Enantioselective Rhodium-Catalyzed Allylation of Aliphatic Imines: Synthesis of Chiral C Aliphatic Homoallylic Amines

Article abstract of DOI:10.1021/acs.orglett.0c02069

Reported herein is a method for the efficient syntheses of optically active 1-alkyl homoallylic amines in yields up to 95%, 13.5:1 dr, and 98% ee under mild, aqueous reaction conditions, via the Rh-catalyzed asymmetric allylation of aliphatic aldimines. This method provides a streamlined synthetic platform for the preparation of indolizidine and piperidine alkaloids, thus demonstrating its usefulness.

Full text of DOI:10.1021/acs.orglett.0c02069

pubs.acs.org/OrgLett
Letter
Enantioselective Rhodium-Catalyzed Allylation of Aliphatic Imines:
Synthesis of Chiral C‑Aliphatic Homoallylic Amines
Wei-Sian Li, Ting-Shen Kuo, Meng-Chi Hsieh, Ming-Kang Tsai, Ping-Yu Wu, and Hsyueh-Liang Wu*
Cite This: https://dx.doi.org/10.1021/acs.orglett.0c02069
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Reported herein is a method for the efficient
syntheses of optically active 1-alkyl homoallylic amines in yields up
to 95%, 13.5:1 dr, and 98% ee under mild, aqueous reaction
conditions, via the Rh-catalyzed asymmetric allylation of aliphatic
aldimines. This method provides a streamlined synthetic platform
for the preparation of indolizidine and piperidine alkaloids, thus
demonstrating its usefulness.
ince it was introduced by Tomioka1a and Hayashi,1b the
Srhodium-catalyzed asymmetric addition of organoboron
reagents2,3 to aldimines has proven to be a trustworthy route to
chiral α-branched amines.3−8 Aliphatic aldimines, compared to
their aryl counterparts, have remained underexploited,
primarily hampered by their intrinsically lower stability, their
susceptibility to decomposition, self-condensation, and imine−
enamine tautomerization. An advantage of these rhodium-
catalyzed protocols is the mild reaction conditions,5 which
permit the arylation of challenging aliphatic aldimines
employing an (R,R)-Deguphos,6a a chiral diene,6b and chiral
bis(phosphoramidite) ligands (Scheme 1).6c Alkenyl boron
reagents have also been found to be compatible prenucleo-
philes in the diastereoselective7a,b and enantioselective7c
alkenylation of aliphatic aldimines. While these approaches
are known to produce enantioenriched 1-aryl and 1-alkenyl
alkylamines, similar allylation reactions to afford the corre-
sponding homoallylic amines8,9 remain unexplored.10,11 Hence,
developing the enantioselective allylation of aliphatic aldimines
would be highly desirable to address this deficiency. We report
herein on the first asymmetric allylation of aliphatic aldimines
in the presence of rhodium/chiral bicyclo[2.2.1]heptadiene
catalysts12,13 to afford optically active C-aliphatic homoallylic
amines and its use in the total syntheses of natural indolizidine
and piperidine alkaloids.
We first examined the asymmetric addition of potassium
allyltrifluoroborate (2a) with the Ts-protected aldimine 1a in
the presence of 3 mol % of a catalyst generated in situ from
[RhCl(C2H4)2]2 and the chiral diene ligand L1 (Table 1). The
desired adduct 3aa was obtained in 18% yield with 88% ee in
dioxane at 60 °C when no H2O was added (entry 1),13 with
the formation of the α,β-unsaturated imine 4a, derived from
the self-condensation of 1a, and 4a-degradation accounting for
the low product yield. While adding molecular sieves failed to
improve the yield (entry 2),6a adding H2O mitigated the
formation of 4a, with 3aa being produced in up to 96% yield
and 93% ee (entries 3 and 4). Among various solvents, THF
(entry 6) was found to be optimal (entries 4−8) and was used
in further investigations due to its comparatively low toxicity.14
Using L2, an optimal ligand for the alkenylation of aryl
aldimines,4c 3aa was produced in only 29% yield with 70% ee
(entry 9), but using L3, a well-known ligand for the arylation1j
and allyation13 of aryl aldimines, 3aa was produced in 95%
Scheme 1. Rh-Catalyzed Asymmetric Addition of
Organoboron Reagents to Imines
Received: June 23, 2020
https://dx.doi.org/10.1021/acs.orglett.0c02069
© XXXX American Chemical Society
Org. Lett. XXXX, XXX, XXX−XXX
A

Organic Letters
pubs.acs.org/OrgLett
Letter
a
a
Table 1. Optimization for Asymmetric Allylation of 1a
Scheme 2. Substrate Scope (I)
entry
variation from above conditions
yield (%)
ee (%)
b
1
none
18
36
86
96
85
95
92
83
29
95
27
88
89
92
93
92
92
92
90
70
92
−92
2
3
4
5
6
7
8
9
10
11
12
13
14
15
MS 4 Å (100 wt %) was added
H2O (1.0 equiv) was added
H2O (2.0 equiv) was added
Toluene instead of dioxane, 6.5 h
THF instead of dioxane, 3 h
DME instead of dioxane, 3 h
CH3CN instead of dioxane, 1.5 h
L2 instead of L1 in THF, 6 h
L3 instead of L1 in THF, 3 h
L4 instead of L1 in THF, 15 h
L5 instead of L1 in THF, 15 h
L6 instead of L1 in THF, 15 h
2b instead of 2a, 17 h
c
d
a
N.R.
N.R.
23
55
N.D.
N.D.
84
88
Conditions: 1 (P = Ts) and 5 (P = Ns, 4-NO2-C6H4SO2) (0.2
mmol), 2a (0.4 mmol), [RhCl(C2H4)2]2 (1.5 mol %), L1 (3.6 mol
%), H2O (2.0 equiv) in THF (1 mL) at 60 °C.
c
d
2c instead of 2a, 3 h
a
Conditions: compound 1a (0.2 mmol), 2a (0.4 mmol), [RhCl-
nitrophenylsulfonyl) group were tolerated, providing 6ca and
6ea in 60% and 61% yields with 83% and 96% ee, respectively.
In subsequent experiments, the addition reaction of
potassium (E)-crotyl trifluoroborate ((E)-2d) with 1a was
examined (Scheme 3). The adducts were isolated in a
combined yield of 91% with a 4.5/1 (syn-7ad/anti-8ad)
diastereomeric ratio, and the major isomer syn-7ad was
obtained in 95% ee. Conducting this reaction at 40 °C slightly
enhanced the dr to 5.2/1, though in a lower yield (51%),
without losing high enantioselectivity (94% ee). The
crotylation of various aliphatic aldimines furnished the
corresponding adducts in 44−87% yields with dr ranging
from 5.0/1 to 13.5/1 and with 85−98% ee. The absolute
configuration of the adduct syn-7qd was unambiguously
determined by an X-ray crystallographic analysis to be (3R,
4R). Similarly, high enantioselectivity was observed in the
allylation of (E)-2e, giving the syn-7ke in 97% ee. When (Z)-
2d and ( )-2f were used in the crotylation reaction of 1a at 60
°C, syn-7ad was produced as the major isomer (syn-7ad/anti-
8ad 1.5/1 and 2.8/1; 92% and 94% ee, respectively). The
reaction conducted at 40 °C using (Z)-2d afforded the anti-
8ad (7ad/8ad 1/2.2) in 19% yield with 92% ee, whereas major
syn-7ad was obtained (7ad/8ad 3.2/1) in 37% yield with 96%
ee utilizing ( )-2f. Moreover, potassium allyl trifluoroborate
2g underwent allylation with 1a to give 7ag in 52% yield and
94% ee.16
(C2H4)2]2 (1.5 mol %), L (3.6 mol %) in dioxane (1 mL). Isolated
yields of 3aa are reported. The ee values of 3aa were determined by
chiral HPLC analysis. 5% of 4a was isolated. No reaction. Not
b
c
d
determined.
yield and 92% ee (entry 10). The use of the bicyclo[2.2.2]-
octadiene ligand L4 gave 3aa with −92% ee, but in only 27%
yield (entry 11). In contrast, no reaction occurred in the cases
of the bicyclo[3.3.0]octadiene ligand L5 (entry 12) and (S)-
BINAP (L6) (entry 13), indicating the critical nature of the
catalytic activity and enantioselectivity of diene ligands in this
transformation. Furthermore, using 2b and 2c,15 sodium and
cesium analogs of 2a afforded 3aa in only 23% yield with 84%
ee and 55% yield with 88% ee, respectively (entries 14 and 15).
Based on these optimal conditions, the scope of the reaction in
THF with respect to aldimines was further examined (Scheme
2).
Aldimines prepared from ethanal, propanal, butanal, and
hexanal afforded 3ba−3ea in 56−90% yields and 90−95% ee.
Although α-branched aldimines were unfavorable reaction
partners, providing the adducts 3fa and 3ga both in 65% yield
with 81% ee and 63% ee, respectively, β-branched congeners
were compatibly producing adducts 3ha and 3ia in 94% and
91% yields with 90% and 86% ee. This high asymmetric
induction is not limited to simple linear aliphatic aldimines
containing no functionalities; substrates adorned with various
functional groups on the aliphatic chain ranging from an
aromatic ring, a benzyloxy group, a chloride, a phthalimido
group, and an olefin also smoothly underwent allylation,
providing 3ja−3ra in 51−92% yields with 91−96% ee. No
erosion of catalytic activity or enantioselectivity was observed
when the reaction was carried out on a larger scale (for
products 3ka, 3na, and 3oa). Substrates bearing an Ns (4-
Syntheses of naturally occurring alkaloids were performed to
demonstrate the synthetic applications of this protocol
(Schemes 4−7). When the Ts-protected homoallylic amine
3na was treated with (Boc)2O and Mg, it was smoothly
transformed into the corresponding Boc-protected product 9,
which, on one-pot catalytic hydrogenation and hydrogenolysis,
gave the amino alcohol 10 in high yield. The ensuing
sequential steps involving mesylation and base mediated N-
B
https://dx.doi.org/10.1021/acs.orglett.0c02069
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
a
which was produced in 91% yield from the catalytic
hydrogenolysis of 13, involving mesylate formation, Boc
deprotection, cyclization, and acidification with methanolic
HCl, supplied (R)-coniceine·HCl in 76% yield (Scheme 5).18
Scheme 3. Substrate Scope (II)
Scheme 5. Asymmetric Synthesis (R)-Coniceine·HCl
The oxidation of 14 using PCC gave the corresponding
aldehyde 15, which was utilized in the straightforward
synthesis of (−)-indolizidine 167B (Scheme 6). Treating 15
Scheme 6. Asymmetric Synthesis and Formal Synthesis of
(−)-Indolizidine 167B
with propyl magnesium bromide provided the corresponding
alcohol in 86% yield, and a subsequent PCC oxidation
furnished 16 in 92% yield. The final operations, involving the
removal of the Boc protecting group, cyclizing reductive
amination, and acidification, gave the hydrochloride salt of
(−)-indolizidine 167B in 75% yield.19 The synthetic
significance of 15 was also demonstrated in the facile
preparation of 18 for the formal syntheses of indolizidine
alkaloids (−)-167B20 and (−)-209D.21 The Pinnick oxidation
of 15 produced the corresponding acid 17 in 78% yield, and
subsequent sequential reactions involving Boc deprotection
and amide formation gave 18 in 53% yield.
a
Reaction conditions: 1 (0.2 mmol), 2 (0.4 mmol), [RhCl(C2H4)2]2
(1.5 mol %), L1 (3.6 mol %), H2O (7.2 μL) in THF (1 mL) at 60 °C.
The ratio of 7 and 8 was determined by 1H NMR analysis. The
combined isolated yield of 7 and 8 is reported. The ee of the major
diastereomer was determined by HPLC analysis.
Scheme 4. Asymmetric Synthesis (S)-Coniine·HCl
In a two-step operation, 3oa was readily converted into the
Boc-protected amine 19, which, after base-mediated cycliza-
tion, gave 20 in 76% yield. The Tsuji−Wacker oxidation of 20
gave the corresponding ketone in 81% yield, and the Boc
protecting group was then removed by treatment with TFA to
afford (−)-pelletierine in 93% yield (Scheme 7).22
In summary, a quest for the straightforward synthesis of
optically active C-aliphatic homoallylic amines led us to
develop the first successful Rh(I)-catalyzed allylation of
aliphatic aldimines, employing a catalyst in situ generated
from the chiral diene ligand L1. The asymmetric addition of
various potassium allyltrifluoroborates with assorted aliphatic
aldimines furnished the corresponding enantioenriched homo-
allylic amines in up to 13.5:1 dr, 95% yield, and 98% ee.
Notably, the major diastereomers with (3R,4R)-configuration
cyclization provided the piperidine 11 in 62% yield from 10.
Removal of the Boc group under acidic conditions afforded the
hydrochloride salt of (S)-coniine in 96% yield (Scheme 4).17
In the preparation of (R)-coniceine, the hydroboration and
oxidation of 9 furnished the alcohol 12 in 74% yield, and the
subsequent cyclization by the stepwise treatment with
methanesulfonyl chloride and NaH afforded 13 in 89% yield
in two steps. Finally, the sequential transformations of 14,
C
https://dx.doi.org/10.1021/acs.orglett.0c02069
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Scheme 7. Asymmetric Synthesis of (−)-Pelletierine
REFERENCES
■
(1) For selected examples of rhodium-catalyzed enantioselective 1,2-
arylation of aryl imines, see: (a) Kuriyama, M.; Soeta, T.; Hao, X.;
Chen, Q.; Tomioka, K. J. Am. Chem. Soc. 2004, 126, 8128.
(b) Tokunaga, N.; Otomaru, Y.; Okamoto, K.; Ueyama, K.;
Shintani, R.; Hayashi, T. J. Am. Chem. Soc. 2004, 126, 13584.
(c) Weix, D. J.; Shi, Y.; Ellman, J. A. J. Am. Chem. Soc. 2005, 127,
1092. (d) Duan, H.-F.; Jia, Y.-X.; Wang, L.-X.; Zhou, Q.-L. Org. Lett.
2006, 8, 2567. (e) Wang, Z.-Q.; Feng, C.-G.; Xu, M.-H.; Lin, G.-Q. J.
Am. Chem. Soc. 2007, 129, 5336. (f) Okamoto, K.; Hayashi, T.; Rawal,
V. H. Chem. Commun. 2009, 4815. (g) Nishimura, T.; Noishiki, A.;
Tsui, C.; Hayashi, T. J. Am. Chem. Soc. 2012, 134, 5056.
(h) Nishimura, T.; Noishiki, A.; Ebe, Y.; Hayashi, T. Angew. Chem.,
Int. Ed. 2013, 52, 1777. (i) Wang, H.; Jiang, T.; Xu, M.-H. J. Am.
Chem. Soc. 2013, 135, 971. (j) Chen, C.-C.; Gopula, B.; Syu, J.-F.;
Pan, J.-H.; Kuo, T.-S.; Wu, P.-Y.; Henschke, J. P.; Wu, H.-L. J. Org.
Chem. 2014, 79, 8077. (k) Wang, H.; Li, Y.; Xu, M.-H. Org. Lett.
2014, 16, 3962. (l) Jiang, T.; Chen, W.-W.; Xu, M.-H. Org. Lett. 2017,
19, 2138. (m) Syu, J.-F.; Lin, H.-Y.; Cheng, Y.-Y.; Tsai, Y.-C.; Ting,
Y.-C.; Kuo, T.-S.; Janmanchi, D.; Wu, P.-Y.; Henschke, J. P.; Wu, H.-
L. Chem. - Eur. J. 2017, 23, 14515. (n) Shan, H.; Zhou, Q.; Yu, J.;
Zhang, S.; Hong, X.; Lin, X. J. Org. Chem. 2018, 83, 11873.
were obtained when using (Z)-2d and ( )-2c at 60 °C. The
syntheses of (S)-coniine·HCl, (R)-coniceine·HCl, (−)-indoli-
zidine 167B, and (−)-pelletierine clearly demonstrate the
applicability of this approach.
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c02069.
(2) For seminal reviews, see: (a) Fagnou, K.; Lautens, M. Chem. Rev.
2003, 103, 169. (b) Marques, C. S.; Burke, A. ChemCatChem 2011, 3,
635. (c) Tian, P.; Dong, H.-Q.; Lin, G.-Q. ACS Catal. 2012, 2, 95.
(3) Chiral Amine Synthesis: Methods, Developments and Applications;
Nugent, T. C., Ed.; Wiley-VCH: Weinheim, Germany, 2010.
Experimental procedures, complete characterization
data, HPLC chromatograms, and NMR spectra (PDF)
Accession Codes
(4) For rhodium-catalyzed 1,2-alkenylation of aryl imines, see:
(a) Shintani, R.; Takeda, M.; Soh, Y.-T.; Ito, T.; Hayashi, T. Org. Lett.
2011, 13, 2977. (b) Luo, Y.; Carnell, A. J.; Lam, H. W. Angew. Chem.,
Int. Ed. 2012, 51, 6762. (c) Gopula, B.; Chiang, C.-W.; Lee, W.-Z.;
Kuo, T.-S.; Wu, P.-Y.; Henschke, J. P.; Wu, H.-L. Org. Lett. 2014, 16,
632. (d) Cui, Z.; Chen, Y.- J.; Gao, W.-Y.; Feng, C.-G.; Lin, G.-Q. Org.
Lett. 2014, 16, 1016. (e) Gopula, B.; Zeng, H.-W.; Wu, P.-Y.;
Henschke, J. P.; Wu, H.-L. J. Chin. Chem. Soc. 2018, 65, 312.
CCDC 1995023 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.
AUTHOR INFORMATION
Corresponding Author
(5) For seminal reviews, see: (a) Hayashi, T.; Yamasaki, K. Chem.
Rev. 2003, 103, 2829. (b) Johnson, J. B.; Rovis, T. Angew. Chem., Int.
̈
Ed. 2008, 47, 840. (c) Defieber, C.; Grutzmacher, H.; Carreira, E. M.
■
Hsyueh-Liang Wu − Department of Chemistry, National
Taiwan Normal University, Taipei 11677, Taiwan;
orcid.org/0000-0001-7462-8536; Email: hlw@
ntnu.edu.tw
Angew. Chem., Int. Ed. 2008, 47, 4482. (d) Edwards, H. J.; Hargrave, J.
D.; Penrose, S. D.; Frost, C. G. Chem. Soc. Rev. 2010, 39, 2093.
(6) For rhodium-catalyzed arylation of aliphatic imines, see:
(a) Trincado, M.; Ellman, J. A. Angew. Chem., Int. Ed. 2008, 47,
5623. (b) Cui, Z.; Yu, H.-J.; Yang, R.- F.; Gao, W.-Y.; Feng, C.-G.;
Lin, G.-Q. J. Am. Chem. Soc. 2011, 133, 12394. (c) Kato, N.; Shirai,
T.; Yamamoto, Y. Chem. - Eur. J. 2016, 22, 7739.
(7) For diastereoselective rhodium-catalyzed alkenylation of
aliphatic imines, see: (a) Brak, K.; Ellman, J. A. J. Am. Chem. Soc.
2009, 131, 3850. (b) Brak, K.; Ellman, J. A. J. J. Org. Chem. 2010, 75,
3147. For the enantioselective version, see: (c) Qian, X.-W.; Xue, Z.-
J.; Zhao, Q.; Cui, Z.; Chen, Y.-J.; Feng, C.-G.; Lin, G.-Q. Org. Lett.
2017, 19, 5601.
(8) For rhodium-catalyzed allylation of cyclic sulfamate imines, see:
(a) Luo, Y.; Hepburn, H. B.; Chotsaeng, N.; Lam, H. M. Angew.
Chem., Int. Ed. 2012, 51, 8309. (b) Hepburn, H. B.; Chotsaeng, N.;
Luo, Y.; Lam, H. M. Synthesis 2013, 45, 2649. (c) Hepburn, H. B.;
Lam, H. M. Angew. Chem., Int. Ed. 2014, 53, 11605. (d) Martínez, J.
I.; Smith, J. J.; Hepburn, H. B.; Lam, H. M. Angew. Chem., Int. Ed.
2016, 55, 1108.
(9) For a seminal review, see: (a) Puentes, C. O.; Kouznetsov, V. J. J.
Heterocycl. Chem. 2002, 39, 595. (b) Ciufolini, M. A.; Hermann, C.
W.; Whitmire, K. H.; Byrne, N. E. J. Am. Chem. Soc. 1989, 111, 3473.
(c) Kim, G.; Chu-Moyer, M. Y.; Danishefsky, S. J. J. Am. Chem. Soc.
1990, 112, 2003. (d) Nicolaou, K. C.; Mitchell, H. J.; van Delft, F. L.;
Rubsam, F.; Rodriguez, R. M. Angew. Chem., Int. Ed. 1998, 37, 1871.
(e) Felpin, F.-X.; Girard, S.; Vo-Thanh, G. R.; Robins, J.; Villieras, J.;
Lebreton, J. J. Org. Chem. 2001, 66, 6305.
Authors
Wei-Sian Li − Department of Chemistry, National Taiwan
Normal University, Taipei 11677, Taiwan
Ting-Shen Kuo − Department of Chemistry, National Taiwan
Normal University, Taipei 11677, Taiwan
Meng-Chi Hsieh − Department of Chemistry, National Taiwan
Normal University, Taipei 11677, Taiwan
Ming-Kang Tsai − Department of Chemistry, National Taiwan
Normal University, Taipei 11677, Taiwan; orcid.org/0000-
0001-9189-5572
Ping-Yu Wu − Oleader Technologies, Co., Ltd., Hsinchu 30345,
Taiwan
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c02069
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the Ministry of Science and
Technology of the Republic of China (104-2628-M-003-001-
MY3 and 107-2113-M-003-014-MY3) is gratefully acknowl-
edged.
(10) For diastereoselective allylation of aliphatic imines, see:
(a) Foubelo, F.; Yus, M. Tetrahedron: Asymmetry 2004, 15, 3823.
(b) Li, S.-W.; Batey, R. A. Chem. Commun. 2004, 1382. (c) Bertrand,
D
https://dx.doi.org/10.1021/acs.orglett.0c02069
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
M. B.; Wolfe, J. P. Org. Lett. 2006, 8, 2353. (d) Sun, X.-W.; Xu, M.-H.;
Lin, G.-Q. Org. Lett. 2006, 8, 4979. (e) Reddy, L. R.; Hu, B.; Prashad,
M.; Prasad, K. Org. Lett. 2008, 10, 3109. (f) Nishikawa, Y.; Kitajima,
M.; Kogure, N.; Takayama, H. Tetrahedron 2009, 65, 1608.
(g) Vilaivan, T.; Winotapan, C.; Banphavichit, V.; Shinada, T.;
Ohfune, Y. J. Org. Chem. 2005, 70, 3464. (h) Cook, G. R.; Maity, B.
C.; Kargbo, R. Org. Lett. 2004, 6, 1741. (i) Balasubramanian, N.;
Mandal, T.; Cook, G. R. Org. Lett. 2015, 17, 314. For enantioselective
allylation of aliphatic aldimines, see: (j) Lou, S.; Moquist, P. N.;
Schaus, S. E. J. Am. Chem. Soc. 2007, 129, 15398. (k) Vieira, E. M.;
Snapper, M. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2011, 133, 3332.
(l) Shikora, J. M.; Chemler, S. R. Org. Lett. 2018, 20, 2133. (m) Liu,
J.; Cao, C.-G.; Sun, H.-B.; Zhang, X.; Niu, D. J. Am. Chem. Soc. 2016,
138, 13103. (n) Wei, L.; Zhu, Q.; Xiao, L.; Tao, H.-Y.; Wang, C.-J.
Nat. Commun. 2019, 10, 1.
(11) For seminal reviews on transition-metal-catalyzed allylation of
imines, see: (a) Yamamoto, Y.; Asao, N. Chem. Rev. 1993, 93, 2207.
(b) Ellman, J. A.; Owens, T. D.; Tang, T. P. Acc. Chem. Res. 2002, 35,
984. (c) Robak, M. T.; Herbage, M. A.; Ellman, J. A. Chem. Rev. 2010,
110, 3600. (d) Kennedy, J. W. J.; Hall, D. G. Angew. Chem., Int. Ed.
2003, 42, 4732. (e) Friestad, G. K.; Ding, H. Synthesis 2005, 2005,
2815. (f) Friestad, G. K.; Mathies, A. K. Tetrahedron 2007, 63, 2541.
(g) Kobayashi, S.; Mori, Y.; Fossey, J. S.; Salter, M. M. Chem. Rev.
́
́
2011, 111, 2626. (h) Yus, M.; Gonzalez-Gomez, J. C.; Foubelo, F.
Chem. Rev. 2011, 111, 7774. (i) Huo, H.-X.; Duvall, J. R.; Huang, M.-
Y.; Hong, R. Org. Chem. Front. 2014, 1, 303.
(12) (a) Wei, W.-T.; Yeh, J.-Y.; Kuo, T.-S.; Wu, H.-L. Chem. - Eur. J.
2011, 17, 11405. (b) Huang, K.-C.; Gopula, B.; Kuo, T.-S.; Chiang,
C.-W.; Wu, P.-Y.; Henschke, J. P.; Wu, H.-L. Org. Lett. 2013, 15,
5730. (c) Gopula, B.; Tsai, Y.-F.; Kuo, T.-S.; Wu, P.-Y.; Henschke, J.
P.; Wu, H.-L. Org. Lett. 2015, 17, 1142. (d) Gopula, B.; Yang, S.-H.;
Kuo, T.-S.; Hsieh, J.-C.; Wu, P.-Y.; Henschke, J. P.; Wu, H.-L. Chem. -
Eur. J. 2015, 21, 11050. (e) Fang, J.-H.; Jian, J.-H.; Chang, H.-C.;
Kuo, T.-S.; Lee, W.-Z.; Wu, P.-Y.; Wu, H.-L. Chem. - Eur. J. 2017, 23,
1830. (f) Jian, J.-H.; Hsu, C.-L.; Syu, J.-F.; Kuo, T.-S.; Wu, P.-Y.; Wu,
H.-L. J. Org. Chem. 2018, 83, 12184. (g) Jian, J.-H.; Zeng, H.-W.; Kuo,
T.-S.; Wu, P.-Y.; Wu, H.-L. Org. Lett. 2019, 21, 9468. (h) Chang, C.-
A.; Uang, T.-Y.; Jian, J.-H.; Zhou, M.-Y.; Chen, M.-L.; Kuo, T.-S.; Wu,
P.-Y.; Wu, H.-L. Adv. Synth. Catal. 2018, 360, 3381.
(13) Chiang, P.-F.; Li, W.-S.; Jian, J.-H.; Kuo, T.-S.; Wu, P.-Y.; Wu,
H.-L. Org. Lett. 2018, 20, 158.
(14) (a) See: International Conference on Harmonisation (ICH).
Guideline Q3C (R5): Impurities: Guideline for Residual Solvents;
ICH: Geneva, 2011. (b) Laird, T. Org. Process Res. Dev. 2012, 16, 1.
(15) Amatore, C.; Jutand, A.; Le Duc, G. Chem. - Eur. J. 2012, 18,
6616.
(16) For the discussion of resulting stereochemical outcomes, please
see Supporting Information.
(17) [α]2D1 +9.3 (c 0.3, EtOH). For comparison, see: Kondekar, N.
B.; Kumar, P. Synthesis 2010, 2010, 3105. [α]2D5 −8.6 (c 0.25, EtOH)
for R-isomer.
(18) [α]2D1 −1.2 (c 1.0, EtOH). For comparison, see: Zill, N.;
Schoenfelder, A.; Girard, N.; Taddei, M.; Mann, A. J. Org. Chem.
2012, 77, 2246. [α]2D0 −1.5 (c 1.0, EtOH).
(19) [α]2D1 −98.3 (c 1.0, CH2Cl2). For comparison, see: Roa, L. F.;
Gnecco, D.; Galindo, A.; Teran, J. L. Tetrahedron: Asymmetry 2004,
15, 3393. [α]2D0 +107.4 (c 1.0, CH2Cl2) for the enantiomeric isomer.
(20) Pinho, V. D.; Burtoloso, A. C. B. Tetrahedron Lett. 2012, 53,
876.
(21) Nukui, S.; Sodeoka, M.; Sasai, H.; Shibasaki, M. J. Org. Chem.
1995, 60, 398.
(22) [α]2D2 −24.3 (c 1.0, EtOH). For comparison, see: Takahata, H.;
Kubota, M.; Takahashi, S.; Momose, T. Tetrahedron: Asymmetry
1996, 7, 3047. [α]2D5 −22.1 (c 4.1, EtOH)
E
https://dx.doi.org/10.1021/acs.orglett.0c02069
Org. Lett. XXXX, XXX, XXX−XXX