COMMUNICATION
Table 3. Cross-coupling of 1-chlorodecene with nBuMgCl and iPrMgCl
in the presence of various iron-based catalytic systems.
or FeCl2 (Table 1, entry 5). It is interesting to note that the
yields obtained with iron arylthiolates are better than that
previously obtained by using [FeACTHNUTRGNENUG(acac)3] and NMP as a co-
solvant (Table 1, entry 2). Interestingly, only 1% iron 2-
naphthylthiolate is enough to efficiently catalyze the reac-
tion (Table 1, entry 6).
To study the scope and limitations of the reaction, we
chose to use iron 2-naphthylthiolate as the precatalyst
(Table 1, entries 5 and 6). Indeed, this iron thiolate always
RMgCl
Catalytic System
Yield
[%][a]
1
2
3
4
5
6
7
8
BuMgCl
BuMgCl
BuMgCl
BuMgCl
BuMgCl
iPrMgCl
iPrMgCl
iPrMgCl
[Fe
(acac)3] (5%), NMP (9 equiv)[b]
87
87
85
93
93
50
85
86
[Fe(S-2-naphthyl)2][c] (5%)
[Fe(S-2-naphthyl)2][d] (5%)
gave similar or slightly higher yields than [FeACTHNUGTRENUNG(SPh)2]. For in-
[Fe(S-2-naphthyl)2][d] (5%), NMP (7.5%)
[Fe(S-2-naphthyl)2][d] (5%), LiCl[e] (10%)
[Fe(S-2-naphthyl)2][d] (5%)
stance, the coupling of (E)-1-bromooct-1-ene with BuMgCl
led to a 90% yield of (E)-5-dodecene 3 with the 2-naphthyl-
derived catalyst instead of 85% with the phenyl-derived one
(Scheme 2).
[Fe(S-2-naphthyl)2][d] (5%), NMP (7.5%)
[Fe(S-2-naphthyl)2] (5%), LiCl[e] (10%)
[a] Determined by GC analysis. Hexadecane (C16H34) was used as the in-
ternal standard. [b] Based on OctCH=CHCl. [c] Prepared from FeCl3.
[d] Prepared from FeCl2. [e] Prepared from FeCl2·2LiCl, see ref. [9].
Alkenyl chlorides also react with alkyl Grignard reagents
in the presence of iron 2-naphthylthiolate (Table 3, entries 2
and 3). However, they are less reactive than the correspond-
ing bromides and generally gave slightly lower yields (about
5–7% less). However, we have determined that it is possible
to improve these results by working with a precatalyst ob-
tained by mixing iron 2-naphthylthiolate and NMP (1:1.5)[8]
(Table 3, entry 4). It is important to note that only 7.5%
NMP is then necessary instead of the 900% (9 equiv) re-
quired when the reaction is performed with FeCl3 or [Fe-
Scheme 2. Stereoselectivity of the reaction.
Furthermore, we have found that the reaction is highly
stereoselective (Scheme 2). Thus, (Z)- and (E)-1-bromooct-
1-enes afforded the corresponding (Z)- and (E)-olefins 3
and 4, respectively, with complete retention of configura-
tion.
Moreover, the scope of the reaction is very wide and vari-
ous mono- or disubstituted alkenyl bromides were success-
fully used (Table 2). Indeed, alkenyl bromides and iodides
led to similar yields (Table 2, entries 6 and 7).
AHCTUNGTERG(NNUN acac)3] as the catalyst. Finally, we found that NMP can be
completely eliminated because similar results were obtained
by adding 2 equivalents of LiCl to the iron 2-naphthylthio-
late[9] (Table 3, entry 5).
The beneficial influence of NMP or LiCl is more impor-
tant when the coupling is performed with a secondary alkyl
Grignard reagent. Thus, the reaction of iPrMgCl with 1-
chlorodecene led to only a 50% yield of 2-methyldodec-3-
ene in the presence of iron 2-naphthylthiolate (Table 3,
entry 6), whereas 85 and 86% yields were obtained in the
presence of iron 2-naphthylthiolate complexed with NMP
(Table 3, entry 7) or LiCl (Table 3, entry 8), respectively. It
should be noted that the same coupling performed accord-
Table 2. Iron-catalyzed coupling of alkenyl bromides or iodides with pri-
mary alkyl Grignard reagents.
Alkenyl halide
Product
Yield
[%][a]
1
2
3
93
92
85
ing to the previous procedure ([FeACHTUNGTRNEUNG
(acac)3] (5%)/NMP)[1c]
leads to only a 62% yield. Various alkenyl chlorides
(Table 4, entries 1–3), as well as secondary alkyl Grignard
reagents (Table 4, entries 3–5 and 7–9), were coupled suc-
cessfully under these reaction conditions. It is also possible
to introduce a tertiary alkyl group, although the yield is
lower because a competitive b-hydrogen elimination reac-
tion probably occurs (Table 4, entry 6). It should be noted
that these results compare advantageously to those obtained
4
87
5
6
90
93
with the previous procedure ([Fe
ACHTUNGTERN(NGNU acac)3] (1%), NMP
(9 equiv)).[1c]
The reaction is highly chemoselective, and thus, various
functionalized Grignard reagents were used successfully
(Table 5). It is interesting to note that the use of a magnesi-
7
93
[a] Yield of the pure isolated product. Precatalyst: [Fe(S-2-naphthyl)2].
Chem. Eur. J. 2012, 18, 5860 – 5863
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5861