An investigation of the reactions of substituted homoallylic alcohols with various oxidation reagents

Article abstract of DOI:10.3390/70200104

Substituted homoallylic alcohols have been synthesised both by [2,3]-Wittig rearrangement of unsymmetrical bis-allylic ethers and reaction of alkenyl chloromethyl oxiranes with Mg/THF. These substrates were then oxidized using four different oxidants. When the substituted homoallylic alcohols were oxidized with pyridinium chlorochromate or zinc chlorochromate nonahydrate the corresponding carbonyl compounds were produced. The same substrates formed the corresponding allylic oxidation products together with epoxidation products when oxidized with t-BuOOH. When and t-BuOOH and catalytic amounts of OsO ₄ were used the allylic oxidation reaction was prevented and the only products formed were those in which the substituted double bond was epoxidized.

Full text of DOI:10.3390/70200104

Molecules 2002, 7, 104-111
molecules
ISSN 1420-3049
http://www.mdpi.org
An Investigation of the Reactions of Substituted Homoallylic
Alcohols with Various Oxidation Reagents
1
,*
2
S. Servi and A. Acar
1
Department of Chemistry, Fõrat University, Faculty of Science and Arts, 23169, Elazõğ, Turkey.
Department of Chemistry, Uludağ University, Faculty of Science and Arts, Bursa, Turkey.
2
*
Author to whom correspondence should be addressed; e-mail: sservi@firat.edu.tr
Received: 19 June 2001; in revised form 6 November 2001 / Accepted: 25 January 2002 / Published
8 February 2002
2
Abstract: Substituted homoallylic alcohols have been synthesised both by [2,3]-Wittig
rearrangement of unsymmetrical bis-allylic ethers and reaction of alkenyl chloromethyl
oxiranes with Mg/THF. These substrates were then oxidized using four different
oxidants. When the substituted homoallylic alcohols were oxidized with pyridinium
chlorochromate or zinc chlorochromate nonahydrate the corresponding carbonyl
compounds were produced. The same substrates formed the corresponding allylic
oxidation products together with epoxidation products when oxidized with t-BuOOH.
When and t-BuOOH and catalytic amounts of OsO were used the allylic oxidation
4
reaction was prevented and the only products formed were those in which the substituted
double bond was epoxidized.
Keywords: Substituted homoallylic alcohols, oxidation reagents, osmium tetroxide,
t-butyl hydroperoxide.
Introductıon
Oxidation reactions are very important processes for biological systems and in organic chemistry.
There are numerous oxidation reagents for organic compounds and new ones are added to this list

Molecules 2002, 7
105
almost every day. It is well known that different organic substrates can be converted into varied
oxidation products depending on the type of oxidant used. For example, Zn(ClCrO ) ·9H O (ZCC) is
3
2
2
an oxidant which can be used under very mild conditions [1]. Pyridinium chlorochromate (PCC) will
oxidize a primary alcohol to an aldehyde and stop at that stage. PCC also does not attack double bonds
[
2,3].
t-Butyl hydroperoxide (t-BuOOH) oxidizes olefins to epoxides and allylic oxidation products in
the presence of a Cr(VI) catalyst. The allylic oxidation and the t-BuOOH decomposition are free-
radical reactions, but the epoxidation is evidently not [4]. Under microwave irradiation 3Å molecular
sieves promote the oxidation of secondary (linear and cyclic) and benzylic alcohols to the
corresponding carbonyl compounds by t-BuOOH. Under the same conditions α,β-unsaturated alcohols
are converted into α,β–epoxy alcohols in a regio-and diasteroselective manner [5]. OsO can be used to
4
oxidize alkenes to 1,2-diols (syn hydroxylation). If t-BuOOH is used with OsO allylic alcohols have
4
been converted into α,β-epoxy alcohols. Beck and Seifert have investigated the oxidation of steroidal
allylic alcohols with t-BuOOH and catalytic amounts of OsO [6].
4
Substituted homoallylic alcohols have been used in the synthesis of pheromones and antibiotics
7,8] and these compounds show very strong antimicrobial activities [9]. Various methods have been
[
reported in the literature for the synthesis of substituted homoallylic alcohols [10-15]. The oxidation
reactions of substituted homoallylic alcohols have not been investigated in detail. Therefore we have
now studied the oxidation of these compounds with four different oxidation reagent systems.
Results and Discussion
When compounds 4a-d were oxidized with PCC (Method A) or ZCC (Method B) the
corresponding carbonyl compounds 5a-d were formed (Scheme 1).
Scheme 1. The oxidation of substituted homoallylic alcohols by Methods A and B.
R
3
O
R2
Method A
+
R1
H
(PCC)
R1
O
R3
5
a-d
6d
R2
R1
OH
R3
R3
R2
R2
O
O
O
Method B
ZCC)
R1
H
+
+
+
R1
H
(
R1
O
R1
O
5
a-d
6a
6d
7d
a: R =R =H, R = CH ; b: R = H, R = R = CH c: R = CH , R = R = H; d: R = phenyl, R = R =H
1
2
3
3
2
1
3
3;
1
3
2
3
1
2
3

Molecules 2002, 7
106
On the other hand, 2-methyl-1,5-hexadiene-3,4-dione (6a) together with 5a was formed when 4a
was oxidized with ZCC. This could be expected since ZCC in CH Cl is reported to be a strong
2
2
oxidizing agent that oxidizes benzylic and allylic C-H bonds to give carbonyl groups [1]. Compound
6
a was thus formed from oxidation of both the allylic hydrogen and hydroxyl groups of 4a.
Oxidation of 4d with PCC and ZCC produced benzaldehyde (6d), 3-Phenylpropenal (7d) and 1-
phenyl 1,5-hexadiene-3-one (5d). The yield of benzaldehyde formed is higher when Method A is used
compared to Method B. Thus the oxidation products of 4d included small molecules (such as 6d and
7
d), formed by the breakage of the bonds close to the phenyl group
The oxidation of olefinic molecules containing allylic hydrogen atoms is thought to follow two
possible pathways: allylic oxidation and direct attack on the double bond. When using oxygen-transfer
reagent, such as t-BuOOH or H O and a metal catalyst, the metal can serve as a relay for the transfer
2
2
of the oxygen atom from the hydroperoxide to the olefin via an oxometal intermediate. The
dismutation of t-BuOOH in the presence of transition–metal catalysts to produce t-BuOH and O has
2
been documented [4]. t-BuOOH oxidizes olefins to epoxides and allylic oxidation products in the
presence of a transition-metal catalyst. Catalytic epoxidation and allylic oxidation reactions follow
different paths. The epoxidation is an oxygen transfer reaction (Scheme 2) while the allylic oxidation
follows a free radical reaction. The epoxidation could occur via the activation of the peroxidic
oxygens.
Scheme 2. The oxidation of substituted homoallylic alcohols by Methods C-D.
H
H
O
Method C
Method D
O
O
+
OH
R1
OH
(t-BuOOH)
(t-BuOOH/OsO4)
R1
R1
O
R
1
O
O
8
c,d
4c,d
9c,d
1
0c,d
c: R =CH ; d: R = phenyl
1
3
1
When the substituted homoallylic alcohols 4c,d are oxidized with t-BuOOH under OsO catalysis
Method C), the substituted double bonds of 4c,d were epoxidized and no allylic oxidation products
4
(
are formed. Thus, when compound 4d was oxidized by this method only the α,β−epoxyalcohol and
benzaldehyde were formed.
Compounds 4c,d when oxidized with only t-BuOOH (Method D) gave allylic oxidation products
and epoxidation products. The oxidation reaction of 4c,d with t-BuOOH shows completely radical
character. While all the substituted-1,5-hexadien-3-ols 4a-d have allylic hydrogen and hydroxyl
groups, compound 4d compound has benzylic hydrogens in addition to allylic hydrogen and hydroxyl
groups. t-BuOOH thus oxidized the hydroxyl group to a carbonyl group and simultaneously one or
both of double bonds were converted to an epoxide.

Molecules 2002, 7
107
Acknowledgements
We are indebted to the Fõrat University Research Foundation (FÜNAF) for financial support of this
work (Project number: 295)
Experimental
General
CrO , ZnCl , n-Bu NHSO , n-BuLi (1.6 M hexane solution), t-BuOOH (as 3M isooctane solution),
3
2
4
4
pyridine, trans-2-butene-1-ol, trans-3-phenyl-2-propene-1-ol, t-BuOH were obtained from commercial
sources and all the solvents were used without further purification. PCC and ZCC have been prepared
according to the literature [1,2]. Oxidation reaction times were determined with thin layer
chromatography (aluminium sheets silica gel 60 F ) and the products were purified by column
2
54
chromatography using one of the following eluent systems: (A) 5:1 hexane-ethyl acetate; (B) 4:1
hexane-ethyl acetate; (C): 4:1:1 hexane-ethyl acetate-acetone: (D) 4:1:1:0.5 hexane-ethyl acetate-
acetone-dimethyl ether. IR spectra (NaCl, thin film) were measured on a Mattson series FT-IR 1000
1
13
model spectrometer and H- and C-NMR spectra were measured on a JEOL FX-90 Q instrument at
0 and 22.5 MHz, respectively, using CDCl as solvent. Shift values are reported in ppm relative to
9
3
TMS. GC/MS (eV, EI) and elemental analysis measurement were determined in The Scientific and
Technical Research Council of Turkey (TUBITAK). Substituted homoallyllic alcohol starting
materials were prepared as outlined in Scheme 3.
Scheme 3. Synthetic routes for the synthesis of substituted homoallylic alcohols
R3
R3
R2
R2
R1
Mg, THF
6
0oC
Cl
R1
OH
O
4
a,b
3a,b
OH
KOH
n-BuLi
Br
O
+
R1
n-Bu NHSO
R1
R1
OH
4
4
1
c,d
2c,d
4
c,d
a: R =R = H, R = CH ; b: R = R = CH , R = H; c: R = CH ; d: R = C H
1
2
3
3
1
3
3
2
1
3
1
6
5

Molecules 2002, 7
108
Compounds 3a,b and 4a,b were prepared as described in the literature [9,11-12]. Unsymmetrical
bis-allylic ethers 2c-d were synthesised from trans-2-butene-1-ol (1c) or trans-3-phenyl–2-propene-1-
ol (1d) with allyl bromide, KOH and n-Bu NHSO as phase transfer catalyst. Substituted homoallylic
4
4
alcohols 4c,d have then been synthesised via a [2,3]-Wittig rearrangement reaction of the
o
unsymmetrical bis allyl ethers under an argon atmosphere and at –75 C in high yields according to
literature methods [13-15].
Unsymmetric bis allyl ethers:
o
(
2E)-1-(Allyloxy)-2-butene (2c): Yield: 69%; Rf: 0.713 (eluent system A); b.p: 48-49 C (50 mmHg);
1
IR: 3080, 1650, 1130, 960, 936; H-NMR: 1.57-1.71 (d, J=7 Hz, 3H), 3.88 (m, 4H), 5.02-5.22 (m, 2H),
13
5
.22-6.15 (m, 3H); C-NMR: 17.6, 71, 116.3, 128.4, 128.7, 135.5; Anal.Calcd.for C H O: C, 75.0; H,
7
12
1
0.7; Found: C, 74.6; H, 10.4.
o
[
3-(Allyloxy) prop-1-enyl]benzene (2d): Yield: 71%; Rf: 0.658 (eluent system A); b.p: 118-120 C (10
1
mmHg); IR: 3080, 3040, 1657, 1140, 965, 750-700; H-NMR: 3.95 (m, 4H), 4.84 -5.35 (m, 2H), 5.54-
.66 (m, 3H), 6.94-7.53 (m, 5H); C-NMR: 70.6, 116.2, 124.9, 127, 128.5, 130.9, 131.5, 134.3; Anal.
1
3
6
Calcd. for C H O: C, 82.8; H, 8.0; Found: C, 83.1; H, 8.3.
1
2
14
o
(
5E)-1,5-Heptadiene-4-ol (4c): Yield: 62%; Rf: 0.586 (eluent system A); b.p: 72-74 C (35 mmHg); IR:
1
3
600-3200, 3040, 1651, 1260, 1065, 935; H-NMR: 0.94-1.02 (d, J = 4 Hz, 3H), 2.23 (m, 2H), 3.94 (q,
J = 6 Hz, 1H ), 5.14 (m, 2H), 5.82 (m, 3H); C-NMR: 16.0, 38.6, 76.7, 116.2, 139.3, 140.8; Anal.
Calcd. for C H O: C, 75.0; H, 10.7; Found: C, 75.4; H, 10.9.
1
3
7
12
o
1
(E)-Phenyl-1,5-hexadiene-3-ol (4d): Yield: 72%; Rf: 0.504 (eluent system B); b.p: 130-132 C (2
1
mmHg); IR: 3600-3200, 3040, 1651, 1260,740; H-NMR: 3.78-4.25 (m, 3H), 4.95-5.46 (m, 2H ), 5.6-
.72 (m, 3H) 7.1-7.8 (m, 5H); C-NMR: 71.8, 117, 127.3, 128.5, 129.4, 133, 135.8, 137.7; Anal.
1
3
6
Calcd. for C H O: C , 82.8; H, 8.1; Found: C, 82.1; H, 7.9.
1
2
14
Oxidation Reactions of Substituted Homoallylic Alcohols: Method A: Oxidation of 4a-d with PCC
(General Method)
PCC (1.5 mmol) is dissolved in CH Cl (2 mL) and then NaOAc (0.03 mmol) is added to this
2
2
solution. The substituted homoallylic alcohol (1 mmol) dissolved in CH Cl (15 mL) and then added
2
2
dropwise to the PCC solution. After 1-2 hours, the reaction is checked by TLC to determine
completion. The reaction mixture is filtered, the residues are washed with twice with ether, dried with
MgSO , and concentrated in vacuo give the crude product that was purified by column
4
chromatography over silica gel.

Molecules 2002, 7
109
Method B: Oxidation of 4a-d with ZCC (General Method).
A solution of substituted homoallylic alcohol (8 mmol) in CH Cl (70 mL) was prepared in a 200
2
2
mL round-bottomed flask equipped with a magnetic stirrer. The ZCC (16 mmol) was added in four
separate portions within 15 min. with vigorous stirring. Stirring was continued for 2 hours. The
mixture was diluted with CH Cl (120 mL) and filtered. The filtrate was evaporated on a rotatory
2
2
evaporator under reduced pressure.
Method C: OsO -catalyzed oxidation of 4c,d with t-BuOOH
4
Compound 4c or 4d (50 mmol) was dissolved in t-BuOH (125 mL) and 20 % aqueous NEt OH
4
(
6.5 mL), t-BuOOH (3 M isooctane, 34 mL, 103 mmol) and OsO solution (2.5 % in t-BuOH, 2.6 mL
4
0
,2 mmol) were added. After standing for 12 hour in room temperature, 5% Na SO solution (65 mL)
2
3
was added, then the reaction mixture was extracted with diethyl ether, the ether phase was washed with
saturated NaCl solution, dried over MgSO and the solvent was distilled in vacuo.
4
Method D: Oxidation of 4c,d with t-BuOOH
Oxidation of compounds 4c and 4d with t-BuOOH is described in Method C. In this method the
OsO was omitted.
4
Oxidation Products
5
-Methyl-1,5-hexadiene-3-one (5a): Yields: 67.5% (Method A), 62.4% (Method B); Rf: 0.737 (eluent
1
system C); IR: 3080, 1680, 1625, 935; H-NMR: 2.2 (s, CH , 3H), 4.47 (s, CH , 2H), 4.75 (s, =CH ,
3
2
2
2
H), 6.27-6.31 (m, CH =CH, 3H); Anal. Calcd. for C H O: C, 76.4; H, 9.1; Found: C 75.0; H, 8.8;
2
7
10
+.
GC/MS: M 110, base peak: 55.
(
5E)-2-Methyl-1,5-heptadiene-4-one (5b): Yields: 58.3% (Method A), 46.7% (Method B); Rf: 0.713
1
(
eluent system C); IR: 3040, 1680, 1625, 990, 935; H-NMR: 2.10 (d, CH , 3H, J=7 Hz ), 2.24 ( s,
3
CH , 3H), 4.43 (s, CH , 2H), 4.72 (s, =CH , 2H), 6.02-6.76 (m, CH=CH, 2H); Anal. Calcd. for
3
2
2
+
C H O: C, 77.4; H, 9.7 Found: C, 77.1; H, 9.5; GC/MS: M 124, base peak: 109.
8
12
(
5E)-1,5-Heptadien-4-one (5c): Yields: 50.3% (Method A), 42.2% (Method B); Rf: 0.702 (eluent
1
system C); IR: 3040, 1680, 1625, 990; H-NMR: 1.97 (d, J=7 Hz, CH , 3H), 4.37 (m, CH , 2H), 5.05-
5
3
2
1
3
.63 (m, CH =CH, 3H), 6.02-6.76 (m, CH=CH, 2H) ; C-NMR: 17, 37, 124, 128, 130, 137, 197; Anal.
2
Calcd. for C H O: C, 76.4; H, 9.1; Found: C, 76.8; H, 8.9.
7
10
(
1E)-1-Phenyl-1,5-hexadiene-3-one (5d): Yields: 48.2% (Method A), 36.1% (Method B); Rf: 0.512
1
(
eluent system C); IR: 3040, 1680, 1625, 1080, 990, 760; H-NMR: 4.34 (m, CH , 2H), 5.0-5.71 (m,
2

Molecules 2002, 7
110
1
3
CH =CH, 3H), 6.25-6.91 (m, CH=CH, 2H), 7.17-7.33 (m, aromatic protons, 5H); C-NMR: 37, 123,
2
1
27, 128, 129, 131, 137, 197; Anal. Calcd. for C H O: C, 83.7; H, 7.0; Found: C, 83.2; H,7.3;
12
12
+.
GC/MS: M 172, base peak: 171.
2
-Methyl-1,5-hexadiene-3,4-dione (6a): Yield: 3.0%; Rf: 0.711 (eluent system C); IR: 1625, 1680;
1
H-NMR: 2.57 (s, CH , 3H), 4.84 (s, CH =, 2H), 6.21-6.35 (m, CH =CH, 3H); Anal. Calcd. for
C H O : C, 67.7; H, 6.5; Found: C, 67.3; H, 6.8; GC/MS: M 124, base peak: 109.
3
2
2
+.
7
8
2
1
3
3
-[3-Methyloxiranyl]-but-3-en-1-ol (8c): Yield: 48.8%; Rf: 0.644 (eluent system D); IR: 3450-3340,
1
060, 1642, 1250, 965; H-NMR: 1.32 (d, CH , 3H, J=7 Hz), 2.98 (s, OH, 1H), 3.41(m, CH , 2H),
3
2
.94-4.40 (m, CH-, 1H), 4.26-4.98 (m, CH-CH, 2H), 5.11-5.73 (m, CH =CH, 3H); Anal. Calcd. for
2
+.
C H O : C, 65.6; H,9.4; Found: C , 65.7; H, 9.6; GC/MS: M 128, base peak: 55.
7
12
2
1
1
4
-[3-Phenyloxiranyl]-but-3-en-1-ol (8d): Yield: 32.2%; Rf: 0.486 (eluent system D); IR: 3480-3550,
1
641, 1245, 970, 740; H-NMR: 3.38 (m, CH , 2H), 3.76 (s, OH, 1H), 4.23-4.35 (m, CH-,1H), 4.42-
2
.83 (m, CH-CH, 2H), 5.05-5.67 (m ,CH =CH, 3H) , 7.2-7.3 (m, aromatic protons, 5H); Anal. Calcd.
2
+
.
for C H O : C, 75.8; H, 6.3; Found: C, 75.1; H,6.7; GC/MS: M 190, base peak: 91.
1
2
14
2
1
-[3-Methyloxirane-2-yl]-3-butene-1-one (9c): Yield: 10.8%; Rf: 0.630 (eluent system D); IR: 3040,
1
1
715, 1640, 1080, 1245, 970, 760; H-NMR: (1.41, CH , J=7 Hz), 3.95 (m, CH , 2H), 4.29-5.25 (m,
3
2
CH-CH, 2H), 5.1-5.67 (m, CH =CH, 3H), 7.2-7.3 (m, aromatic protons, 5H); Anal. Calcd. for
2
+.
C H O : C, 66.7; H, 7.4; Found: C, 66.9; H, 7.9; GC/MS: M 126, base peak: 59.
7
10
2
1
-[3-Phenyloxiranyl]-but-3-en-1-one (9d): Yield: 16.4%; Rf: 0.442 (eluent system D); IR: 3040, 1715,
1
1
640, 1245, 1080, 970, 765; H-NMR: 3.95 (m, CH , 2H), 4.66-5.49 (m, CH-CH, 2H), 5.10-5.71 (m,
2
CH -CH, 3H), 7.2-7.3 (m, aromatic protons, 5H); Anal. Calcd. for C H O : C, 76.6; H, 6.4; Found:
2
12 12
2
+
.
C, 76.2; H, 6.9; GC/MS: M 188, base peak: 118.
1
1
4
-[3-Methyloxiranyl]-2-oxiranyletanone (10c): Yield: 33.2%; Rf: 0.656 (eluent system D); IR: 1720,
1
250, 1100; H-NMR: 1,34 (d, CH , 3H, J=7 Hz), 3.42 (m, CH , 2H), 3.81-4.69 (m, CH -CH, 3H),
3
2
2
.78-5.41 (m, CH-CH, 2H); Anal. Calcd. for C H O C, 59,2; H, 7,0.Found: C, 59.9 ;H,7.4; GC/MS:
7
10
3
+
.
M 142, base peak: 71.
2
1
2
-Oxiranyl-1-[3-phenyloxiranyl]ethanone (10d): Yield: 13.4%; Rf: 0.357 (eluent system D); IR: 3040,
1
715, 1250, 1100; H-NMR: 3.40 (m,CH , 2H), 3.77-4.66 (m, CH -CH, 3H), 6.34-6.93 (m, CH-CH,
2
2
H), 7.2-7.3 (m, aromatic protons, 5H); Anal. Calcd. for C H O : C, 70.6; H, 5.9; Found: C,70.2;
1
2
12
3
+.
H,5.6; GC/MS: M 204, base peak: 130.

Molecules 2002, 7
111
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