Transition metal-catalyzed hydro-, sila-, and stannastannation of cyclopropenes: Stereo- and regioselective approach toward multisubstituted cyclopropyl synthons

Article abstract of DOI:10.1021/ja027095k

The first highly efficient, stereo- and regioselective palladium-catalyzed hydro-, sila-, and stannastannation of cyclopropenes to give multisubstituted cyclopropylstannanes have been developed. It was shown that the addition across the double bond of cyc

Full text of DOI:10.1021/ja027095k

Published on Web 09/10/2002
Transition Metal-Catalyzed Hydro-, Sila-, and Stannastannation of
Cyclopropenes: Stereo- and Regioselective Approach toward
Multisubstituted Cyclopropyl Synthons
Marina Rubina, Michael Rubin, and Vladimir Gevorgyan*
Department of Chemistry, UniVersity of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061
Received May 29, 2002
Table 2. Pd-Catalyzed Hydrostannation of Cyclopropenes
Cyclopropylstannanes, highly attractive versatile synthons, are
extensively used nowadays as stable precursors for a number of
cyclopropylmetal reagents with defined configurations.1 Further-
more, they are employed in Pd-catalyzed oxidative homocoupling,2
Stille cross-coupling reactions,3 as well as in various destannylative
transformations4 and rearrangements into other useful organotin
derivatives.5 Although more than a few methods for the preparation
of cyclopropylstannanes have been developed,6 usually these
methods lack generality and, in most cases, are limited to the
preparation of mono- to trisubstituted cyclopropanes. A direct
hydrostannation7 of the cyclopropene double bond potentially can
be seen as a very attractive, straightforward, and atom-economic
alternative route to highly substituted cyclopropylstannanes. The
54 kcal/mol of strain energy in cyclopropene versus cyclopropane
is a reason for the high affinity of its double bond toward various
addition reactions.8 However, transition metal-catalyzed hydrostan-
nation of cyclopropenes has never been reported, probably because
of a general belief that, except for some scattered reports,9
palladium, as well as some other transition metal complexes, is
well known to cause ring-opening,10 oligomerization,11 or poly-
merization12 of cyclopropenes.13 Herein we wish to report the first
highly stereo- and regioselective transition metal-catalyzed hydro-,
sila-, and stannastannation reactions of cyclopropenes14 which allow
for the synthesis of up to pentasubstituted cyclopropane derivatives
in very good yields.
Table 1. Catalyst Optimization for Hydrostannation of 1a
a
a
#
catalyst
time
3, %
4, %
3:4a
1
Ru(PPh3)3Cl2
Pt(PPh3)4
20 h
67
66
75
32
2
36
15
19
3
4
4
1
96:4
94:6
95:5
97:3
2
20 h
3
Rh(PPh3)3Cl
Ni(dppp)Cl2
20 h
4
20 h
5
Ni(dppe)2
5 h
6
Pd(PPh3)2Cl2
5 min
5 min
5 min
5 min
5 min
5 min
5 min
5 min
5 min
16
14
15
>1
6
69:31
52:48
56:44
7
TCPCb
8
Pd(OAc)2/TDMPP
Pd2dba3/o-Tol3P
[π-allyl-PdCl]2/MOP
[π-allyl-PdCl]2/MOPb
Pd(PPh3)4
9
10
11
12
13
14
29
32
79
86d
20
83:17
80:20
98:2
>99:1
46:54
8
>1
>1
24
c
Pd(PPh3)4
none
a Isolated yield. b Formation of 5% of 4ab was detected. c Combined
yield of 4:1 mixture of 3ea:4ea. d Combined NMR yield of 4:1 mixture of
3fa:4fa. e NMR yield. f Formation of 5% of 4ha was observed.
a GC data. b TCPC ) [1,2,3,4-tetrakis(methoxycarbonyl)-1,3-butadiene-
1,4-diyl]palladium. c Reaction was performed at -78 °C. d Isolated yield.
1, Table 1). The ruthenium, platinum, rhodium, and nickel
complexes tested initiated rather slow reactions which produced
moderate to good yields of products albeit with high facial
selectivity (Table 1, entries 1-4). Most of the Pd-catalysts showed
high reaction rates, but yields and selectivity were disappointingly
Initially, we tested hydrostannation of disubstituted cyclopropene
1a15 in the presence of a number of transition metal catalysts (eq
* To whom correspondence should be addressed. E-mail: vlad@uic.edu.
9
11566
J. AM. CHEM. SOC. 2002, 124, 11566-11567
10.1021/ja027095k CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
Table 3. Pd-Catalyzed Distannation and Silastannation of
Cyclopropenes
Acknowledgment. The support of the National Science Foun-
dation (CHE-0096889) is gratefully acknowledged.
Supporting Information Available: Experimental details (PDF).
This material is available free of charge via the Internet at http://
pubs.acs.org.
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low (entries 6-11). In contrast, Pd(PPh3)4 gave both a very good
yield and a very high facial selectivity (entry 12). Optimization of
the reaction conditions showed that this reaction can be carried
out at as low as -78 °C! Still, the reaction was complete in less
than 5 min, and virtually a single facial isomer 3aa was isolated in
86% yield (entry 13). A control experiment with no catalyst
demonstrated that there is a background reaction which proceeds,
probably, via a free radical mechanism producing nonselectively a
1:1 mixture of 3aa and 4aa in moderate yield accompanied with a
notable amount of oligomeric products (entry 14). The best
conditions (Table 1, entry 13) were applied to the hydrostannation
reaction of differently substituted cyclopropenes (eq 2, Table 2).15
The hydrostannation of most of the 3,3-disubstituted cyclopropenes
was governed by steric effects regardless of the tin hydride source;
addition across the cyclopropene double bond proceeded from the
least hindered face (Table 2, entries 1-8).16,17 Surprisingly,
cyclopropenes 1e,f revealed a notable directing effect. Apparently,
a coordination of oxygen to palladium affected the facial selectivity
of hydrostannation favoring the addition from the more sterically
hindered face (entries 9,10).18 Trisubstituted cyclopropene 1g
reacted smoothly to provide cyclopropylstannane 3ga as a single
stereo- and regioisomer (entry 11). Hydrostannation of 1h,i,
however, required the use of a [(π-allyl)PdCl]2/MOP19 catalyst
system to get cyclopropylstannanes 3ha and 3ia with high facial
selectivity and good yields (entries 12,13). Finally, tetrasubstituted
cyclopropene 1j underwent smooth hydrostannation to produce the
corresponding pentasubstituted cyclopropylstannane 3ja in 82%
isolated yield as a single reaction product (entry 14).20
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1889.
To further test the scope of this methodology, we examined the
Pd-catalyzed silastannation and distannation reactions (eq 3, Table
3).15 Among the systems tested, Pd(OAc)2 in combination with
Walborsky’s ligand6l gave the best results. The reactions proceeded
with high facial selectivity which was entirely controlled by steric
factors. All tetrasubstituted cyclopropanes 6aa-db were obtained
as sole reaction products in good to very high yields (Table 3).
In conclusion, the first transition metal-catalyzed hydro-, sila-,
and stannastannation of cyclopropenes have been demonstrated.
This method allows for the efficient and straightforward synthesis
of stereodefined multisubstituted building blocks not easily available
by other methods.
(15) For experimental procedures, see Supporting Information.
(16) Syn-stereoselectivity of addition was unambiguously proved by hydrostan-
nation of 1a with Bu3SnD. See Supporting Information for details.
(17) Good scalability was demonstrated by preparation of 11 mmol of 3aa
(80% yield). See Supporting Information for details.
(18) For examples on directing effect in hydrostannation, see: (a) Betzer, J.-
F.; Delaloge, F.; Muller, B.; Pancrazi, A.; Prunet, J. J. Org. Chem. 1997,
62, 7768. (b) Rice, M. B.; Whitehead, S. L.; Horvath, C. M.; Muchnij, J.
A.; Maleczka, R. E., Jr. Synthesis 2001, 1495.
(19) MOP ) (RS)-2-(diphenylphosphino)-2′-methoxy-1,1′-binaphthyl.
(20) Initial experiments using chiral (R)-(+)-MOP ligand with cyclopropene
1b revealed poor asymmetric induction (12% ee). Further investigation
of the chiral version of this reaction is currently under way in our
laboratories.
JA027095K
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J. AM. CHEM. SOC. VOL. 124, NO. 39, 2002 11567