Temperature-controlled divergent synthesis of 4-alkoxy- or 4-alkenyl-chromanes via inverse electron-demand cycloaddition with in situ generated ortho-quinone methides

Article abstract of DOI:10.1016/j.tetlet.2018.03.090

The temperature-controlled divergent synthesis of 4-alkoxy- or 4-alkenyl-chromanes via inverse electron-demand cycloaddition with in situ generated ortho-quinone methides under identical reaction conditions except for thermal condition has been developed. At room temperature, the reaction generated 4-methoxychromanes, whereas the reaction performed at room temperature to 100 °C gave 4-alkenylchromanes. Trifluoromethanesulfonic acid was efficiently suitable in the reaction to give the 4-substituted chromanes. This divergent synthetic strategy exhibits a new method giving carbon–carbon or carbon–oxygen bond by controlling the reaction temperature.

Full text of DOI:10.1016/j.tetlet.2018.03.090

Accepted Manuscript
Temperature-controlled divergent synthesis of 4-alkoxy- or 4-alkenyl-chro-
manes via inverse electron-demand cycloaddition with in situ generated ortho-
quinone methides
Kenta Tanaka, Mami Kishimoto, Yujiro Hoshino, Kiyoshi Honda
PII:
S0040-4039(18)30427-1
https://doi.org/10.1016/j.tetlet.2018.03.090
TETL 49859
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
22 January 2018
24 March 2018
30 March 2018
Please cite this article as: Tanaka, K., Kishimoto, M., Hoshino, Y., Honda, K., Temperature-controlled divergent
synthesis of 4-alkoxy- or 4-alkenyl-chromanes via inverse electron-demand cycloaddition with in situ generated
ortho-quinone methides, Tetrahedron Letters (2018), doi: https://doi.org/10.1016/j.tetlet.2018.03.090
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.
Temperature-controlled divergent synthesis
of 4-alkoxy- or 4-alkenyl-chromanes via
inverse electron-demand cycloaddition with
in situ generated ortho-quinone methides
Leave this area blank for abstract info.
Kenta Tanaka, Mami Kishimoto, Yujiro Hoshino*, Kiyoshi Honda*

1
Tetrahedron Letters
Temperature-controlled divergent synthesis of 4-alkoxy- or 4-alkenyl-chromanes via
inverse electron-demand cycloaddition with in situ generated ortho-quinone methides
Kenta Tanaka, Mami Kishimoto, Yujiro Hoshino*, Kiyoshi Honda*
Graduate School of Environment and Information Sciences, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The temperature-controlled divergent synthesis of 4-alkoxy- or 4-alkenyl-chromanes via inverse
electron-demand cycloaddition with in situ generated ortho-quinone methides under identical
reaction conditions except for thermal condition has been developed. At room temperature, the
reaction generated 4-methoxychromanes, whereas the reaction performed at room temperature to
100 ºC gave 4-alkenylchromanes. Trifluoromethanesulfonic acid was efficiently suitable in the
reaction to give the 4-substituted chromanes. This divergent synthetic strategy exhibits a new
method giving carbon-carbon or carbon-oxygen bond by controlling the reaction temperature.
Available online
Keywords:
Divergent synthesis
Chromanes
2009 Elsevier Ltd. All rights reserved.
Ortho-quinone methide
Inverse-electron-demand cycloaddition
1. Introduction
Divergent synthesis is one of useful synthetic methods in
organic chemistry. One such protocol involves the use of
substrate- and/or reaction condition-controlled divergent
synthesis, in which two different products are obtained by only
changing operations such as catalyst (Scheme 1a),1 solvent
(Scheme 1b),2 substrate,3 and the loading amount of catalyst.4
More recently, temperature-controlled divergent synthesis has
been emerging. The approaches include selective synthesis of
isoxazoline N-oxides and isoxazoles under ultrasonication,5
redox-neutral Rh-catalyzed C−H bond annulation of N-
methoxybenzamides affording hydrophenanthridone and
dibenzo[b,d]pyran-6-one,6 BF3·OEt2 catalyzed divergent
synthesis of sulfinate esters and sulfones via C-O and C-S bond
formation from alcohols and TosMIC,7 and oxidation of α-
hydroxy amides in the presence of IBX, giving isatins and α-
formyl amides.8 Despite the availability of these methods, to the
best our knowledge, few reports have been reported on
temperature-controlled methods and it has been still desirable.
ortho-Quinone methides (o-QM) are key reactive
intermediates with wide range of applications in organic
synthesis.9 In recent years, catalytic asymmetric reactions
including o-QM are rapidly growing areas and have been
investigated by many researchers.10 In this context, we performed
the acid catalyzed generation of o-QM from salicylaldehyde in
the presence of trimethyl orthoformate under mild conditions.11
In addition, inverse-electron-demand [4+2] cycloaddition
reaction of electron-rich arylalkynes with salicylaldehydes to
give 2H-chromene were investigated.12 Although arylalkynes
known to have low reactivity for inverse-electron-demand [4+2]
cycloaddition,13 the reaction smoothly proceeded to afford the
desired products in good yields. Recently, when we examined the
Scheme 1. Selected example of reaction condition-controlled
divergent synthesis

2
Tetrahedron
methoxysalicylaldehyde was conducted, the starting material was
consumed within 1 h. But the complex mixture was generated,
and no trace of the product was detected. While 1,1-
diphenylethylene containing p-chloro groups afforded the
corresponding product in good yield, the reaction with bis(m-
fluorophenyl)ethylene did not proceed but recovered the starting
materials at room temperature or 60 ºC (3k). Because meta-
substituted fluoride groups on benzene ring are good electron
withdrawing groups, the latter substrate would be an unfavorable
dienophile for inverse-electron-demand cycloaddition reaction.
On the other hand, ethylene bearing electron donating group was
well tolerated to give the corresponding product in high yield 3l.
2-Hydroxy-1-naphthoaldehyde gave the desired product 3m and
chromene 4m (Figure 2) as an inseparable mixture in 33% and
32% yields, respectively. When the ratio of amounts of the
starting materials was changed, chromene 4m was selectively
obtained in 66% yield. Chromene 4m is known as photochromic
materials,15 and it means that the present method might be a
facile method for the one-pot synthesis of chromene-based
photochromic materials from easily available starting materials in
good yields. A high yield was obtained with the use of 2-
phenylpropene as a substrate 3n. Ethylene having dialkyl groups
afforded the product in low yield 3o.
Figure 1. Selective examples of bioactive compound and natural product
of chromanes
reaction of salicylaldehydes with alkenes, an unexpected reaction
was observed, which afforded 4-alkoxy or 4-alkenylchromanes,
depended on temperature. The reaction prompted us to
investigate a new method giving carbon-carbon or carbon-
oxygen bond by controlling the reaction temperature. Herein, we
report the temperature-controlled divergent synthesis of 4-
alkoxy- or 4-alkenyl-chromanes using 1,1-disubstituted ethylenes
with various salicylaldehydes under identical conditions except
for the reaction temperature via inverse electron-demand
cycloaddition with in situ generated o-QM (Scheme 1c). This
synthetic strategy exhibits a new method giving carbon-carbon or
carbon-oxygen bond by controlling only the reaction
temperature. The chromanes having carbon-carbon or carbon-
oxygen bond of 4-position represent important structural motifs
in natural compounds and medicinal chemistry (Figure 1).14
Table 1. Optimization of the reaction conditionsa
2. Result and discussion
We initially investigated the reaction of 5-nitrosalicylaldehyde
(1a) with 1,1-diphenylethylene (2a) using a variety of acid
catalysts and solvents at room temperature. While soft Lewis acid
catalyst gave no product (Table 1, entry 1), the use of Sc(OTf)3,
which is a hard Lewis acid catalyst and is used in [4+2]
cycloaddition of salicylaldehydes with ethylenes by Yadav and
coworkers in 2002,9d afforded the desired chromane 3a (entry 3).
Although p-TsOH·H2O and HBF4·OEt2 gave the product in low
yields, a more strong Brønsted acid, TfOH, smoothly led to the
formation of the desired product in high yield (entry 6). TfOH is
an inexpensive organic catalyst, the use of which is much easier
than that of Sc(OTf)3 While high polar solvents such as DMF and
DMSO were crucial for this reaction (entries 7 and 8), CH3CN
gave the product in 69% yield (entry 9). In addition, the reaction
in medium polar solvent, CH2Cl2, afforded a good yield (entries
11). Decreasing the amount of 2a or catalyst did not improve the
yields (entry 12 and 13). The best yield of the desired product
was achieved by 5-nitrosalicylaldehyde (1.0 equiv.), 1,1-
diphenylethylene (3.0 equiv.), CH(OMe)3 (2.0 equiv.), TfOH (20
mol%) in toluene at room temperature (entry 6).
entry
1
solvent
toluene
toluene
toluene
toluene
toluene
toluene
MeOH
DMF
catalyst
Pd(OAc)2
BF3·OEt2
Sc(OTf)3
p-TsOH·H2O
HBF4·OEt2
TfOH
yield (%)
N.R
trace
15
2
3
4
8
5
18
6
85
7
TfOH
N.R
N.R
69
8
TfOH
9
CH3CN
THF
TfOH
10
11
12b
13c
TfOH
25
CH2Cl2
toluene
toluene
TfOH
79
With the optimal conditions in hand,
a variety of
TfOH
71
salicylaldehydes and 1,1-disubstituted ethylenes were examined
to evaluate the generality of the reaction (Scheme 2). The parent
salicylaldehyde gave the product 3b in good yield. Moreover, the
substrates bearing electron withdrawing groups also efficiently
proceeded to afford products 3c-3g in excellent yields.
Importantly, 5-methoxysalicylaldehyde was found to be suitable
for this transformation 3h. In our previous work, electron
donating groups was not suitable substituents for the reaction
with alkynes.12 In addition, when the ratio of equivalents of
starting materials was changed, the yield of the product was
increased to 87% yield. However, when the 4-
TfOH
63
a
All reactions were carried out with 1a (0.5 mmol), 2a (1.5
mmol), CH(OMe)3 (1.0 mmol), catalyst (20 mol%) in solvent
(5.0 mL) at room temperature for 1 h.
b The amount of 2a was 1.0 mmol.
c The amount of TfOH was 10 mol%.

3
a Salicylaldehyde (2.0 mmol) and ethylene (1.0 mmol) were used for
2.5 h. The yield of product was decided basis on ethylene. b 3 h. c 3 h
at 60 ºC. d 0 ºC.
a The reaction was carried out from 0 ºC (1 h) to 100 ºC (1 h).
Scheme 4. The synthesis of 4-alkenylchromanes
Scheme 2. The reaction of salicylaldehydes with 1,1-
disubstituted ethylenes at room temperature
Next we examined the transformation of chromane. As
mentioned above, some 2,2-disubstituted chromens are intriguing
compounds, which can display photochromic property.
Therefore, we examined the transformations of 4-
methoxychromane to chromene, as shown in Scheme 3. When
the treatment of 4-methoxychromane with TfOH was carried out
at 100 ºC, 4-alkenyl chromane 5a was unexpectedly obtained in
35% yield instead of chromene 4a (eq 1). It implies that the
elimination of methoxy group from chromane 3a would be
occurred to afford chromene, which, then, would be attacked at
the 4 position by 1,1-diphenylethylene, derived from retro-Diels-
Alder reaction of 3a, to give 4-alkenyl chromane 5a. To confirm
this working hypothesis, the reaction of 4-methoxy chromane
with 1,1-diphenylethylene was performed under acidic
conditions. Expectedly, 4-alkenyl product 5a was obtained in
good yield (eq 2). For this reason, it is anticipated that one-pot
synthesis of 4-alkenylchromanes from salicylaldehydes could
proceed. Thus, the reaction of 5-nitrosalicylaldehyde with 1,1-
diphenylethylene at room temperature to 100 ºC was carried out
in one-pot, and the desired product was obtained in good yield
(eq 3). These process present a useful synthetic method of
selective direct synthesis of 4-alkoxy and 4-alkenyl chromanes
by only controlling temperature.
a 1H-NMR yield. b 2-Hydroxy-1-naphthoaldehyde (2.0 equiv.) and
ethylene (1.0 equiv.) were used for 6 h. The yield of product was
decided basis on ethylene.
Figure 2. The by-product of the reaction of 2-hydroxy-1-naphthoaldehyde
The generality of the formation of 4-alkenylchromanes was
evaluated in Scheme 4. When the parent salicylaldehyde was
used, the product 5b was obtained in good yield. Moreover, the
substrates having various electron withdrawing group gave
chromanes 5c-5g in high yields. 5-Methoxy group was well
tolerated to give 89% yield (5h). In contrast, the complex mixture
was generated, and no desired product was observed in the
reaction of 4-methoxysalicylaldehyde (5i). We also demonstrated
the reactions with some 1,1-diphenylethylene derivatives. An
excellent yield was obtained when bis(p-dichlorophenyl)ethylene
was used (5j). In addition, the substrates possessing methoxy
groups were also accommodated to this transformation (5k). 2-
Scheme 3. The reaction of 4-methoxychromane 3a

4
Tetrahedron
Hydroxy-1-naphthoaldehyde afforded the desired product in
high yield (5l). A complex mixture was obtained when 1-Methyl-
1-phenylethylene and 1,1-dialkylethylene were used (5m and
5n). While the reactions were suitable both electron donating and
electron withdrawing groups, ethylenes need to possess two
benzyl groups. It is well known that phenyl group can stabilize
benzyl cation,16 and its effect may need the reaction (vide infra).
Scheme 6. The reaction of chromene 4m with ethylene 2a
A
plausible reaction mechanism for the reaction of
salicylaldehydes with disubstituted ethylenes is depicted in
Scheme 5. First, salicylaldehyde dimethylacetal 7 would be
formed by the reaction of salicylaldehyde 6 with CH(OMe)3 in
the presence of TfOH. Subsequently, o-QM is generated by
elimination of methanol from salicylaldehyde dimethylacetal 7.
o-QM would react with 1,1-disubstituted ethylene via invers-
electron-demand Diels-Alder reaction to give the cyclic product
9. On the basis of the formation of 4-alkenylchroman 5a from 4-
methoxychromane 3a under reaction conditions (Scheme 3, eq
1), it is thought that retro-Diels-Alder reaction should occurred
when the reaction temperature increased to 100 °C. Elimination
of methoxy group in the presence of TfOH afforded chromene
10. Protonation of the olefinic double bond of the chromene 10
gave intermediate 11 (path A). On the other hand,
dihydropyrylium 14 was a resonance structure of intermediate 11,
which would be directly generated from 4-methoxy chromane 9
(path B). It is suggested that 12 would be obtained via path C or
path D. 1,1-Disubstituted ethylene attacked to Intermediate 11 to
yield stable dibenzyl cation 12 (path C).17 The formation of
dihydropyrylium 14 would induce ring-opening via cleavage of
C-O single bond to produce stable dibenzyl cation intermediate,
which would react with 1,1-disubstituted ethylene via inverse-
electron-demand Diels-Alder reaction to afford 12 (path D).18
Finally, the loss of a proton from 12 then furnished the desired
product 13. When the reaction of chromene 4m with ethylene 2a
was carried out, the staring material 4m was consumed. But the
complex mixture was generated, and no trace of chromane 5l was
detected (Scheme 6). Based on the result, path B and path C or
path D may be more probable than path A. The scope and
mechanism are currently under investigation and will be reported
in due course.
Conclusion
In conclusion, we have developed the temperature-controlled
divergent synthesis of 4-alkoxy- or 4-alkenyl-chromanes via
inverse electron-demand cycloaddition with in situ generated
ortho-quinone methides in the presence of Brønsted acid catalyst.
While, at room temperature, the reaction generated 4-
methoxychromanes, the reaction at 100 ºC gave 4-
alkenylchromanes. The salicylaldehydes having electron
withdrawing groups were well-tolerated. In addition, 5-methoxy
salicylaldehyde was good suitable in these reaction conditions.
Ethylene bearing electron donating group afforded the desired
products in good yield. The strategy exhibits a new method
giving carbon-carbon or carbon-oxygen bond by controlling the
reaction temperature. The present reaction provides versatile
access to functionalized 4-substituted chromanes that would be a
useful tool for the synthesis of natural product and biologically
active molecules.
References and notes
1.
(a) Rao, W.; Yin, X.; Shi, B. Org. Lett. 2015, 17, 3758-3761.
Other catalyst-controlled reactions, see: (b) Bai, J.-F.; Sasagawa,
H.; Yurino, T.; Kano, T.; Maruoka, K. Chem. Comm. 2017, 53,
8203-8206. (c) Feng, J.-J.; Lin, T.-Y.; Zhu, C.-Z.; Wang, H.; Wu,
H.-H.; Zhang, J. J. Am. Chem. Soc. 2016, 138, 2178-2181. (d) Li,
M.; Gonzalez-Esguevillas, M.; Berritt, S.; Yang, X.; Bellomo, A.;
Walsh, P. J. Angew. Chem., Int. Ed. 2016, 55, 2825-2829. (e) Jin,
L.-K.; Wan, L.; Feng, J.; Cai, C. Org. Lett. 2015, 17, 4726-4729.
(f) Gao, W.-C.; Hu, F.; Tian, J.; Li, X.; Wei, W.-L.; Chang, H.-H.
Chem. Commun. 2016, 52, 13097-13100.
2.
3.
4.
(a) Hua, M.-Q.; Wang, W.; Liu, W.-H.; Wang, T.; Zhang, Q.;
Huang, Y.; Zhu, W.-H. J. Fluor. Chem. 2016, 181, 22-29. Other
solvent-controlled synthesis, see: (b) Ye, Y.; Zheng, C.; Fan, R.
Org. Lett. 2009, 11, 3156-3159. (c) Rossi, E.; Abbiati, G.;
Attanasi, O. A.; Rizzato, S.; Santeusanio, S. Tetrahedron, 2007,
63, 11055-11065.
(a) Chen, K.; Zhu, Z.-Z.; Liu, J.-X.; Tang, X.-Y.; Wei, Y.; Shi, M.
Chem. Commun. 2016, 52, 350-353. Other substrate-controlled
syntheses, see: (b) Luo, K.; Zhang, L.; Ma, J.; Sha, Q.; Wu, L. J.
Org. Chem. 2017, 82, 6978-6985. (c) Manna, M. K.; Hossian, A.;
Jana, R. Org. Lett. 2015, 17, 672-675. (d) Lin, C.; Shen, Y.;
Huang, B.; Liu, Y.; Cui, S. J. Org. Chem. 2017, 82, 3950-3956.
(a) Wang, J.-L.; Li, H.-J.; Wang, H.-S.; Wu, Y.-C. Org. Lett.
2017, 19, 3811-3814. Other loading-controlled synthesis;(b) Xin,
X.; Liu, X.; Zhang, D.; Zhang, R.; Liang, Y.; Han, F.; Dong, D.
Org. Bio. Chem. 2014, 12, 5477-5483.
5.
6.
Rouf, A.; Sahin, E.; Tanyeli, C. Tetrahedron 2017, 73, 331-337.
Yang, W.; Wang, J.; Wei, Z.; Zhang, Q.; Xu, X. J. Org. Chem.
2016, 81, 1675-1680.
7.
8.
9.
Naresh, P.; Radha K. P.; Lakshmi, P. Y. Synth. Commun. 2017,
47, 1239-1249.
Wang, Y.; Cheng, X.; Zhan, Z.; Ma, X.; Nie, R.; Hai. L.; Wu, Y.
RSC Adv., 2016, 6, 2870-2874.
(a) Bai, W.-J.; David, J. G.; Feng, Z.-G.; Weaver, M. G.; Wu, K.-
L.; Pettus, T. R. R. Acc. Chem. Res. 2014, 47, 3655-3664. (b)
Jaworski, A. A.; Scheidt, K. A. J. Org. Chem. 2016, 81, 10145-
10153. (c) Pathak, T. P.; Sigman, M. S. J. Org. Chem. 2011, 76,
9210-9215. (d) Yadav, J. S.; Reddy, B. V. S.; Parisse, C.;
Carvalho, P.; Rao, T. P. Tetrahedron Lett. 2002, 43, 2999-3002.
Scheme 5. The proposal reaction mechanism
10. Jaworski, A. A.; Scheidt, K. A. J. Org. Chem. 2016, 81, 10145-
10153.

5
11. Miyazaki, H.; Honda, Y.; Honda, K.; Inoue, S. Tetrahedron Lett.
2000, 41, 2643-2647. (b) Miyazaki, H.; Honda, K.; Asami, M.;
Inoue, S. J. Org. Chem. 1999, 64, 9507-9511. (c) Inoue, S.; Wang,
P.; Nagao, M.; Hoshino, Y.; Honda, K. Synlett 2005, 3, 469-472.
(d) Shrestha, K. S.; Honda, K.; Asami, M.; Inoue, S. Bull. Chem.
Soc. Jpn. 1999, 72, 73-83.
12. (a) Tanaka, K.; Sukekawa, M.; Shigematsu, Y.; Hoshino, Y.;
Honda, K. Tetrahedron 2017, 73, 6456-6464. (b) Tanaka, K.;
Hoshino,Y.; Honda, K. Heterocycles 2017, 95, 474-486. (c)
Tanaka, K.; Hoshino, Y.; Honda, K. Tetrahedron Lett. 2016, 57,
2448-2450. (d) Tanaka, K.; Shigematsu, Y.; Sukekawa, M.;
Hoshino, Y.; Honda, K. Tetrahedron Lett. 2016, 57, 5914-5918.
13. (a) Nakayama, J.; Yamaoka, S; Nakanishi, T; Hoshino M. J Am
Chem Soc. 1988, 110, 6598-6599. (b) Soenen, D. R.; Zimpleman,
J. M.; Boger, D. L. J. Org. Chem. 2003, 68, 3593-3598. (c)
Kranjc, K.; Stefane, B.; Polanc, S.; Kocevar, M. J. Org. Chem.
2004, 69, 3190-3193.
14. (a) Nicolaou, K. C.; Pfefferkorn, J. A.; Barluenga, S.; Mitchell, H.
J.; Roecker, A. J.; Cao, G.-Q. J. Am. Chem. Soc. 2000, 122, 9968-
9976. (b) Bharate, S. B.; Singh, I. P. Tetrahedron Lett. 2006, 47,
7021-7024. (c) Xie, L.; Takeuchi, Y.; Cosentino, M.; Lee, K.-H. J.
Med. Chem. 1999, 42, 2662-2672. (d) Lee, T. T-Y.; Kashiwada,
Y.; Huang, L.; Snider, J.; Cosentino, M.; Lee, K.-H. Bioorg. Med.
Chem. 1994, 2, 1051-1056. (e) Rapposelli, S.; Breschi, M. C.;
Calderone, V.; Digiacomo, M.; Martelli, A.; Testai, L.; Vanni,
M.;Balsamo, A. Eur. J. Med. Chem. 2011, 46, 966-973.
15. (a) Hobley, J.: Malatesta, V.; Millini, R.; W. Giroldini, L.; Wis,
Goto, M.; Kishimoto, M.; Fukumura H. Chem Commun. 2000,
1339-1340. (b) Rebiere N.; Moustrou, C.; Meyer, M.; Samat, A.;
Guglielmetti, R.; Micheau, J-C.; Aubard, J. J. Phys. Org. Chem.
2000, 13, 523-530.
16. (a) Okuyama, T. Acc. Chem. Res. 2002, 35, 12-18. (b) Byrne, P.
A.; Kobayashi, S.; t ein, E.-U.; Ammer, J.; Mayer H. J.
Am. Chem. Soc. 2017, 139, 1499-1511. (c) Wang, X.; Gensch, T.;
Glorius , F. Org. Chem. Front., 2016, 3, 1619-1623. (d) Gharpure,
S. J.; Shelke, Y. G.; Kumar, D. P. Org. Lett. 2015, 17, 1926-1929.
17. Breese, A.; Cotterill, W. D.; Iqbal, M.; Livingstone, R. J. Chem.
Res. (S) 1998, 9, 532-533.
18. Luan, Y.; Sun, H.; Schaus, S. E. Org. Lett. 2011, 13, 6480-6483.

6
Tetrahedron
Highlights
・ The temperature-controlled synthesis of 4-substituted
chromanes has been developed.
・The strategy affords a new method giving C-C or C-O
bond by controlling temperature.
・ The present reaction provides versatile access to
functionalized chromanes.