Direct and Asymmetric Nickel(II)-Catalyzed Construction of Carbon-Carbon Bonds from N-Acyl Thiazinanethiones

Article abstract of DOI:10.1021/acs.orglett.8b03757

A wide array of new N-acyl thiazinanethiones are employed in a number of direct and enantioselective carbon-carbon-bond-forming reactions catalyzed by nickel(II) complexes. The electrophilic species are mostly prepared in situ from ortho esters, methyl et

Full text of DOI:10.1021/acs.orglett.8b03757

Letter
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Direct and Asymmetric Nickel(II)-Catalyzed Construction of Carbon−
Carbon Bonds from N‑Acyl Thiazinanethiones
Stuart C. D. Kennington, Adam J. Taylor, Pedro Romea,* Fel
ix Urpí,*,† Gabriel Aullon,‡
̀ ́
†
†,§
,†
#
†
†,¶
Merce Font-Bardia, Laura Ferre, and Jesus Rodrigalvarez
̀ ́
†Department of Inorganic and Organic Chemistry, Section of Organic Chemistry, and Institute of Biomedicine (IBUB), University
of Barcelona, Carrer Martí i Franques 1-11, 08028 Barcelona, Catalonia, Spain
Department of Inorganic and Organic Chemistry, Section of Inorganic Chemistry, University of Barcelona, Carrer Martí i Franques
-11, 08028 Barcelona, Catalonia, Spain
́
‡
́
1
#
Unitat de Difraccio
de RX, CCiTUB, Universitat de Barcelona, Carrer Sole i Sabarís 1-3, 08028 Barcelona, Catalonia, Spain
́ ́
*
S Supporting Information
ABSTRACT: A wide array of new N-acyl thiazinanethiones are
employed in a number of direct and enantioselective carbon−
carbon-bond-forming reactions catalyzed by nickel(II) complexes.
The electrophilic species are mostly prepared in situ from ortho
esters, methyl ethers, acetals, and ketals, which makes the overall
process highly efficient and experimentally straightforward.
Theoretical calculations indicate that the reactions proceed
through an open transition state in a S 1-like mechanism. The
N
utility of this novel procedure has been demonstrated by the
asymmetric preparation of synthetically useful intermediates and the total synthesis of peperomin D.
he stereocontrolled construction of carbon−carbon
ensuing removal of the thiazinanethione scaffold provides
enantiomerically pure compounds in high yields and in a
straightforward manner (Scheme 1).
T
bonds from metal enolates holds a prominent position
among carbon-backbone-forming methods in asymmetric
1
synthesis. Unfortunately, most of the reported methods
hinge on the stoichiometric generation of the enolate and
subsequent reaction with the chosen electrophile, so they do
Scheme 1. Direct, Asymmetric, and Catalytic C−C-Bond-
Forming Reactions
2
not meet the current demands for economy in synthesis.
3
Organocatalysis does meet such challenges, but the source of
nucleophiles is often restricted to aldehydes and a few
4
privileged compounds. Hence, there is a lack of direct,
catalytic, and asymmetric transformations based on metal
enolates from nonactivated carboxylic derivatives. In this
context, pioneering studies underlined the benefits of working
with easily removable scaffolds attached to the carboxylic
5
−7
moiety.
This led Kobayashi to use amides in highly
8
enantioselective aldol and Michael additions, and similarly,
Evans described aldol reactions and orthoester alkylations from
N-acyl thiazolidinethiones, Kumagai and Shibasaki also
9
reported a number of reactions based on 7-azaindoline
1
0,11
We were aware from the very beginning that such a
challenging process called for (a) the catalytic formation of an
enolate possessing the necessary chiral environment in parallel
to (b) the generation of the required electrophile for (c) the
installation of up to two new stereocenters while (d)
minimizing undesired reactions. Therefore, we carried out a
careful examination of all the species involved in such a
process.
amides.
Inspired by such precedents and taking advantage
of our own experience in S 1-like stereoselective trans-
N
1
2
13
formations and the isolobal principle, we envisaged that
treatment of N-acyl thioimides with easy to handle chiral
nickel(II) complexes might catalytically produce the corre-
sponding metal enolates. These would then be capable of
taking part in asymmetric carbon−carbon-bond-forming
reactions with cationic intermediates. According to such
ideas, we herein report that the direct TESOTf-mediated
addition of N-acyl thiazinanethiones to a wide array of
electrophiles catalyzed by chiral nickel(II) complexes and the
Received: November 23, 2018
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b03757
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Exploratory studies on the addition of N-propanoyl
derivatives 1a−5a to 4,4′-dimethoxybenzhydryl methyl ether
in the presence of commercially available (Me P) NiCl
2
and a 96% yield after chromatographic purification (entry 8 in
Table 1).
The optimized conditions were then applied to a broad array
of N-acyl thiazinanethiones 5 (Table 2). The reaction proved
to be sensitive to the bulk of the acyl group, so the catalyst
loading had to be increased to 10 mol % for the sterically
hindered (R: i-Pr) thiazinanethione 5d (compare entries 1−4
in Table 2). Otherwise, it tolerated the presence of common
functional groups as alkenes, alkynes, and carboxylic esters as
well as Cα-benzyl or phenyl ethers, in most cases with an
outstanding enantiocontrol (ee up to 98%) and yields from 78
to 96% (entries 5−9 in Table 2). Unfortunately, the synthesis
of the azidoacetyl thiazinanethione counterpart proved
troublesome, but a parallel alkylation reaction was carried
out successfully with the N-azidoacetyl thiazolidinethione 4j
3
2
demonstrated the crucial role of the exocyclic CS bond
(Scheme 2). Indeed, oxazolidinone 1a and thiazolidinone 2a
Scheme 2. Assessment of the Scaffold
(
entry 10 in Table 2). Significantly, the results for 10i and 9j
make this alkylation a new approach to the asymmetric
synthesis of α-hydroxy and α-amino acids respectively (entries
9
and 10 in Table 2).
The thiazinanethione scaffold of the products 10 was easily
did not react at all, whereas thiazolidinethione 4a and
thiazinanethione 5a were converted into the alkylated products
quantitatively.
1
4−16
removed to release alkylated products (Scheme 3).
Indeed, reduction of 10a with NaBH led to alcohol 11a
4
with a yield of 87%, whereas treatment of 10a with methanol
afforded ester 12a with a 96% yield. In turn, (S)-α-
methylbenzylamine and morpholine reacted smoothly with
10a to produce amides 13a and 14a, respectively, in yields up
to 96%. At this point, absolute configuration of adducts 10 was
firmly established by chemical correlation of 11a−12a and X-
Therefore, we focused our attention on the alkylation of 4a
and 5a promoted by a few chiral complexes (L*NiCl in Table
2
1
), easily prepared by simple heating of mixtures of NiCl and
2
9b
the corresponding diphosphines in CH CN. Initial screening
3
of the reaction conditions revealed that both substrates were
appropriate platforms to carry out such alkylations. Thereby,
treatment of thiazolidinethione 4a with 4,4′-dimethoxybenz-
hydryl methyl ether, TESOTf, and 2,6-lutidine in the presence
17
ray analysis of amide 13a. Interestingly, thiazinanethione may
also act as a coupling reagent and permitted us to obtain
diastereomerically pure N-acyl amino acid 15f by simple
addition of methyl (S) leucinate to adduct 10f with an 89%
yield.
of 5 mol % L*NiCl at −20 °C for 15 h produced the
2
quantitative and enantioselective (ee up to 96%) conversion
into the alkylated adduct 9a (entries 1−3 in Table 1). Even
better, parallel reactions from thiazinanethione 5a afforded
adduct 10a as a single enantiomer (entries 4−6 in Table 1).
Importantly, the temperature could be raised to 0 °C without
any detrimental effect, which enabled us to dramatically reduce
the reaction time and to scale down the catalyst loading
Once the feasibility of the catalytic and asymmetric
alkylation of 5 with 4,4′-dimethoxybenzhydryl methyl ether
was established, we examined the synthetic potential of such a
transformation through the use of other electrophiles
represented in Scheme 1. The reactions with trimethyl
orthoformate, a dimethyl ketal, and a tropylium salt, which
involve the installation of a single stereocenter, proceeded
smoothly and led to enantiomerically pure adducts 16a−18a
(
5
compare entries 6−9 in Table 1). Eventually, the alkylation of
a with a mere 1 mol % of [(R)-DTBM-SEGPHOS]NiCl
2
took place at 0 °C in just 10 min and gave 10a with a 98% ee
Table 1. Initial Trials on the Direct and Asymmetric Reactions Catalyzed by Chiral Nickel(II) Complexes
a
b
c
entry
substrate
L*NiCl2
mol %
temp (°C)
t (h)
ee (%)
conversion (%)
yield (%)
1
2
3
4
5
6
7
8
9
4a
4a
4a
5a
5a
5a
5a
5a
5a
[(R)-BINAP]NiCl2
[(R)-TolBINAP]NiCl2
[(R)-DTBM-SEGPHOS]NiCl2
[(R)-BINAP]NiCl2
[(R)-TolBINAP]NiCl2
[(R)-DTBM-SEGPHOS]NiCl2
[(R)-DTBM-SEGPHOS]NiCl2
[(R)-DTBM-SEGPHOS]NiCl2
[(R)-DTBM-SEGPHOS]NiCl2
5
5
5
5
5
5
2
1
1
−20
−20
−20
−20
−20
−20
−20
0
15
15
15
15
15
15
1
94
95
96
96
98
98
98
98
92
>97
>97
>97
>97
>97
>97
>97
>97
>97
0.2
0.2
96
20
a
b
1
c
Established by chiral HPLC. Established by H NMR. Isolated yield after column chromatography.
B
DOI: 10.1021/acs.orglett.8b03757
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 2. Direct and Enantioselective Alkylation with (4-MeOPh) CHOMe Catalyzed by a Chiral Nickel(II) Complex
2
b
entry
substrate
R
mol % L*NiCl2
t (h)
adduct
ee (%)
yield (%)
1
2
3
4
5
6
7
8
9
5a
5b
5c
5d
5e
5f
5g
5h
5i
Me
Et
Bn
i-Pr
1
2
2
10
2
2
2
10
2
0.2
2
2
2
2
2
2
2.5
4
2
10a
10b
10c
10d
10e
10f
10g
10h
10i
98
95
96
98
98
98
95
95
95
95
96
88
81
78
78
96
78
85
93
93
(CH ) CHCH
2
2
2
(CH ) CCH
2
3
(CH ) CO Me
2
2
2
OPh
OBn
N3
1
0
4j
2
9j
a
b
Established by chiral HPLC. Isolated yield after column chromatography.
Scheme 3. Removal of the Thiazinanethione Scaffold
Scheme 4. Reactions with Other Electrophiles
Coordination of this species to the thioimide moiety enhances
the acidity of 5 and facilitates the deprotonation of the Cα
position. At the same time, the TESOTf reacts with the
benzhydryl methyl ether and produces the corresponding
(
ee ≥97%) after slight adjustments of the former experimental
conditions (Scheme 4). More concretely, the reaction with
trimethyl orthoformate was carried out at −40 °C to suppress
the competitive alkylation of the exocyclic CS bond, whereas
the addition to the dimethyl ketal lasted for 6 h, probably
because of the steric bulk of the oxo carbenium intermediate.
Besides these results, it is important to highlight that the
19
carbocation, which in turn adds to the nickel(II) enolate.
Once the carbon−carbon bond is formed, the alkylated adduct
10a is released and the nickel(II) complex may start a new
catalytic cycle (Scheme 5).
related reaction with 4-MeOPhCH(OMe) , which involves the
Eventually, we considered the synthesis of peperomin D (20
in Scheme 6), a secolignan metabolite isolated from Peperomia
2
simultaneous construction of two new stereocenters, was also
satisfactory and afforded the syn adduct 19a (dr 75:25, 98% ee
for the syn diastereomer) and with a high overall yield (Scheme
2
0
glabielle.
Featuring a five-membered lactone with a
benzhydryl appendage at the β position, we envisaged that it
might be synthesized through alkylation of thiazinanethione 5k
with the appropriate benzhydryl methyl ether in the presence
4
).
An S 1-like mechanism based on the approach of cationic
N
21
reagents to the Re face of a putative chiral nickel enolate
of [(S)-DTBM-SEGPHOS]NiCl2. Indeed, quenching the
accounts for all these results. [(R)-DTBM-SEGPHOS]NiCl is
reaction mixture with LiBH gave chemoselectivily the hydroxy
2
4
a robust and bench stable nickel(II) complex with a distorted
square planar geometry which can be seen in the crystal
ester 21, which was then treated with Amberlyst resin to obtain
the desired lactone 22 with an excellent stereocontrol (95%
ee) and a 51% yield. Remarkably, just a single chromatographic
purification was required. The installation of the α-stereocenter
was next accomplished by substrate-controlled alkylation of 22
1
7
structure obtained; it does not catalyze the alkylation
reaction but it is easily activated in situ with TESOTf to
18
produce the true catalyst containing two triflate ligands.
C
DOI: 10.1021/acs.orglett.8b03757
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 5. Mechanistic Model
Experimental procedures and characterization data
(PDF)
NMR spectra (PDF)
Accession Codes
CCDC 1857787−1857788 contain the supplementary crys-
tallographic 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
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
*
E-mail: pedro.romea@ub.edu.
E-mail: felix.urpi@ub.edu.
*
ORCID
Pedro Romea: 0000-0002-0259-9155
Fel
̀
ix Urpí: 0000-0003-4289-6506
: 0000-0001-7519-4522
Gabriel Aullon
́
Present Addresses
§
A.J.T.: School of Chemistry, University of Glasgow, Glasgow
Scheme 6. Synthesis of Peperomin D
G12 8QQ, United Kingdom.
J.R.: Department of Chemistry, University of Cambridge,
¶
Cambridge CB2 1EW, United Kingdom
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Financial support from the Spanish Ministerio de Economia y
Competitividad (Grant No. CTQ2015-65759-P) and the
Generalitat de Catalunya (2017SGR 271) as well as a
doctorate studentship to S.C.D.K. (Generalitat de Catalunya)
and an Erasmus+ grant to A.J.T. are acknowledged.
■
́
DEDICATION
■
Dedicated to the memory of recently deceased Professor Josep
Castells.
with MeI, which allowed us the isolation of enantiomerically
pure peperomin D 20 with an overall yield of 42% over three
steps.
REFERENCES
■
(
1) Carreira, E. M.; Kvaerno, L. Classics in Stereoselective Synthesis;
Wiley-VCH: Weinheim, 2009.
In summary, we have demonstrated the utility of N-acyl
thiazinanethiones in a number of direct, chemo- and
enantioselective carbon−carbon-bond-forming reactions usu-
(
2) (a) Trost, B. M. The atom economy − a search for synthetic
efficiency. Science 1991, 254, 1471−1477. (b) Trost, B. M. Atom
Economy−A Challenge for Organic Synthesis: Homogeneous
Catalysis Leads the Way. Angew. Chem., Int. Ed. Engl. 1995, 34,
ally promoted by 1−5 mol % of [DTBM-SEGPHOS]NiCl .
2
2
(
59−281.
The thiazinanethione scaffold can be smoothly released from
the resulting adducts to provide a broad array of enantiomeri-
cally pure intermediates. Theoretical studies suggest that these
transformations proceed through an open transition state in an
SN1-like mechanism, in which the configuration of the α-
stereocenter is absolutely controlled by the chiral biphosphine.
The efficiency of such an alkylation has been proved in the
total synthesis of peperomin D, a five-membered lactone
containing two stereocenters.
3) (a) Beeson, T. D.; Mastracchio, A.; Hong, J.-B.; Ashton, K.;
MacMillan, D. W. C. Enantioselective Organocatalysis Using SOMO
Activation. Science 2007, 316, 582−585. (b) Nicewicz, D. A.;
MacMillan, D. W. C. Merging Photoredox Catalysis with Organo-
catalysis: The Direct Asymmetric Alkylation of Aldehydes. Science
2
(
008, 322, 77−80.
4) Ooi, T.; Maruoka, K. Recent Advances in Asymmetric Phase-
Transfer Catalysis. Angew. Chem., Int. Ed. 2007, 46, 4222−4266.
(5) (a) Yamada, Y. M. A.; Yoshikawa, N.; Sasai, H.; Shibasaki, M.
Direct Catalytic Asymmetric Aldol Reactions of Aldehydes with
Unmodified Ketones. Angew. Chem., Int. Ed. Engl. 1997, 36, 1871−
ASSOCIATED CONTENT
Supporting Information
■
1
872. (b) Yoshikawa, N.; Yamada, Y. M. A.; Das, J.; Sasai, H.;
*
S
Shibasaki, M. Direct Catalytic Asymmetric Aldol Reaction. J. Am.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b03757.
Chem. Soc. 1999, 121, 4168−4178.
(6) (a) Trost, B. M.; Ito, H. A. Direct Catalytic Enantioselective
Aldol Reaction via a Novel Catalyst Design. J. Am. Chem. Soc. 2000,
D
DOI: 10.1021/acs.orglett.8b03757
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
1
22, 12003−12004. (b) Trost, B. M.; Bartlett, M. J. ProPhenol-
(16) For a recent example of transamidation driven by activation of
the amide bond, see Li, G.; Szostak, M. Highly selective transition-
metal-free transamidation of amides and amidation of esters at room
temperature. Nat. Commun. 2018, 9, 4165−4172.
Catalyzed Asymmetric Additions by Spontaneously Assembled
Dinuclear Main Group Metal Complexes. Acc. Chem. Res. 2015, 48,
6
(
88−701.
7) (a) Harada, S.; Handa, S.; Matsunaga, S.; Shibasaki, M. Direct
(17) For the X-ray data, see Supporting Information. Crystallo-
Catalytic Asymmetric Mannich-Type Reactions of N-(2-
Hydroxyacetyl)pyrrole as an Ester-Equivalent Donor. Angew. Chem.,
Int. Ed. 2005, 44, 4365−4368. (b) Morimoto, H.; Lu, G.; Aoyama, N.;
Matsunaga, S.; Shibasaki, M. Lanthanum Aryloxide/Pybox-Catalyzed
Direct Asymmetric Mannich-Type Reactions Using a Trichloromethyl
Ketone as a Propionate Equivalent Donor. J. Am. Chem. Soc. 2007,
graphic data for amide 13a and [(R)-DTBM-SEGPHOS]NiCl have
2
been also deposited at Cambridge Crystallographic Data Centre as
supplementary publication number CCDC 1857787 and CCDC
1857788, respectively.
(18) Suzuki, T.; Hamashima, Y.; Sodeoka, M. Asymmetric
Fluorination of α−Aryl Acetic Acid Derivatives with the Catalytic
1
29, 9588−9589.
8) (a) Saito, S.; Kobayashi, S. Highly anti-Selective Catalytic Aldol
Reactions of Amides with Aldehydes. J. Am. Chem. Soc. 2006, 128,
System NiCl
2007, 46, 5435−5439.
(19) Theoretical calculations were carried out using QM/MM
algorithm methodology to localise the transition states. These show
that one of the phosphine ligands hinders the approach of said
carbocation to the Si face of the enolate (ΔΔG‡ ≈ 2.7 kcal mol )
and thus determines the π−face selectivity of the addition. For details
of theoretical calculations, see Supporting Information.
2
−Binap/R SiOTf/2,6-Lutidine. Angew. Chem., Int. Ed.
3
(
8
704−8705. (b) Suzuki, H.; Sato, I.; Yamashita, Y.; Kobayashi, S.
Catalytic Asymmetric Direct-Type 1,4-Addition Reactions of Simple
−
1
Amides. J. Am. Chem. Soc. 2015, 137, 4336−4339.
(9) (a) Evans, D. A.; Downey, C. W.; Hubbs, J. L. Ni(II)
Bis(oxazoline)-Catalyzed Enantioselective Syn Aldol Reactions of N-
Propionylthiazolidinethiones in the Presence of Silyl Triflates. J. Am.
Chem. Soc. 2003, 125, 8706−8707. (b) Evans, D. A.; Thomson, R. J.
Ni(II) Tol-BINAP-Catalyzed Enantioselective Orthoester Alkylations
of N-Acylthiazolidinethiones. J. Am. Chem. Soc. 2005, 127, 10506−
(
20) Delle Monache, F.; Compagnone, R. S. A Secolignan from
Peperomia Glabella. Phytochemistry 1996, 43, 1097−1098.
21) For a previous total synthesis of peperomin D, see Sibi, M. P.;
(
Johnson, M. D.; Punniyamurthy, T. Enantioselective synthesis of
peperomins A, C, D, and analogs − Examination of diastereoselective
cuprate conjugate additions to N-enoyl-4-diphenylmethyl-2-oxazoli-
dinones. Can. J. Chem. 2001, 79, 1546−1555.
1
(
0507.
10) (a) Weidner, K.; Kumagai, N.; Shibasaki, M. A Designed Amide
as an Aldol Donor in the Direct Catalytic Asymmetric Aldol Reaction.
Angew. Chem., Int. Ed. 2014, 53, 6150−6154. (b) Weidner, K.; Sun,
Z.; Kumagai, N.; Shibasaki, M. Direct Catalytic Asymmetric Aldol
Reaction of an α−Azido Amide. Angew. Chem., Int. Ed. 2015, 54,
6
236−6240. (c) Liu, Z.; Takeuchi, T.; Pluta, R.; Arteaga, F. A.;
Kumagai, N.; Shibasaki, M. Direct Catalytic Asymmetric Aldol
Reaction of α−Alkylamides. Org. Lett. 2017, 19, 710−713.
(11) Kumagai, N.; Shibasaki, M. Nucleophilic and Electrophilic
Activation of Non-Heteroaromatic Amides in Atom-Economical
Asymmetric Catalysis. Chem. - Eur. J. 2016, 22, 15192−15200.
(
12) (a) Romo, J. M.; Galvez, E.; Nubiola, I.; Romea, P.; Urpí, F.;
́
Kindred, M. Diastereoselective Methyl Orthoformate Alkylations of
Chiral N-Acylthiazolidinethiones Catalyzed by Nickel(II) Complexes.
́
Adv. Synth. Catal. 2013, 355, 2781−2786. (b) Fernandez-Valparis, J.;
Romo, J. M.; Romea, P.; Urpí, F.; Kowalski, H.; Font-Bardia, M.
Stereoselective Alkylation of (S)-N-Acyl-4-isopropyl-1,3-thiazolidine-
2
3
-thiones Catalyzed by (Me P) NiCl . Org. Lett. 2015, 17, 3540−
3
2
2
543. (c) Kennington, S. C. D.; Ferre, M.; Romo, J. M.; Romea, P.;
́
Urpí, F.; Font-Bardia, M. Diastereoselective and Catalytic α−
Alkylation of Chiral N-Acyl Thiazolidinethiones with Stable
Carbocationic Salts. J. Org. Chem. 2017, 82, 6426−6433. (d) Fernan-
́
dez-Valparis, J.; Romea, P.; Urpí, F.; Font-Bardia, M. Stereoselective
and Catalytic Synthesis of anti-β-Alkoxy-α-azido Carboxylic Deriva-
tives. Org. Lett. 2017, 19, 6400−6403.
(13) (a) Hoffmann, R. Building Bridges Between Inorganic and
Organic Chemistry (Nobel Lecture). Angew. Chem., Int. Ed. Engl.
1
982, 21, 711−724. (b) Elian, M.; Chen, M. M. L.; Mingos, M. P.;
Hoffmann, R. Comparative Bonding Study of Conical Fragments.
Inorg. Chem. 1976, 15, 1148−1155.
(14) Likely, the good leaving group character of the thiazinanethione
scaffold as well as the distorted amide bond of 10a are the reasons for
its smooth conversion into a variety of intermediates. For a recent
review on the structure and reactivity of twisted amides, see Liu, C.;
Szostak, M. Twisted Amides: From Obscurity to Broadly Useful
Transition-Metal-Catalyzed Reactions by N−C Amide Bond
Activation. Chem. - Eur. J. 2017, 23, 7157−7173.
(15) For a parallel analysis on the structure and reactivity of related
N-acyl thiazolidinethiones, see (a) Yamada, S. Structure and
Reactivity of a Highly Twisted Amide. Angew. Chem., Int. Ed. Engl.
1
993, 32, 1083−1085. (b) Cosp, A.; Larrosa, I.; Anglada, J. M.; Bofill,
J. M.; Romea, P.; Urpí, F. Studies on the Intramolecular C−H···X (X
O, S) Interactions in (S)-N-Acyl-4-isopropyl-1,3-thiazolidine-2-
thiones and Related 1,3-Oxazolidin-2-ones. Org. Lett. 2003, 5, 2809−
812.
=
2
E
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