[4+2] cycloaddition of intermediates generated from arynes and DMF

Article abstract of DOI:10.1016/j.tetlet.2013.12.119

The trapping reaction of the transient intermediate ortho-quinone methides, generated by the insertion of arynes into a carbon-oxygen double bond of DMF, with dienophiles was investigated. The [4+2] cycloaddition products were obtained when the diesters of acetylenedicarboxylic acid were employed as dienophiles.

Full text of DOI:10.1016/j.tetlet.2013.12.119

Accepted Manuscript
[4+2] Cycloaddition of intermediates generated from arynes and DMF
Eito Yoshioka, Hirofumi Tamenaga, Hideto Miyabe
PII:
S0040-4039(14)00083-5
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.12.119
TETL 44082
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
13 November 2013
6 December 2013
18 December 2013
Please cite this article as: Yoshioka, E., Tamenaga, H., Miyabe, H., [4+2] Cycloaddition of intermediates generated
from arynes and DMF, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2013.12.119
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
To create your abstract, type over the instructions in the template box below.
Fonts or abstract dimensions should not be changed or altered.
[4+2] Cycloaddition of intermediates
generated from arynes and DMF
Leave this area blank for abstract info.
Eito Yoshioka, Hirofumi Tamenaga, and Hideto Miyabe

1
Tetrahedron Letters
journal homepage: www.els evier.com
[4+2] Cycloaddition of intermediates generated from arynes and DMF
Eito Yoshiokaa, Hirofumi Tamenagaa and Hideto Miyabea,∗
aSchool of Pharmacy, Hyogo University of Health Sciences, Minatojima, Kobe 651-8530, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The trapping reaction of the transient intermediate ortho-quinone methides, generated by the
insertion of arynes into carbon-oxygen double bond of DMF, with dienophiles was investigated.
The [4+2] cycloaddition products were obtained when the diesters of acetylenedicarboxylic acid
were employed as dienophiles.
Available online
2013 Elsevier Ltd. All rights reserved.
Keywords:
Aryne
Cycloaddition
Amide
Three-component reaction
Acetylenedicarboxylic acid diester
element σ−bonds.8 In contrast, less is known about the
corresponding π−bond insertion.9 Recently, we reported the
efficient insertion into the C=O π−bond of sterically less
hindered formamides,13 which was successfully applied into the
sequential transformation by trapping the transient intermediates
with nucleophiles such as dialkylzincs,14 active methylenes,15,16
and methines17 (Figure 1). In these transformations, ortho-
quinone methide B would be formed from the [2+2] adduct
benzoxetene A, which was also supported by our calculated
data.14 Our laboratory is newly interested in trapping the ortho-
quinone methides B with dienophiles.18 In this paper, we describe
the study on the three-component coupling reaction involving the
hetero Diels-Alder reaction of intermediates B and dienophiles.
In the past decade, arynes have gained increasing attention as
highly reactive species for constructing the multi-substituted
arenes with structural diversity and complexity.1,2 This is mainly
due to the use of ortho-(trimethylsilyl)aryl triflates as mild aryne
precursors, which were first reported by Kobayashi and co-
workers.3 In recent years, the utility of arynes, derived in this
manner, was demonstrated in the transition metal-catalyzed
reactions, the transition metal-free reactions and so on.4-12 These
studies have achieved remarkable success, particularly in multi-
component coupling reactions.
To test the possibility of hetero Diels-Alder reaction, our
experiments began with the investigation of reaction of an aryne
precursor, 3-methoxy-2-(trimethylsilyl)phenyl triflate 1, with
N,N-dimethylformamide (DMF)19 and acetylenedicarboxylic acid
dimethyl ester 2a (Table 1). DMF was employed as a solvent,
and the effect of fluoride ion sources was initially studied.
Although the use of anhydrous TBAF or KF did not promote the
reaction (entries 1 and 2), the formation of the desired [4+2]
cycloaddition product 3a was observed when 3 equivalents of
CsF were employed (entries 3-6). The reaction proceeded
effectively at 25 °C (entries 3 and 4), although chemical yield
decreased by changing the temperature from 25 to 0 °C (entry 5).
The heating activation at 50 °C accelerated the reaction to give
3a in 79% only after being stirred for 15 min (entry 6). These
results suggest that the present reaction proceeded through ortho-
quinone methide B predominantly formed from benzoxetene A.
Figure 1. Intermediates generated from arynes and amides.
As the transition metal-free reactions, considerable effort has
been directed toward the insertion of arynes into various element-
———
We also calculated the HOMO energy of an intermediate
ortho-quinone methide (−5.20 eV), which was higher than
∗ Corresponding author. Tel.: +81-78-304-3094; fax: +81-78-304-2794; e-mail: miyabe@huhs.ac.jp

2
Tetrahedron
HOMO energy of furan (−6.53 eV) as a typical diene.20 Thus,
Table 2. Reaction of 1 with DMF and several dienophilesa
the concerted mechanism can be rationalized considering the
overlap of HOMO of quinone methide with LUMO of dienophile
2a (−1.89 eV), although the ionic stepwise mechanism cannot be
excluded.
Table 1. Reaction of precursor 1 with DMF and dienophile 2aa
OMe
CO2Me
TMS
OTf
H
NMe2
Reagent
+
+
O
CO2Me
2a
1
OMe NMe2
OMe
CO2Me
CHO
OH
+
O
CO2Me
Entry
Dienophiles
Time (h)
Product (% yield)b
3b (76)
3c (71)
3d (4), 5 (26)
4 (98)
3a
4
1
2
3
4
2b
2c
2d
2e
1
5
1
1
Entry
Reagent
(3.0 equiv)
TBAF
KF
CsF
CsF
T (°C)
Time (h)
Product
(% yield)b
4 (19)c
nrd
1
2
3
4
5
25
25
25
25
0
2.5
2
2
3
15
0.25
a Reactions were carried out with 1 (1.0 equiv), 2b-e (2.0 equiv), and
CsF (3.0 equiv) in DMF (0.1 M solution of 1) at 25 °C.
b Isolated yield.
3a (85)
3a (80)
3a (31)
3a (79)
CsF
CsF
When ethyl 2-butynoate 6 was used, we observed the
interesting side reaction (Scheme 2). Surprisingly, the coumarin
derivative 7 was isolated in 29% yield as a major product from
the complex reaction mixture. In this transformation, ethyl 2-
butynoate 6 acted as not dienophile but nucleophile for trapping
the unstable quinone methide E. We assume that the reaction of
E with the anion F, generated by the addition of fluoride ion to 6,
led to the formation of coumarin 7 via the intermediate G.21
6
50
a
Reactions were carried out with 1 (1.0 equiv), 2a (2.0 equiv), and
reagent (3.0 equiv) in DMF (0.1 M solution of 1).
b Isolated yield.
c Triflate 1 was recovered in 21% yield.
d No reaction; Triflate 1 was recovered in 86% yield.
The slow decomposition of [4+2] cycloaddition product 3a
was observed during the purification by preparative TLC using
precoated silica gel plates. Therefore, the stability of 3a was
checked under the reaction conditions (Scheme 1). In the
presence of CsF, treatment of product 3a with DMF at 25 °C or
50 °C did not lead to decomposition. Almost quantitative
recovery of 3a was confirmed by 1H NMR study.
Scheme 1. Stability of product 3a under the reaction conditions.
Scheme 2. Reaction of 1 with DMF and ethyl 2-butynoate 6.
On the basis of the above results, we next studied the reaction
of aryne precursor 1 with several dienophiles having carbon-
carbon triple bond at 25 °C (Table 2). As expected,
acetylenedicarboxylic acid diethyl ester 2b worked well to give
the adduct 3b in 76% yield (entry 1). Under analogous reaction
conditions, the bulky di-tert-butyl ester of acetylenedicarboxylic
acid 2c has shown the good reactivity to give the product 3c in
71% yield (entry 2). When methyl propiolate 2d was employed
as a dienophile, the desired hetero Diels-Alder reaction did not
proceed effectively probably because of the instability of the
initially formed [4+2] cycloaddition product 3d having a mono-
ester group and other side reactions (entry 3). Although the
products were complicated, the [4+2] cycloaddition product 3d
and its isomer 5 could be isolated in 4% and 26% yields,
respectively. In the case of methyl 3-phenylpropiolate 2e, [4+2]
cycloaddition did not take place, but salicylaldehyde derivative 4
was obtained in 98% yield as a result of hydrolysis of
intermediates with contaminated water. (entry 4).
We next tested the reactivity of dienophiles having carbon-
carbon double bond. However, dimethyl maleate, dimethyl
fumarate and maleimide did not act as dienophiles for trapping
quinone methide E. When cyclohexenone 8 was employed, we
observed a different type of three-component coupling reaction
giving the tricyclic compound
9 (Scheme 3). In this
transformation, the use of KF as fluoride ion source led to an
enhancement in chemical yield. In the presence of KF (3 equiv),
the reaction was carried out in DMF at 80 °C. Compound 9 was
isolated in 40% yield, though it was slowly decomposed under
acidic conditions. It assumes that this reaction would involve the
trapping reaction of quinone methide E with anion H. The
tricyclic compound 11 was obtained in 34% yield even when
bulky ketone 10 was employed. To learn about the reactivity of
quinone methide E, the reaction of salicylaldehyde derivative 4
with 10 was also evaluated under the similar reaction conditions.
However, sufficient conversion into 11 did not be observed; thus,

3
the route involving the addition of anion H to quinone methide E
not detected and the adduct 13 was recovered. In the absence of
was supported.
CsF, treatment of salicylaldehyde with dienophile 2a in DMF
gave the adduct 14 in 20% yield. These results indicate that the
adduct 14 was formed from salicylaldehyde. The contaminated
water promoted the hydrolysis of quinone methide E giving
salicylaldehyde under the diluted concentration.
NMe2
OH
CO2Me
CO2Me
CsF (3.0 equiv)
DMF, 25 °C, 3 h
O
CO2Me
O
CO2Me
13
was recoverd.
14
(not detected)
OH
13
(0.02 M)
CO2Me
CO2Me
CHO
OH
CO2Me
+
DMF, 25 °C, 5 h
O
CO2Me
14
(20%)
(0.02 M)
2a
(2.0 equiv)
O
O
CO2Me
14
CO2Me
Scheme 4. Formation of adduct 14.
In contrast, the formation of 2H-chromene 15 was observed
when 3 equivalents of CsF were employed in the reaction of
salicylaldehyde with dienophile 2a (Scheme 5). In the presence
of CsF, the condensation of salicylaldehyde with dienophile 2a
proceeded effectively to give chromene 15 in 87% yield. It
assumes that this transformation would promote by the
generation of anion J from dienophile 2a and fluoride ion.21
Scheme 3. Reaction with cyclohexenones 8 and 10.
The effect of concentration on chemical efficiency was
studied in [4+2] cycloaddition using an aryne precursor 12 and
dienophile 2a (Table 3). The good result was obtained, when the
reaction was carried out in 0.1 M solution of 12 in DMF (entry
1). The desired adduct 13 was obtained in 59% yield after being
stirred at 80 °C for 10 min. As shown in Tables 1 and 2, 0.1 M
solution of an aryne precursor 1 in DMF similarly gave the good
results. In contrast, the formation of undesired adducts 14 and/or
15 was observed under the diluted concentration (entries 2 and
3). When the reaction using 0.02 M solution of 12 was carried
out at 80 °C for 10 min, the desired adduct 13 was obtained in
45% yield, accompanied by 12% yield of adduct 14 and 8% yield
of 2H-chromene 15 (entry 2). A significant amount of adduct 14
was obtained at 25 °C (entry 3).
Table 3. Effect of concentrationa
Scheme 5. CsF-promoted reaction of salicylaldehyde with 2a.
Finally, the aryne precursor 16 was tested (Scheme 6).
Reaction of 16 gave the desired adduct 17 in 26% yield.
NMe2
CsF (3.0 equiv)
TMS
OTf
CO2Me
2a
(2.0 equiv)
Entry Concentration T (°C) Time Product
of 12
(min) (% yield)b
O
CO2Me
DMF, 80 °C, 10 min
17
(26%)
16
1
2
3
0.1 M
0.02 M
0.02 M
80
80
25
10
10
60
13 (59)
13 (45), 14 (12) , 15 (8)
13 (31), 14 (35)
Scheme 6. [4+2]-Reaction of aryne precursor 16.
a Reactions were carried out with 12 (1.0 equiv), 2a (2.0 equiv), and
CsF (3.0 equiv) in DMF.
In conclusion, we have shown that the three-component
coupling reaction starting from the π-bond insertion of arynes
proceeded through [4+2] cycloaddition of intermediates ortho-
quinone methides with dienophiles. Although the usable
dienophiles were limited to diesters of acetylenedicarboxylic
acid, the present reaction offers opportunities for further
exploration with intriguing possibilities in aryne chemistry.
b Isolated yield.
Next, the formation of adduct 14 was studied. The hydrolysis
of adduct 13 with contaminated water did not proceed under the
reaction conditions (Scheme 4). The formation of adduct 14 was

4
Tetrahedron
J. Am. Chem. Soc. 2008, 130, 1558; (e) Pintori, D. G.; Greaney,
M. F. Org. Lett. 2010, 12, 168; (f) Łaczkowski, K. Z.; Carcía, D.;
Peña, D.; Cobas, A.; Pérez, D.; Guitián, E. Org. Lett. 2011, 13,
960; (g) Aoki, T.; Koya, S.; Yamasaki, R.; Saito, S. Org. Lett.
2012, 14, 4506; (h) Saito, N.; Nakamura, K.; Shibano, S.; Ide, S.;
Minami, M.; Sato, Y. Org. Lett. 2013, 15, 386; (i) Yoshida, H.;
Yoshida, R.; Takaki, K. Angew. Chem. Int. Ed. 2013, 52, 8629.
9. For the insertion into π-bond, see: (a) Zbiral, E. Tetrahedron Lett.
1964, 5, 3963; (b) Gompper, R.; Kutter, E.; Seybold, G. Chem.
Ber. 1968, 101, 2340; (c) Heaney, H.; Jablonski, J. M.; McCarty,
C. T. J. Chem. Soc., Perkin Trans. 1 1972, 2903; (d) Nakayama,
J.; Yoshida, M.; Simamura, O. Chem. Lett. 1973, 451; (e)
Nakayama, J.; Midorikawa, H.; Yoshida, M. Bull. Chem. Soc. Jpn.
1975, 48, 1063; (f) Miki, S.; Ema, T.; Shimizu, R.; Nakatsuji, H.;
Yoshida, Z. Tetrahedron Lett. 1992, 33, 1619; (g) Aly, A. A.;
Mohamed, N. K.; Hassan, A. A.; Mourad, A.-F. E. Tetrahedron
1999, 55, 1111; (h) Okuma, K.; Shiki, K.; Sonoda, S.; Koga, Y.;
Shioji, K.; Kitamura, T.; Fujiwara, Y.; Yokomori, Y. Bull. Chem.
Soc. Jpn. 2000, 73, 155; (i) Okuma, K.; Okada, A.; Koga, Y.;
Yokomori, Y. J. Am. Chem. Soc. 2001, 123, 7166; (j) Okuma, K.;
Nojima, A.; Nakamura, Y.; Matsunaga, N.; Nagahora, N.; Shioji,
K. Bull. Chem. Soc. Jpn. 2011, 84, 328; (k) Biswas, K.; Greaney,
M. F. Org. Lett. 2011, 13, 4946; (l) Chakrabarty, S.; Chatterjee, I.;
Tebben, L.; Studer, A. Angew. Chem. Int. Ed. 2013, 52, 2968; (m)
Li, R.; Wang, X.; Wei, Z.; Wu, C.; Shi, F. Org. Lett. 2013, 15,
4366.
10. For the [2+2+2] cycloaddition, see: (a) Peña, D.; Escudero, S.;
Pérez, D.; Guitián, E.; Castedo, L. Angew. Chem. Int. Ed. 1998,
37, 2659; (b) Peña, D.; Pérez, D.; Guitián, E.; Castedo, L. J. Am.
Chem. Soc. 1999, 121, 5827; (c) Sato, Y.; Tamura, T.; Mori, M.
Angew. Chem. Int. Ed. 2004, 43, 2436; (d) Qiu, Z.; Xie, Z. Angew.
Chem. Int. Ed. 2009, 48, 5729; (d) Iwayama, T.; Sato, Y. Chem.
Commun. 2009, 5245; (e) Lynett, P. T.; Maly, K. E. Org. Lett.
2009, 11, 3726; (f) Patel, R. M.; Argade, N. P. Org. Lett. 2013, 15,
14.
11. For the [3+2] cycloaddition, see: (a) Jin, T.; Yamamoto, Y.
Angew. Chem. Int. Ed. 2007, 46, 3323; (b) Huang, X.-C.; Liu, Y.-
L.; Liang, Y.; Pi, S.-F.; Wang, F.; Li, J.-H. Org. Lett. 2008, 10,
1525; (c) Dai, M.; Wang, Z.; Danishefsky, S. J. Tetrahedron Lett.
2008, 49, 6613; (d) Huang, X.; Zhang, T. Tetrahedron Lett. 2009,
50, 208; (e) Wu, C.; Fang, Y.; Larock, R. C.; Shi, F. Org. Lett.
2010, 12, 2234; (f) Spiteri, C.; Keeling, S.; Moses, J. E. Org. Lett.
2010, 12, 3368; (g) Hong, D.; Chen, Z.; Lin, X.; Wang, Y. Org.
Lett. 2010, 12, 4608; (h) Kovács, S.; Csincsi, Á. I.; Nagy, T. Zs.;
Boros, S.; Timári, G.; Novák, Z. Org. Lett. 2012, 14, 2022.
12. For the [4+2] cycloaddition, see: (a) Ikawa, T.; Nishiyama, T.;
Nosaki, T.; Takagi, A.; Akai, S. Org. Lett. 2011, 13, 1730; (b)
Bhojgude, S. S.; Kaicharla, T.; Bhunia, A.; Biju, A. T. Org. Lett.
2012, 14, 4098; (c) Li, J.; Wang, N.; Li, C.; Jia, X. Org. Lett.
2012, 14, 4994; (d) Kaicharla, T.; Bhojgude, S. S.; Biju, A. T.
Org. Lett. 2012, 14, 6238.
Acknowledgments
This work was partially supported by a Grant-in-Aid for
Scientific Research from the ministry of Education, Culture,
Sports, Science and Technology of Japan.
Supplementary Material
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/??????????????????
References and notes
1. For reviews, see: (a) Kessar, S. V. In Comprehensive Organic
Synthesis; Trost, B. M.; Flemming, I. Eds.; Pergamon, Oxford,
1991, vol. 4, pp. 483-515; (b) Saito, S.; Yamamoto, Y. Chem. Rev.
2000, 100, 2901; (c) Pellissier, H.; Santelli, M. Tetrahedron 2003,
59, 701; (d) Wenk, H. H.; Winkler, M.; Sander, W. Angew. Chem.
Int. Ed. 2003, 42, 502; (e) Peña, D.; Pérez, D.; Guitián, E. Angew.
Chem. Int. Ed. 2006, 45, 3579; (f) Yoshida, H.; Ohshita, J.; Kunai,
A. Bull. Chem. Soc. Jpn. 2010, 83, 199.
2. For some recent studies, see: (a) Gerfaud, T.; Neuville, L.; Zhu, J.
Angew. Chem. Int. Ed. 2009, 48, 572; (b) Sha, F.; Huang, X.
Angew. Chem. Int. Ed. 2009, 48, 3458; (c) Ikawa, T.; Takagi, A.;
Kurita, Y.; Saito, K.; Azechi, K.; Egi, M.; Kakiguchi, K.; Kita, Y.;
Akai, S. Angew. Chem. Int. Ed. 2010, 49, 5563; (d) Biju, A. T.;
Glorius, F. Angew. Chem. Int. Ed. 2010, 49, 9761; (e) Cheong, P.
H.-Y.; Paton, R. S.; Bronner, S. M.; Im, G.-Y. J.; Garg, N. K.;
Houk, K. N. J. Am. Chem. Soc. 2010, 132, 1267; (f) Goetz, A. E.;
Bronner, S. M.; Cisneros, J. D.; Melamed, J. M.; Paton, R. S.;
Houk, K. N.; Garg, N. K. Angew. Chem. Int. Ed. 2012, 51, 2758;
(g) Hamura, T.; Chuda, Y.; Nakatsuji, Y.; Suzuki, K. Angew.
Chem. Int. Ed. 2012, 51, 3368; (h) Zeng, Y.; Zhang, L.; Zhao, Y.;
Ni, C.; Zhao, J.; Hu, J. J. Am. Chem. Soc. 2013, 135, 2955.
3. Himeshima, Y.; Sonoda, T.; Kobayashi, H. Chem. Lett. 1983,
1211.
4. For the coupling reactions, see: (a) Yoshikawa, E.; Yamamoto, Y.
Angew. Chem. Int. Ed. 2000, 39, 173; (b) Henderson, J. L.;
Edwards, A. S.; Greaney, M. F. J. Am. Chem. Soc. 2006, 128,
7426; (c) Liu, Z.; Larock, R. C. Angew. Chem. Int. Ed. 2007, 46,
2535; (d) Jeganmohan, M.; Bhuvaneswari, S.; Cheng, C.-H.
Angew. Chem. Int. Ed. 2009, 48, 391; (e) Gerfaud, T.; Neuville,
L.; Zhu, J. Angew. Chem. Int. Ed. 2009, 48, 572; (f) Li, R.-J.; Pi,
S.-F.; Liang, Y.; Wang, Z.-Q.; Song, R.-J.; Chen, G.-X.; Li, J.-H.
Chem. Commun. 2010, 46, 8183.
5. For transition metal-catalyzed insertion into σ-bond, see: (a)
Yoshida, H.; Honda, Y.; Shirakawa, E.; Hiyama, T. Chem.
Commun. 2001, 1880; (b) Yoshida, H.; Okada, K.; Kawashima,
S.; Tanino, K.; Ohshita, J. Chem. Commun. 2010, 46, 1763.
6. For the reactions of arynes with nucleophile followed by
electrophile, see: (a) Yoshida, H.; Fukushima, H.; Ohshita, J.;
Kunai, A. Angew. Chem. Int. Ed. 2004, 43, 3935; (b) Zhao, J.;
Larock, R. C. Org. Lett. 2005, 7, 4273; (c) Yoshida, H.;
13. The reaction of benzenediazonium chloride or benzenediazonium-
2-carboxylate with DMF, see: Yaroslavsky, S. Tetrahedron Lett.
1965, 6, 1503.
14. (a) Yoshioka, E.; Kohtani, S.; Miyabe, H. Org. Lett. 2010, 12,
1956; (b) Yoshioka, E.; Miyabe, H. Tetrahedron 2012, 68, 179.
15. Yoshioka, E.; Kohtani, S.; Miyabe, H. Angew. Chem. Int. Ed.
2011, 50, 6638.
Fukushima, H.; Ohshita, J.; Kunai, A. J. Am. Chem. Soc. 2006,
128, 11040; (d) Okuma, K.; Nojima, A.; Matsunaga, N.; Shioji, K.
Org. Lett. 2009, 11, 169; (e) Okano, K.; Fujiwara, H.; Noji, T.;
Fukuyama, T.; Tokuyama, H. Angew. Chem. Int. Ed. 2010, 49,
5925; (f) Bhunia, A.; Roy, T.; Pachfule, P.; Rajamohanan, P. R.;
Biju A. T. Angew. Chem. Int. Ed. 2013, 52, 10040.
16. For a related example, see: Yoshida, H.; Ito, Y.; Ohshita, J. Chem.
Commun. 2011, 47, 8512.
17. Yoshioka, E.; Tanaka, H.; Kohtani, S.; Miyabe, H. Org. Lett.
2013, 15, 3938.
7. For the reactions via the nucleophilic addition and subsequent
protonation, see: (a) Liu, Z.; Larock, R. C. Org. Lett. 2004, 6, 99;
(b) Jeganmohan, M.; Cheng, C.-H. Chem. Commun. 2006, 2454;
(c) Sha, F.; Huang, X. Angew. Chem. Int. Ed. 2009, 48, 3458; (d)
Jones, E. P.; Jones, P.; Barrett, A. G. M. Org. Lett. 2011, 13, 1012;
(e) Pirali, T.; Zhang, F.; Miller, A. H.; Head, J. L.; McAusland,
D.; Greaney, M. F. Angew. Chem. Int. Ed. 2012, 51, 1006.
8. For the insertion into σ-bond, see: (a) Yoshida, H.; Shirakawa, E.;
Honda, Y.; Hiyama, T. Angew. Chem. Int. Ed. 2002, 41, 3247; (b)
Liu, Z.; Larock, R. C. J. Am. Chem. Soc. 2005, 127, 13112; (c)
Tambar, U. K.; Ebner, D. C.; Stoltz, B. M. J. Am. Chem. Soc.
2006, 128, 11752; (d) Gilmore, C. D.; Allan, K. M.; Stoltz, B. M.
18. For the reactions via π-bond insertion and [4+2] cycloaddition,
see: (a) Yoshida, H.; Watanabe, M.; Fukushima, H.; Ohshita, J.;
Kunai, A. Org. Lett. 2004, 6, 4049; (b) Alajarin, M.; Lopez-
Leonardo, C.; Raja, R.; Orenes, R.-A. Org. Lett. 2011, 13, 5668.
19. For reviews, see: (a) Muzart, J. Tetrahedron 2009, 65, 8313; (b)
Abu-Shanab, F. A.; Sherif, S. M.; Mousa, S. A. S. J. Heterocycl.
Chem. 2009, 46, 801; (c) Ding, S.; Jiao, N. Angew. Chem., Int. Ed.
2012, 51, 9226.
20. See: Supplementary data
21. For the reaction of a fluoride ion with electrophilic alkynes, see:
Gorgues, A.; Stephan, D.; Cousseau, J. J. Chem. Soc., Chem.
Commun. 1989, 1493.