A highly efficient and practical preparation of 2,4-pentadienyltitaniums and their γ-selective addition reaction with aldehydes and ketones

Article abstract of DOI:10.1016/S0022-328X(00)00911-6

A variety of penta-2,4-dienyltitanium complexes including those having a functional group were readily prepared from a divalent titanium reagent, Ti(O-i-Pr)₄/2i-PrMgCl, and penta-1,4-dien-3-ol or penta-2,4-dien-1-ol derivatives, and the organotitaniums thus prepared reacted with aldehydes and ketones smoothly to afford the corresponding penta-1,4-dien-3-yl carbinols highly predominantly in excellent yield.

Full text of DOI:10.1016/S0022-328X(00)00911-6

Journal of Organometallic Chemistry 624 (2001) 151–156
www.elsevier.nl/locate/jorganchem
A highly efficient and practical preparation of
2,4-pentadienyltitaniums and their g-selective addition reaction
with aldehydes and ketones
Sentaro Okamoto, Fumie Sato *
Department of Biomolecular Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama,
Kanagawa 226-8501, Japan
Dedicated to Professor Jean Normant in recognition of his outstanding contribution to organometallic chemistry
Abstract
A variety of penta-2,4-dienyltitanium complexes including those having a functional group were readily prepared from a
divalent titanium reagent, Ti(O–i-Pr)4/2i-PrMgCl, and penta-1,4-dien-3-ol or penta-2,4-dien-1-ol derivatives, and the organotita-
niums thus prepared reacted with aldehydes and ketones smoothly to afford the corresponding penta-1,4-dien-3-yl carbinols highly
predominantly in excellent yield. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: 2,4-Pentadienylmetal; Titanium; 1-(Penta-1,4-dien-3-yl)alkanol; Aldehyde; Ketone; Addition
enyltitaniums are readily prepared and that they react
with aldehydes and ketones with excellent g-selectivity.
1. Introduction
Preparation of penta-2,4-dienylmetals and their reac-
tion with aldehydes and ketones have attracted much
interest [1]. As shown in Eq. (1), the reaction can give
two types of products, i.e. conjugated penta-2,4-dien-l-
yl carbinols (1) via the reaction at the a- and/or o-
(1)
position(s) and non-conjugated penta-1,4-dien-3-yl
carbinols (2) through the reaction at the g-position.
From the synthetic viewpoint, the greatest concerns in
the community of organic chemists have been to
achieve easy accessibility to the reagent and to realize
high regioselectivity of the reaction. It has been re-
vealed that the regioselectivity can be controlled effi-
ciently by selecting a proper metal reagent. The
reagents which show excellent g-selectivity include the
compounds of indium [1w,x], chromium [1f,t], zinc
[1a–c,v], silicon [1s], and boron [1j,k,u], and the readi-
ness of access to these reagents varies depending on the
metal. Herein, we report that a variety of penta-2,4-di-
Recently, we reported an efficient method for prepar-
ing allyltitaniums from a divalent titanium reagent
Ti(O–i-Pr)4/2i-PrMgX (X=Cl or Br) (3) [2] and read-
ily available allylic alcohol derivatives such as acetates
and carbonates, which proceeds via an oxidative addi-
tion pathway [3]. With this result, we were interested in
the preparation of penta-2,4-dienyltitaniums from 3
and 1,4-pentadien-3-ol derivatives (4) such as ethyl
carbonates and acetates and their reaction with alde-
hydes and ketones (Eq. (2)). As a variety of 4 can be
prepared readily, we expected that the reaction might
open up an efficient and practical access to a variety of
1 or 2.
* Corresponding author.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00911-6

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S. Okamoto, F. Sato / Journal of Organometallic Chemistry 624 (2001) 151–156
Table 1
Preparation of Penta-2,4-dienyltitaniums from 3 and 4, and their reaction with aldehydes and ketones a
aldehydes and ketones are summarized in Table 1. As
can be seen from the table, various kinds of pentadi-
enyltitanium compounds can be prepared readily from
the corresponding 4, and they react with aldehydes and
ketones with excellent g-regioselectivity to afford penta-
1,4-dien-3-yl carbinols (2) in excellent yield. Several
characteristic features can be seen from the table. As a
variety of 1,4-pentadien-3-ol derivatives are prepared
readily from the corresponding a,b-unsaturated alde-
hyde and vinyllithium or magnesium compound, we
mostly used 4 as the substrate; however, the corre-
sponding 2,4-pentadien-1-ol derivatives can be used
(2)
2. Results and discussion
The results of the preparation of penta-2,4-dienyltita-
niums from 3 and 4 and their reaction with a variety of

S. Okamoto, F. Sato / Journal of Organometallic Chemistry 624 (2001) 151–156
153
instead of 4 as shown in entry 9 (vs. entry 2). Since an
organotitanium reagent shows high chemoselectivity
[3,4], it is possible to carry out the reaction with alde-
hydes and ketones having a functional group (entries
4–6). It is also feasible to prepare functionalized penta-
2,4-dienyltitaniums from 4 having a functional group
such as ester moiety (entry 13)1. Thus, penta-1,4-dien-3-
yl carbinols having a variety of functional groups can
be readily synthesized in a one-pot reaction. In regard
to the diastereoselectivity of the reaction, the reaction
of substituted pentadienyltitaniums with aldehydes gave
the corresponding but-3-en-1-ol derivatives with anti-
stereochemistry preferentially (entry 11), as is the case
reported for g-substituted allyltitaniums [3,4]. For the
reaction with chiral a-amino aldehydes, the reaction
proceeded with high diastereoselectivity as represented
by the reaction shown in entry 6 [5].
pounds [1r]2,3. As the present reaction can be carried
out starting from pentadienyl alcohol derivatives by
using inexpensive and non-toxic metallic reagents and
the reaction procedure is operationally simple, we be-
lieve that the present method is synthetically advanta-
geous over previous methods, and thus, the method
might be used widely to prepare various kinds of penta-
1,4-dien-3-yl carbinols including those having func-
tional groups4. Further investigation on the scope of
the present reaction and synthetic utilization of the
resulting penta-1,4-dien-3-yl carbinols is underway in
our laboratory.
3. Experimental
3.1. General
The predominant production of g-addition prod-
uct(s) 2 and the diastereoselectivity observed for the
reaction shown in entry 11 can be explained by assum-
ing that the generated allyltitanium would exist mostly
as a primary alkyl derivative in order to avoid the steric
repulsion, and the addition reaction with carbonyl com-
pounds proceeds through the six-membered chair-like
transition structure illustrated in Eq. (3), in which the
substituent at the g-position of the allylic titaniums is in
the preferred equatorial position [3,4].
1H- and 13C-NMR spectra were recorded in CDCl3 at
300 and 75 MHz, respectively, on a Varian Gemini-
2000 spectrometer. Chemical shifts are reported in parts
per million (ppm, l) relative to Me4Si (l 0.00). IR
spectra were recorded on an FT-IR spectrometer
(JASCO F’TIIR-230). Elemental analyses were per-
formed on an elemental automatic analyzer. All reac-
tions sensitive to oxygen and/or moisture were
performed under an argon atmosphere. Dry solvents
(THF and ethyl ether) were purchased from Kanto
Chemicals. Ti(O–i-Pr)4 was distilled under reduced
pressure and was stored under argon. i-PrMgCl was
prepared from magnesium turnings and i-PrCl in ether.
(3)
3.2. Preparation of penta-2,4-dienyltitaniums and their
reaction with carbonyl compounds
To a solution of ethyl-1,4-pentadien-3-yl carbonate
(219 mg, 1.4 mmol) and Ti(O–i-Pr)4 (444 ml, 1.5 mmol)
in diethyl ether (10 ml) was added i-PrMgCl (2.1 ml,
1.43 M in diethyl ether, 3.0 mmol) at −50°C. After
stirring at −50 to −40°C for 2 h, to the mixture was
added carbonyl compound (1.0 mmol) at −40°C. The
resulting mixture was allowed to warm to 0°C over 1 h
and then quenched by addition of saturated aqueous
NaHCO3 (0.3 ml). After addition of NaF (1.5 g) and
Celite (1.5 g), the mixture was filtered through a pad of
Celite with diethyl ether. The filtrate was concentrated
In summary, we have developed an efficient method
for preparing a variety of penta-2,4-dienyltitanium
compounds by the reaction of penta-1,4-dien-3-ol or
penta-2,4-dien-1-ol derivatives with a Ti(O-i-Pr)4/2i-
PrMgCl reagent, and have found that their addition
reaction with aldehydes and ketones proceeds with
excellent g-regioselectivity. As mentioned in the intro-
duction section, a variety of pentadienylmetals which
afford selectively penta-1,4-dien-3-yl carbinols by their
reaction with carbonyl compounds have been devel-
oped. Among them, pentadienylmetals which can be
prepared starting from readily available pentadienyl
alcohol derivatives are restricted to the chromium com-
2 Penta-2,4-dienylindium, zinc (and also chromium) compounds
were prepared from penta-2,4-dienyl halides, while pentadienylsilanes
and boranes were synthesized from pentadienyllithiums or potassiums
via transmetallation reaction. See Ref. [1].
3 The reductive coupling of pentadienyl acetates with carbonyl
compounds using a Pd(0)–SmI2 reagent has been reported; however,
the regioslectivity is moderate and is highly dependent on the struc-
ture of the substrates, see Ref. [1n].
1 For the preparation of allyltitaniums with functional groups, see
Refs. [3a,e,f].
4 For examples of utilization of penta-1,4-dien-3-yl carbinols in
organic synthesis: Refs. [1o,u,v,x] and refs. cited therein.

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S. Okamoto, F. Sato / Journal of Organometallic Chemistry 624 (2001) 151–156
in vacuo to give a crude residue, which was analyzed by
1H-NMR and GC to determine the ratio of regioiso-
mers. The residue was subjected to column chromatog-
raphy on silica gel (hexanes/diethyl ether) to give a
mixture of 1 and 2. The combined yield and ratio of the
resulting 1 and 2 are indicated in Table 1. In the case of
the reaction for entries 12 and 13 in Table 1, the
reaction was carried out using 4 (1.0 mmol), Ti(O–i-
Pr)4 (1.3 mmol), i-PrMgCl (2.6 mmol), and acetone (1.3
mmol), and the yield indicated in the table is based on
4.
3.2.3. 5-(N,N-Dibenzyl)amino-3-6inylhex-1-en-4-ol
(entry 6, Table 1)
The diastereo ratio was determined by 1H-NMR
analysis based on peak intensity of methyl protons
[major: l 1.11 (d, J=6.6Hz) vs. minor: l 1.14 (d,
J=6.9Hz)] to be 95:5. The stereochemistry was specu-
lated in analogy with the reported reactions of a-amino
aldehydes with allyl and propargylorganometallic
reagents [5]. Colorless oil. Data for the major (anti-)-
1
isomer: H-NMR (300 MHz, CDCl3) l 1.11 (d, J=6.6
Hz, 3H, CH3), 2.84 (quintet, J=6.6 Hz, 1H, CHN),
3.10–3.23 (m, 1H, allylic CH), 3.43 and 3.76 (2d,
J=13.8 and 13.8 Hz, CH2Ph), 3.68 (dd, J=4.8, 5.1
Hz, 1H, CHO), 4.82–5.07 (m, 4H, CHꢀCH2), 5.53
(ddd, J=7.8, 10.5,17.4 Hz, 1H, CHꢀCH2), 5.69 (ddd,
J=7.8, 10.5, 17.1 Hz, 1H, CHꢀCH2), 7.15–7.42 (m,
1OH, Ph); 13C-NMR (75 MHz, CDCl3) 6 8.1, 50.5,
54.4, 54.5, 75.0, 116.1, 118.0, 126.8, 128.2, 129.0, 136.2,
138.2, 140.3; IR (neat) 3456, 3062, 3026, 2975, 2931,
2803, 1946, 1810, 1701, 1636, 1601, 1493, 1453, 1376,
1243, 1143, 1072, 1027,1001,916,747,698 cm−1. Anal.
Calc. for C22H27NO: C, 82.20; H, 8.47; N, 4.36. Found:
C, 81.90; H, 8.54; N, 4.60%.
1
The H- and 13C-NMR data of the resulting adducts,
3-vinylundec-1-en-4-ol (entry 1) [1w], 4-phenyl-3-vinyl-
but-1-en-4-ol (entries 2 and 9) [1s,w], and (E)-6-phenyl-
3-vinylhex-1,5-dien-4-ol (entry 3) [1s], were in good
agreement with those reported.
3.2.1. 1-(3-Acetoxyphenyl)-2-6inylbut-3-en-1-ol (entry
4, Table 1)
The aldehyde was added as a solution in ether to the
1
mixture of the pentadienyltitanium. Colorless oil. H-
NMR (300 MHz, CDCl3) l 2.27 (br 5, 1H, OH), 2.29
(s, 3H, CH3), 3.08 (q, J=7.2 Hz, 1H, allylic proton),
4.62 (d, J=6.3 Hz, 1H, CHO), 5.03 (dt, J=17.4, 1.5
Hz, 1H, CHꢀCH2), 5.08 (dt, J=9.0, 1.2 Hz, 1H,
CHꢀCH2), 5.16 (ddd, J=1.2, 1.8, 17.1 Hz, 1H,
CHꢀCH2), 5.23 (ddd, J=1.0, 1.5, 10.5 Hz, 1H,
CHꢀCH2), 5.71 (ddd, J=7.2, 10.5, 17.4 Hz, 1H,
CHꢀCH2), 5.83 (ddd, J=8.1, 10.5,17.4 Hz, 1H,
CHꢀCH2), 7.00 (ddd, J=0.9, 2.1, 9.0 H, 1H, Ar), 7.07
(t, J=4.2 Hz, 1H, Ar), 7.17 (d, J=7.5 Hz, 1H, Ar),
7.34 (t, J=8.0 Hz, 1H, Ar); 13C-NMR (75 MHz,
CDCl3) 6 20.9, 55.8, 75.6, 117.3, 118.3, 120.0, 120.6,
124.3, 129.0, 136.4, 136.6, 143.9, 150.6, 169.5; IR (neat)
3473, 3077, 2979, 2876, 2064, 1766, 1635, 1610, 1590,
1486, 1444, 1371, 1207, 1139, 1015, 917, 799, 750, 700
cm−1. Anal. Calc. for C14H1603: C, 72.39; H, 6.94.
Found: C, 72.08; H, 7.26%.
3.2.4. 1-(Penta-1,4-dien-3-yl)cyclohexan-1-ol (entry 7,
Table 1)
1
Colorless oil. H-NMR (300 MHz, CDCl3) l 1.05–
1.80 (m, 1OH, 5×CH2), 2.73 (t, J=8.6 Hz, 1H, allylic
proton), 5.04–5.20 (m, 4H, CHꢀCH2), 5.92 (ddd, J=
8.6, 10.5, 18.9 Hz, 2H, CHꢀCH2); 13C-NMR (75 MHz,
CDCl3) 621.6, 25.6, 35.0, 59.5,72.2, 117.3, 137.0; IR
(neat) 3462, 3074, 2933, 2668, 1830, 1634, 1448, 1354,
1263, 1135, 1038, 1001, 963, 914, 803, 759, 691 cm−1
.
Anal. Calc. for C11H18O: C, 79.47; H, 10.91. Found: C,
79.80; H, 10.57%.
3.2.5. 5-(Penta-1,4-dien-3-yl)nonan-5-ol (entry 8,
Table 1)
1
Colorless oil. H-NMR (300 MHz, CDCl3) l 0.91 (t,
3.2.2. 1-(4-Cyanophenyl)-2-6inylbut-3-en-1-ol (entry 5,
Table 1)
J=7.1 Hz, 6H, CH3), 1.17–1.60 (m, 12H, CH2), 2.88
(t, J=8.4 Hz, 1H, CH), 5.05–5.17 (m, 4H, CHꢀCH2),
5.93 (ddd, J=8.4, 10.2, 18.6 Hz, 2H, CHꢀCH2); 13C-
NMR (75 MHz, CDCl3) l 14.0, 23.2, 25.2, 36.5, 56.4,
75.0, 117.0, 137.3; IR (neat) 3477, 3074, 2956, 2935,
2871, 1828, 1633, 1465, 1415, 1378, 1341, 1260, 1126,
1001, 912, 812, 731, 687 cm−1. Anal. Calc. for
C14H26O: C, 79.94; H, 12.46. Found: C, 79.52; H,
12.46%.
The aldehyde was added as a solution in THF to the
1
mixture of the pentadienyltitanium. Colorless oil. H-
NMR (300 MHz, CDCl3) l 2.36 (d, J=2.7 Hz, 1H,
OH), 3.05 (q, J=7.5 Hz, 1H, allylic CH), 4.67 (dd,
J=2.7, 6.6 Hz, 1H, CHO), 4.96–5.27 (m, 4H,
CHꢀCH2), 5.69 (ddd, J=7.2, 10.2, 17.4 Hz, 1H,
CHꢀCH2), 5.81 (ddd, J=8.4, 10.2, 18.3 Hz, 1H,
CHꢀCH2), 7.43 (d, J=8.1 Hz, 2H, Ar), 7.63 (d, J=8.1
Hz, 2H, Ar); 13C-NMR (75 MHz, CDCl3) 656.2, 75.3,
111.2, 117.9, 118.9, 119.1, 127.6, 131.9, 135.7, 136.0,
147.3; IR (neat) 3468, 3078, 3005, 2979, 2878, 2228,
1925, 1845,1635, 1609, 1504, 1412, 1301, 1198, 1046,
998, 921, 835, 763, 684 cm−1. Anal. Calc. for
C13H13NO: C, 78.36; H, 6.58; N, 7.03. Found: C, 78.06;
H, 6.75; N, 7.08%.
3.2.6. 1-(Hexa-1,4-dien-3-yl)cyclohexan-1-ol (entry 10,
Table 1)
Colorless oil. The olefinic stereoisomers could not be
separated by column chromatography. For the (E)-iso-
mer: 1H-NMR (300 MHz, CDCl3) l 1.05–2.00 (m,
1OH, CH2), 1.71 (d, J=4.5 Hz, 3H, CH3), 2.62–2.72
(m, 1H, CH), 5.02–5.14 (m, 2H, CHꢀCH2), 5.44–5.57

S. Okamoto, F. Sato / Journal of Organometallic Chemistry 624 (2001) 151–156
155
(m, 2H, CHꢀCH), 5.89(ddd, J=8.7, 10.2, 18.9 Hz, 1H,
CHꢀCH2); 13C-NMR (75 MHz, CDCl3) l 18.1, 21.6,
21.7, 25.7, 34.9, 35.0, 58.5, 72.3, 116.6, 128.2, 129.3,
27.02, 28.2, 28.7, 59.0, 63.7, 66.9, 71.6, 116.8, 129.5,
131.7, 137.4, 154.9. Selected peaks for (Z)-isomer: H-
NMR l 1.18 (s, 6H, CCH3), 3.08 (dd, J=8.4, 9.3 Hz,
1
1
137.7. Selected peaks for the (Z)-isomer: H-NMR (300
1H, CH). IR (neat) 3473, 3075 2975, 2935, 1745, 1635,
1466, 1403, 1369, 1262, 1166, 1006, 915, 792 cm−1
.
MHz, CDCl3) l 3.08 (t, J=9.0 Hz, 1H, CH), 5.42–
5.69 (m, 2H, CHꢀCH), 5.86 (ddd, J=7.8, 10.8, 18.9
Hz, 1H, CHꢀCH2); 13C-NMR (75 MHz, CDCl3) l 34.5,
52.5, 73.0, 126.4, 128.5, 137.3. IR (neat) 3462, 2933,
2856, 1635, 1448, 1375, 1262, 1135, 998, 970, 911, 835
cm−1. Anal. Calc. for C12H20O: C, 79.94; H, 11.18.
Found: C, 79.56; H, 11.12%.
Anal. Calc. for C14H24O4: C, 65.60; H, 9.44. Found: C,
65.48; H, 9.43%.
Acknowledgements
We thank the Ministry of Education, Science, Sports
and Culture (Japan) for financial support.
3.2.7. 1-Phenyl-2-6inyl-4-methylpent-3-en-1-ol (entry
11, Table 1)
Diastereomeric ratio was determined to be 90:10 by
1H-NMR analysis. Colorless oil. (R*,S*)-isomer (major
diastereomer: H-NMR (300 MHz, CDCl3) l 1.34 (d,
References
1
J=1.2 Hz, 3H, CH3), 1.61 (d, J=1.5 Hz, 3H, CH3),
2.23 (d, J=3.3 Hz, 1H, OH), 3.18–3.32 (m, 1H, CH),
4.50 (dd, J=3.3, 7.5 Hz, 1H, CHO), 5.03 (br d, J=9.6
Hz, 1H, CHꢀC(CH3)2), 5.10–5.20 (m, 2H, CHꢀCH2),
5.72–5.87 (m, 1H, CHꢀCH2), 7.20–7.40 (m, 5H, Ph);
13C-NMR (75 MHz, CDCl3) l 17.7,25.7, 51.5, 76.4,
116.9, 122.2, 126.8, 127.3, 127.9, 134.5, 138.1, 142.3.
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Yamauchi, A. Nakamura, T. Sei, Y. Kai, N. Yasuoka, N. Kasai,
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2835.
Selected
peaks
for
(R*,R*)-isomer
(minor
diastereomer): 1H-NMR (300 MHz, CDCl3) l 4.64–
4.80 (m, 1H, CHO), 5.62 (ddd, J=6.6, 10.5, 17.2 Hz,
1H, CHꢀCH2); 13C-NMR (75 MHz, CDCl3) 6 73.3,
116.0, 122.3, 136.5, 137.5, 142.1. IR (neat, a mixture of
diastereomers) 3419, 3029, 2969, 2913, 2728, 1944,
1810, 1671, 1635, 1493, 1453, 1375, 1194, 1027, 915,
843, 761, 700 cm−1. Anal. Calc. for C14H18O: C, 83.12;
H, 8.97. Found: C, 83.15; H, 8.74%.
3.2.8. 2,5-Dimethyl-4-6inylhex-2-en-5-ol (santolina
alcohol) [6] (entry 12, Table 1)
Colorless oil. 1H-NMR (300 MHz, CDCl3) l 1.16
and 1.18 (2s, each 3H, 2×CH3), 1.66 (d, J=1.2 Hz,
3H, CH3), 1.76 (d, J=1.2 Hz, 3H, CH3), 2.98 (dd,
J=8.7, 9.9 Hz, 1H, CH), 5.03–5.12 (m, 2H, CHꢀCH2),
5.16 (br d, J=8.7 Hz, 1H, CHꢀC(CH3)2), 5.72–5.87
(m, CHꢀCH2); 13C-NMR (75 MHz, CDCl3) l 18.1,
26.1, 26.5, 26.9, 54.4, 72.5, 116.4, 122.7, 134.9, 138.0;
IR (neat) 3421, 3076, 2973, 2929, 1733, 1635, 1455,
1375, 1260, 1139, 998, 912, 849, 786 cm−1
.
3.2.9. Ethyl 6-(2-hydroxyprop2-yl)octa-4,7-dien-1-yl
carbonate (entry 13, Table 1)
Colorless oil. Data for (E)-isomer: 1H-NMR (300
MHz, CDCl3) l 1.17 (s, 6H, CCH3), 1.31 (t, J=7.1 Hz,
3H, CH2CH3), 1.62–1.86 (m, 3H, CH2 and OH), 2.10–
2.20 (m, 2H, allylic CH2), 2.64–2.77 (m, 1H, CH), 4.14
(t, J=6.3 Hz, 2H, OCH2CH2), 4.19 (q, J=7.1 Hz,
OCH2CH3), 5.05–5.16 (m, 2H, CHꢀCH2), 5.43–5.60
(m, 2H, CHꢀCH), 5.85 (ddd, J=8.1, 10.2, 18.6 Hz, 1H,
CHꢀCH2); 13C-NMR (75 MHz, CDCl3) l 14.2, 26.97,
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