Scheiper et al.
was rapidly filtered off under inert atmosphere. Removal of
the solvent at -78 °C in high vacuum afforded the title
complex as a dark red solid. CAUTION: [Me4Fe][Li2(OEt2)2]
is highly moisture sensitive and can ignite when exposed to
air. It can be stored at -78 °C for several month without
noticeable decomposition.
SCHEME 5
Rep r esen ta tive P r oced u r e for th e Rea ction of En ol
Tr ifla tes w ith [Me4F e][Li2(OEt2)2]: (6R)-Isop r op yl-1,3(S)-
d im eth ylcycloh exen e (4). A chilled, golden-yellow solution
of [Me4Fe][Li2(OEt2)2] (135 mg, 0.49 mmol) in THF (4 mL) was
added to a solution of trifluoromethanesulfonic acid 6-isopro-
pyl-3-methylcyclohex-1-enyl ester 3 (139 mg, 0.49 mmol) in
THF (5 mL) at -30 °C, causing an immediate color change to
orange. After being stirred for 15 min at this temperature, the
reaction was carefully quenched with NH4Cl (5 mL) and
diluted with Et2O, the layers were separated, and the aqueous
phase was extracted with Et2O (3 × 5 mL). The combined
organic layers were dried over Na2SO4, and the solvent was
evaporated. Purification of the residue by flash chromatogra-
engage in cross coupling with 1,4-dichlorobenzene 5
under otherwise identical conditions. The reasons for this
distinct behavior are not yet clear and are subject to
further investigations.
In summary, the present study helps to define the
scope and limitations of iron-catalyzed cross couplings
with various types of electrophiles and illustrates some
of the major advantages of this method. Investigations
aiming at a further expansion of this powerful technique,
its implementation into target oriented synthesis, and
the refinement of the as yet incomplete mechanistic
understanding are actively pursued in our laboratory and
will be reported in due course.
phy on silica (pentane) provided the title compound as a
1
colorless oil (60 mg, 80%). [R]20 ) +5.2 (c ) 2.33, CHCl3). H
D
NMR (400 MHz, CDCl3): δ 5.30-5.29 (m, 1H), 2.12-1.96 (m,
3H), 1.79-1.73 (m, 1H), 1.69-1.61 (m, 4H), 1.32-1.22 (m, 1H),
1.04-0.95 (m, 1H), 0.93 (d, J ) 7.0 Hz, 3H), 0.92 (d, J ) 7.0
Hz, 3H), 0.68 (d, J ) 6.8 Hz, 3H). 13C NMR (100 MHz,
CDCl3): δ 135.8, 131.2, 44.3, 31.8, 30.9, 27.7, 22.3, 21.9, 21.7,
20.7, 15.6. IR (film): 3025, 2958, 2926, 2868, 2851, 1454, 1385,
842 cm-1. MS (EI): m/z (rel int) 152 (27 [M+]), 137 (12), 109
(100), 95 (15), 82 (31), 79 (8), 67 (51), 55 (13), 41 (14), 27 (4).
HRMS: calcd for C11H20 152.156500, found 152.156542.
Rep r esen ta tive P r oced u r e for Ir on -Ca ta lyzed Rea c-
tion s of Acid Ch lor id es w ith Gr ign a r d Rea gen ts. Hen e-
icos-2-yn -15-on e (Ta ble 2, En tr y 24). A solution of hexyl-
magnesium bromide (2 M in Et2O, 0.65 mL, 1.3 mmol) was
added via syringe to a solution of pentadec-13-ynoic acid
chloride (257 mg, 1.0 mmol) and Fe(acac)3 (11 mg, 0.03 mmol)
in THF at -78 °C under argon, causing an immediate color
change from bright red to dark brown/black. After being stirred
for 15 min at that temperature, the reaction was quenched
with saturated aqueous NH4Cl (10 mL) and the mixture was
extracted with tert-butyl methyl ether (3 × 20 mL) after
reaching ambient temperature. The combined organic layers
were dried over MgSO4, the solvent was evaporated, and the
residue was purified by flash chromatography on silica (hex-
anes/EtOAc, 100/1 f 30/1) providing the title compound as a
white solid (243 mg, 79%). 1H NMR (400 MHz, CDCl3): δ 2.38
(t, J ) 7.5 Hz, 4H), 2.11 (m, 2H), 1.78 (t, J ) 2.5 Hz, 3H), 1.55
(m, 4H), 1.46 (quint, J ) 7.2 Hz, 2H), 1.31 (m, 20H), 0.88 (t, J
) 6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3): δ 211.9, 79.6, 75.4,
43.0, 31.8, 29.7 (*2), 29.6 (*2), 29.4, 29.3, 29.2, 29.1 (*2), 24.1,
24.0, 22.7, 18.8, 14.2, 3.6. IR (film): 2953, 2927, 2914, 2849,
2254, 1701, 1471, 1420, 909, 734. MS (EI): m/z (rel intensity)
306 ([M+], 18), 291 (2), 249 (8), 239 (26), 221 (24), 211 (2), 141
(11), 129 (12), 113 (79), 97 (13), 95 (46), 85 (28), 79 (11), 68
(57), 67 (32), 58 (31), 55 (53), 43 (100), 41 (44). HRMS: calcd
306.292265, found 306.292584. Anal. Calcd for C21H38O: C,
82.28; H, 12.50. Found: C, 82.15; H, 12.59.
Rep r esen ta tive P r oced u r es for Selective Mon oa lk y-
la tion Rea ction s. 1-Ch lor o-4-octylben zen e (7). Meth od
A. A solution of octylmagnesium bromide (0.4 M in THF, 120
mL) was added over 15 min to a solution of 1,4-dichlorobenzene
5 (4.67 g, 31.8 mmol) and Fe(acac)3 (1.13 g, 3.2 mmol) in THF
(200 mL) and NMP (15 mL), causing an immediate color
change from red to dark brown/black and a slight increase in
temperature (ca. 40 °C). After the mixture was stirred for 30
min, additional octylmagnesium bromide (0.4 M in THF, 22
mL) and Fe(acac)3 (565 mg, 1.6 mmol) were introduced, and
stirring was continued for 30 min. The reaction was quenched
with dilute HCl, the aqueous phase was repeatedly extracted
with tert-butyl methyl ether, the combined organic layers were
dried (Na2SO4) and evaporated, and the residue was purified
by distillation (bp 65 °C, 10-4 Torr) to give product 7 as a
Exp er im en ta l Section
R ep r esen t a t ive P r oced u r e for t h e Ir on -Ca t a lyzed
Rea ction of En ol Tr ifla tes w ith Gr ign a r d Rea gen ts:
8-Tetr a d ecyl-1,4-d ioxa sp ir o[4.5]d ec-7-en e (Ta ble 1, En tr y
8). A solution of C14H29MgCl (1 M in THF, 0.6 mL, 0.6 mmol)
was rapidly added to a solution of trifluoromethanesulfonic
acid 1,4-dioxaspiro[4.5]dec-7-en-8-yl ester (154 mg, 0.5 mmol)
and Fe(acac)3 (9 mg, 5 mol %) in THF (10 mL) and NMP (0.46
mL) at -30 °C under argon, causing an immediate color
change from orange-red to brown/black. The mixture was
stirred for 15 min at that temperature before it was quenched
with NH4Cl (5 mL). The aqueous phase was repeatedly
extracted with Et2O, the combined organic layers were dried
over Na2SO4, and the solvent was evaporated. Purification of
the residue by flash chromatography on silica (hexanes/EtOAc,
30:1) provided 8-tetradecyl-1,4-dioxaspiro[4.5]dec-7-ene (110
mg, 65%) as a colorless oil. 1H NMR (400 MHz, CD2Cl2): δ
5.27 (m, 1H), 3.92 (s, 4H), 2.19 (m, 2H), 2.11 (m, 2H), 1.95 (m,
2H), 1.71 (t, J ) 6.5 Hz, 2H), 1.38 (m, 2H), 1.27 (m, 22H), 0.88
(t, J ) 7.0 Hz, 3H). 13C NMR (100 MHz, CD2Cl2): δ 118.1,
108.4, 64.6, 37.5, 36.0, 32.3, 31.6, 30.1, 30.1, 30.0, 29.9, 29.8,
29.8, 28.2, 27.9, 23.1, 14.3. IR (film): 2924, 2853, 1671, 1377,
1119, 1060, 947, 861, 722 cm-1. MS (EI): m/z (rel int.) 336 (34
[M+]), 254 (4), 153 (9), 139 (5), 99 (7), 86 (100), 81 (3),67 (4),
55 (4), 43 (8). HRMS: calcd for C22H40O2 336.302830, found
336.302668.
All other compounds were prepared analogously. Their
analytical and spectroscopic data are compiled in the Sup-
porting Information.
P r ep a r a tion of [Me4F e][Li2(OEt2)2].25a A solution of
anhydrous FeCl3 (2.0 g, 12.3 mmol) in Et2O (40 mL) was added
dropwise at -78 °C to a solution of MeLi (38.4 mL, 1.6 M in
Et2O, 61.5 mmol) in Et2O (40 mL). The dark brown reaction
mixture was stirred at -78 °C for 12 h, and stirring was
continued for an additional 10 h at -30 °C. During this period
of time, the color changed from dark brown to orange with
concomitant formation of a white precipitate. The reaction
mixture was allowed to reach 0 °C before the precipitated LiCl
3948 J . Org. Chem., Vol. 69, No. 11, 2004