Benzyl bromide addition to pentafluorobenzaldehyde by Zaitsev-Barbier reaction promoted with complex systems underlain by iron pentacarbonyl

Article abstract of DOI:10.1134/S1070428009080119

Iron pentacarbonyl promots addition of benzyl bromide to benzaldehydes by Zaitsev-Barbier reaction only in the presence of nucleophilic additives [HMPT or (S)-N-benzoyl-2-methoxycarbonylpyrrolidine].

Full text of DOI:10.1134/S1070428009080119

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 8, pp. 1181−1184. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.B. Terent’ev, T.T. Vasil’eva, A.A. Ambartsumyan, O.V. Chakhovskaya, N.E. Mysova, K.A. Kochetkov, 2009, published in
Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 8, pp. 1192−1195.
Benzyl Bromide Addition to Pentafluorobenzaldehyde
by Zaitsev–Barbier Reaction Promoted with Complex Systems
Underlain by Iron Pentacarbonyl
A. B. Terent’ev†, T. T. Vasil’eva,A. A. Ambartsumyan,
O. V. Chakhovskaya, N. E. Mysova, and K. A. Kochetkov
Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences
Moscow,119991 Russia
e-mail: const@ineos.ac.ru
Received July 28, 2008
Abstract—Iron pentacarbonyl promots addition of benzyl bromide to benzaldehydes by Zaitsev–Barbier reaction
only in the presence of nucleophilic additives [HMPT or (S)-N-benzoyl-2-methoxycarbonylpyrrolidine].
DOI: 10.1134/S1070428009080119
of Fe(CO)5] and at higher temperature (110 instead of
80°C) we succeeded in preparation of reaction products
of benzyl bromide (Ia) and pentafluorobenzyl bromide
(Ib) with aldehydes IIa–IIc, secondary alcohols IIIa–
IIIe, although in low yields (see the scheme and the table).
Benzyl bromide as a rule does not enter into the radical
addition and telomerization reactions under the conditions
of peroxide initiation [1] but it is possible to attain
a selective homolysis of the C-Br bond with subsequent
addition to a C=C bond at the use metal complex catalysts:
systems CuBr–dipyridyl [2] or Fe(CO)5–HMPT [3, 4],
and also of the other metal complexes. In all events
alongside the addition products a large quantity of dibenzyl
is formed, sometimes it is the main reaction product.
We applied as nucleophilic additives HMPTand a chiral
amide, (S)-N-benzoyl-2-methoxycarbonylpyrrolidine (IV),
in chlorobenzene or heptane.Alongside the target product
practically always dibenzyl and decafluorodibenzyl were
obtained (runs nos. 2, 3, 5, 6, 9, 10), and the best yields
of alcohols III were attained at the use of penta-
fluorobenzaldehyde (IIb) (runs nos. 6, 7). Yet although
the use of amide (S)-(IV) instead of HMPT in
chlorobenzene did not result in qualitative changes (runs
nos. 5, 6), the application of amide (S)-(IV) in heptane
prevented the dibenzyl formation with the retention of
the yield of alcohol IIIc (run no. 7).
The extension of the addition of alkyl halides to the
C=C bond in the presence of systems including Fe(CO)5
to the C=O bonds (by the Zaitsev–Barbier reaction [5–
9] ) proved to be very successful [10]. For instance, in
the presence of Fe(CO)5 under standard conditions
reactions were effectively carried out with benzaldehyde
(IIa), pentafluorobenzaldehyde (IIb), 4-chlorobenz-
aldehyde (IIc) to add to these compounds various aliphatic
organohalogen substances [11] except for benzyl bromide
(Ia).
Scheme.
In this study we for the first time succeeded in addition
of substituted benzyl bromides Ia and Ib to benzaldehydes
IIa–IIc by the Zaitsev–Barbier reaction with the
promotion by complex system underlain by Fe(CO)5 and
containing a series of nucleophilic cocatalysts.
Ar'
*
Fe(CO)5
Nu_
Ar
ArCH2Br + Ar'CHO
IIa_IIc
OH
IIIa_IIIe
Ia, Ib
I, Ar = C6H5 (a), C6F5 (b); II, Ar' = C6H5 (a), C6F5 (b),
4-C6H4Cl (c); III,Ar =Ar’= C6H5 (a), C6F5 (b);Ar = C6H5,
Ar' =C6F5 (c), Ar = C6H5,Ar' = 4-ClC6H4 (d);Ar = C6F5,
Ar' = C6H5 (e).
Whereas in the absence of nucleophilic additives the
reaction did not occur, at their addition [0.5 mol per 1 mol
† Deceased.
1181

TERENT’EV et al.
Reactions of benzyl bromides Ia and Ib with benzaldehydes IIa–IIc
1182
Run
no.
Benzyl
Solvent
Dibenzyl
Reaction products
(yield, %)
Aldehyde
Cocatalyst
bromide
(temperature)
(decafluorodibenzyl), %
1
2
Ia
Ia
Ia
Ia
Ia
Ia
Ia
Ia
Ib
Ib
IIb
IIa
IIc
IIb
IIb
IIb
IIb
IIb
IIb
IIa
(S)-(IV)
HMPT
HMPT
-
C6H6 (80°C)
ClC6H5 (110°C)
ClC6H5 (110°C)
ClC6H5 (110°C)
ClC6H5 (110°C)
ClC6H5 (110°C)
C7H16 (98°C)
−
10
−
IIIa (15)
IIId (17 )
−
3
5
4
-
5
HMPT
(S)-(IV)
(S)-(IV)
HMPT
HMPT
HMPT
6
IIIc (18)
IIIc (20)
IIIc (28)
−
6
5
7
-
8
C7H16 (98°C)
-
9
ClC6H5 (110°C)
ClC6H5 (110°C)
(10–12)
(11–13)
IIIb (3.5)
10
IIIe (5)
alkylmagnesium halide, and it is difficult to apply the
Grignard reaction for preparation of perfuoro-containing
hydroxy compounds of the series under consideration
[18]. The developed mode of alkylation of compound IIb
supplements the known procedures of preparation of
secondary polyfluorinated hydroxy compounds by
nucleophilic perfluoroalkylation [19] and by employing
derivatives of difficultly available iron tetracarbonyl
iodides [20].
Formerly in Zaitsev–Barbier reactions involving
pentafluorobenzaldehyde (IIb) [11] a strong reduction in
adducts yields was observed in the process with a electro-
philic reagent as compared to a nucleophilic one.
Analogous trend we also observed in reactions of
aldehydes with electrophilic pentafluorobenzyl bromide
(Ib) resulting in the prevailing formation of decafluoro-
dibenzyl (runs nos. 9, 10).
We showed earlier by UV spectroscopy that in the
systems containing Fe(CO)5 and nucleophilic additives
charge-transfer complexes were observed [12], and
especially in the system Fe(CO)5–(S)-(IV) formed
a complex with an intensive charge transfer band [13].
Proceeding from the data on these complexes [14] arising
from the interaction between Fe(CO)5 and Lewis bases
and from the data on the formation of anion-radical
species which were observed by ESR method [15, 16] it
was presumable that the benzylation of aldehydes
occurred by the standard route of addition products
formation we had suggested previously [17]. Therewith
first the activating complexing occurs [15] at the addition
of a number of compounds reacting with Fe(CO)5, like
DMF, HMPT, or amide IV [13]. Apparently other
nucleophiles may act like these activating additives [15],
and we actively look for these compounds. The use of
amide (S)-(IV) did not result in the stereoselectivity of
the process, and the secondary alcohol IIIc was obtained
in a racemic form.
Thus we succeeded for the first time in addition of
benzyl bromide to the C=O bond of benzaldehydes IIa–
IIc in the presence of Fe(CO)5 and a nucleophilic additive
[HMPT or (S)-(IV)] and in developing the conditions
where the target alcohol IIIc formed in heptane solution
without dibenzyl.
EXPERIMENTAL
Mass spectra were measured on an instrument VG-
7070E (ionizing electrons energy 70 eV). The analysis of
reaction mixtures by GLC was carried out on a chromato-
graph LKhM-80, steel column (1300 × 3 mm), stationary
phase 15% SKTFT-50X on Chromaton-N-AW, carrier
gas helium, flow rate 60 cm3/min, detector catharometer,
1
ramp 50–250°C at a rate 6 deg/min. H and 19F NMR
spectra were registered on a spectrometer Bruker WP-
300 at 300 and 282 ΜHz respectively from solutions in
CDCl3, chemical shifts were reported with respect to
TMS and CF3CO2H. All organic reagents were purified
by distillation. Pentafluorobenzyl bromide and
pentafluorobenzaldehyde were purchased from PIM,
The organomagnesium compounds from perfluoroalkyl
halides are known to be commonly prepared by an
exchange between perfluoroalkyl halides with
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

BENZYL BROMIDE ADDITION TO PENTAFLUOROBENZALDEHYDE
1183
[C6H5CHOH]+ (70), 92 [C7H8]+ (100), 79 [C6H7]+(45),
77 [C6H5]+ (24).
Russia. Fe(CO)5 from Fluka (97%) was used without
additional purification.
1,2-Bis(pentafluorophenyl)ethanol (IIIb) [18].
Mass spectrum, m/z (Irel, %): 378 [Μ]+ (0), 197
[C6F5CHOH]+ (100), 181 [C6F5CH2]+ (38), 169 (26), 149
[C6F5]+ (20), 119 (23), 99 (19).
1-(Pentafluorophenyl)-2-phenylethanol (IIIc). (a)
(see the table, run no. 7). A solution of 0.2 g (1 mmol) of
compound IIb, 0.18 ml (1 mmol) of benzyl bromide (Ia),
0.27 ml (2 mmol) of Fe(CO)5, and 0.10 g of (S)-(IV) in
1 ml of heptane was heated at reflux (98°C) for 4 h.
Vigorous evolution of CO proceeded for 2 h. The mixture
was diluted with 2 ml of benzene, treated with 1 N
hydrochloric acid, washed thrice with water, the water
layer was extracted with benzene, the combined benzene
extracts were dried with MgSO4. The residue was
evaporated, then filtered through a silica gel bed (eluent
hexane– ethyl acetate, 10:1). According to GLC data the
product did not contain initial compounds. Yield 0.081 g
1-(4-Chlorophenyl)-2-phenylethanol (IIId) [22].
Mass spectrum, m/z (Irel, %): 232/234 [Μ]+* (<1),
214/216 [Μ – H2O]+ (19), 179 [M – OH – Cl]+ (15), 178
[M – H2O – Cl]+ (17), 141 [C6H4ClCHOH]+ (62), 139
[C6H4ClCO]+ (16), 92 (100), 91 [C7H7]+ (26), 77 [C6H5]+
(37).
2-(Pentafluorophenyl)-1-phenylethanol (IIIe)
[23]. Mass spectrum, m/z (Irel, %): 288 [Μ]+ (0), 270 [Μ
– H2O]+ (12), 250 [Μ – H2O – HF]+ (9), 219 (7), 201
(4), 181 [C6F5CH2]+ (13), 108 (11), 107 [C6H5CHOH]+
(87), 79 [C6H7]+ (100), 77 [C6H5]+ (59), 51 [CF2H]+ (23),
39 [C3H3]+ (6).
1
28%, mp 59–60OC [18]. H NMR spectrum, δ, ppm:
2.65–2.67 d (2H, OH, J 6.18 Hz), 3.13–3.41 q.d (2H,
CHCH2, AΒ part of AΒX system, JAB 13.47, JAX 6.3,
JBX 8.1 Hz), 5.30 m (1H, CHCH2, X part of AΒX system),
7.22–7.24 m (2H, Ar), 7.25–7.37 m (3H, Ar). 19F NMR
spectrum, δ, ppm: –65.72÷–65.77 q.d (2F,Ar, J 14.4 Hz),
–77.23 t (1F, Ar, J 20.8 Hz), –84.34... –84.21 q.d (2F, Ar,
J 20.8 Hz). Mass spectrum, m/z (Irel, %): 288 [Μ]+ (0),
270 [Μ – H2O]+ (6), 250 [Μ – H2O – HF]+ (8), 197
[C6F5CHOH]+ (89), 167 [C6F5]+ (14), 99 (30), 92 [C7H8]+
(100), 91 [C7H7]+ (100), 65 (79), 51 (51), 39 [C3H3]+
(64), 29 [C2H5] (10). Found, %: C 58.74; H 3.07; F 32.26.
C14H9F5O. Calculated, %: C 58.34; H 3.15; F 32.96.
Decafluorobenzyl. Mass spectrum, m/z (Irel, %): 362
[Μ]+ (11), 291 (1), 181 [M/2]+ (100), 161 [C7HF4]+ (1).
The study was carried out under a financial support
of the Russian Foundation for Basic Research (grant no.
06-03-32820) and of the program of the Presidium of the
Russian Academy of Sciences P-8.
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