Substituted Benzothietes: Synthesis and a Quantum Chemical Investigation of Their Cycloreversion Properties

Article abstract of DOI:10.1021/acs.orglett.0c01261

A flexible synthesis for highly substituted benzothietes that does not require flash-vacuum pyrolysis was developed. This allows for the use of a number of functional groups and nonvaporizable molecules. Highly stabilized derivatives were isolated. The molecular orbital properties of various benzothietes were evaluated by density functional methods. The mechanism of the cycloreversion of the four-membered ring was compared to that of the oxygen-containing analogues.

Full text of DOI:10.1021/acs.orglett.0c01261

pubs.acs.org/OrgLett
Letter
Substituted Benzothietes: Synthesis and a Quantum Chemical
Investigation of Their Cycloreversion Properties
Nils L. Ahlburg, Andres R. Velarde, Matthew T. Kieber-Emmons, Peter G. Jones, and Daniel B. Werz*
Cite This: https://dx.doi.org/10.1021/acs.orglett.0c01261
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: A flexible synthesis for highly substituted benzothietes that does not require flash-vacuum pyrolysis was developed.
This allows for the use of a number of functional groups and nonvaporizable molecules. Highly stabilized derivatives were isolated.
The molecular orbital properties of various benzothietes were evaluated by density functional methods. The mechanism of the
cycloreversion of the four-membered ring was compared to that of the oxygen-containing analogues.
Lacking a method that allows the convenient synthesis of a
enzothietes consist of a thietane annelated to a benzene.
BAs heteroatom analogues of benzocyclobutanes, they can range of benzothietes, we tested the applicability of o-quinone
methide strategies to their S analogues, but the unique
properties of sulfur limit the number of adaptable strategies.
For example, thiols cannot be used along with oxidizing agents,
whereas thiosilyl moieties undergo Brook rearrangement or
lead to SEAr-type side reactions. The only viable method was a
variation of the procedure reported by Pettus that uses an
elegant rearrangement−elimination sequence.14,15
The reaction conditions from 1 to 2 were optimized starting
from various protecting groups (Table 1). All precursors were
synthesized from the corresponding thiols according to known
procedures (see the Supporting Information). The best results
among the carbonate-based protecting groups were obtained
using the electron-rich, mildly shielding p-MeO-phenyl oxy-
carbonyl group (entry 2) and Cbz (entry 3) moiety. The
remaining groups (entries 4−7) either provided little
regioselectivity or were unstable under the reaction conditions.
Boc protection, analogous to the original method of Pettus,15 is
not applicable. The tert-butyl thiocarbonate releases CO2 in
the presence of catalytic amounts of magnesium salt, forming
the corresponding tert-butyl thioether. Optimum conditions
were achieved using an N,N-dimethylcarbamate group (entry
1). The reaction was further optimized with regard to
stoichiometry, duration, and temperature. The choice of
undergo electrocyclic ring-opening reactions leading to a
dearomatized six-membered ring system. The oxygen counter-
parts of benzothietes are well-known in their ring-opened form
as o-quinone methides. Commonly, they are generated in situ
and immediately further transformed. Today, o-quinone
methides are widely employed in the synthesis of a variety of
oxygen-containing aromatic compounds, including complex
natural products.1−3 They can be accessed by various strategies
such as oxidation, internal elimination, and transition metal
catalysis; however, benzothietes have been studied only to a
small extent, and literature reports of their use in organic
synthesis are rare. This fact is certainly rooted in the lack of
convenient and reliable methods for the synthesis of
benzothietes and their precursors. Once in hand, they show
a remarkable range of reactivity.4 The procedures are tedious,
with the exception of a few carbene-based methods, and the
methods of Okuma and Kobayashi allow for an only limited
number of different substituents on the four-membered ring.5,6
Older methods rely on either flash-vacuum pyrolysis or high-
energy ultraviolet (UV) irradiation (e.g., by Schweig,7 Aron,8
Meier,9 Boekelheide,10 Katritzky,11 and Plomp12). Scheme 1
provides an overview of the most important procedures.
Flash-vacuum pyrolysis is unsuitable if the starting material
cannot be evaporated or if it decomposes under harsh
conditions. Okuma’s procedure enables the synthesis of stable
benzothietes that are sterically and electronically shielded;
however, only highly sterically hindered thioketones can be
employed. Upon scaling up the reaction, we found a steep
decrease in the yield. The addition of arynes to bisaromatic or
less hindered thioketones exclusively produces xanthenes.13
Received: April 13, 2020
https://dx.doi.org/10.1021/acs.orglett.0c01261
© XXXX American Chemical Society
Org. Lett. XXXX, XXX, XXX−XXX
A

Organic Letters
pubs.acs.org/OrgLett
Letter
derived benzothietes formed only in trace amounts. Derivatives
that carry a strongly shielding tert-butyl group on the benzylic
carbon were isolated by common purification methods (flash
column chromatography on silica gel). Except for 9e,
secondary or primary carbons next to the benzylic carbon
were not tolerated (Scheme 2); however, compound 9e is the
first benzothiete that bears a secondary carbon atom adjacent
to the benzylic position.
Scheme 1. Existing Methods for the Preparation of
Benzothietes (top) and Our Novel Method (bottom)
a
Scheme 2. Benzothiete Scope
Table 1. Optimization of Reaction Conditions
a
entry
compound
protecting group
time
yield (%)
b
1
1a
1b
1c
1d
1e
1f
-C(O)NMe2
-C(O)O(PMP)
-Cbz
-Alloc
-C(O)OMe
-Troc
10 min
2 h
15 h
10 min
15 h
15 h
34
20
19
16
15
15
14
75
b
2
a
b
Reactions were performed on a 0.2 mmol scale (thiol) using 3 equiv
3
of Grignard reagent at −20 °C. The reaction mixture was stirred for
30 min at −20 °C and then warmed to the indicated temperature.
9a−g were prepared from 5, 10a and 10b from 6, and 11a and 11b
from 7. For the large scale, see the Supporting Information.
b
4
b
5
b
6
b
7
1g
1a
-C(O)OPh
-C(O)NMe2
2 h
45 min
c
8
a
All products were synthesized from pivalophenones 5−7.
The use of benzophenones (e.g., 4 and 8) gave only trace
amounts of the corresponding products, surprisingly even upon
treatment with tert-butyl magnesium halides. None of the
products show signs of decomposition upon purification and
can be stored for months in a freezer. To the best of our
knowledge, compounds 9g, 10b, and 11b are the first examples
of heterocycle-bearing benzothietes. We see a clear advantage
in our two-component reaction over the existing procedures.
The use of Grignard reagents allows for straightforward late
stage modification in comparison to existing methods. Of
course, their usage sets a limit on functional group tolerance.
We were able to crystallize compound 10b (see section 3 of
the Supporting Information); to the best of our knowledge,
this is the first crystal structure of a benzothiete. The crystals
contain two independent molecules, in both of which the
thienyl group is disordered over two orientations, but this
disorder was successfully refined. The benzene ring is neither
distorted nor dearomatized; the carbon−sulfur bond lengths
Determined by GC-MS measurement, undecane standard, measured
b
at 10, 45, 120, 360, and 900 min, respective maximum shown. With
0.2 mmol of thiosalicylic aldehyde, 0.4 mmol of PhMgCl (2.0 M in
c
THF), 0.2 mmol/min, THF (5 mL), −60 °C. With 0.2 mmol of
thiosalicylic aldehyde, 0.3 mmol of PhMgCl (2.0 M in THF), 0.2
mmol/min, THF (5 mL), −20 °C, triple flash column chromatog-
raphy of the starting material.
solvent had an immense effect. Coordinating ethers (DME,
THF, and dioxane) perform the best. Less polar solvents do
not dissolve the starting material at low temperatures. Various
metal−organic species were tested. Phenyllithium provided
little conversion. Normant and Gilman cuprates show no
reaction, even at room temperature. Additives did not improve
the yield.
The product’s stability depends on the electronic and steric
properties of the electrophilic carbon. Bisaryl-substituted
benzothietes and those prepared from aldehydes are stable in
solution but decompose upon purification. Acetophenone-
B
https://dx.doi.org/10.1021/acs.orglett.0c01261
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Figure 1. Molecular structures of compound 10b in the solid state
(50% ellipsoid probability). Only the major positions of the
disordered thienyl rings are shown. Bond lengths (angstroms) and
angles (degrees) in the two independent molecules: S1−C4,
1.771(1), 1.771(1); S1−C8, 1.927(1), 1.919(1); C4−S1−C8,
74.80(4), 75.07(5).
Scheme 3. Proposed Mechanism
and angles are within the conventional ranges for carbon−
sulfur single bonds (Figure 1). The X-ray structure establishes
that the benzothiete does not possess any o-quinone-like
properties.
We assume a mechanism analogous to the formation of
o-quinone methides as proposed by Pettus (Scheme 3).15 The
thiocarbamate is sufficiently deactivated to provide absolute
regioselectivity for the Grignard attack.
To predict the stability of benzothietes and the effect of
substituents and to explain the differences compared to
o-quinone methides, a computational study was conducted.
We investigated the thermodynamics of the thermal ring
opening of the monoarylated benzothiete with several
representative substituents in electronic key positions (Figure
2). The BMK (Boese−Martin for kinetics) functional was
employed for these studies and gives reliable results for the
dissociation of C−S bonds.16
The transition state for the thermal ring opening, connecting
the benzothietane to the product structure, is composed of a
single imaginary frequency at which the C−S bond breaks.
Both the thermodynamics and the barrier height of the
reaction were dependent on the substituents; consequently, we
evaluated a wide range of substituents.
Figure 2. Two-dimensional Hammett plots of monoarylated
benzothietes: (top) activation energy ΔAU and (bottom) reaction
energy ΔRU. Energy differences calculated from bond length scans.
Numerical values in section 4.2.10 of the Supporting Information.
BMK 6-311+g(d,p) (with dispersion).
To approximate the reaction coordinates, linear transits were
performed in which the C−S bond was systematically
lengthened. These calculations provided results in excellent
agreement with transition states and intrinsic reaction
coordinates at reduced computational costs (see Figure S3
for an exact energy diagram from IRCs). Because the change in
entropy of the molecule upon ring opening is negligible, the
differences in total energies ΔU of the respective process are a
good estimate for the change in Gibbs energy ΔG (for ΔRS ≈
0, ΔRU ≈ ΔRG ≈ ΔRH; for ΔAS ≈ 0, ΔAU ≈ ΔAG ≈ ΔAH).
C
https://dx.doi.org/10.1021/acs.orglett.0c01261
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
The substituent para to the benzylic carbon (Rphenyl
;
Hammett constant, σphenyl) has a strong influence on the
activation energy ΔAU and the total reaction energy ΔRU.
Electron-withdrawing groups para to the benzylic carbon
significantly stabilize the HOMO, which is strongly correlated
with an increase in ΔRU (section 4.2.11 of the Supporting
Information). As a result, the energy required for the cleavage
of the C−S bond and the related activation energy increase
steeply. The electron-withdrawing functional groups para to
the chalcogen (Rbenzo; Hammett constant, σbenzo) similarly
stabilize the cleaved system and reduce the activation and
reaction energy necessary for the ring opening; however, this
dependence of the reaction energy on the electronic properties
of the benzo substituent is only weakly correlated, which
indicates that the stabilization of the benzylic carbon is far
more important to the total energy than the substituent effects
on the electronegative sulfur. For ΔAU, this was substantiated
by a mathematical separation of the effects of Rphenyl and Rbenzo
after a Young−Jencks−Yukawa−Tsuno analysis provided only
unsatisfying results; no σ scale sufficiently depicted our
reaction (section 4.2.12 of the Supporting Information).17
For fixed functional groups Rbenzo, the effect of different
substituents Rphenyl can be linearized in a Hammet−Brown
model [for all substituents, R2 > 0.98 (section 4.2.11 of the
Supporting Information)].18 The resulting ρ values are
approximately affinely dependent on σm,benzo (R2 = 0.85).
For the Rphenyl = NMe2 substituent, when the other
substituent is varied from methoxy (σ = −0.27) to nitro (σ
= 0.78), ΔRU exhibits the expected behavior. However, with
Hammett constants lower than that of the methoxy group, we
observe a sudden drop in the reaction energy ΔRU, which
suggests an orbital effect that exceeds simple charge effects, as
the net charge on the sulfur is not correlated with ΔRU.
The HOMO of the dimethylamino-bearing and isopropoxy-
bearing (Rbenzo = NMe2 and OiPr, respectively) benzothiete
possesses an additional node, indicating that these strongly
electron-donating groups additionally stabilize the benzylic
meta position; this effect outweighs the decrease in the HOMO
Figure 3. MO-IRC plot of the ring opening of phenyl benzothiete to
phenyl o-thioquinone methide (top) and phenyl benzoxetane to
phenyl o-quinone methide (bottom) (HOMO−3 to LUMO+3).
BMK/6-311+g(d,p) (with dispersion).
bond is lengthened and finally broken by internal electron
transfer. However, the molecular orbitals show that the relative
contributions of O versus S are very different in the LUMOs.
The S contributions in the HOMO and LUMO vary from 50%
and 43% in the closed form to 40% and 21% in the open form.
The analogous O contributions range from 18% and 2% to
12% and 9%, which indicates significantly less oxygen character
in these frontier molecular orbitals. These values indicate a
substantially more covalent C−S interaction in the benzothiete
compared to C−O in the benzoxetane, which is consistent
with the observed thermodynamic preference. We expect that
this observation is general with regard to benzothietes;
substituent effects alone are not likely to be strong enough
to overcome covalency differences between E−C bonds, which
are dependent primarily on the valence shell ionization energy
of the chalcogen.
In summary, we have developed a versatile two-component
reaction to synthesize benzothietes from Grignard reagents and
S-protected thiosalicylic ketones and aldehydes that does not
rely on flash-vacuum pyrolysis or high-intensity irradiation. We
have studied the bonding properties in benzothietes and
compared them to the related, well-established o-quinone
methides. Our findings indicate that for sulfur the closed-ring
form is preferred (as also demonstrated by X-ray crystallog-
raphy) because of ring strain effects and its lower electro-
negativity and consequently higher valence shell ionization
energy, leading to significantly enhanced covalency.
energy. The opposite effect can be observed in the Rphenyl
=
NO2 row of the reaction energy ΔRU. The energy increases
again as we pass Rbenzo = Br (σ = −0.23) en route to even
electron-poorer substituents.
Benzothietes, in contrast to o-quinone methides, are more
stable in their closed-ring form, even though C−S bonds are
typically ∼20 kcal/mol weaker than C−O bonds because of
the higher valence shell ionization energy of sulfur.19 As an
example, the H-substituted monoarylated benzothiete is
favored by 16.8 kcal/mol over the open form. In contrast,
the monoarylated o-quinone methide is favored over the
benzoxetane by 10.4 kcal/mol. A computational homodesmic
(HD2) reaction scheme was employed to estimate the
difference in ring strain (section 4.2.22 of the Supporting
Information).20 The S derivative releases approximately 10.5
kcal/mol of ring strain, accounting for nearly 50% of the
energetic difference.
To investigate this thermodynamic peculiarity, we first
calculated the intrinsic reaction coordinate for the ring-
opening reaction of the phenyl benzothiete and phenyl o-
quinone methide.21 The comparable qualitative structure of
the MO-IRC plots indicates that the elemental cycloreversion
mechanism of the heteroatom-bearing four-membered rings is
similar. As one can clearly see from the plots (Figure 3), the
E−C antibonding LUMO decreases in energy as the E−C
D
https://dx.doi.org/10.1021/acs.orglett.0c01261
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
̌
́
Skalamera, D
̵
.; Basaric, N.; Phillips, D. L. J. Org. Chem. 2019, 84,
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01261.
■
8630−8637. (d) Sun, M.; Ma, C.; Zhou, S.-J.; Lou, S.-F.; Xiao, J.; Jiao,
sı
Y.; Shi, F. Angew. Chem., Int. Ed. 2019, 58, 8703−8708. (e) Ukis, R.;
̈
Schneider, C. J. Org. Chem. 2019, 84, 7175−7188. (f) Goricke, F.;
Schneider, C. Angew. Chem., Int. Ed. 2018, 57, 14736−14741.
(g) Hodík, T.; Schneider, C. Chem. - Eur. J. 2018, 24, 18082−18088.
(h) Jiang, F.; Luo, G.-Z.; Zhu, Z.-Q.; Wang, C.-S.; Mei, G.-J.; Shi, F. J.
Org. Chem. 2018, 83, 10060−10069. (i) Kretzschmar, M.; Hofmann,
F.; Moock, D.; Schneider, C. Angew. Chem., Int. Ed. 2018, 57, 4774−
4778. (j) Lam, H.; Qureshi, Z.; Wegmann, M.; Lautens, M. Angew.
Chem., Int. Ed. 2018, 57, 16185−16189. (k) Li, L.-Z.; Wang, C.-S.;
Guo, W.-F.; Mei, G.-J.; Shi, F. J. Org. Chem. 2018, 83, 614−623.
(l) Spanka, M.; Schneider, C. Org. Lett. 2018, 20, 4769−4772.
(m) Liu, S.-J.; Jiang, X.-L.; Wu, S.-F.; Tu, M.-S.; Mei, G.-J.; Shi, F.
Synthesis 2018, 50, 2416−2422. (n) Suneja, A.; Schneider, C. Org.
Lett. 2018, 20, 7576−7580. (o) Nielsen, C.; Abas, H.; Spivey, A.
Synthesis 2018, 50, 4008−4018. (p) Jiang, X.-L.; Liu, S.-J.; Gu, Y.-Q.;
Mei, G.-J.; Shi, F. Adv. Synth. Catal. 2017, 359, 3341−3346. (q) Ma,
1
Detailed experimental procedures, analytical data, H
and 13C NMR spectra of all new compounds, and
computational results, including Cartesian coordinates
(PDF)
Accession Codes
CCDC 1993935 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
́
J.; Zhang, X.; Basaric, N.; Phillips, D. L. J. Am. Chem. Soc. 2017, 139,
18349−18357. (r) Wang, C.-S.; Cheng, Y.-C.; Zhou, J.; Mei, G.-J.;
Wang, S.-L.; Shi, F. J. Org. Chem. 2018, 83, 13861−13873. (s) Hodík,
T.; Schneider, C. Org. Biomol. Chem. 2017, 15, 3706−3716.
AUTHOR INFORMATION
Corresponding Author
■
̌
́
(t) Skalamera, D̵.; Mlinaric-Majerski, K.; Martin Kleiner, I.; Kralj,
̈
Daniel B. Werz − Technische Universitat Braunschweig, Institute
́
M.; Oake, J.; Wan, P.; Bohne, C.; Basaric, N. J. Org. Chem. 2017, 82,
6006−6021. (u) Kretzschmar, M.; Hodík, T.; Schneider, C. Angew.
Chem., Int. Ed. 2016, 55, 9788−9792. (v) Alamsetti, S. K.; Spanka, M.;
Schneider, C. Angew. Chem., Int. Ed. 2016, 55, 2392−2396. (w) Bera,
K.; Schneider, C. Org. Lett. 2016, 18, 5660−5663. (x) Wang, J.-R.;
Jiang, X.-L.; Hang, Q.-Q.; Zhang, S.; Mei, G.-J.; Shi, F. J. Org. Chem.
2019, 84, 7829−7839.
of Organic Chemistry, 38106 Braunschweig, Germany;
orcid.org/0000-0002-3973-2212; Email: d.werz@tu-
braunschweig.de
Authors
̈
Nils L. Ahlburg − Technische Universitat Braunschweig,
Institute of Organic Chemistry, 38106 Braunschweig, Germany
Andres R. Velarde − Department of Chemistry, University of
Utah, Salt Lake City, Utah 84112-0850, United States
Matthew T. Kieber-Emmons − Department of Chemistry,
University of Utah, Salt Lake City, Utah 84112-0850, United
States; orcid.org/0000-0002-6357-5579
(3) (a) Feng, Z.-G.; Bai, W.-J.; Pettus, T. R. R. Angew. Chem., Int. Ed.
2015, 54, 1864−1867. (b) Li, G.; Liu, H.; Lv, G.; Wang, Y.; Fu, Q.;
Tang, Z. Org. Lett. 2015, 17, 4125−4127. (c) Lukeman, M.; Simon,
H.; Wan, P.; Wang, Y.-H. J. Org. Chem. 2015, 80, 11281−11293.
(d) Lee, A.; Younai, A.; Price, C. K.; Izquierdo, J.; Mishra, R. K.;
Scheidt, K. A. J. Am. Chem. Soc. 2014, 136, 10589−10592.
(4) Meier, H. Molecules 2012, 17, 1548−1570.
(5) Okuma, K.; Shiki, K.; Sonoda, S.; Koga, Y.; Shioji, K.; Kitamura,
T.; Fujiwara, Y.; Yokomori, Y. Bull. Chem. Soc. Jpn. 2000, 73, 155−
161.
̈
Peter G. Jones − Technische Universitat Braunschweig, Institute
of Inorganic and Analytical Chemistry, 38106 Braunschweig,
Germany
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01261
(6) Kobayashi, K.; Ueyama, T. Heterocycles 2019, 98, 126.
(7) Schulz, R.; Schweig, A. Tetrahedron Lett. 1980, 21, 343−346.
(8) Hortmann, A. G.; Aron, A. J.; Bhattacharya, A. K. J. Org. Chem.
1978, 43, 3374−3378.
Notes
(9) (a) Meier, H.; Mayer, A. Synthesis 1996, 1996, 327−329.
The authors declare no competing financial interest.
̈
(b) Meier, H.; Mayer, A.; Groschl, D. Sulfur Rep. 1994, 16, 23−56.
(c) Meier, H. J. Prakt. Chem./Chem.-Ztg. 1996, 338, 383−385.
(d) Voigt, E.; Meier, H. Angew. Chem., Int. Ed. Engl. 1976, 15, 117.
(e) Voigt, E.; Meier, H. Chem. Ber. 1977, 110, 2242−2248.
(10) Mao, Y. L.; Boekelheide, V. Proc. Natl. Acad. Sci. U. S. A. 1980,
77, 1732−1735.
ACKNOWLEDGMENTS
■
The authors thank the Studienstiftung des deutschen Volkes
for a Ph.D. fellowship to N.L.A. Computer time was in part
provided by the Extreme Science and Engineering Discovery
Environment (XSEDE), which is supported by National
Science Foundation Grant ACI-1053575 (TG-CHE130047
and TG-MCB190043).
̈
(11) Rumpf, N.; Groschl, D.; Meier, H.; Oniciu, D. C.; Katritzky, A.
R. J. Heterocycl. Chem. 1998, 35, 1505−1508.
(12) (a) van Tilborg, W. J. M.; Plomp, R. Recl. Trav. Chim. Pays-Bas
1977, 96, 282−286. (b) van Tilborg, W. J. M.; Plomp, R. J. J. Chem.
Soc., Chem. Commun. 1977, 130.
REFERENCES
(13) Okuma, K.; Shiki, K.; Shioji, K. Chem. Lett. 1998, 27, 79−80.
(14) 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.
(15) Jones, R. M.; van de Water, R. W.; Lindsey, C. C.; Hoarau, C.;
Ung, T.; Pettus, T. R. R. J. Org. Chem. 2001, 66, 3435−3441.
(16) (a) Shi, J.; Hu, X.-R.; Liang, S. Heteroat. Chem. 2011, 22, 97−
105. (b) Boese, A. D.; Martin, J. M. L. J. Chem. Phys. 2004, 121,
3405−3416.
(17) (a) Tsuno, Y.; Fujio, M. The Yukawa-Tsuno Relationship in
Carbocationic Systems. In Advances in Physical Organic Chemistry;
Bethell, D., Ed.; Elsevier Textbooks, s.l., 1999; pp 267−385.
(b) Tsuno, Y.; Kusuyama, Y.; Sawada, M.; Fujii, T.; Yukawa, Y.
Bull. Chem. Soc. Jpn. 1975, 48, 3337−3346. (c) Yukawa, Y.; Tsuno, Y.
■
(1) Selected reviews: (a) Yang, B.; Gao, S. Chem. Soc. Rev. 2018, 47,
7926−7953. (b) Jaworski, A. A.; Scheidt, K. A. J. Org. Chem. 2016, 81,
10145−10153. (c) Caruana, L.; Fochi, M.; Bernardi, L. Molecules
2015, 20, 11733−11764. (d) Singh, M. S.; Nagaraju, A.; Anand, N.;
Chowdhury, S. RSC Adv. 2014, 4, 55924−55959. (e) Willis, N. J.;
Bray, C. D. Chem. - Eur. J. 2012, 18, 9160−9173. (f) Pathak, T. P.;
Sigman, M. S. J. Org. Chem. 2011, 76, 9210−9215. (g) van de Water,
R. W.; Pettus, T. R.R. Tetrahedron 2002, 58, 5367−5405.
(h) Wojciechowski, K. Eur. J. Org. Chem. 2001, 2001, 3587.
(2) Selected publications: (a) Chen, P. K.; Wong, Y. F.; Yang, D.;
Pettus, T. R. R. Org. Lett. 2019, 21, 7746−7749. (b) Kallweit, I.;
Schneider, C. Org. Lett. 2019, 21, 519−523. (c) Ma, J.; Sekutor, M.;
̌
E
https://dx.doi.org/10.1021/acs.orglett.0c01261
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Bull. Chem. Soc. Jpn. 1959, 32, 965−971. (d) Yukawa, Y.; Tsuno, Y.;
Sawada, M. Bull. Chem. Soc. Jpn. 1966, 39, 2274−2286. (e) Young, P.
R.; Jencks, W. P. J. Am. Chem. Soc. 1977, 99, 8238−8248. (f) Morita,
T. Bull. Chem. Soc. Jpn. 1959, 32, 893−896.
(18) (a) Okamoto, Y.; Brown, H. C. J. Org. Chem. 1957, 22, 485−
494. (b) Brown, H. C.; Okamoto, Y. J. Am. Chem. Soc. 1957, 79,
1913−1917.
(19) Luo, Y.-R. Handbook of bond dissociation energies in organic
compounds; CRC Press: Boca Raton, FL, 2003.
(20) (a) Dudev, T.; Lim, C. J. Am. Chem. Soc. 1998, 120, 4450−
4458. (b) Wheeler, S. E.; Houk, K. N.; Schleyer, P. v. R.; Allen, W. D.
J. Am. Chem. Soc. 2009, 131, 2547−2560. (c) Fukui, K. Acc. Chem.
Res. 1981, 14, 363−368.
(21) Hratchian, H. P.; Schlegel, H. B. J. Chem. Phys. 2004, 120,
9918−9924.
F
https://dx.doi.org/10.1021/acs.orglett.0c01261
Org. Lett. XXXX, XXX, XXX−XXX