solvent
T/t (h)
Yieldb
1
2
3
4
5
6
7c
H2SO4
—
—
H2O
—
H2O
—
MeOH
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
ꢀ40 ꢁC/1
ꢀ20 ꢁC/2
ꢀ20 ꢁC/2
r.t./2
Mixture
Trace
77%
18%
32%
BF3$OEt2
BF3$OEt2
CF3SO3H
CF3SO3H
SnCl4
r.t./2
ꢀ40 ꢁC/1
Mixture
78%
BF3$OEt2
H2O
ꢀ20 ꢁC/2
a
Reaction conditions: divinyl ketone 2i (0.1 M in CH2Cl2), acid (2
To conrm the mechanism, isotopic labeling experiments
were conducted (Scheme 3). When the propargylic acetate
1a-18O with an 18O-enriched carbonyl oxygen atom was synthe-
sized and subjected to the optimized reaction conditions, 18O-
b
c
equiv.), additive (1 equiv.). Isolated yield. Reaction was carried out
on scale of 0.2 M of 2i.
Table 4 Substrate scope of interrupted Nazarov cyclization
Entry
1
Starting material
Solvent
Yieldb
78%
2
64%
Scheme 2 Plausible mechanism for the formation of 2a.
3
4
75%
Mixture
5c
34%
a
Reaction conditions: divinyl ketone 2 (0.2 M in CH2Cl2), BF3$OEt2 (2
equiv.), H2O (1 equiv.). b Isolated yield. c Reaction carried out at 0 ꢁC.
Scheme 3 Isotope labeling experiments.
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labeled 8-oxabicyclo[3.2.1]octane 2a-18O was isolated in 78% temperature (Table 3, entries 1 and 6). Reaction on larger scale
yield and 18O containing carbonyl fragment was detected (0.2 M) also proceeded smoothly and afforded 3i in 78% yield
(PhC18O+ with m/z 107.0393). Conversely, 18O label was present (Table 3, entry 7).
in benzyl benzoate 6-18O instead of 8-oxabicyclo[3.2.1]octane
With the optimal interrupted Nazarov cyclization conditions
2a-18O when propargylic benzoate 1s-18O with an 18O-enriched in hand, ve 8-oxabicyclo[3.2.1]octane derivatives 2 containing
ester oxygen was used as the starting material. The following divinyl ketone motif were investigated. Similar with cyclo-
conclusions could be drawn from the isotopic labeling results hexenyl ketone 2i, substituted cyclohexenyl ketone 2j and
detected by high-resolution mass spectrometry: rstly, 8-oxa- cyclooctenyl ketone 2k could also undergo conversion to the
bicyclo[3.2.1]octane was generated exclusively from allene corresponding polycyclic products 3j and 3k in good yields
intermediate via gold-catalyzed 1,3-acyloxy migration rather (Table 4, entry 3 and 4). In addition, b-substituted ketone 2m
than two sequential 1,2-acyloxy migration since scrambling of could be applied to form the 11-oxatricyclo[5.3.1.0]undecane 3l,
18O-label was not detected in 5 or 2a. Secondly, Ferrier rear- which was the core structure of homalomenol C (Table 4, entry
rangement was initiated by gold-catalyzed 1,3-acyloxy migration 5). However, a-substituted ketone 2l decomposed under the
and its byproduct benzyl oxoanion quenched the reaction, same condition (Table 4, entry 2).
accounting for the high efficiency and rapid rate for this
The high degree of torquoselectivity of 11-oxatricyclo-
transformation.
[5.3.1.0]undecane 3 is quite interesting in this study and we
In order to investigate whether Nazarov cyclization could proposed the mechanism as follow (Scheme 4): activated by the
proceed sequentially aer tandem 1,3-acyloxy migration/Ferrier BF3$OEt2, the pentadienyl cation I was generated and following
rearrangement, a variety of Lewis and Brønsted acids were by a 4p conrotatory electrocyclization to afford the cyclo-
examined with 2a but gave either intractable mixtures or pentenyl cation intermediate II with complete exo selectivity.
incomplete consumption of starting material. To our delight, The similiar result about high exo selectivity for Nazarov cycli-
when the divinyl ketone derivative 2i was used as the substrate zation of norbornene derivatives17b and bicyclo[3.2.1]octane17g,h
instead, the interrupted Nazarov cyclization product 3i was were previously reported by West et al. and it was ascribed to the
furnished. The stereochemistry of compound 3i was conrmed alkene predistortion such as transition state allylic bond stag-
by X-ray structure analysis of its derivative.16 Use of 2 equivalent gering,17b combination of alkene pyramidalization,17c
BF3$OEt2 with 1 equivalent H2O as additive produced the nonequivalent orbital extension,17d steric crowding17e and
optimal yield of 11-oxatricyclo[5.3.1.0]undecane 3i (Table 3, torsional strain.17f Houk and co-workers have shown that bicy-
entry 3), while using CF3SO3H or in absence of H2O also effected clo[3.2.1]octane derivatives without through-space interaction
conversion to 3i, albeit in lower yield (Table 3, entries 2, 4 and would reach quite high exo selectivity in electrocyclization in
5). H2SO4 and SnCl4 were examined but an intractable mixture DFT calculations.17a In our case, the nonconjugated alkene does
was observed even when the reaction was conducted at a lower not involve this reaction and the cycloalkene motifs create more
Scheme 4 Proposed mechanism of interrupted Nazarov cyclization.
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steric repulsion and torsional strain in the transition state
which further promote the exo stereoselectivity. Sequentially,
the external H2O trapped the cyclopentenyl cation II from the
endo face of the polycyclic system which is less bulky aer
electrocyclization. Finally, the intermediate IV was transformed
into 11-oxatricyclo[5.3.1.0]undecane 3 through hydrogen shi
and enol–keto tautomerism.
2010, 132, 8842–8843; (c) N. Shimada, M. Anada,
S. Nakamura, H. Nambu, H. Tsutsui and S. Hashimoto,
Org. Lett., 2008, 10, 3603–3606; (d) D. M. Hodgson,
´
A. H. Labande, F. Y. T. M. Pierard and M. A. Exposito
Castro, J. Org. Chem., 2003, 68, 6153–6159; (e) S. Kitagaki,
M. Anada, O. Kataoka, K. Matsuno, C. Umeda,
N. Watanabe and S.-I. Hashimoto, J. Am. Chem. Soc., 1999,
121, 1417–1418.
7 (a) J. Fu, Y. Gu, H. Yuan, T. Luo, S. Liu, Y. Lan, J. Gong and
Z. Yang, Nat. Commun., 2015, 6, 8617, DOI: 10.1038/
Conclusion
˜
ncomms9617; (b) H. Faustino, I. Alonso, J. L. Mascarenas
In summary, a novel homogeneous gold-catalyzed tandem 1,3-
acyloxy migration/Ferrier rearrangement was developed
successfully to access disubstituted 8-oxabicyclo[3.2.1]octane
with high efficiency and complete diastereoselectivity using
glycal-derived propargylic esters. The resultant products could
then undergo an interrupted Nazarov cyclization serving as an
efficient strategy for the facile synthesis of diastereomerically
pure 11-oxatricyclo[5.3.1.0]undecanes which was applied to
synthesize the core structure of homalomenol C. More studies
on mechanism and natural product synthesis are currently in
progress.
˜
and F. Lopez, Angew. Chem., Int. Ed., 2013, 52, 6526–6530;
(c) B. Li, Y.-J. Zhao, Y.-C. Lai and T. P. Loh, Angew. Chem.,
Int. Ed., 2012, 51, 8041–8045.
8 (a) K. C. Nicolaou, D. J. Edmonds and P. G. Bulger, Angew.
Chem., Int. Ed., 2006, 45, 7134–7186; (b) J.-C. Wasilke,
S. J. Obrey, R. T. Baker and G. C. B. Bazan, Chem. Rev.,
2005, 105, 1001–1020.
9 (a) A. S. K. Hashmi, W. Yang, Y. Yu, M. M. Hansmann,
M. Rudolph and F. Rominger, Angew. Chem., Int. Ed., 2013,
52, 1329–1332; (b) J. W. Cran and M. E. Kra, Angew.
Chem., Int. Ed., 2012, 51, 9398–9402; (c) W. Rao, D. Susanti
and P. W. H. Chan, J. Am. Chem. Soc., 2011, 133, 15248–
15251; (d) S. Bhunia and R.-S. Liu, J. Am. Chem. Soc., 2008,
Acknowledgements
´
130, 16488–16489; (e) N. Marion, P. de Fremont,
We gratefully acknowledge Nanyang Technological University
(RG6/13 and RG132/14) and the Ministry of Education, Singa-
pore (MOE 2013-T3-1-002) for the nancial support of this
research. We thank Dr Ganguly Rakesh for X-ray analysis.
`
G. Lemiere, E. D. Stevens, L. Fensterbank, M. Malacria and
S. P. Nolan, Chem. Commun., 2006, 2048–2050; (f) L. Zhang
and S. Wang, J. Am. Chem. Soc., 2006, 128, 1442–1443; (g)
A. Buzas and F. Gagosz, J. Am. Chem. Soc., 2006, 128,
12614–12615; (h) X. Shi, D. J. Gorin and F. D. Toste, J. Am.
Chem. Soc., 2005, 127, 5802–5803; (i) V. Mamane, T. Gress,
Notes and references
¨
1 R. Ratnayake, D. Covell, T. T. Ransom, K. R. Gustafson and
H. Krause and A. Furstner, J. Am. Chem. Soc., 2004, 126,
J. A. Beutler, Org. Lett., 2009, 11, 57–60.
8654–8655.
2 J. Xu, D. Q. Jin, C. Liu, C. Xie, Y. Guo and L. Fang, J. Agric. 10 F. D. Toste, in Modern Gold Catalyzed Synthesis, ed. A. S. K.
Food Chem., 2012, 60, 8051–8058.
3 (a) L. R. Salgueiro, R. Vila, F. Tomi, X. Tomas, S. Canigueral,
Hashmi and F. D. Toste, Wiley-VCH, Weinheim, 2012, pp.
75–134.
˜
J. Casanava, A. P. D. Cunha and T. Adzet, Phytochemistry, 11 (a) R. Dorel and A. M. Echavarren, Chem. Rev., 2015, 115,
1997, 45, 1177–1183; (b) T. V. Sung, L. Kutschabsky,
A. Porzel, W. Steglich and G. Adam, Phytochemistry, 1992,
31, 1659–1661.
4 (a) B. Lo, S. Lam, W.-T. Wong and P. Chiu, Angew. Chem., Int.
Ed., 2012, 51, 12120–12123; (b) J. Huang and R. P. Hsung, J.
Am. Chem. Soc., 2005, 127, 50–51; (c) M. Harmata,
S. K. Ghosh, X. Hong, S. Wacharasindhu and
P. Kirchhoefer, J. Am. Chem. Soc., 2003, 125, 2058–2059; (d)
C. B. W. Stark, U. Eggert and H. M. R. Hoffmann, Angew.
Chem., Int. Ed., 1998, 37, 1266–1268.
9028–9072; (b) L. Fensterbank and M. Malacria, Acc. Chem.
Res., 2014, 47, 953–965; (c) R. K. Shiroodi and
V. Gevorgyan, Chem. Soc. Rev., 2013, 42, 4991–5001; (d)
X.-Z. Shu, D. Shu, C. M. Schienebeck and W. Tang, Chem.
Soc. Rev., 2012, 41, 7698–7711; (e) A. S. Dudnik,
N. Chernyak and V. Gevorgyan, Aldrichimica Acta, 2010, 43,
37–46; (f) S. Wang, G. Zhang and L. Zhang, Synlett, 2010,
692–706; (g) D. J. Gorin, B. D. Sherry and F. D. Toste,
´
˜
´
Chem. Rev., 2008, 108, 3351–3378; (h) E. Jimenez-Nunez
and A. M. Echavarren, Chem. Commun., 2007, 333–346; (i)
A. S. K. Hashmi, Chem. Rev., 2007, 107, 3180–3211.
5 (a) A. Orue, U. Uria, E. Reyes, L. Carrillo and J. L. Vicario,
Angew. Chem., Int. Ed., 2015, 54, 3043–3046; (b) 12 (a) S. P. Simeonov, J. P. Nunes, K. Guerra, V. B. Kurteva and
M. R. Witten and E. N. Jacobsen, Angew. Chem., Int. Ed.,
2014, 53, 5912–5916; (c) N. Z. Burns, M. R. Witten and
E. N. Jacobsen, J. Am. Chem. Soc., 2011, 133, 14578–14581;
C. A. Afonso, Chem. Rev., 2016, 116, 5744–5893; (b) M. J. Di
Grandi, Org. Biomol. Chem., 2014, 12, 5331–5345; (c)
M. A. Cavitt, L. H. Phun and S. France, Chem. Soc. Rev.,
2014, 43, 804–818; (d) W. T. Spencer III, T. Vaidya and
A. J. Frontier, Eur. J. Org. Chem., 2013, 3621–3633; (e)
N. Shimada, C. Stewart and M. A. Tius, Tetrahedron, 2011,
67, 5851–5870; (f) T. N. Grant, C. J. Rieder and F. G. West,
Chem. Commun., 2009, 5676–5688; (g) H. Pellissier,
´
˜
(d) F. Lopez, L. Castedo and J. L. Mascarenas, Org. Lett.,
2002, 4, 3683–3685.
6 (a) F. Rodier, M. Rajzmann, J.-L. Parrain, G. Chouraqui and
L. Commeiras, Chem.–Eur. J., 2013, 19, 2467–2477; (b)
K. Ishida, H. Kusama and N. Iwasawa, J. Am. Chem. Soc.,
This journal is © The Royal Society of Chemistry 2017
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View Article Online
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Tetrahedron, 2005, 61, 6479–6517; (h) M. A. Tius, Eur. J. Org. 16 See Section E, Table 2 (9, CCDC 1520731) in the ESI† for the
Chem., 2005, 2193–2206. crystal structure.
13 Preparation of all the propargyl ester substrates 1 is included 17 (a) A. Patel, F. G. West and K. N. Houk, J. Org. Chem., 2015,
in Section B, general procedure A and B in the ESI.†
14 See Section E, Table 1 (2b, CCDC 1436794) in the ESI† for the
crystal structure.
80, 2790–2795; (b) R. D. Mazzola Jr, T. D. White,
H. R. Vollmer-Snarr and F. G. West, Org. Lett., 2005, 7,
2799–2801; (c) S. Giese, R. D. Mazola Jr, C. M. Amann,
A. M. Arif and F. G. West, Angew. Chem., Int. Ed., 2005, 44,
6546–6549; (d) N. G. Rondan, M. N. Paddon-Row,
P. Caramella, J. Mareda, P. H. Muller and K. H. Houk, J.
Am. Chem. Soc., 1982, 104, 4976–4978; (e) N. G. Rondan,
M. N. Paddon-Row, P. Caramella and K. H. Houk, J. Am.
Chem. Soc., 1981, 103, 2436–2438; (f) S. Inagaki,
H. Fujimoto and K. Fukui, J. Am. Chem. Soc., 1976, 98,
4054–4061; (g) H. C. Brown, J. H. Kawakami and K.-T. Liu,
J. Am. Chem. Soc., 1973, 95, 2209–2216; (h)
P. V. R. Schleyer, J. Am. Chem. Soc., 1967, 89, 701–703.
15 (a) R. Roy, P. Rajasekaran, A. Mallick and Y. D. Vankar, Eur. J.
´
Org. Chem., 2014, 5564–5573; (b) A. M. Gomez, F. Lobo,
´
C. Uriel and J. C. Lopez, Eur. J. Org. Chem., 2013, 7221–
7262; (c) E. Kumaran, M. Santhi, K. K. Balasubramanian
and S. Bhagavathy, Carbohydr. Res., 2011, 346, 1654–1661;
(d) R. Balamurugan and S. R. Koppolu, Tetrahedron, 2009,
65, 8139–8142; (e) P. Nagaraj and N. G. Ramesh, Eur. J.
Org. Chem., 2008, 4607–4614; (f) S. Kashyap, S. Rao
Vidadala and S. Hotha, Tetrahedron Lett., 2007, 48, 8960–
8962.
Chem. Sci.
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