Nazarov Cyclization and Tandem [4 + 2]-Cycloaddition Reactions of Donor-Acceptor Cyclopropanes

Article abstract of DOI:10.1021/acs.orglett.7b02061

The development of aryl vinyl/divinyl donor-acceptor cyclopropanes (DACs) as novel Nazarov cyclization (NC) precursors is described. The 1,3-zwitterion, generated from DACs embedded in the divinyl framework, acts as a pentadienyl cation, a requisite for Nazarov cyclization. A cyclic allyl cation in the course of NC was trapped with external nucleophiles to provide an interrupted NC product. Indeed, an allyl cation in this reaction is analogous to a 1,4-zwitterion that on reaction with dipolarophiles provided an easy access to substituted pyrans with excellent yield and diastereoselectivity via NC followed by a formal [4 + 2] cycloaddition.

Full text of DOI:10.1021/acs.orglett.7b02061

Letter
pubs.acs.org/OrgLett
Nazarov Cyclization and Tandem [4 + 2]-Cycloaddition Reactions of
Donor−Acceptor Cyclopropanes
,†
†
‡
§
Gangarajula Sudhakar,* S. K. Mahesh, S. Phani Babu Vemulapalli, and Jagadeesh Babu Nanubolu
†
‡
§
Department of CPC (Organic Chemistry-II), Centre for NMR and Structural Chemistry, Centre for X-ray Crystallography,
CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India
*
S Supporting Information
ABSTRACT: The development of aryl vinyl/divinyl donor−
acceptor cyclopropanes (DACs) as novel Nazarov cyclization
(
NC) precursors is described. The 1,3-zwitterion, generated from
DACs embedded in the divinyl framework, acts as a pentadienyl
cation, a requisite for Nazarov cyclization. A cyclic allyl cation in
the course of NC was trapped with external nucleophiles to
provide an interrupted NC product. Indeed, an allyl cation in this
reaction is analogous to a 1,4-zwitterion that on reaction with
dipolarophiles provided an easy access to substituted pyrans with excellent yield and diastereoselectivity via NC followed by a
formal [4 + 2] cycloaddition.
onor−acceptor cyclopropanes (DACs) are distinctive and
Scheme 1. Our Previous and Present Plan of Work
1
D
versatile building blocks in organic synthesis. Most of the
studied DACs have a common substitution pattern, i.e. electron-
acceptor groups (usually an ester or a carbonyl group) vicinally
positioned adjacent to an electron-donor substituent on the
cyclopropane backbone. Polarizability of the highly π character
1,2 C−C bond is amplified by the presence of a 1,1-diester/
dicarbonyl as an electron-withdrawing group (EWG) and
electron-rich aromatic group in a three-membered ring with an
inherent angle and torsional strains. This intrinsic character o2f
DACs was utilized in various reactions such as ring opening,
3
4
cycloaddition/annulation, and rearrangement and was also
5
employed in the synthesis of natural products and their analogs.
Although different types of DAC reactivity are known, only the
generation of 1,3-zwitterions was extensively exploited, and other
possible DAC reactivity has been underexplored thus far. In this
direction, Tamilov et al. reported the generation of 1,2- and 1,4-
6
direction, we pondered whether the dienyl framework strategi-
cally amalgamated in place of a donor group could be an endowed
DAC for this purpose as shown in Scheme 1B.
dipoles as a new type of DAC reactivity. Nonetheless, the
reactivity phenomenon of DACs combined with a framework
suitable for another consecutive reaction would be of great
importance in organic synthesis to assemble many carbo- and
When two EWGs and two EDGs are placed vicinally on the
cyclopropane (1,1-EWGs and 2,2-dienyl as EDGs system), the
envisioned 1,2 C−C bond ring opening could bemuch faster than
the archetypal single donor group system. This extra EDG (vinyl/
aryl) could also allow further elaboration in the products as an
additional functional group handle. Dienyl DAC 1 does serve as a
sourceof1,3-zwitterion1Acomparedwithtraditionalreactionsof
DACs. But in this case, 1 would be a latent pentadienyl cation to
undergo 4π-electrocyclization. Moreover, the formation of
concomitant cyclic allyl cation IB in 4π-electrocyclization could
readily be trapped by various nucleophiles to provide interrupted
Nazarov cyclization product 3 or undergo elimination to furnish
1
e,i,3l,o
heterocyclic compounds. Research groups of Kerr
Waser
and
1
d,h,3b,i,5b
contributed significantly in this area of research.
Besides, some examples of DAC reactivity combined with other
7
reactions exist; Vicario et al. reported organocatalytically
7a
generated DACs in domino reactions, Alaniz et al. reported
aza-Pianacatelli rearrangement initiated by ring opening of
7
b
7e,f
7g−j
7k
DACs, and the Yadav, France,
and Waser research
groups reported homo-Nazarov cyclization from DACs. Because
8
of our interest in Nazarov cyclization, particularly in the
9
generation of alternate Nazarov cyclization precursors, we
8a
8b
recentlydevelopeddienyloxyranes andaziridines asnovelNC
precursors (Scheme 1A). Continuing our interest, we envisaged
the possibility of generating a pentadienyl cation, the requisite for
Nazarov cyclization, by initiating ring opening of DACs. In this
Received: July 6, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b02061
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
classical NC product 2 (Scheme 1B). On the other hand, the
cyclic allyl cation is analogous to the 1,4-zwitterion, and this
complementary function (1,4-zwitterion) could be employed in
reacting with dipolarophiles to provide a facile access to [4 + 2]-
cycloaddition product 4 (Scheme 1B). Herein, we communicate
thedevelopmentandpotential syntheticexploration ofarylvinyl/
divinyl donor−acceptor cyclopropanes as novel Nazarov
cyclization precursors for the first time.
To begin the proposed study, we employed aryl vinyl DAC 1a
with several Lewis acids and trifluoroacetic acid (see the
Supporting Information (SI) for the synthesis of 1a and for
optimization of reaction conditions). When 1a was subjected to
and 2j has one quaternary and three tertiary carbons.
Furthermore, 2j (2D NMR confirmed the structure, SI) was
obtained as a single isomer from (−)-myrtenal containing aryl
vinyl DAC 1j. This may be due to the torquoselective conrotatory
electrocyclization (see the SI). To broaden the substrate scope,
we next examined various aromatic groups. In general, more
activated DACs bearing electron-donating functionalities in the
vicinal phenyl ring participated in the reaction more efficiently.
The substrate without an EDG on the aryl moiety (1k) also
underwent the reaction successfully (2k), but with a relatively
loweryield(78%). Itisworthmentioningthatthefluoroatomwas
erroneously assumed to have electron-withdrawing character on
the reactivity of the aromatic group, but indeed it has not affected
0
.1 equiv of BF ·OEt , the formation of 2a was observed in almost
3 2
11
quantitative yield (Scheme 2). With BF ·Et O, dienyl DACs with
the reactivity to a great extent. Under standard conditions, 2l
3
2
12
was obtained in 76% yield, comparable with a 2k yield.
A
a
Scheme 2. Nazarov Cyclization of Dienyl DACs
naphthalene substrate was also suitable for this reaction, thus
producing the desired product 2m in 96% yield. Heteroarenes
were then employed to probe the generality of transformations
further. Substrate with a pyridine moiety required an excess
amount of triflic acid (see the SI) and a longer reaction time to
furnish the desired product (2n) with a yield of 78%. The slow
reactivity of this substrate is presumably due to coordination of
acid with the Lewis basic nitrogen. However, a thiophene moiety
containing product 2o was obtained in a yield of 89% under
standard reaction conditions (Scheme 2). Having synthesized a
wide variety of indenes from aryl vinyl DACs, we subsequently
became interested in evaluating divinyl DAC. To our delight,
under optimized reaction conditions, 2p was obtained in almost
quantitative yield from a symmetrical dienyl DAC 1p (see the SI
13
for its synthesis and X-ray crystal structure).
With the ability to form these indenes and cyclopentadiene in
hand, we next questioned if the cyclic allyl cation III (Scheme 3)
a
Scheme 3. Interrupted Nazarov Cyclization
a
Reaction conditions: 1 (0.1 mmol), CH Cl (0.1 M) with respect to
2
2
1
at −78 °C were added BF ·OEt .
3
2
different ester groups (1b and 1c) were tested to verify the effect
of the ester group in the conversion of the product. Obtaining 2b
in 96% yield and 2c in 93% yield (comparable with a yield of 2a)
implies that there is no such profound effect of the ester group.
With optimized conditions in hand for the reaction of aryl vinyl
DAC, we decided to investigate the substrate scope, and the
results are depicted in Scheme 2. At first, we examined a series of
substratesincorporating the3,5-dimethoxyphenyl moiety(1d−j)
with varying substitutions on the vinyl group. Compounds with
alkyl or aryl substitution at the β-position show similar reactivity,
with ethyl 1d and with phenyl 1e proceeding smoothly under
optimized conditions to give indenes 2d−e in excellent yield. A
substrate with phenyl at the α-position and isopropyl group at the
β-position 1f also provided 2f in 94% yield. Disubstitution at the
β-position in the NC precursor slows down the reaction due to
a
Reaction conditions: 1p (0.1 mmol), Nu (0.2 mmol), CH Cl (0.1
2
2
M) with respect to 1p at −78 °C were added BF ·OEt .
3
2
generated from symmetrical dienyl DAC 1p via pentadienyl
cation II would allow its participation in the interrupted NC.
First, we tested Et SiH. Gratifyingly, we isolated 3a as an
14
14l
3
inseparable diastereomer mixture (dr 9:1) in 80% yield (Scheme
3). Next, allylTMS was examined, and we isolated 3b as a single
diastereomer in 76% yield. With trimethylaluminum, 3c was
obtained in very good yield. Further, the cyclic allyl cation was
trapped with 1-methylindole to attain a corresponding product
from a Nazarov cyclization/Friedel−Crafts reaction sequence
(interrupted NC). Here, in the major product 3d (56%), the
indole group and phenyl group on an adjacent carbon are in
antirelation, whereas in the minor product 3d′ (41%), the indole
group, and phenyl group are in syn-relation. Similarly, indole
1
0
steric hindrance, but the formation of indene with quaternary
carbon 2g in excellent yield from 1g is remarkable. Indenes with
polycyclic 2h−j (95−97% yields) were obtained from 1h−j,
respectively. Of note, compound 2i has two quaternary carbons
B
DOI: 10.1021/acs.orglett.7b02061
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
without any protection on nitrogen also participated in the
reaction, obtaining 3e (49%), and 3e′ (40%) in a similar yield and
diastereomeric ratio. The structures of 3e and 3e′ were confirmed
by 2D NMR (see the SI). The selectivity in this interrupted NC
Indole-3-carboxaldehyde also reacted and produced 4f in 88%
yield. Further, aliphatic aldehydes such as pivalaldehyde and
isobutyraldehyde also reacted, providing 4g (94%) and 4h (95%).
The relative configuration of 4h was further confirmed by 2D
NMR(SI). Similarto4a, themajor isomer4b−hisalsoassociated
with the inseparable isomer ranging from ∼10−30% (based on
14d,e
stands in line with a report by the West group.
Typically, DACs were used to generate 1,3-zwitterions, but
DACs embedded with divinyl offered a pentadienyl cation (II)
and subsequently a cyclic allyl cation (III) via 4π-electro-
cyclization. As this cyclic allyl cation (III) is analogous to the 1,4-
zwitterion (IV, Scheme 4), we further questioned if the 1,4-
1
the H NMR; see the SI for the structures s4b−h, assigned based
on the analogy to s4a).
The previous reports
14d,e
and our interpretation based on the
relative configurations of 4a, 4a′, and 4e (single crystal X-ray
analysis), 4a, 4a′, and 4h (2D NMR), we propose the most
probable six-membered cyclic transition state V, in which
dipolarophile attacks from the opposite side to the phenyl
group (α to carbocation). And, the upcoming alkyl/aryl group in
the dipolarophile attains a pseudoequatorial position, which
accounts for the diastereoselectivity of the major product
a
Scheme 4. Nazarov Cyclization and [4 + 2]-Cycloaddition
(
Scheme 4). Unfortunately, 1p with the application of the
standard conditions to styrene and imines as dipolarophiles failed
to afford the desired product. The unsuccessful reaction could be
attributed to the low reaction temperature. At rt or above, only
standard NC product 2p was observed along with a small amount
of exomethylene containing cyclopentene s2p (see the SI for its
structure). This implies that the transient cyclic allyl cation is
perhaps trapped only if the dipolarophile is reactive enough at a
lower temperature. Otherwise, the cyclic allyl cation leads to the
elimination of a proton to form 2p.
Furthermore, on addition of maleic anhydride to 1p, the
tricyclic product 5a was obtained. This formation of 5a can be
explained from the initially formed cyclopentadiene 2p which
reacted with the dienophile to provide a Diels−Alder product.
This was further ascertained by adding maleic anhydride to
preformed 2p (1p was first stirred with BF ·Et O until the
3
2
complete formation of 2p), which provided 5a in 96% yield and
with completeendo selectivity(2D NMRconfirmedthestructure,
SI). Similarly, dimethylacetylenedicarboxylate wasalsoreacted to
afford 5b in 82% yield. Notably, highly substituted polycyclic
systemswithadditionalfunctionalgroupsin5a−bcanprovidethe
possibility of further functionalization.
a
Reaction conditions: 1p (0.1 mmol), CH Cl (0.1 M) with respect to
2
2
1
p, aldehyde (0.4 mmol) at −78 °C were added BF ·OEt .
3
2
zwitterion (IV) would allow its participation in a formal [4 + 2]-
cycloaddition reaction. The successful reaction can provide a
novel method to build up polycyclic molecules of high diversity in
structure. For instance, aldehyde participation in the proposed
cycloaddition would afford a highly functionalized tetrahydropyr-
an ring containing a product which is an important structural
motif present in a wide range of antibiotic natural products,
In summary, 1,3-zwitterions generated from DACs embedded
with dienyl groups were explored to undergo 4π-electro-
cyclization, and the concomitant cyclic allyl cation was trapped
to provide an interrupted Nazarov cyclization product.
Furthermore, we found that these new dienyl DACs are not
only capable of providing a dienyl cation (1,3-zwitterions) for 4π-
electrocyclization but also capable of generating complementary
functionality, the 1,4-zwitterion/cyclic allyl cation. This was
successfully employed in various [4 + 2]-cycloaddition reactions
to provide bi- and tricyclic products in excellent yield and
diastereoselectivity. The formation of C−C bonds is a
fundamental reaction; up to 3 C−C bonds or 2 C−C and 1 C−
O bonds and up to five contiguous stereocenters (5a) were
achieved with this method. Our current research efforts are
directed toward functionalized donor−acceptor cyclopropanes
and expanding the method to other heterocyclic compounds; the
results will be reported in due course.
15
pheromones, and marine toxins. Under optimized reaction
conditions, when 1p was treated with benzaldehyde, as expected,
a formal [4 + 2]-cycloaddition product was obtained in column
chromatographically separable4a(*2R)and4a′(*2S)(dr8:2)in
9
8% combined yield (Scheme 4). The major isomer 4a is
associated with a small amount of inseparable isomer (s4a (*2S
and *7aR); see the SI for its structure and dr 95:5 based on the H
1
NMR). The structures of 4a, s4a, and 4a′ were deduced by using
2
D NMR (see the SI). Further, the structures of 4a and 4a′ were
13
confirmed by single crystal X-ray analysis. Next, by addition of
electron-rich p-methoxy benzaldehyde, 4b and 4b′ were isolated
in 96% yield with 7:3 dr. Further, 2-naphthaldehyde and p-
bromobenzaldehyde also provided 4c and 4c′ (96%) and 4d and
ASSOCIATED CONTENT
■
4
d′ (94%) with 7:3 dr. Notably, an aryl group bearing an electron-
*
S
Supporting Information
withdrawingsubstrate(p-nitrobenzaldehyde)provided4ein92%
yield and no separable minor isomer was observed. The structure
of 4e was further confirmed using single-crystal X-ray analysis.
TheSupportingInformationisavailablefreeofchargeontheACS
Publications website at DOI: 10.1021/acs.orglett.7b02061.
13
C
DOI: 10.1021/acs.orglett.7b02061
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Supplementary schemes, tables, experimental procedures,
Letter
(4) (a) Brand, C.; Rauch, G.; Zanoni, M.;Dittrich, B.; Werz, D. B. J. Org.
Chem. 2009, 74, 8779. (b)Schneider, T. F.;Kaschel, J.;Dittrich, B.;Werz,
D. B. Org. Lett. 2009, 11, 2317. (c) Schneider, T. F.; Kaschel, J.; Awan, S.
I.; Dittrich, B.; Werz, D. B. Chem. -Eur. J. 2010, 16, 11276. (d) Kaschel, J.;
Schneider, T. F.; Kratzert, D.; Stalke, D.; Werz, D. B. Angew. Chem., Int.
Ed. 2012, 51, 11153. (e) Kaschel, J.; Schneider, T. F.; Kratzert, D.; Stalke,
D.; Werz, D. B. Org. Biomol. Chem. 2013, 11, 3494. (f) Kaschel, J.;
Schmidt, C. D.; Mumby, M.; Kratzert, D.; Stalke, D.; Werz, D. B. Chem.
Commun. 2013, 49, 4403. (g) Schmidt, C. D.; Kaschel, J.; Schneider, T.
F.; Kratzert, D.; Stalke, D.; Werz, D. B. Org. Lett. 2013, 15, 6098.
1
13
2D NMR, H and C NMR spectra, X-ray crystallographic
information (PDF)
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: gsudhakar@iict.res.in.
ORCID
(
2
h) Borisov, D. D.; Novikov, R. A.; Tomilov, Y. V. Angew. Chem., Int. Ed.
016, 55, 12233.
5)(a)Kreuzer, A.;Kerres, S.;Ertl, T.;Ru
Gangarajula Sudhakar: 0000-0003-3498-5584
Notes
(
̈
cker, H.;Amslinger, S.;Reiser,
O. Org. Lett. 2013, 15, 3420. (b) Racine, S.; de Nanteuil, F.; Serrano, E.;
Waser, J. Angew. Chem., Int. Ed. 2014, 53, 8484. (c) Gharpure, S. J.;
Nanda, L. N.; Shukla, M. K. Org. Lett. 2014, 16, 6424.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors wish to thank Science and Engineering Research
Board (SERB), DST, New Delhi, India for a research grant
■
(6) Selected example: (a) Novikov, R. A.; Tarasova, A. V.; Korolev, V.
A.; Timofeev, V. P.; Tomilov, Y. V. Angew. Chem., Int. Ed. 2014, 53, 3187.
(7) (a) Sanchez-Diez, E.; Vesga, D. L.; Reyes, E.; Uria, U.; Carrillo, L.;
Vicario, J. L. Org. Lett. 2016, 18, 1270. (b) Chen, H.; Zhang, J.; Wang, D.
Z. Org. Lett. 2015, 17, 2098. (c) Wenz, D. R.; de Alaniz, J. R. Org. Lett.
(
EMR/2016/002289). WealsothanktheUGC, NewDelhi, India
for the award of a Senior Research Fellowship (S.K.M.) and Dr. B.
Jagadeesh, Head, Centre for NMR, for NMR analytical support.
2
013, 15, 3250. (d) Wurz, R. P.; Charette, A. B. Org. Lett. 2005, 7, 2313.
(e) Yadav, V. K.; Kumar, N. V. Chem. Commun. 2008, 3774. (f) Yadav, V.
K.; Kumar, N. V.; Hulikal, V. Tetrahedron Lett. 2014, 55, 2015. (g) Patil,
D. V.; Phun, L. H.; France, S. Org. Lett. 2010, 12, 5684. (h) Phun, L. H.;
Patil, D. V.; Cavitt, M. A.; France, S. Org. Lett. 2011, 13, 1952. (i) Aponte-
Guzman, J.; Taylor, J. E., Jr.; Tillman, E.; France, S. Org. Lett. 2014, 16,
REFERENCES
■
(
1) For recent reviews on donor−acceptor cyclopropane, see: (a) Liao,
S.; Sun, X.; Tang, Y. Acc. Chem. Res. 2014, 47, 2260. (b) Novikov, R. A.;
Tarasova, A. V.; Korolev, V. A.; Timofeev, V. P.; Tomilov, Y. V. Angew.
Chem., Int. Ed. 2014, 53, 3187. (c) Cavitt, M. A.; Phun, L. H.; France, S.
Chem. Soc. Rev. 2014, 43, 804. (d)deNanteuil, F.; DeSimone, F.; Frei, F.;
Benfatti, F.; Serrano, E.; Waser, J. Chem. Commun. 2014, 50, 10912.
3
2
788. (j) Shenje, R.; Williams, C. W.;Francois, K. M.;France, S. Org. Lett.
014, 16, 6468. (k) De Simone, F.; Andres, J.; Torosantucci, R.; Waser, J.
Org. Lett. 2009, 11, 1023.
8) (a) Sudhakar, G.; Satish, K. Chem. - Eur. J. 2015, 21, 6475.
b) Sudhakar, G.; Reddy, K. J.; Nanubolu, J. B. Org. Biomol. Chem. 2015,
3, 8875. (c) Sudhakar, G.; Raghavaiah, J.; Mahesh, G.; Singarapu, K. K.
Org. Biomol. Chem. 2016, 14, 2866.
9)Reviews:(a)Spencer, W.T., III;Vaidya, T.;Frontier, A.J. Eur. J. Org.
Chem. 2013, 2013, 3621−3633. (b) Tius, M. A. Chem. Soc. Rev. 2014, 43,
979. Recent paper: (c) Fradette, R. J.; Kang, M.; West, F. G. Angew.
Chem., Int. Ed. 2017, 56, 6335.
10)Denmark, S. E.;Habermas, K. L.;Hite, G. L. Helv. Chim. Acta1988,
1, 168.
(
(
1
(
1
e) Grover, H. K.; Emmett, M. R.; Kerr, M. A. Org. Biomol. Chem. 2015,
3, 655. (f) Ivanov, K. L.; Villemson, E. V.; Budynina, E. M.; Ivanova, O.
A.; Trushkov, I. V.; Melnikov, M. Y. Chem. - Eur. J. 2015, 21, 4975.
g) Wang, L.; Tang, Y. Isr. J. Chem. 2016, 56, 463. (h) Racine, S.;
Vuilleumier, J.; Waser, J. Isr. J. Chem. 2016, 56, 566. (i) Kerr, M. A. Isr. J.
Chem. 2016, 56, 476. (j) Pandey, A. K.; Ghosh, A.; Banerjee, P. Isr. J.
Chem. 2016, 56, 512.
2) (a)Lin, S.; Li, L.;Liang, F.;Liu, Q. Chem. Commun. 2014, 50, 10491.
b)Garve, L.K. B.;Barkawitz, P.;Jones, P. G.;Werz, D. B. Org. Lett. 2014,
6, 5804. (c) Talukdar, R.; Tiwari, D. P.; Saha, A.; Ghorai, M. K. Org. Lett.
014, 16, 3954. (d) Selvi, T.; Srinivasan, K. J. Org. Chem. 2014, 79, 3653.
(
(
2
(
(
1
2
(
5
(
(
7
(11) Rosenthal, J.; Schuster, D. I. J. Chem. Educ. 2003, 80, 679.
(12) In 2k and 2l, a small amount of an intramolecular cyclopent-
e) Venukumar, P.; Sudharani, C.; Sridhar, P. R. Chem. Commun. 2014,
0, 2218.
3) For selected examples of [3 + 2] cycloaddition reactions, see:
a) Rakhmankulov, E. R.; Ivanov, K. L.; Budynina, E. M.; Ivanova, A. O.;
annulation product was formed (see the Supporting Information).
13) The crystal structures of compounds were deposited (CCDC
numbers: (1p) 1550328; (4a) 1567507; (4a′) 1567508, (4e) 1550329).
14) For selected examples: (a) Schatz, D. J.; Kwon, Y.; Scully, T. W.;
(
(
(
Chagarovskiy, A. O.; Skvortsov, D. A.; Latyshev, G. V.; Trushkov, I. V.;
Melnikov, M. Y. Org. Lett. 2015, 17, 770. (b) de Nanteuil, F.; Serrano, E.;
Perrotta, D.;Waser, J. J. Am. Chem. Soc. 2014, 136, 6239. (c)Chakrabarty,
S.; Chatterjee, I.; Wibbeling, B.; Daniliuc, C. D.; Studer, A. Angew. Chem.,
Int. Ed. 2014, 53, 5964. (d) Mackay, W. D.; Fistikci, M.; Carris, R. M.;
Johnson, J. S. Org. Lett. 2014, 16, 1626. (e) Zhu, M.; Liu, J.; Yu, J.; Chen,
L.; Zhang, C.; Wang, L. Org. Lett. 2014, 16, 1856. (f) Xu, H.; Qu, J.-P.;
Liao, S.; Xiong, H.; Tang, Y. Angew. Chem., Int. Ed. 2013, 52, 4004.
West, F. G. J. Org. Chem. 2016, 81, 12494. (b) William, R.; Leng, W. L.;
Wang, S.; Liu, X.-W. Chem. Sci. 2016, 7, 1100. (c) LeFort, F. M.; Mishra,
V.; Dexter, G. D.; Morgan, T. D. R.; Burnell, D. J. J. Org. Chem. 2015, 80,
5
877. (d) Wu, Y. -Ku; Dunbar, C. R.; McDonald, R.; Ferguson, M. J.;
West, F. G. J. Am. Chem. Soc. 2014, 136, 14903. (e) Kwon, Y.; Scadeng,
O.; McDonald, R.; West, F. G. Chem. Commun. 2014, 50, 5558.
(f) William, R.; Wang, S.; Ding, F.; Arviana, E. N.; Liu, X.-W. Angew.
Chem., Int. Ed. 2014, 53, 10742. (g) Boudreau, J.; Courtemanche, M. A.;
Marx, V. M.; Burnell, D. J.; Fontaine, F. G. Chem. Commun. 2012, 48,
(
1
g) Xiong, H.; Xu, H.; Liao, S.; Xie, Z.; Tang, Y. J. Am. Chem. Soc. 2013,
35,7851. (h)Goldberg, A.F.G.;O’Connor, N. R.;Craig, R.A.;Stoltz, B.
1
2
1250. (h) Marx, V. M.; LeFort, F. M.; Burnell, D. J. Adv. Synth. Catal.
011, 353, 64. (i) Marx, V. M.; Burnell, D. J. Org. Lett. 2009, 11, 1229.
M. Org. Lett. 2012, 14, 5314. (i) de Nanteuil, F.; Waser, J. Angew. Chem.,
Int. Ed. 2011, 50, 12075. (j) Sathishkannan, G.; Srinivasan, K. Org. Lett.
(
(
j) Grant, T. N.; Rieder, C. J.; West, F. G. Chem. Commun. 2009, 5676.
k) Basak, A. K.; Tius, M. A. Org. Lett. 2008, 10, 4073. (l) Giese, S.; West,
2
011, 13, 6002. (k) Pohlhaus, P. D.; Sanders, S. D.; Parsons, A. T.; Li, W.;
Johnson, J. S. J. Am. Chem. Soc. 2008, 130, 8642. (l) Carson, C. A.; Kerr,
M. A. J. Org. Chem. 2005, 70, 8242. For selected examples of [3 + 3]
cycloaddition reactions, see: (m) Zhang, H.-H.; Luo, Y.-C.; Wang, H.-P.;
Chen, W.; Xu, P.-F. Org. Lett. 2014, 16, 4896. (n) Talukdar, R.; Tiwari, D.
P.;Saha, A.;Ghorai, M. A. Org. Lett. 2014, 16, 3954. (o)Young, I. S.;Kerr,
M.A. Angew. Chem., Int.Ed. 2003,42, 3023. Forselectedexamplesof[4+
F. G. Tetrahedron Lett. 1998, 39, 8393.
15) For selected examples, see: (a) Imai, H. S.; Kamwa, H.; Tokunaga,
T.; Fujita, S.; Furuya, T.; Matsumoto, H.; Shimizu, M. J. Antibiot. 1987,
0, 1483. (b) Schummer, D.; Gerth, K.; Reichenbach, H.; Hofle, G.
(
4
̈
Liebigs Ann. 1995, 1995, 685. (c) Bode, H. B.; Zeeck, A. J. Chem. Soc.
Perkin Trans 1 2000, 323. (d) Horton, P. A.; Koehn, F. E.; Longley, R. E.;
McConnell, O. J.J. Am.Chem. Soc. 1994,116,6015.(e)Grafe, U.;Schade,
W.; Roth, M.; Radics, L.; Incze, M.; Ujszaszy, K. J. Antibiot. 1984, 37, 836.
3], [8+3], and[2+2]reactions, see:(p)Ivanova, O. A.;Budynina, E. M.;
Grishin, Y. K.; Trushkov, I. V.; Verteletskii, P. V. Angew. Chem., Int. Ed.
2
2
008, 47, 1107. (q) Rivero, A. R.; Fernan
013, 15, 4928. (r) Halskov, K. S.; Kniep, F.; Lauridsen, V. H.; Iversen, E.
́
dez, I.; Sierra, M. A. Org. Lett.
H.; Donslund, B. S.; Jørgensen, K. A. J. Am. Chem. Soc. 2015, 137, 1685.
D
DOI: 10.1021/acs.orglett.7b02061
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