Chiral Lewis Acid Catalyzed Reactions of α-Diazoester Derivatives: Construction of Dimeric Polycyclic Compounds

Article abstract of DOI:10.1002/anie.201810030

An unexpected homologation/dyotropic rearrangement/interconversion/[3+2] cycloaddition cascade reaction of α-diazoester-terminated N-propyl-substituted isatin derivatives was achieved in the presence of a chiral N,N′-dioxide/Sc^III catalyst. This catalytic manifold allows rapid construction of several classes of dimeric polycyclic compounds with good yields and high levels of diastereo- and enantioselectivity (up to 99 % ee). Furthermore, macrocyclic dimers can be obtained by an intermolecular homologation process.

Full text of DOI:10.1002/anie.201810030

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Accepted Article
Title: Chiral Lewis Acid Catalyzed Reactions of α-Diazoester
Derivatives: Construction of Dimeric Polycyclic Compounds
Authors: Fei Tan, Xiaohua Liu, Yan Wang, Shunxi Dong, Han Yu, and
Xiaoming Feng
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COMMUNICATION
Chiral Lewis Acid Catalyzed Reactions of -Diazoester
Derivatives: Construction of Dimeric Polycyclic Compounds
Fei Tan, Xiaohua Liu,* Yan Wang, Shunxi Dong, Han Yu, and Xiaoming Feng*
Abstract: An unexpected cascade homologation/dyotropic
rearrangement/interconversion/[3+2] cycloaddition reaction of  - the backbone of oxindole unit. Herein, we demonstrate a chiral
diazoester-terminated N-propyl substituted isatin derivatives was Lewis acid promoted enantioselective cascade reactions of
steps (Scheme 1, left), depending on the length of the tether and
achieved in the presence of a chiral N,N'-dioxide-Sc(III) complex isatin derivatives 1 bearing an -diazoester-terminated N-propyl
catalyst. This catalytic manifold allows a rapid construction of several substituent. The formation of dimeric tetrahydrofuran-bridged
classes of dimeric polycyclic compounds with good yield and high
level of diastereo- and enantioselectivity (up to 99% ee).
products 2 possibly involves intramolecular homologation of
isatin, dyotropic rearrangement,[7] interconversion and formal
Furthermore, in cases of the substrates with other alkyl linkage, the intermolecular [3+2]-cycloaddition. One exception is the
reactions proceeded to give macrocyclic dimers via intermolecular-
homologation process.
generation of ring-expansion product 3 from a naphthalene-ring-
containing isatin derivative via intramolecular homologation.
Moreover, the substrates with two- or four-carbon alkyl tether
between isatin skeleton and  -diazoester unit undergo
intermolecular homologation to deliver macrocyclic products 4.
As molecules consisting of two complex monomeric units with
multiple chiral centers have been found in a number of natural
products,[8] the discovery of novel dyotropic reaction and
dimerization process is supposed to be useful for the rapid and
efficient construction of complex target molecules.
Cascade or domino reactions provided concise and efficient
methods for rapid construction of complex molecules from
simple starting materials.[1] Remarkable progress has been
made in the area of asymmetric organocatalytic cascade or
domino reactions over the past two decades.[1b-f] In addition,
metal-complex-involved processes also attracted considerable
interest, thereof the enantioselective version, in sharp contrast,
was rare.[2] Generally, the nature of the ligands bound to metal
precursors displays an appreciable influence on both the rates
(
slowdown, maintenance, or acceleration) and the selectivities of
the transformations.[3] In consequence, developing single metal
complex catalyst promoted cascade reaction for one-pot
synthesis of complicate compounds with high diastereo- and
enantioselectivity is fascinating but challenging.

-Diazo carbonyl compounds are a type of important
synthons exhibiting rich and unexpected chemistry.[4]
Enantioselective catalytic homologation of ketones and  -
diazoesters has proven efficient to build quaternary carbon
stereocenters, enabling the rapid generation of structural
complexity.[4e,5] The Maruoka group reported the first case of
enantioselective ring expansion of cyclohexanone with  -
diazoester catalyzed by chiral AlMe
3
/BINOL complex.[5a] Later on,
our group utilized chiral N,N'-dioxide-metal Lewis acid catalysts
to accomplish both intermolecular[5b,c] and intramolecular[5d]
homologation reaction of  -diazoesters. We attempted to
combine the intramolecular strategy and key skeleton of isatin to
build polycyclic molecules containing quaternary carbon center
from the simple substrates 1 (Scheme 1, center). In principle,
initiated by the nucleophilic attack of diazo-carbon to either
carbonyl group (path a and path b), various cyclic products (a–d)
could be generated. In fact, unique cascade reactions occurred
Scheme 1. Possible reactions of isatin-derivatives 1 bearing an -diazoester-
terminated N-alkyl substituent.
The length of the tether between isatin skeleton and  -
diazoester unit has a direct influence on the intramolecular
reaction by the ring-size of the reaction intermediate with a
range of conformations, so we initially synthesized the substrate
1
a bearing a three-carbon chain for the reaction (Table 1). A
series of metal salts combined with chiral N,N'-dioxide L-RaPr
was tested (See SI Table S1 for details). Only Sc(OTf) yielded
the compound 2a in 19% yield and 99% ee as the major product
Table 1, entry 1). The structure of 2a was later determined to be
in the presence of a chiral scandium(III) complex of N,N'-
dioxide,[6] affording optically active dimeric polycyclic product 2,
2
3
ring-expansion compound 3 (also as the proposed product a), or
macrocyclic dimer 4 as the major one via several interesting
(
a novel dimeric multiple-ring scaffold with five chiral centers by
X-ray crystallographic analysis.[9] Other metal salts, such as
[*]
F. Tan, Prof. Dr. X. H. Liu, Y. Wang, Dr. S. X. Dong, H. Yu, Prof. Dr.
X. M. Feng
Y(OTf)
3
,
La(OTf)
3
,
Gd(OTf)
3
,
and Yb(OTf)
3
,
led to the
Key Laboratory of Green Chemistry & Technology, Ministry of
Education, College of Chemistry, Sichuan University
Chengdu 610064, China
decomposition of 1a (entry 2). Next, the influence of N,N'-dioxide
ligands was studied. With respect to the amino acid backbone,
E-mail: liuxh@scu.edu.cn; xmfeng@scu.edu.cn
2
the ligand L-PrPr derived from L-proline afforded 2a in 31%
yield and 42:58 d.r., with 95% ee and 8% ee for each
diastereomer (entry 3). L-Pipecolic acid derived N,N'-dioxide L-
Supporting information for this article is given via a link at the end of
the document.
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Angewandte Chemie International Edition
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COMMUNICATION
PiPr
2
produced 2a in 37% yield with an inversion of
diastereomeric control in the reaction (entry 6 versus entry 5).
Finally, investigation of the additives (See SI Table S7 for details)
showed that the addition of benzoic acid or strong base
hampered the generation of 2a (entries 7–8). To our delight, the
diastereoselection and a decrease in enantioselectivity (entry 4).
The product 2a was identified as the isotactic dimer which
contains two precursors with the same configuration, whereas
the other diastereomer 2a' was identified as a syndiotactic dimer
which generated from a pair of enantiomers according to X-ray
addition of 10 mol% of NaBArF
increased the total yield to 97%,
4
and the major isomer 2a was obtained in 80% yield with 99% ee
crystal analysis.[9] Ligand L
bearing a two-carbon tether
(entry 9 versus entry 5). In contrast, using BOX ligand instead of
2
-RaPr
2
sharply improved the yield of 2a with retained ee value, but the
third diastereomer 2a'' emerged at the same time because of the
existence of five contiguous stereocarbon centers in the
products (entry 5 versus entry 1). The total yield reached to 84%
and the optically pure isomer 2a was isolated in 70% yield (entry
L
2
-RaPr
2
led to decomposition of the substrate without
generation of the dimeric product 2a (entry 10). In the absence
of ligand, decomposition of 1a was sluggish and no desired
dimers were detected (entry 11). These results indicated that not
only central metal but also chiral ligand were crucial for the
reactivity. Currently, the origin of this remarkable ligand-
accelerated catalysis[3a] is not fully understood. We hypothesized
Table 1. Optimization of the reaction conditions.
2 2
that the coordination of L -RaPr
to central metal ScIII manifested
in a stronger chiral Lewis acid, as well as a more favorable
interaction and steric effect with 1a.
After establishing the optimized conditions (Table 1, entry 9),
we examined the generality of the reaction (Table 2). Three-
carbon tethered isatin derivatives 1 with variation of the ester
groups of diazoester unit or at the aryl substituent of the isatin
backbone could undergo the enantioselective cascade reaction
Table 2. Scope of ester groups and substituents at the aryl ring of isatin.
Entry[a]
R1
R2
Yield [%][b]
72 (2b)
d.r.[c]
86:14
90:10
92:8
90:10
–[e]
ee [%][d]
>99
99
Entry[a]
Metal salt
Sc(OTf)
Yb(OTf)
Ligand
Yield [%][b]
d.r.[c]
ee [%][d]
1
2
3
4
5
6
7
8
9
Me
H
1
3
L-RaPr
L-RaPr
2
2
19
>19:1[d]
–
>99/–
–
nPr
H
99 (2c)
2
3
–
iPr
H
99 (2d)
>99
>99
>99
–
3
Sc(OTf)
Sc(OTf)
Sc(OTf)
Sc(OTf)
Sc(OTf)
Sc(OTf)
Sc(OTf)
Sc(OTf)
Sc(OTf)
3
3
3
3
3
3
3
3
3
L-PrPr
L-PiPr
2
31
38:62
20:80
–[e]
95/8
61/7
>99/–
>99/31
>99/–
–
Allyl
Benzyl
Cholesteryl
nPr
H
99 (2e)
4
2
37
H
89 (82) (2f)
62 (2g)
5
L
2
L
2
L
2
L
2
L
2
-RaPr
-RaEt
2
84 (70)
H
92:8
89:11
–[e]
6
2
70
54:46
>19:1[d]
–
4-F
5-F
6-F
7-F
5-Cl
5-Br
5-I
74 (2h)
>99
>99
>99
>99
>99
>99
>99
>99
>99
7[f]
8[g]
-RaPr
-RaPr
-RaPr
3
2
2
2
nPr
87 (66) (2i)
77 (71) (2j)
76 (72) (2k)
82 (63) (2l)
82 (74) (2m)
83 (73) (2n)
74 (55) (2o)
72 (51) (2p)
–
nPr
–[e]
9[h]
97 (80)
–[e]
>99/–
–
10
11
12
13
14
15
nPr
–[e]
1 [
0
h]
BOX
–
–
–
–
nPr
–[e]
1 [
1
h]
–
–
nPr
–[e]
[
a] Metal salt (10 mol%) and ligand (10 mol%) was stirred in tetrahydrofuran
0.2 mL) at 30 °C for 0.5 h. After evaporation in vacuo, 1a (0.1 mmol) in
CH Cl (0.05 M) were added at 30 °C, and the catalytic system continued
–[e]
nPr
(
2
2
–[e]
–[e]
nPr
5-Me
5-MeO
stirring at 30 °C for 3 h. [b] Isolated yield, and data in the parentheses related
to the isolated yield of major diastereomer 2a. [c] Determined by 1H NMR
analysis. [d] Determined by HPLC analysis. [e] Mixture of three-pair
nPr
diastereomers, not determined. [f] 20 mol% PhCO
2
H was added. [g] 20 mol%
was added. DMAP 4-
sodium tetrakis[3,5-
DMAP was added. [h] 10 mol% NaBArF
[a] The same conditions as described in footnote [a] and [h] of Table 1. [b-e]
The same with those in footnote [b-e] of Table 1.
4
=
NaBArF
dimethylaminopyridine,
4
=
bis(trifluoromethyl)phenyl]borate.
well to yield the desired dimer 2. It was found that ester groups
5
). Moreover, it was found that the amide units of the ligand also
made a difference, and the less bulky groups at the 2,6-position
of the aniline (L -RaEt ) resulted in both low yield and poor
investigated (1b–1g) had
a
negligible effect on the
enantioselectivity in all cases (≥99% ee), whereas the
2
2
diastereoselection and isolated yield of the major isomers
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COMMUNICATION
depends on substituents of ester. (entries 1-6). Substrate 1b
with methyl ester lowered the yield and diastereoselectivity,
while bulkier esters (1c–1f) gave higher yield and
diastereoselectivity (entries 1-3). Remarkably, substrate 1g with
multiple chiral center contained cholesteryl ester underwent the
reaction smoothly to generate 2g in 62% yield with 92:8 d.r.
enantioselectivity of the dimeric products 2r and 2r' (Scheme 2b).
The relative configuration of minor diastereomer 2r' was
determined from X-ray crystal structure,[9] which is a syndiotactic
dimer generated from a pair of enantiomers of the intermediate.
The substrate 1t containing a four-carbon-unit chain produced a
macrocyclic dimer 4t in a yield of 25% with >99% ee (Scheme
2c), which was later defined to be a scaffold containing two
quinoline-2,4(1H,3H)-dione units linked by two four-carbon
chains via an X-ray crystallography analysis.[9] It was generated
through intermolecular homologation between the 3-carbonly
group of isatin skeleton and the diazoester unit from two
reactants separately, however, the rearrangement sequence is
different from an intermolecular ring-expansion example in our
previous study.[5b] Shortening the length of tether to two-carbon
unit (1s) led to the formation of a new dimer 4s in 11% yield with
98:2 d.r. and 93% ee (Scheme 2d). The structure was similar to
dimer 4t according to 2D-NMR spectral analysis. However,
when the length of carbon-tether further increased, the catalytic
reaction of 1u and 1v became slow and messy. The
aforementioned results imply that the length of of alkyl tethers in
substrates had a considerable effect on the reaction pathway.
Additionally, the carbonyl group of isatin was proved to be
essential, since no reaction occurred when substrate 1w or 1x
was utilized.
(
entry 6). Next, the influence of position and electronic nature of
substituents on the aromatic ring of isatin was evaluated (entries
-15). All the substrates (1h–1k) with a fluoro-substituent at
7
different position of isatin produced the products (2h–2k) with
excellent enantioselectivity (>99% ee), and 5-fluoro-substituted
isatin 1i provided a higher yield (87%), while the others exhibited
better diastereoselectivity (entries 7-10). The electronic property
of the substituents at the C5 position of the isatins (1l–1p)
displayed an obvious impact upon the yield and
diastereoselection (entires 11-15). 5-Chloro-substituted 1l
yielded the dimers with lower diastereoselectivity in comparison
with 5-bromo (1m) and 5-iodo (1n) substituted ones (entries 11-
13). 5-Methyl and 5-methoxyl substituted substrates 1o and 1p
gave lower yield and diastereoselectivity than 5-halo substituted
ones (entries 14-15 vs entries 11-13).
Scheme 2. Scope of the tethers linking isatin and -diazoester and others.
It is noteworthy that the substrate 1q containing
a
naphthalene ring gave a ring-expansion product 3q via the shift
of nitrogen of isatin with 78% yield (Scheme 2a). None of the
ester-shift and the corresponding dimers were detected probably
owing to the steric hindrance. The determination of the structure
and enantioselectivity was confirmed after the transformation
Scheme 3. Proposed cascade process embodied in the formation of dimer 2.
Based on previous studies[5b-d,6] and control experiments,
we propose a cascade process as shown in Scheme 3a (See SI
[
9]
into phenylhydrazine derivative 5q (Scheme 2a) . Nevertheless,
the tethers that connect the isatin and the diazoester units
exhibit a substantial effect on the reaction, which could be
envisioned that the stereo-arrangement, steric hinderance, and
conformation limitation of the ring with different size would affect
the rearrangement (Scheme 2b–2d). Introducing a methyl group
to the middle carbon of the three-carbon-unit tether (1r) did not
affect the reaction process but lowered both the yield and the
for details). When the substrate 1a is mixed with the L
2
-
RaPr /Sc(OTf)
2
3
catalyst,[9] the nucleophilic addition of diazo-
carbon to the carbonyl group of the amide might proceed to yield
the intermediate A. Subsequently, the migration of oxygen or
2
nitrogen with the release of N result in the generation of
intermediate C and D, respectively. Alternatively, the exclusion
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Angewandte Chemie International Edition
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COMMUNICATION
of N
2
, and nucleophilic addition of N-atom of the isatin to the
York, 1998; c) Y. Zhang, J. Wang, Chem. Commun. 2009, 5350; d) S.-
F. Zhu, Q.-L. Zhou, Acc. Chem. Res. 2012, 45, 1365; e) A. Ford, H.
Miel, A. Ring, C. N. Slattery, A. R. Maguire, M. A. McKervey, Chem.
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Chem. Rev. 2016, 116, 2937; g) Y. Xia, D. Qiu, J. Wang, Chem. Rev.
carbene intermediate might generate ylide intermediate B,
followed by a [1,2]-rearrangement to provide intermediate 3a. It
is interesting that a stereospecific dyotropic reaction takes place
from intermediate C or D through highly synchronous symmetry-
allowed mechanism.[7a,b] This pathway allows the formation of
ester or oxygen rearrangement intermediate E or F. Then, an
intramolecular amine attacks the carbonyl group of six-
membered ring in E yields the intermediate G. Finally, aza-ring
breaks to afford the ring-expansion product 6a, which can
interconvert into the precursor Int and tautomer Int' to undergo
formal [3+2] cycloaddition. Thus, the dimeric product 2a and the
related diastereomers are afforded.
2017, 117, 13810.
[
5]
For selected examples, see: a) T. Hashimoto, Y. Naganawa, K.
Maruoka, J. Am. Chem. Soc. 2011, 133, 8834; b) W. Li, X. H. Liu, X. Y.
Hao, Y. F. Cai, L. L. Lin, X. M. Feng, Angew. Chem. Int. Ed. 2012, 51,
8644; Angew. Chem. 2012, 124, 8772; c) W. Li, X. H. Liu, F. Tan, X. Y.
Hao, J. F. Zheng, L. L. Lin, X. M. Feng, Angew. Chem. Int. Ed. 2013, 52,
1
0883; Angew. Chem. 2013, 125, 11083; d) W. Li, F. Tan, X. Y. Hao, G.
Wang, Y. Tang, X. H. Liu, L. L. Lin, X. M. Feng, Angew. Chem. Int. Ed.
015, 54, 1608; Angew. Chem. 2015, 127, 1628.
2
[6]
For selected reviews of N,N′-dioxide ligands, see: a) X. H. Liu, L. L. Lin,
X. M. Feng, Acc. Chem. Res. 2011, 44, 574; b) X. H. Liu, L. L. Lin, X. M.
Feng, Org. Chem. Front. 2014, 1, 298; c) X. H. Liu, H. F. Zheng, Y. Xia,
L. L. Lin, X. M. Feng, Acc. Chem. Res. 2017, 50, 2621; d) X. H. Liu, S.
X. Dong, L. L. Lin, X. M. Feng, Chin. J. Chem. 2018, 36, 791.
We speculated that 6a was the key intermediate which could
undergo dimerization process to form the polycyclic dimer 2a. In
order to prove it, the substrate 7a was synthesized and treated
with mCPBA to give the dimerization product 8a' probably via
intermediate 6a (Scheme 3b). Product 8a' is in accord with the
esterification of the diastereomer 2a' with 3-chlorobenzoic acid.
This result supports the cascade process we proposed above.
In summary, we have developed a mild catalytic system for
the highly chemo- and enantioselective homologation/dyotropic
transformation/[3+2]-cycloaddition of -diazoester-terminated N-
alkyl substituted isatin derivatives. Several classes of polycyclic
compounds were readily obtained in good chemical yield with
high level of stereoselectivity. It also showed that the length of
tether in substrates affected the chemoselectivity. Meanwhile,
chiral Lewis acid catalyst was found to be crucial to the reactivity
and stereoselectivity in the cascade reactions. The utility of the
methodology in the synthesis of relative biologically active
molecules is in progress.
[7]
For selected reviews, see: a) I. Fernández, M. A. Sierra, F. P. Cossío,
Chem. Eur. J. 2006, 12, 6323; b) I. Fernández, F. P. Cossío, M. A.
Sierra, Chem. Rev. 2009, 109, 6687; c) T. Mahmood, M. Arshad, M. A.
Gilani, Z. Iqbal, K. Ayub, J. Mol. Model. 2015, 21, 321; d) C. L.
Hugelshofer, T. Magauer, Nat. Prod. Rep. 2017, 34, 228.
[8]
For selected reviews of dimeric natural products, see: a) T. Voloshchuk,
N. S. Farina, O. R. Wauchope, M. Kiprowska, P. Haberfield, A. Greer, J.
Nat. Prod. 2004, 67, 1141; b) M. Vrettou, A. A. Gray, A. R. E. Brewer, A.
G. M. Barret, Tetrahedron 2007, 63, 1487; c) A. M. Harned, K. A. Volp,
Nat. Prod. Rep. 2011, 28, 1790. For a related example, see: d) K. Chen,
Z.-Z. Zhu, Y.-S. Zhang, X.-Y. Tang, M. Shi, Angew. Chem. Int. Ed.
2
014, 53, 6645; Angew. Chem. 2014, 126, 6763.
CCDC 1836741 (2a), CCDC 1859973 (2a'), CCDC 1836744 (5q),
CCDC 1853772 (2r'), CCDC 1836743 (4t), and CCDC 1836738 (L
RaPr /Sc(OTf) ) contain the supplementary crystallographic data for
[9]
2
-
2
3
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
Acknowledgements
We thank the National Natural Science Foundation of China
(
Nos. 21625205 and 21432006) for financial support.
Keywords: asymmetric catalysis • cascade reaction • chiral
Lewis acid • -diazoester • dyotropic transformation • polycyclic
compound
[
1]
For selected reviews, see: a) L. F. Tietze, G. Brasche, K. Gericke in
Domino Reactions in Organic Synthesis, Wiley-VCH, Weinheim,
Germany, 2006; b) A. M. Walji, D. W. C. MacMillan, Synlett 2007, 1477;
c) H. Pellissier, Chem. Rev. 2013, 113, 442; d) P.-F. Xu, W. Wang in
Catalytic Cascade Reactions, Wiley-VCH, Weinheim, 2013; e) C. M. R.
Volla, I. Atodiresei, M. Rueping, Chem. Rev. 2014, 114, 2390; f) H. B.
Hepburn, L. Dell’Amico, P. Melchiorre, Chem. Rec. 2016, 16, 1787.
For selected examples, see: a) S. Zhu, D. W. C. MacMillan, J. Am.
Chem. Soc. 2012, 134, 10815; b) X. H. Zhao, X. H. Liu, H. J. Mei, J.
Guo, L. L. Lin, X. M. Feng, Angew. Chem. Int. Ed. 2015, 54, 4032;
Angew. Chem. 2015, 127, 4104; c) C. R. Jamison, J. J. Badillo, J. M.
Lipshultz, R. J. Comito, D. W. C. MacMillan, Nat. Chem. 2017, 9, 1165.
For a review of ligand-accelerated catalysis, see: a) D. J. Berrisford, C.
Bolm, K. B. Sharpless, Angew. Chem. Int. Ed. 1995, 34, 1059; Angew.
Chem. 1995, 107, 1159. For selected reviews related to reversal of
diastereoselectivity by ligands, see: b) M. Bihani, J. C. G. Zhao, Adv.
Synth. Catal. 2017, 359, 534. c) L. L. Lin, X. M. Feng, Chem. Eur. J.
[
2]
3]
[
2
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018, 118, 5080.
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4, 1091; b) M. P. Doyle, M. A. Mckervey, T. Ye in Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds, Wiley, New
9
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COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
F. Tan, X. H. Liu,* Y. Wang, S. X. Dong,
H. Yu, X. M. Feng*
Page No. – Page No.
Chiral Lewis Acid Catalyzed
Reactions of -Diazoester
Derivatives: Construction of Dimeric
Polycyclic Compounds
A highly chemo- and enantioselective homologation/dyotropic transformation/
interconversion/[3+2]-cycloaddition cascade process of  -diazoester-terminated
isatin derivatives with a three-carbon tether was achieved. Dimeric polycyclic
compounds containing multiple quaternary carbon centers were synthesized in one-
pot assisted by chiral N,N’-dioxide-Sc(III) complex catalyst. Other intermolecular
homologation occurred to give macrocyclic dimers from the related substrates with
two- or four-carbon tether.
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