A Domino Strategy for the Synthesis of 2H-Pyrans from Propargyl Vinyl Ethers

Article abstract of DOI:10.1002/ejoc.201801847

Stable monocyclic 2H-pyrans are synthesized from readily available tertiary propargyl vinyl ethers via a metal-free all-pericyclic domino manifold involving a sequential propargyl Claisen rearrangement/[1,3]H-shift/oxa-6π electrocyclization set of reactions. The wide scope of this protocol is exemplified by the synthesis of 21 different 2H-pyrans incorporating a varied substitution pattern at the ring.

Full text of DOI:10.1002/ejoc.201801847

A Journal of
Accepted Article
Title: A Domino Strategy for the Synthesis of 2H-Pyrans from Propargyl
Vinyl Ethers.
Authors: David Tejedor, Samuel Delgado-Hernández, Raquel Diana-
Rivero, Abián Díaz-Díaz, and Fernando García-Tellado
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201801847
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10.1002/ejoc.201801847
European Journal of Organic Chemistry
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A Domino Strategy for the Synthesis of 2H-Pyrans from Propargyl
Vinyl Ethers.
David Tejedor[a], Samuel Delgado-Hernández, [a] [b] Raquel Diana-Rivero, [a] [b] Abián Díaz-Díaz, [a] [b] and
Fernando García-Tellado*[a]
Abstract: Stable monocyclic 2H-pyrans are synthesized from readily
available tertiary propargyl vinyl ethers via a metal-free all-pericyclic
domino manifold involving
rearrangement [1,3]H-shift
a
sequential propargyl Claisen
/
/
oxa-6 electrocyclization set of
reactions. The wide scope of this protocol is exemplified by the
synthesis of 21 different 2H-pyrans incorporating a varied substitution
pattern at the ring.
Introduction
Stable 2H-pyrans are challenging targets in current organic
synthesis.[1] In fact, the 2H-pyran core constitutes a sub-structural
motive present in a wide array of natural products,[2] and also it is
a key intermediate in organic synthesis.[3] For these reasons,
there is an ongoing interest in the synthesis of this class of
oxygenated heterocycles. Strategies designed towards their
synthesis need to take into account the known tendency of 2H-
pyrans to undergo a ring-opening conversion to their 1-oxatriene
form (Scheme 1).[4] Typically, this valence isomerization
equilibrium is governed by the 1-oxatriene form, except in a few
cases where the 2H-pyran form is favored. In these cases,
significant steric interactions disfavor planarity, and consequently,
the -delocalization through the conjugated system. Studies on
these equilibria[5] have shown that the 2H-pyran form is stabilized
by the presence of electron-withdrawing groups at the C-5
position (R5 in Scheme 1; electronic factors), disubstitution at the
C-2 position (R2/R2’≠H)(steric factors) or annulation (entropic trap).
Prototypical examples of stable 2H-pyrans are 2H-chromenes
(1),[6] 2,2,4-trimethyl-2H-pyran[7] (2) (favored by steric factors) and
methyl 2,2-dimethyl-2H-pyran-5-carboxylate[8] (3) (favored by a
combination of steric and electronic factors) (Scheme 1).
Scheme 1. 1-Oxatriene/2H-pyran valence isomerization. Prototypical examples
of stable 2H-pyrans.
rearrangement of propargyl vinyl ethers (PVEs).[10] Kirsch and col.
showed that PVEs bearing a methine carbon atom at the
propargylic position (4, Scheme 2b), rearranged to trisubstituted
2H-pyran-5-carboxylates (2HPCs) 5 through a two-step, one pot
reaction entailing
rearrangement and
a
a
silver-catalyzed propargyl Claisen
tandem base-catalyzed allene-diene
isomerization/oxa 6-electrocyclization reaction.[10e] Among other
requirements, substitution at the C-6 position (R6≠ H) was
essential for the stability of the 2H-pyran ring. We report herein
an efficient, general, metal-free domino alternative to this strategy,
which is amenable to be used with PVEs featuring a quaternary
carbon center at the propargylic position and a varied functional
substitution at the terminal alkyne position.
From a synthetic point of view, these heterocycles are
commonly synthesized by the so-called “1-oxatriene pathway”,
Results and Discussion
which entails
a
tandem Knoevenagel/6-electrocyclization
reaction of 1,3-dicarbonyl compounds and 2-alkenals (a formal
[3+3] cycloaddition) (Scheme 2a).[2b],[9] Alternatives to this tandem
strategy have merged from the well-studied Claisen
Over the last years, our group has been focused on the
development of metal-free domino processes as sustainable
alternatives to metal catalyzed synthetic methodologies.[11] In this
line of thought, we have reported the implementation of a robust,
highly efficient and predictable protocol for the synthesis of PVEs
6 (Scheme 2c), which bear a quaternary carbon atom at the
propargylic position (the so-called tertiary PVEs).[12] These PVEs
are easily accessible from ketones, through a two-step procedure
entailing: 1) generation of the tertiary propargylic alcohol, and 2)
transformation of the alcohol into the corresponding -alkoxy-
acrylate derivative 6. We have also shown that the microwave
irradiation of these tertiary PVEs 6 in the presence of catalytic
amounts of imidazole generates salicylaldehyde derivatives 8
through an all-pericyclic domino process (Scheme 2c).[13] During
these studies, we discovered that this process could be funneled
[a]
Dr. D. Tejedor, Mr. S. Delgado-Hernández, Mrs. R. Diana, Mr. A.
Díaz-Díaz and Dr. F. García-Tellado
Instituto de Productos Naturales y Agrobiología, Consejo Superior
de Investigaciones Científicas, Astrofísico Francisco Sánchez 3,
38206 La Laguna, Tenerife, Spain.
E-mail: fgarcia@ipna.csic.es; dtejedor@ipna.csic.es
Homepage: https://www.ipna.csic.es/dept/qbb/qob/presentacion
Mr. S. Delgado-Hernández, Mrs. R. Diana-Rivero and Mr. A. Díaz-
Díaz, Doctoral and Postgraduate School, Universidad de La Laguna
[b]
Supporting information for this article is given via a link at the end of the
document.((Please delete this text if not appropriate))
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10.1002/ejoc.201801847
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Scheme 3. a) Synthetic manifold based on a transient 2H-pyran species. b)
Synthetic manifold based on discrete 2,2-dimethyl2H-pyran-5-carboxylates 12.
Table 1. Synthesis of 2,2,4-trisubstituted 2HPCs 7 from PVEs 6. Yields refer to
isolated product.
Scheme 2. Synthetic approaches to substituted 2H-pyrans from propargyl vinyl
ethers (PVEs). 2HPC = 2H-pyran-5-carboxylate
toward the formation of trisubstituted 2HPCs 7 by a careful control
of the temperature. This discovery opened us an unexplored 3-
step organocatalytic route to these heterocycles using ketones as
highly versatile starting materials and tertiary PVEs 6 as the active
intermediates. Using this domino manifold, we have synthesized
complex cage-like molecules such as 10, through the generation
of
a transient and conveniently functionalized 2H-pyran
intermediate (Scheme 3a).[14] More recently, we have described
the use of this manifold to generate 2,2-dimethyl-2H-pyran-5-
carboxylate derivatives 12, a family of rigid monocyclic dienes
with use in Diels-Alder/retro–Diels-Alder reactions (Scheme 3b).[8]
The particular functional pattern exhibited by derivatives 12, and
in general by the 2,2,4-trisubstituted 2HPCs 7, is not easily
accessible through the 1-oxatriene pathway using standard
methodologies (it requires the synthesis and coupling of
trisubstituted enones or the use of noble metal catalysis).[2b] This
prompted us to tackle a deeper study of this synthetic strategy to
establish the structural and/or functional limits for its practical
(preparative) use (Table 1).
[a]PVE is not isolated. Yield for two steps directly from the propargyl alcohol.
[b]Although isolated, it is quite unstable and it quickly decomposes on standing.
[c]9% unreacted PVE and 27% corresponding salicylaldehyde. [d]16% unreacted
PVE and 9% corresponding salicylaldehyde. [e]NMR yield determined using an
internal standard. 26% unreacted PVE and 60% corresponding salicylaldehyde.
[f]1-oxatriene derivative. Mixture of the corresponding E/Z isomers as seen in
the 1HNMR spectrum of the crude material
The manifold resulted to be efficient and tolerant with regard
to the electronic character of the ketone precursor. Thus, dialkyl,
diaryl and aryl alkyl ketones were cleanly transformed into the
corresponding tertiary PVEs 6, which smoothly rearranged into
the 2HPCs 7 in good to excellent yields (Table 1). A dependency
of the reaction time with the substrate forced us to monitor each
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10.1002/ejoc.201801847
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reaction (TLC) to establish the best reaction time. It spanned from
1 h for the most reactive PVEs (7c-f, 7n, 7o, 7r) to 72 h for the
most reluctant case (toluene, reflux; 7i). With regard to the
substituent R4, the reaction accepted a convenient functional
diversity, including linear (7k, 7n, 7o, 7s) or branched alkyl chains
(7e, 7l, 7p, 7t), aromatic (7h, 7j), esters (7u) and silicon-
containing groups (trimethylsilyl, 7a-g, 7i). These last two groups
of substituents constitute valuable chemical handles amenable for
using in later transformations.
with an ester or an amide at the quaternary propargylic position.[15]
An interesting extension of the protocol is depicted in Scheme
5. Dimeric PVE 15, when submitted at the standard reaction
conditions, delivered the dimer 16 in quantitative yield. Dimer 16
is attractive because it incorporates two units of the 2,2-dimethyl-
2H-pyran core, an excellent reactive cisoide diene for tandem
Diels-Alder/retro-Diels-Alder reactions.[8] With dimer 16 in hand,
we assayed the tandem reaction using 2-(trimethylsilyl)phenyl
trifluoromethanesulfonate (17) as the dienophile precursor
(benzyne) and 16 as a double diene. The reaction needed stirring
at room temperature for 16 h to deliver the expected dimethyl
[2,2'-binaphthalene]-3,3'-dicarboxylate (18)[16] in moderate yield
(46%). This result, which is susceptible to optimization, allows
laying the foundations of a practical and metal-free strategy for
the synthesis of highly conjugated polyaromatic molecules, which
constitute highly appreciated platforms in materials science.[17]
The protocol failed with the secondary 2H-pyran 7g (23% after
isolation; it decomposes on standing) and the unsubstituted
derivative 7q, which was not obtained, delivering in its place the
corresponding 1-oxatriene derivative in almost quantitative yield.
In the case of 7j, endowed with a phenyl group at C-4 and a spiro
center at C-2, the reaction manifold also delivered the
corresponding salicylaldehyde derivative 8 (27% yield; see
Scheme 2c for the general structure). The change of toluene by
benzene as solvent allowed to increase the yield of 7j to 75%,
reducing the amount of salicylaldehyde below 10%, but at the
expense of increasing the amount of recovered PVE 6j from 9%
to 16%. The lowering of the reaction temperature increased the
reaction time from hours to days, because the expected
decelerating effect on both the initial propargyl Claisen
rearrangement and the enolization step ([1,7]H shift; Scheme 2c).
Therefore, while a slower enolization directly benefits the
formation of 2H-pyran ring, the deceleration of the Claisen
rearrangement affects the whole process and, consequently, also
the formation of 2H-pyran. In the case of the 7l, the t-butyl
substituent favors the salicylaldehyde route in detriment of the 1-
oxatriene pathway, and funnels the reaction outcome toward the
salicylaldehyde formation (60% yield; 26% of r.s.m.).
Scheme 5. Extension of the domino strategy to dimeric 2H-pyran 16 and its
applications to the synthesis of dimethyl [2,2'-binaphthalene]-3,3'-dicarboxylate
(18).
The main limitation of this protocol seems to be associated
with a high electrophilicity of the propargylic quaternary carbon
center of PVEs 6. This is the case of PVE 6v, which features an
aromatic and a highly electron withdrawing CF3 group at the
propargylic position (Scheme 4). The high electrophilicity of the
quaternary propargyl center translates to the quaternary allene
central carbon atom, which ultimately translates into a favored 5-
exo-dig O-cyclization on the allenal intermediate to generate the
furan derivative 14. The same reactivity profile was also found in
the propargyl Claisen rearrangement of tertiary PVEs endowed
Conclusions
In summary, we have established and implemented a strategy
for the practical synthesis of methyl 2,2,4-trisubsituted-2H-pyran-
5-carboxylates 7 from tertiary propargyl vinyl ethers 6. The
strategy avoids the use of metals and it is highly tolerant with the
structure and electronic properties of the propargyl vinyl ether.
Although the protocol is quite general, there are some limitations,
mainly related to the electrophilicity of the propargylic carbon
atom of the tertiary PVE (strong electron withdrawing groups at
this position are not allowed) and the nature of the substituent at
C-4, which determines the weight of the 2H-pyran form in the
valence isomerization equilibrium with the corresponding 1-
oxatriene. An interesting application was advanced for the
synthesis of the dimeric platform 16 (incorporating two unis of 2,2-
dimethyl-2H-pyran-5-carboxylate), which was reacted with 2-
(trimethylsilyl)phenyl trifluoromethanesulfonate (17) to generate
the expected dimethyl [2,2'-binaphthalene]-3,3'-dicarboxylate
(18), a convenient building block for accessing highly conjugated
polyaromatic molecules.
Scheme 4. Limitations of the protocol: a high electrophilicity of the quaternary
center of the PVE funnels the reaction toward furan formation.
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10.1002/ejoc.201801847
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3J(H,H) = 7.2 Hz), 1.18-1.33 (m, 3H), 1.39-1.46 (m, 1H), 1.87-1.93 (m, 1H),
2.04-2.09 (m, 1H), 3.62 (s, 3H), 5.40 (d, 1H, 3J(H,H) = 12.1 Hz), 7.29-7.37
(m, 3H), 7.46-7.48 (m, 2H), 7.65 (d, 1H, 3J(H,H) = 12.1 Hz). 13C NMR
(CDCl3, 125 MHz): = -0.3 (3C), 13.8, 22.4, 26.5, 44.2, 50.9, 83.8, 96.0,
99.8, 102.9, 126.3 (2C), 128.3, 128.4 (2C), 140.8, 159.4, 168.0 ppm.
HRMS (ESI+): m/z [M+Na]+ calculated for C20H28O3Si 367.1705, found
367.1708.
Experimental Section
General remarks. 1H NMR and 13C NMR spectra of CDCl3 solutions were
recorded either at 400 and 100 MHz or at 500 and 125 MHz, respectively.
Mass spectra (low resolution) (EI/CI) and HRMS (EI/TOF) were obtained
with
a gas chromatograph/mass spectrometer. Analytical thin-layer
chromatography plates used UV-active silica gel on aluminum. Flash
column chromatography was carried out with silica gel 60 (particle size
less than 0.020 mm) using appropriate mixtures of ethyl acetate and
hexanes as eluents. All reactions were performed in oven-dried glassware.
All materials were obtained from commercial suppliers and used as
received. All melting points are uncorrected. The propargyl alcohols were
prepared by addition of the lithium or magnesium bromide acetylides onto
the appropriate ketones following the standard procedures (see below for
a general procedure). The propargyl vinyl ethers were prepared according
to our previous experimental procedure[¡Error! Marcador no definido.] (see below
for a general procedure). Products 6a,[8] 6e,[18a] 6h,[13] 6i[13] 6j[13] 6k,[18b]
6l,[18b] 6m,[12] 6q[18b], 6r,[18a] 6t,[18a] 6u,[18a] 7a,[8] 7r,[18a] and 18[16] have been
previously described.
(E)-Methyl 3-(1-phenyl-3-(trimethylsilyl)prop-2-ynyloxy)acrylate (6g).
Colorless oil: 1H NMR (CDCl3, 400 MHz): 0.21 (s, 9H), 3.69 (s, 3H),
5.46 (d, 1H, 3J(H,H) = 12.4 Hz), 5.62 (s, 1H), 7.37-7.41 (m, 3H), 7.48-7.52
(m, 2H), 7.69 (d, 1H, 3J(H,H) = 12.4 Hz). 13C NMR (CDCl3, 100 MHz): =
-0.4 (3C), 51.1, 73.6, 95.8, 99.3, 100.0, 127.5 (2C), 128.7 (2C), 129.2,
136.1, 159.9, 167.9 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for
C16H20O3Si 311.1079, found 311.1082.
(E)-Methyl 3-(4-phenyloct-2-yn-4-yloxy)acrylate (6n). Colorless oil: 1H
3
NMR (CDCl3, 500 MHz): 0.84 (t, 3H, J(H,H) = 7.2 Hz), 1.15-1.31 (m,
3H), 1.38-1.46 (m, 1H), 1.86-1.92 (m, 1H), 2.00 (s, 3H), 2.02-2.09 (m, 1H),
3.62 (s, 3H), 5.40 (d, 1H, 3J(H,H) = 12.1 Hz), 7.27-7.30 (m, 1H), 7.32-7.35
(m, 2H), 7.46-7.48 (m, 2H), 7.63 (d, 1H, 3J(H,H) = 12.1 Hz). 13C NMR
(CDCl3, 125 MHz): = 3.8, 13.9, 22.5, 26.6, 44.5, 50.9, 76.9, 83.9, 86.7,
99.4, 126.4 (2C), 128.2, 128.3 (2C), 141.5, 159.7, 168.2 ppm. HRMS
(ESI+): m/z [M+Na]+ calculated for C18H22O3 309.1467, found 309.1469.
General procedure for the synthesis of tertiary propargyl alcohols:
The terminal alkyne (13 mmol) was dissolved in 25 mL of dry THF in a
round-bottom flask. After the mixture was cooled to -78 ºC, a solution of
1,6M BuLi in hexanes (20.8 mL, 13 mmol) was added dropwise. The
temperature was maintained between -78 ºC and -40 ºC for 1 h with stirring
of the solution. Ketone (10 mmol) was then added slowly (if solid, dissolved
in THF), and the stirring was continued overnight allowing the reaction
mixture to warm up to room temperature slowly without additional cooling.
After completion, the reaction was quenched with saturated NH4Cl solution
and extracted with CH2Cl2. This was followed by isolation of the
corresponding product by flash column chromatography (silica gel,
appropriate mixtures of n-hexane/EtOAc) for high boiling alkynes. If the
alkyne used had a relatively low boiling point (< 120 ºC), evaporation of
the solvent and excess reaction led to a crude alcohol which did not need
chromatographic purification.
(E)-Methyl 3-(2-phenylpent-3-yn-2-yloxy)acrylate (6o). Colorless oil: 1H
NMR (CDCl3, 400 MHz): 1.81 (s, 3H), 1.98 (s, 3H), 3.63 (s, 3H), 5.41
(d, 1H, 3J(H,H) = 12.1 Hz), 7.30-7.37 (m, 3H), 7.51-7.53 (m, 2H), 7.65 (d,
1H, 3J(H,H) = 12.1 Hz). 13C NMR (CDCl3, 100 MHz): = 3.7, 32.4, 50.9,
78.2, 80.1, 85.9, 99.7, 125.9 (2C), 128.3, 128.5 (2C), 142.3, 159.3, 168.1
ppm.
(E)-Methyl 3-(5,5-dimethyl-2-phenylhex-3-yn-2-yloxy)acrylate (6p).
Colorless oil: 1H NMR (CDCl3, 400 MHz): 1.30 (s, 9H), 1.80 (s, 3H),
3.63 (s, 3H), 5.39 (d, 1H, 3J(H,H) = 12.1 Hz), 7.28-7.37 (m, 3H), 7.49-7.52
(m, 2H), 7.68 (d, 1H, 3J(H,H) = 12.1 Hz). 13C NMR (CDCl3, 100 MHz): =
27.7, 30.8 (3C), 32.6, 50.9, 77.6, 80.2, 98.9, 99.5, 125.8 (2C), 128.3, 128.5
(2C), 142.5, 159.4, 168.1 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for
C18H22O3 309.1467, found 309.1464.
General procedure for the synthesis of propargyl vinyl ethers 6 from
the corresponding tertiary propargyl alcohols. Methyl propiolate (2.0
mmol) was added dropwise (time of addition 10 min) to a solution of the
propargyl alcohol (1.0 mmol) and DABCO (0.10 mmol) in a 1:9 mixture of
dry CH2Cl2 and hexane (5 mL). The reaction mixture was stirred until
completion (TLC control). The solvent was removed under reduced
pressure, and the residue was purified by flash column chromatography
(silica gel; n-hexane/EtOAc, 90:10).
(E)-Methyl
3-(2-methyl-3-phenylhex-4-yn-3-yloxy)acrylate
(6s).
Colorless oil: 1H NMR (CDCl3, 400 MHz): 0.71 (d, 3H, 3J(H,H) = 6.7
3
Hz), 1.10 (d, 3H, J(H,H) = 6.7 Hz), 2.01 (s, 3H), 2.15-2.21 (m, 1H), 3.61
(s, 3H), 5.39 (d, 1H, 3J(H,H) = 12.1 Hz), 7.28-7.34 (m, 3H), 7.43-7.45 (m,
2H), 7.59 (d, 1H, 3J(H,H) = 12.1 Hz). 13C NMR (CDCl3, 100 MHz): = 3.7,
17.7, 17.8, 42.3, 50.9, 75.6, 87.4, 88.0, 99.2, 127.1 (2C), 128.1 (2C), 128.2,
140.6, 160.0, 168.2 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for
C17H20O3 295.1310, found 295.1313.
(E)-Methyl 3-(3-ethyl-1-(trimethylsilyl)pent-1-yn-3-yloxy)acrylate (6b).
Colorless oil: 1H NMR (CDCl3, 500 MHz): 0.19 (s, 9H), 0.95 (t, 6H,
3J(H,H) = 7.3 Hz), 1.73 (q, 4H, 3J(H,H) = 1.3 Hz), 3.67 (s, 3H), 5.32 (d, 1H,
3J(H,H) = 12.1 Hz), 7.96 (d, 1H, 3J(H,H) = 12.1 Hz). 13C NMR (CDCl3, 125
MHz): = -0.3 (3C), 8.2 (2C), 32.4 (2C), 50.8, 83.3, 95.3, 98.1, 102.8,
159.5, 168.4 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for C14H24O3Si
91.1392, found 291.1392.
(E)-Methyl
3-(1,1,1-trifluoro-2-phenyl-4-(trimethylsilyl)but-3-yn-2-
yloxy)acrylate (6v). Colorless oil: 1H NMR (CDCl3, 400 MHz): 0.28 (s,
9H), 3.66 (s, 3H), 5.60 (d, 1H, 3J(H,H) = 12.1 Hz), 7.39-7.45 (m, 3H), 7.61-
7.63 (m, 2H), 7.65 (d, 1H, 3J(H,H) = 12.1 Hz). 13C NMR (CDCl3, 100 MHz):
= -0.7 (3C), 51.2, 81.3 (q, J(C,F) = 32 Hz), 95.3, 100.2, 102.5, 122.0 (q,
J(C,F) = 285 Hz), 128.1 (2C), 128.6 (2C), 130.3, 132.6, 156.4, 167.2 ppm.
HRMS (ESI+): m/z [M+Na]+ calculated for C17H19F3O3Si 379.0953, found
379.0951.
(E)-Methyl 3-(2-phenyl-4-(trimethylsilyl)but-3-yn-2-yloxy)acrylate (6c).
Colorless oil: 1H NMR (CDCl3, 400 MHz): 0.25 (s, 9H), 1.83 (s, 3H),
3.63 (s, 3H), 5.43 (d, 1H, 3J(H,H) = 12.1 Hz), 7.31-7.38 (m, 3H), 7.52-7.53
(m, 2H), 7.67 (d, 1H, 3J(H,H) = 12.1 Hz). 13C NMR (CDCl3, 100 MHz): =
-0.3 (3C), 32.2, 50.8, 80.0, 94.8, 100.0, 103.6, 125.8 (2C), 128.4, 128.5
(2C), 141.6, 159.0, 167.9 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for
C17H22O3Si 325.1236, found 325.1239.
Representative procedure for the synthesis of methyl 2,2,4-
trisubstituted-2H-pyran-5-carboxylates (7). A solution of propargyl vinyl
ether 6 (1.0 mmol) and imidazole (0.1 mmol) in dry toluene (5 mL) was
stirred under reflux for 72 hours (TLC control). After removing the solvent
(E)-Methyl
3-(3-phenyl-1-(trimethylsilyl)hept-1-yn-3-yloxy)acrylate
(6d). Colorless oil: 1H NMR (CDCl3, 500 MHz): 0.25 (s, 9H), 0.85 (t, 3H,
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10.1002/ejoc.201801847
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at reduced pressure, the products were purified by flash column
chromatography (silica gel, n-hexane/EtOAc 95/5).
Methyl
4-(trimethylsilyl)-1-oxaspiro[5.5]undeca-2,4-diene-3-
carboxylate (7i). Yield: 233.9 mg, 83%. Colorless oil: 1H NMR (CDCl3,
400 MHz): 0.14 (s, 9H), 1.46-1.50 (m, 1H), 1.55-1.65 (m, 7H), 1.85-
1.89 (m, 2H), 3.70 (s, 3H), 5.44 (s, 1H), 7.50 (s, 1H). 13C NMR (CDCl3, 100
MHz): = -0.13 (3C), 21.3 (2C), 25.2, 35.2 (2C), 50.8, 78.1, 110.4, 130.1,
132.8, 154.5, 167.2 ppm. MS (70 eV): m/z (%): 280 (43) [M+], 265 (97),
237 (100), 233 (24), 221 (15), 147 (18), 89 (31), 73 (50). HRMS (ESI+):
m/z [M+Na]+ calculated for C15H24O3Si 280.1495, found 280.1487.
Methyl 2,2-diethyl-4-(trimethylsilyl)-2H-pyran-5-carboxylate (7b).
1
Yield: 426.1 mg, 95%. Colorless oil: H NMR (CDCl3, 500 MHz): 0.15
(s, 9H), 0.88 (t, 6H, 3J(H,H) = 7.4 Hz), 1.50-1.59 (m, 2H), 1.57-1.70 (m,
2H), 3.69 (s, 3H), 5.30 (d, 1H, 3J(H,H) = 1.2 Hz), 7.52 (d, 1H, 3J(H,H) = 1.2
Hz). 13C NMR (CDCl3, 125 MHz): = -0.02 (3C), 7.8 (2C), 31.8 (2C), 50.8,
83.3, 108.5, 130.9, 131.1, 155.4, 167.3 ppm. HRMS (ESI+): m/z [M+Na]+
calculated for C14H24O3Si 91.1392, found 291.1393.
Methyl 4-phenyl-1-oxaspiro[5.5]undeca-2,4-diene-3-carboxylate (7j).
Yield: 191.2 mg, 75%. Colorless oil: 1H NMR (CDCl3, 400 MHz): 1.39-
1.46 (m, 1H), 1.51-1.58 (m, 3H), 1.64-1.71 (m, 4H), 1.93-2.01 (m, 2H), 3.56
(s, 3H), 5.22 (s, 1H), 7.17-7.19 (m, 2H), 7.26-7.32 (m, 3H), 7.64 (s, 1H).
13C NMR (CDCl3, 100 MHz): = 21.5 (2C), 25.2, 35.5 (2C), 50.9, 80.5,
109.2, 122.3, 127.05 (2C), 127.14, 127.7 (2C), 133.1, 139.7, 156.2, 166.0
ppm. HRMS (ESI+): m/z [M+Na]+ calculated for C18H20O3 307.1310, found
307.1313.
Methyl 2-methyl-2-phenyl-4-(trimethylsilyl)-2H-pyran-5-carboxylate
(7c). Yield: 332.0 mg, 100%. Colorless oil: 1H NMR (CDCl3, 400 MHz):
0.20 (s, 9H), 1.70 (s, 3H), 3.69 (s, 3H), 5.76 (d, 1H, 3J(H,H) = 1.3 Hz),
7.28 (tt, 1H, 3J(H,H) = 6.2 and 1.3 Hz), 7.32-7.37 (m, 2H), 7.41-7.44 (m,
2H), 7.57 (d, 1H, 3J(H,H) = 1.3 Hz). 13C NMR (CDCl3, 100 MHz): = -0.1
(3C), 28.2, 50.9, 79.5, 110.4, 125.2 (2C), 127.6, 128.2 (2C), 130.6, 132.3,
144.6, 154.2, 166.9 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for
C17H22O3Si 325.1236, found 325.1231.
Methyl 4-methyl-1-oxaspiro[5.5]undeca-2,4-diene-3-carboxylate (7k).
Yield: 171.1 mg, 77%. Colorless oil: 1H NMR (CDCl3, 400 MHz): nearly 1:1
mixture of tautomers 1.30-1.99 (m, 20H), 1.99 (s, 3H), 2.28 (s, 2H),
3.68 (s, 3H), 3.72 (s, 3H), 4.84 (s, 1H), 4.93 (s, 1H), 5.75 (s, 1H), 7.50 (s,
1H), 7.56 (s, 1H). 13C NMR (CDCl3, 100 MHz): = 20.4, 21.4 (2C), 21.5
(2C), 25.2, 25.4, 34.6 (2C), 36.0 (2C), 41.8, 50.8, 51.0, 79.6, 80.0, 106.7,
108.6, 112.1, 120.0, 127.5, 131.1, 155.6, 155.9, 166.5, 166.7 ppm. HRMS
(ESI+): m/z [M+Na]+ calculated for C13H18O3 245.1154, found 245.1152.
Methyl
2-butyl-2-phenyl-4-(trimethylsilyl)-2H-pyran-5-carboxylate
(7d). Yield: 135.5 mg, 95%. Colorless oil: 1H NMR (CDCl3, 400 MHz):
0.19 (s, 9H), 0.87 (t, 3H, 3J(H,H) = 7.1 Hz), 1.24-1.32 (m, 4H), 1.92-
1.95 (m, 2H), 3.67 (s, 3H), 5.81 (s, 1H), 7.24-7.28 (m, 1H), 7.31-7.38 (m,
4H), 7.61 (s, 1H). 13C NMR (CDCl3, 100 MHz): = -0.1 (3C), 13.9, 22.8,
26.1, 41.6, 50.9, 82.2, 110.5, 125.2 (2C), 127.4, 128.1 (2C), 131.1, 131.6,
144.3, 154.5, 167.0 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for
C20H28O3Si 367.1705, found 367.1707.
Methyl 1-oxaspiro[5.5]undeca-2,4-diene-3-carboxylate (7m). Yield:
123.9 mg, 68%. Colorless oil: 1H NMR (CDCl3, 400 MHz): 1.29-1.37
(m, 1H), 1.45-1.54 (m, 5H), 1.59-1.64 (m, 2H), 1.88-1.93 (m, 2H), 3.71 (s,
3H), 5.22 (d, 1H, 3J(H,H) = 10.3 Hz), 6.24 (d, 1H, 3J(H,H) = 10.3 Hz), 7.45
(s, 1H). 13C NMR (CDCl3, 100 MHz): = 21.2 (2C), 25.1, 36.2 (2C), 51.1,
79.8, 106.9, 118.1, 122.2, 155.0, 166.3 ppm. HRMS (ESI+): m/z [M+Na]+
calculated for C12H16O3 231.0997, found 231.0997.
Methyl
2-isopropyl-2-phenyl-4-(trimethylsilyl)-2H-pyran-5-
carboxylate (7e). Yield: 175.8 mg, 98%. Colorless oil: 1H NMR (CDCl3,
400 MHz): 0.20 (s, 9H), 0.87 (d, 3H, 3J(H,H) = 6.8z), 0.88 (d, 3H,
3J(H,H) = 6.8z), 2.15-2.25 (m, 1H), 3.66 (s, 3H), 5.90 (s, 1H), 7.23-7.32 (m,
5H), 7.63 (s, 1H). 13C NMR (CDCl3, 100 MHz): = -0.1 (3C), 17.1, 17.3,
38.4, 50.8, 84.8, 110.4, 125.5 (2C), 127.3, 127.9 (2C), 129.7, 131.5, 143.6,
154.8, 166.9 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for C19H26O3Si
353.1549, found 353.1548.
Methyl 2-butyl-4-methyl-2-phenyl-2H-pyran-5-carboxylate (7n). Yield:
98.5 mg, 86%. Colorless oil: 1H NMR (CDCl3, 400 MHz):0.86 (t, 3H,
3J(H,H) = 6.8 Hz), 1.26-1.28 (m, 4H), 1.89-1.93 (m, 2H), 2.08 (s, 3H), 3.66
(s, 3H), 5.27 (s, 1H), 7.33-7.38 (m, 5H), 7.61 (s, 1H). 13C NMR (CDCl3, 100
MHz): = 13.9, 20.5, 22.8, 26.1, 42.2, 50.8, 84.0, 108.8, 118.8, 125.1 (2C),
127.3, 128.1 (2C), 128.5, 144.8, 156.0, 166.2 ppm. HRMS (ESI+): m/z
[M+Na]+ calculated for C18H22O3 309.1467, found 309.1476.
Methyl 2,2-diphenyl-4-(trimethylsilyl)-2H-pyran-5-carboxylate (7f).
1
Yield: 306.4 mg, 80%. Colorless oil: H NMR (CDCl3, 400 MHz): 0.22
(s, 9H), 3.68 (s, 3H), 5.93 (s, 1H), 7.26-7.33 (m, 10H), 7.61 (s, 1H). 13C
NMR (CDCl3, 100 MHz): = 0.2 (3C), 51.2, 83.5, 111.2, 127.2 (4C), 128.0
(2C), 128.4 (4C), 131.7, 131.9, 144.2 (2C), 153.8, 167.0 ppm. HRMS
(ESI+): m/z [M+Na]+ calculated for C22H24O3Si 387.1392, found 387.1389.
Methyl 2,4-dimethyl-2-phenyl-2H-pyran-5-carboxylate (7o). Yield:
184.8 mg, 87%. Colorless oil: 1H NMR (CDCl3, 400 MHz): 1.70 (s, 3H),
2.08 (s, 3H), 3.67 (s, 3H), 5.24 (s, 1H), 7.26-7.29 (m, 1H), 7.32-7.36 (m,
2H), 7.42-7.44 (m, 2H), 7.58 (s, 1H). 13C NMR (CDCl3, 100 MHz): = 20.3,
28.8, 50.8, 81.4, 108.7, 119.9, 125.0 (2C), 127.6, 127.8, 128.2 (2C), 145.1,
155.6, 166.1 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for C15H16O3
267.0997, found 267.0999.
Methyl 2-phenyl-4-(trimethylsilyl)-2H-pyran-5-carboxylate (7g). Yield:
33.6 mg, 23%. Colorless oil: 1H NMR (CDCl3, 400 MHz): 0.19 (s, 9H),
3.73 (s, 3H), 5.61 (bs, 1H), 5.70 (bs, 1H), 7.35-7.39 (m, 5H), 7.57 (s, 1H).
13C NMR (CDCl3, 100 MHz): = -0.2 (3C), 51.0, 77.3, 111.3, 127.2, 127.4
(2C), 128.7 (3C), 133.2, 139.3, 154.7, 166.9 ppm. HRMS (ESI+): m/z
[M+Na]+ calculated for C16H20O3Si 311.1079, found 311.1080.
Methyl 4-tert-butyl-2-methyl-2-phenyl-2H-pyran-5-carboxylate (7p).
Yield: 81.9 mg, 87%. Colorless oil: 1H NMR (CDCl3, 400 MHz): 1.25 (s,
9H), 1.68 (s, 3H), 3.65 (s, 3H), 5.43 (s, 1H), 7.24-7.27 (m, 1H), 7.30-7.34
(m, 3H), 7.42-7.34 (m, 2H). 13C NMR (CDCl3, 100 MHz):  28.8, 30.1
(3C), 34.5, 51.3, 80.6, 111.7, 118.7, 125.3 (2C), 127.5, 128.0 (2C), 141.1,
144.8, 154.6, 167.6 ppm. HRMS (ESI+): m/z [M+Na]+ calculated for
C18H22O3 309.1467, found 309.1464.
Methyl 4-phenyl-1-oxaspiro[5.11]heptadeca-2,4-diene-3-carboxylate
(7h). Yield: 123.0 mg, 83%. White crystalline solid. Melting point = 116 -
117ºC. 1H NMR (CDCl3, 400 MHz): 1.30-1.40 (m, 16H), 1.51-1.58 (m,
2H), 1.73-1.80 (m, 2H), 1.86-1.94 (m, 2H), 3.55 (s, 3H), 5.22 (s, 1H), 7.15-
7.17 (m, 2H), 7.26-7.31 (m, 3H), 7.59 (s, 1H). 13C NMR (CDCl3, 100 MHz):
= 19.0 (2C), 22.1 (2C), 22.6 (2C), 26.0, 26.2 (2C), 32.1 (2C), 50.9, 84.2,
109.3, 122.1, 127.07 (2C), 127.11, 127.7 (2C), 132.6, 139.8, 156.1, 165.9
ppm. HRMS (ESI+): m/z [M+Na]+ calculated for C24H32O3 391.2249, found
391.2251.
Methyl 2-isopropyl-4-methyl-2-phenyl-2H-pyran-5-carboxylate (7s).
1
Yield: 126.8 mg, 86%. Colorless oil: H NMR (CDCl3, 400 MHz): 0.85
(d, 3H, 3J(H,H) = 6.8 Hz), 0.86 (d, 3H, 3J(H,H) = 6.8 Hz), 2.08 (s, 3H), 2.13-
2.20 (m, 1H), 3.63 (s, 3H), 5.33 (s, 1H), 7.23-7.35 (m, 5H), 7.62 (s, 1H).
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801847
European Journal of Organic Chemistry
FULL PAPER
13C NMR (CDCl3, 100 MHz): = 17.1, 17.2, 20.7, 38.5, 50.8, 86.7, 108.8,
116.8, 125.4 (2C), 127.2, 127.8 (2C), 128.9, 144.2, 156.3, 166.2 ppm.
HRMS (ESI+): m/z [M+Na]+ calculated for C17H20O3 295.1310, found
295.1308.
Agency for Research, Innovation and the Information Society
(ACIISI) (ProID2017010019 ACIISI/FEDER, EU) for financial
support. S. D. H. thanks La Laguna University and Cajasiete for a
pre-doctoral contract. Authors thank technician Ms. Estefanía
Gámez (IPNA-CSIC) for her experimental assistance.
Methyl 4-tert-butyl-2-isopropyl-2-phenyl-2H-pyran-5-carboxylate (7t).
Yield: 24.0 mg, 93%. Colorless oil: 1H NMR (CDCl3, 500 MHz): 0.79 (d,
Keywords: 2H-dihydropyran • propargyl vinyl ethers • domino
reactions• pericyclic reactions• organocatalysis
3
3
3H, J(H,H) = 6.8 Hz), 0.90 (d, 3H, J(H,H) = 6.8 Hz), 1.26 (s, 9H), 2.16-
2.24 (m, 1H), 3.62 (s, 3H), 5.55 (s, 1H), 7.21-7.24 (m, 1H), 7.26-7.29 (m,
2H), 7.32-7.34 (m, 2H), 7.38 (s, 1H). 13C NMR (CDCl3, 125 MHz): = 17.3,
17.6, 30.1 (3C), 34.8, 38.4, 51.2, 85.9, 111.5, 115.4, 125.9 (2C), 127.3,
127.6 (2C), 141.8, 143.5, 155.2, 167.6 ppm. HRMS (ESI+): m/z [M+Na]+
calculated for C20H26O3 337.1780, found 337.1780.
[1] For recent selected examples, see: a) L. Chang, K. Plevova, S. Thorimbert,
L. Dechoux, L. J. Org. Chem. 2017, 82, 5499-5505; b) C. Ni, X. Tong, J.
Am. Chem. Soc. 2016, 138, 7872- 7875; c) Q. Chong, C. Wang, D. Wang,
H. Wang, F. Wu, X. Xin, B. Wan, Tetrahedron Lett. 2015, 56, 401-403; d)
S. D. Jacob, J. L. Brooks, A. J. Frontier, J. Org. Chem. 2014, 79, 10296-
10302; e) P. Xie, J. Yang, J. Zheng, Y. Huang, Eur. J. Org. Chem. 2014,
1189-1194; f) J. Hu, W. Dong, X. Y. Wu, X. Tong, Org. Lett. 2012, 14, 5530-
5533; g) W. Peng, T. Hirabaru, H. Kawafuchi, T. Inokuchi, Eur. J. Org.
Chem. 2011, 5469-5474.
Dimethyl 2-isopropyl-2-phenyl-2H-pyran-4,5-dicarboxylate (7u). Yield:
1
86.1 mg, 86%. Colorless oil: H NMR (CDCl3, 500 MHz): 0.86 (d, 3H,
3J(H,H) = 6.8 Hz), 0.90 (d, 3H, 3J(H,H) = 6.8 Hz), 2.24-2.29 (m, 1H), 3.65
(s, 3H), 3.79 (s, 3H), 6.20 (s, 1H), 7.25-7.33 (m, 5H), 7.53 (s, 1H). 13C NMR
(CDCl3, 125 MHz): = 17.2, 17.3, 38.4, 51.4, 52.2, 86.9, 107.5, 125.0,
125.6 (2C), 127.4, 127.9, 128,1 (2C), 141.9, 155.6, 164.9, 166.8 ppm.
HRMS (ESI+): m/z [M+Na]+ calculated for C18H20O5 339.1208, found
339.1208.
[2] Y. Tang, J. Oppenheimer, Z. Song, L. You, X. Zhang, R. P. Hsung ,
Tetrahedron 2006, 62, 10785-10813; b) R. P. Hsung, A. V. Kurdyumov, N.
Sydorenko, Eur. J. Org. Chem. 2005, 23-44; c) P. Xie, J. Yang, J. Zheng,
Y. Huang, Eur. J. Org. Chem. 2014, 1189-1194 and references cited
therein.
[3] a) For
a
review of their use in biosynthetic and biomimetic
electrocyclizations, see: C. M. Beaudry, J. P. Malerich, D. Trauner, Chem.
Rev. 2005, 105, 4757-4778; b) For selected examples, see: D. Tejedor, S.
Delgado-Hernández, J. Peyrac, J. González-Platas, F. García-Tellado,
Chem. Eur. J. 2017, 23, 10048-10052; c) A. J. Hall, S. P. Roche, L. M. West,
Org. Lett. 2017, 19, 576-579; d) M. J. Riveira, A. La-Venia, M. P. Mischne,
J. Org. Chem. 2016, 81, 7977-7983; e) A. Carbone, C. L. Lucas, C. J.
Moody, J. Org. Chem. 2012, 77, 9179-9189; f) L. M. Bishop, M. Winkler, K.
N. Houk, R. G. Bergman, D. Trauner, Chem. Eur. J. 2008, 14, 5405-5408;
g) J. P. Malerich, T. J. Maimone, G. I. Elliott, D. Trauner, J. Am. Chem. Soc.
2005, 127, 6276-6283; h) M. Shoji, H. Imai, M. Mukaida, K. Sakai, H.
Kakeya, H. Osada, Y. Hayashi, J. Org. Chem. 2005, 70, 79-91.
Methyl
5-(2,2,2-trifluoro-1-phenylethyl)-4-(trimethylsilyl)furan-3-
carboxylate (14). Yield: 189.7 mg, 94%. Colorless oil: 1H NMR (CDCl3,
400 MHz): 0.35 (s, 9H), 3.80 (s, 3H), 4.95 (q, 1H, 3J(F,H) = 9.3 Hz),
7.32-7.38 (m, 3H), 7.45-7.47 (m, 2H), 8.09 (s, 1H). 13C NMR (CDCl3, 100
MHz): = 0.4 (3C), 49.0 (q, J(C,F) = 29 Hz), 51.4, 117.8, 124.9 (q, J(C,F)
= 281 Hz), 123.6, 128.5, 128.8 (2C), 129.3 (2C), 132.9, 149.0, 153.4, 163.9
ppm. HRMS (ESI+): m/z [M+Na]+ calculated for C17H19F3O3Si 379.0953,
found 379.0950.
[4] Z. A. Krasnaya, Chem. Heterocycl. Com. 1999, 35, 1255-1271.
[5] For a discussion, see: M. Rauser, S. Schroeder, M. Niggemann, Chem. Eur.
J. 2015, 21, 15929-15933 and references cited therein.
[6] a) M. Costa, T. A. Dias, A. Brito, F. Proença, Eur. J. Med. Chem. 2016, 123,
487-507; b) S. V. Paramonov, V. Lokshin, O. A. Fedorov, J. Photochem.
Photobiol. C. Photochem. Rev. 2011, 12, 209-236; c) N. Majumdar, N. D.
Paul, S. Mandal, B. de Bruin, W. D. Wulff, ACS Catal. 2015, 5, 2329-2366.
[7] S. V. Bohm, J. Kuthan, Coll. Czech. Chem. Commun. 1987, 52, 399-408.
[8] D. Tejedor, A. Díaz-Díaz, R. Diana-Rivero, S. Delgado-Hernández, F.
García-Tellado, Org. Lett. 2018, 20, 7987-7990
(2E,2'E)-Dimethyl 3,3'-(2,7-dimethylocta-3,5-diyne-2,7-diyl)bis(oxy)-
diacrylate (15). White crystalline solid (it rearranges upon heating). 1H
NMR (CDCl3, 400 MHz): 1.60 (s, 12H), 3.70 (s, 6H), 5.40 (d, 2H,
3J(H,H) = 12.1 Hz), 7.76 (d, 2H, 3J(H,H) = 12.1 Hz). 13C NMR (CDCl3, 100
MHz): = 28.9 (4C), 51.1 (2C), 70.0 (2C), 75.1 (2C), 80.2 (2C), 100.3 (2C),
157.8 (2C), 168.0 (2C) ppm. HRMS (ESI+): m/z [M+Na]+ calculated for
C18H22O6 357.1314, found 357.1317.
[9] L. G. Voskressensky, A. A. Festa, A. V. Varlamov, Tetrahedron 2014, 70,
551-572.
Dimethyl 2,2,2',2'-tetramethyl-2H,2'H-4,4'-bipyran-5,5'-dicarboxylate
(16). Yield: 334 mg, 100%. White crystalline solid. Melting point = 148-149
ºC. 1H NMR (CDCl3, 400 MHz): 1.41 (s, 12H), 3.60 (s, 6H), 4.98 (s, 2H),
7.41 (s, 2H). 13C NMR (CDCl3, 100 MHz): = 27.7 (4C), 50.8 (2C), 78.7
(2C), 108.6 (2C), 121.1 (2C), 131.4 (2C), 154.2 (2C), 165.9 (2C) ppm.
HRMS (ESI+): m/z [M+Na]+ calculated for C18H22O6 357.1314, found
357.1313.
[10] a) D. Tejedor, G .Méndez-Abt, L. Cotos, F. García-Tellado, Chem. Soc.
Rev. 2013, 42, 458-471; b) Z. B. Zhu, S. F. Kirsch, Chem. Commun. 2013,
49, 2272-2283; for selected examples using: c) Rh (I): D. V. Vidhani, M. E.
Krafft, I. V. Alabugin, J. Org. Chem. 2014, 79, 352-364; d) D. V. Vidhani, M.
E. Krafft, I. V. Alabugin, Org. Lett. 2013, 15, 4462-4465; e) Ag(I): H. Menz,
S. F. Kirsch, Org. Lett. 2006, 8, 4795−4797; f) Au(I): B. D. Sherry, L. Maus,
B. N. Laforteza, F. D. Toste, J. Am. Chem. Soc. 2006, 128, 8132-8133; g)
A. S. K. Hashmi, K. Graf, M. Ackermann, F. Rominger, ChemCatChem
2013, 5, 1200–1204.
Marcador no
Dimethyl [2,2'-binaphthalene]-3,3'-dicarboxylate (18).[¡Error!
definido.]
A solution of dimer 16 (134.6 mg, 0.40 mmol), CsF (330 mg, 2.2
[11] D. Tejedor, S. López-Tosco, G. Méndez-Abt, L. Cotos, F. García-Tellado,
Acc. Chem. Res. 2016, 49, 703-713.
mmol) and 2-(trimethylsilyl)phenyl trifluoromethanesulfonate (17) (0.244
mL, 300 mg, 1 mmol) in acetonitrile (20 mL) was stirred for16 h at room
temperature. The reaction mixture was quenched with water and extracted
using CH2Cl2. After removing the solvent at reduced pressure, the crude
product 18 was purified by flash column chromatography (silica gel,
CH2Cl2/ EtOAc/ hexanes (30/4/66) (68 mg, 46%).
[12] D. Tejedor, S. J. Álvarez-Méndez, J. M. López-Soria, V. S. Martín, F.
García-Tellado, Eur. J. Org. Chem. 2014, 198-205.
[13] D. Tejedor, L. Cotos, D. Márquez-Arce, M. Odriozola-Gimeno, M. Torrent-
Sucarrat, F. P. Cossío, F. García-Tellado, Chem. Eur. J. 2015, 21, 18280-
18289.
[14] D. Tejedor, S. Delgado-Hernández, J. Peyrac, J. Gonzá-lez-Platas, F.
García-Tellado, Chem. Eur. J. 2017, 23, 10048-10052.
[15] Tertiary PVEs armed with an amide or ester group at the quaternary
propargylic position deliver the corresponding furans through the
homologous tandem [3,3] /5-exo-dig O-cyclization reaction. D. Tejedor, L.
Cotos, F. García-Tellado, Org. Lett. 2011, 13, 4422-4425.
Acknowledgments
The authors thank the Spanish Ministry of Economy and Com-
petitiveness (MINECO) and the European Regional Develop-
ment Funds (ERDF) (CTQ2015-63894-P) and the Canarian
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European Journal of Organic Chemistry
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10.1002/ejoc.201801847
European Journal of Organic Chemistry
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Entry for the Table of Contents (Please choose one layout)
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Key Topic: Synthesis, heterocycles
David Tejedor, Samuel Delgado-
Hernández, Raquel Diana-Rivero, Abián
Díaz-Díaz, and Fernando García-
Tellado
*Page No. – Page No.
Text for Table of Contents (about 350 characters)
A Domino Strategy for the Synthesis
of 2H-Pyrans from Propargyl Vinyl
Ethers
Simple and direct: an all-pericyclic domino manifold
transforms propargyl vinyl ethers into 2H-pyrans.
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