Transition-metal-free reductive coupling of 1, 3-butadienes with aldehydes catalyzed by dibutyliodotin hydride

Article abstract of DOI:10.1021/acs.orglett.7b02671

In this study, the Bu₂SnIH-catalyzed direct coupling of 1, 3- dienes with aldehydes was developed. This reaction could be suitable for coupling without the use of transition-metal catalysts. Many types of aldehydes were applied to this reaction. The addition of MeOH promoted the catalytic cycle.

Full text of DOI:10.1021/acs.orglett.7b02671

Letter
pubs.acs.org/OrgLett
Transition-Metal-Free Reductive Coupling of 1,3-Butadienes with
Aldehydes Catalyzed by Dibutyliodotin Hydride
Itaru Suzuki, Yuki Uji, Shujiro Kanaya, Ryosuke Ieki, Shinji Tsunoi, and Ikuya Shibata*
Research Center for Environmental Preservation, Osaka University, 2-4 Yamadaoka, Suita, Osaka 565-0871, Japan
S
* Supporting Information
ABSTRACT: In this study, the Bu2SnIH-catalyzed direct coupling of 1,3-
dienes with aldehydes was developed. This reaction could be suitable for
coupling without the use of transition-metal catalysts. Many types of
aldehydes were applied to this reaction. The addition of MeOH promoted
the catalytic cycle.
Table 1. Optimization of Coupling of 1,3-Butadiene 1 with
Aldehyde 2 Catalyzed by Bu2SnIH
n organic synthesis, allylation of aldehydes is one of the most
important and reliable C−C bond formations for the
a
I
production of homoallylic alcohols. Typically, isolated allylic
metal reagents are prepared in advance from strong bases and
allyl halides that are employed for allylation with many types of
catalysts to either promote the reaction or induce enantiose-
lectivity.1 Recently, reductive coupling between conjugated
butadienes and aldehydes was developed by the Krische2 and
Kimura3 groups. High efficiency and stereoselectivity were
achieved using their methods, although precious transition-
metal catalysts were required. Our group has recently worked
on the hydrostannylation of unsaturated bonds with dibutyltin
halogen hydride (Bu2SnHalH)4 and reported a diene derivative,
vinylcyclopropane, coupled with aldehydes catalyzed by
dibutyliodotin hydride (Bu2SnIH).5 Herein, we report the
effective catalytic activity of dibutyltin halogen hydride in the
direct coupling of 1,3-dienes with aldehydes. To the best of our
knowledge, this reaction is the first example of a coupling
proceeding in the absence of transition metals.
Initially, we investigated the optimized reaction conditions
using 2,3-dimethyl-1,3-butadiene (1a) and 3-phenylpropanal
(2a) at 25 °C for 24 h. According to the typical methods,6
Bu2SnIH was prepared in situ via redistribution between
Bu2SnH2 and Bu2SnI2. The product 3aa was given in a high
yield when the reaction conditions used in our previous
reaction system were applied (Table 1, entry 1). The coupling
was sluggish without the addition of MeOH (Table 1, entry 2).
Other alcohols were ineffective in this reaction and afforded
byproduct 4 (Table 1, entries 3 and 4) in greater amounts than
the desired product 3aa. Byproduct 4 was formed by
competitive reaction during the direct reduction of 2a.
MeCN proved to be a better solvent than THF, toluene, or
DMF (Table 1, entries 5−7). Hydrosilanes were also important
in producing 3aa. Ph2SiH2 was the best hydride source (Table
1, entries 8−11). The radical scavenger TEMPO inhibited this
reaction, which suggested the involvement of a radical pathway
(Table 1, entry 12).
b
yield (%)
entry
1
Si-H/additive (mmol)
solvent
3a
4
c
Ph2SiH2 (1.0)/MeOH (1.0)
Ph2SiH2 (1.0)
MeCN
MeCN
MeCN
MeCN
THF
77 (67)
7
d
2
33
43
50
36
45
14
50
0
67
44
43
30
30
5
3
Ph2SiH2(1.0)/EtOH (1.0)
Ph2SiH2 (1.0)/PrOH (1.0)
Ph2SiH2 (1.0)/MeOH (1.0)
Ph2SiH2 (1.0)/MeOH (1.0)
Ph2SiH2(1.0)/MeOH(1.0)
PhSiH3(1.0)/MeOH (1.0)
Ph3SiH (1.0)/MeOH (1.0)
MePhSiH2 (1.0)/MeOH (1.0)
PMHS (1.0)/MeOH (1.0)
Ph2SiH2(1.0)/MeOH (1.0)/
TEMPO (0.10)
4
5
6
toluene
DMF
7
8
MeCN
MeCN
MeCN
MeCN
MeCN
43
13
12
0
9
10
11
12
32
5
3
0
a
b
All reactions were carried out under argon-flow conditions. Yields
c
1
were determined by H NMR using an internal standard. Isolated
d
yield. The reaction was carried out for 48 h.
hindrance on the α position of carbonyls had little influence on
the allylation that yielded products 3ab−ae (Table 2, entries
2−4). The product 3ac was isolated as a single diastereomer.
Although its stereochemistry was not determined as yet, this
could imply that the reaction proceeded via a Felkin−Anh
model with prenyltin bulky nucleophiles.7 A cyclohexane ring
was successfully introduced with this coupling, and afforded the
With the optimized conditions in hand, various aldehydes
were tested, and the results are shown in Table 2. The reactions
were carried out on a 5 mmol scale. Aliphatic aldehydes were
applicable to this coupling (Table 2, entries 1−6). The steric
Received: August 28, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b02671
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 2. Various Types of Aldehydes 2 Applied to Coupling
with 1,3-Butadiene 1
Scheme 1. Plausible Reaction Mechanism
a
allylstannane 6, and the radical species is regenerated. After
addition of allylstannane 6 to aldehyde 2,8 tin adduct 7 is
protonated with MeOH. As a result, product 3 forms,
accompanied by Bu2SnIOMe,9,10 and is transformed into
Bu2SnIH. MeOH was a better additive than either EtOH or
i-PrOH because the σ-bond metathesis between hydrosilanes
and either Bu2SnIOEt or Bu2SnIOi-Pr would be disturbed by
their bulkiness. This process was validated by the generation of
Bu2SnIH from Bu2SnIOMe and Ph2SiH2 using 119Sn NMR
(Figure S1). The prepared Bu2SnIOMe also was an effective
catalyst for the coupling of 1a with 2a to afford the product 3aa
in a yield that approximated the use of in situ generated
Bu2SnIH from Bu2SnI2 and Bu2SnH2. Thus, the use of
Bu2SnIOMe as a starting catalyst is a desirable alternative for
the generation of Bu2SnIH because Bu2SnH2 is difficult to
handle.
Other dienes such as 1,3-butadiene (2b) and isoprene 2c
reacted with aldehyde 2a to give the corresponding products in
moderate yields (Scheme 2). An excess amount of 1,3-
a
b
All reactions were carried out under argon-flow conditions. Yields
were determined by 1H NMR using an internal standard. Isolated
yields are shown in parentheses. 3ac was isolated as a single
c
diasteomer.
Scheme 2. Butadiene or Isoprene as Diene Sources for
Coupling with 2a
product 3af. The couplings proceeded well when either
electron-rich or -poor aromatic aldehydes were employed to
afford the product 3ag−ak (Table 2, entry 7). Cinnamaldehyde
(2l) coupled with the diene to give the product 3al with an
intact E/Z ratio (Table 2, entry 8). Although the use of a
ketone instead of an aldehyde would avoid the direct reduction
of a carbonyl group, acetophenone was, unfortunately, not
applicable to this reaction wherein the ketone was recovered
quantitatively because of its low reactivity to allylation.
A proposed catalytic cycle employing diene 1a is shown in
Scheme 1. Initially, hydrostannylation to 1a occurs via a radical-
chain mechanism mediated by in situ generated Bu2SnIH from
Bu2SnI2 and Bu2SnH2. Bu2SnIH is homogeneously cleaved by
V-70L to form a tin radical followed by addition to diene 1a.
Hydrostannylation proceeds prior to the direct reduction of
aldehyde 2. Allylic radical 5 is reduced by Bu2SnIH to give
B
DOI: 10.1021/acs.orglett.7b02671
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Yasuda, M.; Baba, A. Chem. Commun. 2007, 4913. (g) Hayashi, N.;
Hirokawa, Y.; Shibata, I.; Yasuda, M.; Baba, A. J. Am. Chem. Soc. 2008,
130, 2912.
(5) Ieki, R.; Kani, Y.; Tsunoi, S.; Shibata, I. Chem. - Eur. J. 2015, 21,
6295.
(6) (a) Neumann, W. P.; Pedain, J. Tetrahedron Lett. 1964, 5, 2461.
(b) Sawyer, A. K.; Brwon, Y. E.; Hanson, E. L. J. Organomet. Chem.
1965, 3, 464.
(7) High diastereoselectivity via the Felkin−Anh model is due to the
steric bulkiness of prenyltin nucleophile 6 in Scheme 1. See: Cherest,
M.; Felkin, H.; Prudent, N. Tetrahedron Lett. 1968, 9, 2199.
(8) Allylation of aldehydes with allylic stannanes has been studied.
See: (a) Pereyre, M.; Quintard, P. J.; Rahm, A. In Tin in Organic
Synthesis; Butterworth: London, 1987; pp 211−229. (b) Davies, A. G.
In Organotin Chemistry; VCH:: Weinheim, 1997; pp 133−142.
(c) Baba, A.; Shibata, I.; Yasuda, M. In Comprehensive Organometallic
Chemistry III; Knochel, P., Ed.; Elsevier: Oxford, 2007; Vol. 9, pp 351−
358.
butadiene was required to yield the product 3ba in a sufficient
yield. Isoprene afforded two different products, 3ca and 3ca′,
depending on the regioselectivity of the hydrostannylation to
isoprene. A loss of diastereoselectivity for products 3ba and 3ca
would imply that the hydrostannylation of the dienes in a
radical manner was so rapid that allylic tins acted as mixtures of
E- and Z- isomers. Unfortunately, terminally substituted dienes
such as cyclohexadiene or piperylene were not reactive for the
coupling as yet.
In conclusion, we developed a transition metal-free reductive
coupling of diene 1 with aldehyde 2. The reaction was catalyzed
by Bu2SnIH and proceeded under mild conditions. The
addition of MeOH was significant, and the product was
smoothly obtained. Various aldehydes and dienes were
applicable to the coupling.
ASSOCIATED CONTENT
* Supporting Information
(9) Bu2SnIOMe has already prepared and identified. See: Davies, A.
G.; Harrison, P. G. J. Chem. Soc. C 1967, 298.
■
S
(10) Yanagisawa’s group reported tin homoallylc alkoxides were
protonated by MeOH and the generated tin methoxides were
regenerated. See: (a) Yanagisawa, A.; Sekiguchi, T. Tetrahedron Lett.
2003, 44, 7163. (b) Yanagisawa, A.; Goudu, R.; Arai, T. Org. Lett.
2004, 6, 4281. (c) Yanagisawa, A.; Satou, T.; Izumiseki, A.; Tanaka, Y.;
Miyagi, M.; Arai, T.; Yoshida, K. Chem. - Eur. J. 2009, 15, 11450.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.7b02671.
Experimental procedures and spectral data (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: shibata@epc.osaka-u.ac.jp.
ORCID
Itaru Suzuki: 0000-0002-4817-9156
Ikuya Shibata: 0000-0002-9619-4019
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful for financial support from The Naito
Foundation. We also thank the Instrumental Analysis Center,
Faculty of Engineering, Osaka University, for assistance with
collecting the spectral data.
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DOI: 10.1021/acs.orglett.7b02671
Org. Lett. XXXX, XXX, XXX−XXX