Switchable Synthesis of Z-Homoallylic Boronates and E-Allylic Boronates by Enantioselective Copper-Catalyzed 1,6-Boration

Article abstract of DOI:10.1002/chem.201801804

The enantioselective Cu-catalyzed 1,6-boration of (E,E)-α,β,γ,δ-unsaturated ketones is described, which gives homoallylic boronates with high enantiomeric purity and unexpectedly high Z-selectivity. By changing the solvent, the outcome can be altered to give E-allylic boronates.

Full text of DOI:10.1002/chem.201801804

A Journal of
Accepted Article
Title: Switchable Synthesis of Z-Homoallylic Boronates and E-Allylic
Boronates by Enantioselective Copper-Catalyzed 1,6-Boration
Authors: Yunfei Luo, Steven M Wales, Stamatis E Korkis, Iain D Roy,
William Lewis, and Hon Wai Lam
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201801804
Link to VoR: http://dx.doi.org/10.1002/chem.201801804
Supported by

10.1002/chem.201801804
Chemistry - A European Journal
COMMUNICATION
Switchable Synthesis of Z-Homoallylic Boronates and E-Allylic
Boronates by Enantioselective Copper-Catalyzed 1,6-Boration
Yunfei Luo, Steven M. Wales, Stamatis E. Korkis, Iain. D. Roy, William Lewis, and Hon Wai Lam*
Abstract: The enantioselective Cu-catalyzed 1,6-boration of (E,E)-
α,β,γ,δ-unsaturated ketones is described, which gives homoallylic
boronates with high enantiomeric purity and unexpectedly high Z-
selectivity. By changing the solvent, the outcome can be altered to
give E-allylic boronates.
acyclic α,β,γ,δ-unsaturated esters and ketones that give
products of type A [(E)-γ,δ].[8b] The ability to access products of
type B and D would also be advantageous to open up additional
avenues for post-boration manipulation. However, to our
knowledge, 1,6-borations of this type are hitherto unknown,
which
is
perhaps
unsurprising
as
they
contain
thermodynamically less-stable Z-alkenes.[10,11] Compared with E-
alkenes, there are fewer effective methods for the highly
stereoselective synthesis of Z-alkenes,[12] and new reactions that
address this issue are therefore valuable.
Herein, we describe enantioselective copper-catalyzed 1,6-
borations of acyclic α,β,γ,δ-unsaturated ketones that give
homoallylic boronates of type D. In addition to containing α-
stereogenic alkyl pinacolboronates, the products possess Z-
conjugated enones with high stereoselectivities. The complete E
to Z isomerization of the alkene next to the ketone is highly
unusual. Furthermore, the outcome of the reaction can be
switched to give E-allylic boronates of type A simply by changing
the reaction solvents and concentration.[13]
During our studies of enantioselective copper-catalyzed 1,6-
borations that give E-allylic boronates of type A,[8b] we
discovered that α,β,γ,δ-unsaturated ketones with a quaternary
center adjacent to the carbonyl group unexpectedly gave
significant quantities of Z-homoallylic boronates of type D. For
example, reaction of α,β,γ,δ-unsaturated ketone 1a (Table 1)
with B2(pin)2 (1.2 equiv) in THF (0.1 M) in the presence of
CuF(PPh3)3·2MeOH (0.20 mol%), Josiphos SL-J001-1 (L1, 0.24
mol%), and iPrOH (2.0 equiv) at room temperature for 15 h, a
1:1 mixture of Z-homoallylic boronate 2a and E-allylic boronate
3a was obtained (entry 1). Interestingly, increasing the quantity
of iPrOH changed the outcome to favor 3a (entry 2). Although
other solvents such as EtOH and cyclohexane did not provide
high selectivities in favor of either product (entries 3 and 4), a
Enantiomerically enriched α-stereogenic alkylboron compounds
have numerous applications in organic synthesis.[ 1 – 3 ] One
important route to these compounds is the catalytic
enantioselective boration of electron-deficient alkenes.[ 4 – 7 ]
Although numerous examples of 1,4-boration are known,[4–7]
only a few examples of 1,6-boration have been described.[8,9]
Aside from promoting 1,6-boration over competing 1,4-boration,
the 1,6-boration of electron-deficient conjugated dienes has the
potential to give four products which differ in the position and/or
the E/Z geometry of the remaining alkene (Scheme 1).
Controlling the selectivity to obtain only one product, especially
for fully acyclic substrates, presents a considerable challenge.
Kobayashi and co-workers have developed Cu(II)-catalyzed
1,6-borations of β,β-disubstituted α,β,γ,δ-unsaturated cyclic
ketones that give products of type C [(E)-α,β],[8a] whereas we
have described enantioselective Cu(I)-catalyzed 1,6-borations of
Scheme 1. Possible products from boration of an α,β,γ,δ-unsaturated carbonyl
compound.
Table 1: Investigation of reaction conditions for the 1,6-boration of 1a.[a]
[]
Dr. Y. Luo, Dr. S. M. Wales, Dr. S. E. Korkis, Dr. W. Lewis, Prof. H.
W. Lam
School of Chemistry, University of Nottingham
University Park, Nottingham, NG7 2RD (UK)
E-mail: hon.lam@nottingham.ac.uk
Homepage: http://www.nottingham.ac.uk/~pczhl/
Dr. S. M. Wales, Dr. S. E. Korkis, Prof. H. W. Lam
The GlaxoSmithKline Carbon Neutral Laboratories for Sustainable
Chemistry, University of Nottingham, Jubilee Campus, Triumph
Road, Nottingham, NG7 2TU (UK)
Entry
Solvent(s)
Concentration (M)
2a:3a[b]
1:1
1
2
3
4
5
6
7
8
THF
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.04
Dr. Y. Luo, Dr. I. D. Roy, Prof. H. W. Lam
iPrOH/THF (1:1)
EtOH
1:14
1:1
EaStCHEM, School of Chemistry, University of Edinburgh
Joseph Black Building, The King’s Buildings, David Brewster Road,
Edinburgh, EH9 3FJ (UK)
cyclohexane
1:1.4
5:1
cyclohexane/THF (4:1)
toluene/THF (4:1)
isohexane/THF (4:1)
cyclohexane/THF (4:1)
Dr. Y. Luo
4.8:1
4:1
School of Chemistry and Chemical Engineering, Hefei University of
Technology, 193 Tunxi Rd, Hefei 230009 (China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/
>19:1
[a] Reactions were conducted using 0.20 mmol of 1a. [b] Determined by 1H
NMR analysis of the unpurified reaction mixtures.
This article is protected by copyright. All rights reserved.

10.1002/chem.201801804
Chemistry - A European Journal
COMMUNICATION
mixture of cyclohexane/THF (4:1) favored Z-homoallylic
boronate 2a (entry 5). Similar results were obtained using
toluene or isohexane in place of cyclohexane (entries 6 and 7).
However, a reaction in cyclohexane/THF (4:1) at a lower
concentration of 0.04 M increased the ratio of 2a:3a to >19:1
(entry 8).
With effective conditions in hand, the scope was
investigated using various α,β,γ,δ-unsaturated ketones with
sterically hindering carbonyl substituents (Scheme 2). These
reactions were generally highly selective for the formation of Z-
homoallylic boronates (ratio of 2:3 from 4:1 to >19:1), which
were isolated pure in 55–87% yield with high enantioselectivities
(86–95% ee). Substrate 1a gave 2a in 85% yield and 92% ee.
The group adjacent to the ketone can be varied to 1-
phenylcyclohexyl (2c and 2d), 2-ethyl-2,3-dihydro-1H-inden-2-yl
(2e), adamantyl (2f), and tert-butyl (2g–2k). Groups containing
silyloxy (2l–2n) or ester (2o and 2p) substituents are also
tolerated, but the ratios of Z-homoallylic boronate to E-allylic
boronate are lower in some cases (2m and 2n).[ 14 ] The
formation of 2l illustrates that an all-carbon quaternary center
adjacent to the ketone is not a strict requirement for this method
to be successful. Regarding the substituent at the δ-carbon,
substrates containing various simple alkyl groups (2a–2h and
2m–2p), oxygenated alkyl groups (2i and 2k), or
a
(phthalimido)methyl group (2j) are tolerated. The 1,6-boration of
1g using a 0.02 mol% catalyst loading also gave good results,
with 2g produced in 75% yield and 94% ee.
Scheme 3. Enantioselective Cu-catalyzed 1,6-boration–oxidation of electron-
deficient dienes to give E-allylic alcohols. Reactions were conducted with 0.30
mmol of 1. Yields are of isolated material. Enantiomeric excesses were
determined by HPLC analysis on a chiral stationary phase. [a] iPrOH/THF
(2:1) was used instead of iPrOH/THF (1:1).
As shown in Table 1, the reaction medium has a critical
influence on the product distribution, with iPrOH/THF (1:1)
favoring the E-allylic boronate (entry 2). Pleasingly, this effect
was general across several substrates (Scheme 3). The E-allylic
boronates are unstable to column chromatography on silica gel,
15
]
and were oxidized with NaBO3·4H2O[
to give the
corresponding allylic alcohols in 42–79% yield over two steps,
and with high enantioselectivities (90–94% ee). With substrate
1g, use of iPrOH/THF (1:1) gave comparable quantities of the Z-
homoallylic boronate and E-allylic boronate. Fortunately,
changing to iPrOH/THF (2:1) gave the E-allylic boronate
exclusively, and after oxidation, 4g was obtained in 72% yield
and 93% ee. Although Ito and co-workers have described the
temperature-controlled, switchable synthesis of allylic and
homoallylic boronates from 1,3-dienes, only two examples using
cyclic rather acyclic 1,3-dienes were reported.[13]
Currently, the reasons for selective formation of Z-
homoallylic boronates as shown in Scheme 2 are not known
(see the Supporting Information for discussion). Furthermore,
the dependence of the product selectivity on the solvent and
concentration are not understood, and insight into these
phenomena awaits the results of mechanistic studies.
Next, the synthetic utility of the products was investigated.
The α-silyloxyketone group of product 2l serves as a useful
handle for further transformation. For example, 2l was converted
into diol 5 in 91% yield and 2.3:1 d.r. by reaction with
NaBO3·4H2O[15] followed by methyllithium (Scheme 4). Selective
protection of the secondary alcohol of 5 as a pivaloyl ester gave
6. Removal of the TBS group of 6 with TBAF and reaction of the
resulting diol with PhI(OAc)2 in the presence of Et3N gave methyl
Scheme 2. Preparation of Z-homoallylic boronates. Reactions were conducted
with 0.30 mmol of 1. Values in parentheses refer to the ratios of 2 to 3, which
were determined by 1H NMR analysis of the crude mixtures. Enantiomeric
excesses were determined by HPLC analysis on a chiral stationary phase. [a]
Using 0.20 mmol of 1e. [b] Results of a reaction conducted with 4.00 mmol of
1g and a 0.02 mol% catalyst loading. [c] Substrate 1j contained minor
impurities, some of which may be alkene stereoisomers.
This article is protected by copyright. All rights reserved.

10.1002/chem.201801804
Chemistry - A European Journal
COMMUNICATION
Scheme 5. 1,3-Dipolar cycloaddition of 2g with 12 and conversion of
pyrrolidine 13 into a crystalline derivative 14.
access chiral, highly substituted pyrrolidines, which are
structures of widespread chemical and biological significance.[20]
Although various dipolarophiles have been employed in these
reactions,[20] Z-acyclic α,β-unsaturated ketones have been
virtually unexplored.[21] This omission is perhaps unsurprising
given that these substrates are more difficult to prepare in high
stereoselectivity compared with their E-configured counterparts,
and addressing this deficiency would give access to a wider
range of functionalized pyrrolidines. Our initial attempts to react
Scheme 4. Further transformations of 2l.
ketone
7 in 82% yield, without affecting the Z-alkene.
Alternatively, reaction of 6 with MAD [methylaluminum bis(2,6-di-
16
]
tert-butyl-4-methylphenoxide)][
triggered
a
pinacol
rearrangement to give methyl ketone 8 in 80% yield, again
without affecting the Z-alkene.
In another example of further manipulation, 2g was reduced
with diisobutylaluminum 2,6-di-tert-butyl-4-methylphenoxide
17
]
Z-homoallylic
boronate
2g
with
methyl
(E)-2-
(Scheme 5).[
This reaction gave a 5:1 mixture of
(benzylideneamino)acetate (12) under various conditions
employed in previously reported examples of 1,3-dipolar
cycloadditions[20] were unsuccessful. However, the reaction of
2g with 12 in the presence of CuF(PPh3)3·2MeOH (10.0 mol%),
(R,R)-Ph-BPE (L2, 10.0 mol%), Et3N (0.3 equiv) and 3 Å
molecular sieves in toluene at room temperature gave
pyrrolidine 13 in 4:1 exo:endo selectivity and high
diastereoselectivity.[22,23] After purification, 13 was obtained in
71% yield. Reaction of 13 with para-nitrophenylsulfonyl chloride
gave 14, the stereochemistry of which was determined by X-ray
crystallography.[19]
diastereomeric alcohols 9a and 9b, which were isolated in 62%
and 12% yield, respectively. The diastereoselectivity is
noteworthy, given the remote 1,5-stereoinduction involved.
Since previous applications of this reagent required
a
coordinating group near the ketone for high
diastereoselectivity,[17] this result suggests that aluminum may
coordinate to one of the oxygen atoms of the pinacolboronate.[18]
Oxidation of 9a with NaBO3·4H2O[15] gave diol 10, which was
converted into diester 11 by acylation with 4-nitrobenzoyl
chloride. X-ray crystallography of 11 allowed determination of
the relative and absolute configuration.[19]
In summary, we have developed switchable, highly
enantioselective copper-catalyzed 1,6-borations to give two
different classes of products. This method can provide
homoallylic boronates containing a (Z)-α,β-unsaturated ketone
with high Z-selectivities (>95:5 Z:E). 1,6-Borations to access this
product class have not been described previously. By changing
the solvent and concentration, and increasing the equivalents of
the protic additive iPrOH, E-allylic boronates are obtained (>95:5
E/Z). The utility of the Z-homoallylic boronates was
demonstrated by a range of further transformations.
Acknowledgements
This work was supported by the European Research Council
[grant number 258580] through
a
Starting Grant; the
Engineering and Physical Sciences Research Council [grant
numbers EP/I004769/1, EP/I004769/2, EP/H031588/1] through
a Leadership Fellowship to H.W.L. and a PhD studentship to
I.D.R.; Pfizer; GlaxoSmithKline; and the University of
Nottingham.
Scheme 5. Reduction of 2g and conversion of 9a into a crystalline derivative.
Finally, 1,3-dipolar cycloadditions of the Z-homoallylic
boronates with azomethine ylides were investigated.
Enantioselective cycloadditions of azomethine ylides with
electron-deficient alkenes are powerful transformations to
Keywords: 1,6-addition · asymmetric catalysis · boron · copper
· enantioselectivity
This article is protected by copyright. All rights reserved.

10.1002/chem.201801804
Chemistry - A European Journal
COMMUNICATION
[1]
a) D. G. Hall, Editor, Boronic Acids: Preparation and Applications in
Organic Synthesis, Medicine and Materials (Volumes 1 and 2), Second
Edition, Wiley-VCH Verlag GmbH & Co. KGaA, 2011.
[8]
[9]
a) T. Kitanosono, P. Xu, S. Kobayashi, Chem. Commun. 2013, 49,
8184-8186. b) Y. Luo, I. D. Roy, A. G. E. Madec, H. W. Lam, Angew.
Chem., Int. Ed. 2014, 53, 4186-4190.
[2]
Reviews of transformation of organoboron compounds by 1,2-
migrations of their ate complexes: a) D. S. Matteson, J. Org. Chem.
2013, 78, 10009-10023. b) D. Leonori, V. K. Aggarwal, Acc. Chem. Res.
2014, 47, 3174-3183.
Enantioselective copper-catalyzed 1,6-borations of para-quinone
methides that give benzylic boronates: a) Y. Z. Lou, P. Cao, T. Jia, Y. L.
Zhang, M. Wang, J. Liao, Angew. Chem., Int. Ed. 2015, 54, 12134-
12138. b) C. Jarava-Barrera, A. Parra, A. López, F. Cruz-Acosta, D.
Collado-Sanz, D. J. Cárdenas, M. Tortosa, ACS Catal. 2016, 6, 442-
446.
[3]
Stereospecific Suzuki–Miyaura couplings of α-stereogenic alkylboron
compounds: a) M. Odachowski, A. Bonet, S. Essafi, P. Conti-Ramsden,
J. N. Harvey, D. Leonori, V. K. Aggarwal, J. Am. Chem. Soc. 2016, 138,
9521-9532. b) J. Y. Ding, T. Rybak, D. G. Hall, Nat. Commun. 2014, 5,
5474. c) L. Li, S. Zhao, A. Joshi-Pangu, M. Diane, M. R. Biscoe, J. Am.
Chem. Soc. 2014, 136, 14027-14030. d) A. Bonet, M. Odachowski, D.
Leonori, S. Essafi, V. K. Aggarwal, Nat. Chem. 2014, 6, 584-589. e) G.
A. Molander, S. R. Wisniewski, M. Hosseini-Sarvari, Adv. Synth. Catal.
2013, 355, 3037-3057. f) G. A. Molander, S. R. Wisniewski, J. Am.
Chem. Soc. 2012, 134, 16856-16868. g) D. L. Sandrock, L. Jean-
Gérard, C.-y. Chen, S. D. Dreher, G. A. Molander, J. Am. Chem. Soc.
2010, 132, 17108-17110. h) D. Imao, B. W. Glasspoole, V. S. Laberge,
C. M. Crudden, J. Am. Chem. Soc. 2009, 131, 5024-5025.
[10] For the enantioselective synthesis of products of type C (Scheme 1) by
one-pot three-component reactions of α,β-unsaturated aldehydes,
B2(pin)2, and Wittig reagents, see ref. [7b].
[11] For copper-catalyzed 1,6-silylation of β,β-disubstituted α,β,γ,δ-
unsaturated carbonyl compounds that give silicon analogues of type B
products (Scheme 1): K.-s. Lee, H. Wu, F. Haeffner, A. H. Hoveyda,
Organometallics 2012, 31, 7823-7826.
[12] W. Y. Siau, Y. Zhang, Y. Zhao, in Stereoselective Alkene Synthesis,
Vol. 327 (Ed.: J. Wang), 2012, pp. 33-58.
[13] Y. Sasaki, C. Zhong, M. Sawamura, H. Ito, J. Am. Chem. Soc. 2010,
132, 1226-1227.
[4]
[5]
Seminal references of copper-catalyzed 1,4-boration: a) K. Takahashi,
T. Ishiyama, N. Miyaura, Chem. Lett. 2000, 29, 982-983. b) H. Ito, H.
Yamanaka, J.-i. Tateiwa, A. Hosomi, Tetrahedron Lett. 2000, 41, 6821-
6825. c) S. Mun, J.-E. Lee, J. Yun, Org. Lett. 2006, 8, 4887-4889. d) J.-
E. Lee, J. Yun, Angew. Chem., Int. Ed. 2008, 47, 145-147. e) V. Lillo, A.
[14] A possible reason for diminished selectivity is the coordinating ability of
the oxygen-containing substituents.
[15] C. N. Farthing, S. P. Marsden, Tetrahedron Lett. 2000, 41, 4235-4238.
[16] K. Maruoka, T. Itoh, H. Yamamoto, J. Am. Chem. Soc. 1985, 107,
4573-4576.
Prieto, A. Bonet, M. M. Diaz-Requejo, J. s. Ramirez, P. J. Perez, E.
[17] S. Iguchi, H. Nakai, M. Hayashi, H. Yamamoto, J. Org. Chem. 1979, 44,
1363-1364.
́
́
́
Fernandez, Organometallics 2008, 28, 659-662.
́
Reviews covering enantioselective copper-catalyzed 1,4-boration: a) E.
C. Neeve, S. J. Geier, I. A. I. Mkhalid, S. A. Westcott, T. B. Marder,
Chem. Rev. 2016, 116, 9091-9161. b) S. Lee, J. Yun, in Synthesis and
Application of Organoboron Compounds, Vol. 49 (Eds.: E. Fernandez,
A. Whiting), 2015, pp. 73-92. c) G. Stavber, Z. Časar, ChemCatChem
2014, 6, 2162-2174. d) A. D. J. Calow, A. Whiting, Org. Biomol. Chem.
2012, 10, 5485-5497. e) E. Hartmann, D. J. Vyas, M. Oestreich, Chem.
Commun. 2011, 47, 7917-7932.
[18] Examples of Lewis acid coordination to one of the oxygen atoms of
pinacolboronates: a) J. W. J. Kennedy, D. G. Hall, J. Am. Chem. Soc.
2002, 124, 11586-11587. b) J. W. J. Kennedy, D. G. Hall, J. Org. Chem.
2004, 69, 4412-4428. c) V. Rauniyar, D. G. Hall, J. Am. Chem. Soc.
2004, 126, 4518-4519.
[19] CCDC 1539447 (11) and 1539448 (14) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[6]
[7]
Enantioselective 1,4-boration catalyzed by metals other than copper: a)
T. Shiomi, T. Adachi, K. Toribatake, L. Zhou, H. Nishiyama, Chem.
Commun. 2009, 5987-5989. b) V. Lillo, M. J. Geier, S. A. Westcott, E.
Fernández, Org. Biomol. Chem. 2009, 7, 4674-4676. c) K. Toribatake,
L. Zhou, A. Tsuruta, H. Nishiyama, Tetrahedron 2013, 69, 3551-3560.
Enantioselective organocatalytic 1,4-borations: a) A. Bonet, H. Gulyás,
E. Fernández, Angew. Chem., Int. Ed. 2010, 49, 5130-5134. b) I.
Ibrahem, P. Breistein, A. Córdova, Angew. Chem., Int. Ed. 2011, 50,
12036-12041. c) I. Ibrahem, P. Breistein, A. Cordova, Chem. Eur. J.
2012, 18, 5175-5179. d) H. Wu, S. Radomkit, J. M. O’Brien, A. H.
Hoveyda, J. Am. Chem. Soc. 2012, 134, 8277-8285. e) S. Radomkit, A.
H. Hoveyda, Angew. Chem., Int. Ed. 2014, 53, 3387-3391. f) E. L.
Cascia, X. Sanz, C. Bo, A. Whiting, E. Fernandez, Org. Biomol. Chem.
2015, 13, 1328-1332. g) M. Sugiura, W. Ishikawa, Y. Kuboyama, M.
Nakajima, Synthesis 2015, 47, 2265-2269. h) H. Wu, J. M. Garcia, F.
Haeffner, S. Radomkit, A. R. Zhugralin, A. H. Hoveyda, J. Am. Chem.
Soc. 2015, 137, 10585-10602.
[20] Reviews: a) T. Hashimoto, K. Maruoka, Chem. Rev. 2015, 115, 5366-
5412. b) R. Narayan, M. Potowski, Z.-J. Jia, A. P. Antonchick, H.
Waldmann, Acc. Chem. Res. 2014, 47, 1296-1310. c) J. Adrio, J. C.
Carretero, Chem. Commun. 2014, 50, 12434-12446. d) C. Nájera, J. M.
Sansano, J. Organomet. Chem. 2014, 771, 78-92. e) G. Pandey, P.
Banerjee, S. R. Gadre, Chem. Rev. 2006, 106, 4484-4517.
[21] a) See footnote 15 of: J. Hernández-Toribio, R. G. Arrayás, B. Martín-
Matute, J. C. Carretero, Org. Lett. 2009, 11, 393-396. b) See the
Supporting Information of: Z. He, T. Liu, H. Tao, C.-J. Wang, Org. Lett.
2012, 14, 6230-6233. Corrected by: Z.-L. He, T.-L. Liu, H. Tao, C.-J.
Wang, Org. Lett. 2014, 16, 5506-5507.
[22] This reaction using (R,R)-BPE (L2) is the stereochemically matched
case. When (S,S)-Ph-BPE (ent-L2) or achiral bisphosphines were used,
complex mixtures of diastereomeric products were obtained.
[23] The minor diastereomers of the exo- and endo-cycloaddition products
are those where the four stereocenters of the pyrrolidine ring are of the
opposite absolute configuration.
This article is protected by copyright. All rights reserved.

10.1002/chem.201801804
Chemistry - A European Journal
COMMUNICATION
COMMUNICATION
Y. Luo, S. M. Wales, S. E. Korkis, I. D.
Roy, W. Lewis, H. W. Lam*
Page No. – Page No.
Switchable Synthesis of Z-Homoallylic
Boronates and E-Allylic Boronates by
Enantioselective Copper-Catalyzed 1,6-
Boration
Flip the switch: The enantioselective Cu-catalyzed 1,6-boration of (E,E)-α,β,γ,δ-
unsaturated ketones is described, which gives homoallylic boronates with high
enantiomeric purity and unexpectedly high Z-selectivity. By changing the solvent,
the outcome can be altered to give E-allylic boronates.
This article is protected by copyright. All rights reserved.