Metallocene-catalyzed diastereoselective epoxidation of allylic alcohols

Article abstract of DOI:10.1016/S0040-4020(00)00266-0

Allylic alcohols undergo an efficient process of diastereoselective epoxidation by t-butyl hydroperoxide (TBHP) in n-hexane solution in the presence of catalytic amounts of mono- and bis-cyclopentadienyl titanium(IV) and zirconium(IV) chlorides. 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00266-0

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 3567±3573
Metallocene-Catalyzed Diastereoselective Epoxidation of
Allylic Alcohols
*
Giorgio Della Sala, Lucia Giordano, Alessandra Lattanzi, Antonio Proto and Arrigo Scettri
Á
Dipartimento di Chimica, Universita degli Studi di Salerno, 84081 Baronissi (SA), Italy
Received 9 December 1999; revised 7 March 2000; accepted 23 March 2000
AbstractÐAllylic alcohols undergo an ef®cient process of diastereoselective epoxidation by t-butyl hydroperoxide (TBHP) in n-hexane
solution in the presence of catalytic amounts of mono- and bis-cyclopentadienyl titanium(IV) and zirconium(IV) chlorides. q 2000 Elsevier
Science Ltd. All rights reserved.
Introduction
In accordance with this mechanism, some common features
of good catalysts are strong Lewis acidity and lability with
respect to ligands substitution.1
One of the typical procedures for the stereoselective
synthesis of 2,3-epoxyalcohols 2, well-known building
blocks in preparative organic chemistry, is represented
by oxidation of related allylic alcohols 1 by alkylhydro-
peroxides catalyzed by d0 transition metal complexes
(Scheme 1).1
In general, the allylic alcohols are particularly reactive
owing to the ability of the alcoholic oxygen to coordinate
to the metal so that an intermediate such as 4 is formed in
which the oxygen transfer is intramolecular.1,2c The prefer-
ence for the oxidations of allylic alcohols compared with
unfunctionalized alkenes is illustrated by the site-selective
oxidation of geraniol (1a) promoted by a variety of metal
catalysts.3 Secondary allylic alcohols are epoxidized often
with remarkable diastereoselectivity and the threo±erythro
ratio depends on the metal and the type of ligands.1b,2c,4
In the past decades several studies were carried out on the
mechanism of this metal-catalyzed epoxidation and some
debates have arisen;2 nowadays the preferred pathway,
proposed by Sharpless (Scheme 2), involves a bidentate
metal-alkylperoxidic intermediate 3, formed as a conse-
quence of a nucleophilic substitution on the metal centre
conducted by hydroperoxide.1,2 The role of the catalyst is
to activate the coordinated hydroperoxide: because of the
electron-withdrawing power of the d0 metal site, the
heterolysis of the O±O bond is considerably facilitated
and so the oxygen atom covalently bonded to the metal is
prone to nucleophilic attack. An alkene, usually, is a strong
enough nucleophile to react with intermediate 3 when the
metal is Mo(VI), W(IV), V(V) or Ti(IV). The following and
generally slow step, then, is an O transfer to the incoming
alkene generating a coordinated epoxide.
Ti(IV)4,5 alkoxides are largely employed as catalysts in
CH2Cl2 for the epoxidation of allylic alcohols;1b Zr(IV)3b,c
alkoxides are also reported to promote this reaction but they
are less active than the former due to the lower Lewis acidity
and thence scarcely used. Complexes of Ti(IV) and Zr(IV)
other than alkoxides are very rarely employed with TBHP.
Titanocene and zirconocene chlorides, for example, are very
well-known and stable compounds and are widely used as
catalysts in many homogeneous reactions; with regards to
metallocene-catalyzed epoxidations of unfunctionalized
Scheme 1.
Keywords: diastereoselection; epoxidation; titanium and compounds; zirconium and compounds.
* Corresponding author. Tel.: 139-089-965-374; fax: 139-089-965-296; e-mail: scettri@ponza.dia.unisa.it
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00266-0

3568
G. Della Sala et al. / Tetrahedron 56 (2000) 3567±3573
Scheme 2.
alkenes, the conversion is slow.8 With polymer-supported
Cp2TiCl2 and CpTiCl3 the activity is slightly enhanced9 as
with the analogous Zr catalysts.10 The lack of data about the
metallocene-catalyzed epoxidations of allylic alcohols
prompted us to undertake a study.
cene chlorides 5±9 (Scheme 3), in spite of their lower
reactivity in comparison with alkoxides, prove to be
valuable catalysts in the epoxidations of allylic alcohols
provided that the reaction is carried out in hydrocarbon
solvents instead of the generally used halogenated solvents.
The switch of ligands from alkoxide to cyclopentadienyl
was expected to affect the epoxidation rate because the latter
is electron-rich and so the metal site is less Lewis acidic.
The rate of chloride displacement by hydroperoxide is also,
probably, slower than alkoxide displacement. Furthermore,
the cyclopentadienyl is known to in¯uence the level of
molecular aggregation and the geometry of the metal centre,
hence the diastereoselectivity for the chiral allylic alcohols.
Results and Discussion
As shown by some preliminary results on the epoxidation of
geraniol (1a) reported in Table 1, the catalytic activities of
metallocenes 6 and 9 in CH2Cl2 are rather low if compared
with those observed in n-hexane (cf. entries 1±2 and 3±4,
Table 1). The catalysts are insoluble in hydrocarbon
solvents even at the temperatures employed (608C), so
there is a preference for an heterogenous system rather
In the present work we show that titanocene and zircono-
Scheme 3.
Table 1. Epoxidation of geraniol (1a) by TBHP catalyzed by Cp2TiCl2 (6) (1a/TBHP/catalyst 1/1/0.02 molar ratio was used) or Cp2ZrCl2 (9) (1a/TBHP/
catalyst 1/1/0.08 molar ratio was used)
Entry
Catalyst
Solvent
Temperature (8C)
Reaction time (h)
Yield (%)a
1
2
3
4
6
6
9
9
CH2Cl2
40
60
40
60
4.0
4.0
7.0
7.0
35
82
n-hexane
CH2Cl2
n-hexane
b
±
71c
1
a Unless otherwise noted all the yields of 2a were determined by H NMR analysis (400 MHz) on the crude reaction mixture.
b No amount of 2a was detected by 1H NMR analysis (400 MHz) on the crude reaction mixture.
c The yield of 2a refers to isolated pure compound.

G. Della Sala et al. / Tetrahedron 56 (2000) 3567±3573
3569
Table 2. Epoxidation of allylic alcohol 1b by TBHP promoted by different titanium (IV) catalysts (in all entries 1b/TBHP/catalyst 1/1/0.02 molar ratio was
used. Solvent: n-hexane (similar results have been obtained in light petroleum); temperature: 608C)
Entry
Catalyst
Reaction time (h)
Yield (%)a
Amount of ketone (%)b
erythro/threo d.r.
1
2
3
4
5
Ti(OiPr)4
TiCl4
5
6
7
4.0
17
5.5
1.0
1.5
47
26
93
92
2
6
76/24
86/14
88/12
84/16
83/17
c
±
±
d
d
.95
±
a All the yields of 2b were determined by 1H NMR analysis (400 MHz) on the crude reaction mixture.
1
b Determined by H NMR analysis (400 MHz) on the crude reaction mixture.
c Amount of ketone not measured.
d Amount of ketone not detected.
than an homogeneous one. These outcomes are in contrast
with those reported for Ti(IV)4±6 and Zr(IV)3c,7 alkoxides
for which CH2Cl2 is the solvent of choice.
Prompted by these promising results we performed a set of
experiments on different primary and secondary allylic
alcohols (Table 3). Good yields of epoxyalcohol are
obtained starting from trisubstituted and disubstituted
substrates. Since the main undesired product recognized
by NMR after the work-up was the unreacted starting
material together with only a small amount of ketone, the
yields may be roughly related to the degrees of conversion
and so to the oxidation rates. According to a Sharpless-type
mechanism (Scheme 2), shorter reaction times are required
for the more nucleophilic trisubstituted allylic alcohols
1a±d in comparison to disubstituted ones 1e,f. Primary
According to this observation we carried out all the subse-
quent tests in hydrocarbon solvents (n-hexane or light
petroleum). As summarized in Table 2, catalysts 5±7 in
these media proved to be more ef®cient than TiCl4
and Ti(OiPr)4 in the epoxidation of the representative
allylic alcohol 1b: yields are much better and erythro-
selectivity is signi®cantly superior to that obtained with
Ti(OiPr)4.
Table 3. Epoxidation of allylic alcohols 1 by TBHP promoted by titanocenes 5±7 (unless otherwise noted 1/TBHP/catalyst 1/1/0.02 molar ratio was used.
Solvent: n-hexane (similar results have been obtained in light petroleum); temperature: 608C)
Entry
Substrate
Catalyst
Reaction
time (h)
Yield
(%)a
Amount of
ketone (%)b
erythro/
threo d.r.
c
1
2
3
5
6
7
28
4.0
30
73
82
80
±
±
±
±
c
±
c
±
c
4
5
6
7
5
6
7
5
5.5
1.0
1.5
1.5
93
92
±
88/12
84/16
83/17
83/17
d
±
d
. 95
91
±
9
8
9
6
6e
7
7e
3.0
6.0
3.0
22
89
60
70
81
6
10
82/18
76/24
79/21
78/22
c
10
11
±
c
±
c
12
13
14
5
6
7
21
3.0
7.5
90
90
85
±
6/94
8/92
8/92
c
±
c
±
c
15
16
17
5
6
7
23
26
28
40
72
80
±
42/58
43/57
44/56
c
±
8
c
18
19
6
7
46
27
24
25
±
±
±
c
±
1
a All the yields of 2 were determined by H NMR analysis (400 MHz) on the crude reaction mixture.
1
b Determined by H NMR analysis (400 MHz) on the crude reaction mixture.
c Amount of ketone not measured.
d Amount of ketone not detected.
e 0.1% mol of catalyst was used.

3570
G. Della Sala et al. / Tetrahedron 56 (2000) 3567±3573
allylic alcohols 1a,f are slightly less reactive than secondary
ones 1b±e. The coordinating role of the hydroxyl group,
according to the hypothesis of Sharpless, is con®rmed by
the site-selective 2,3-epoxidation of geraniol (1a).
threo-selectivity for the A1,3 strained substrates is larger
than erythro selectivity for the A1,2 strained ones. When
Ti(OiPr)4 in CH2Cl2 is employed as catalyst, A1,2 and A1,3
strains are intermediate to those of vanadium-catalyzed and
peracid epoxidations; therefore the dihedral angle is
probably between 50 and 1208.
Reaction rates and yields are somehow dependent on the
titanocene catalyst (CpTiCl3 is the less active) but
erythro±threo ratios are essentially unvaried along the
series 5±7. This means that the structure of the transition
state in the oxygen transfer step, which determines the
diastereoselectivity, is very similar in the three cases.
These considerations can also be made for titanocene-
catalyzed epoxidations. The data previously reported for
Ti(OiPr)4 in CH2Cl2,4 however, have to be regarded with
care for any comparison because the present experiments
are performed in different solvents and in a heterogeneous
system. This fact may in¯uence, as well as the different kind
of ligands, the activity and the diastereoselectivity.
The activity of the bridged titanocene 7 is not signi®cantly
higher than that of Cp2TiCl2 although the former is expected
to undergo a more rapid ligand displacement because of its
greater electrophilicity.11
For the A1,2 strained substrates 1b,c, as expected, good
erythro-selectivities were obtained (slightly better than
Ti(OiPr)4-catalyzed epoxidation);4 for the A1,3 strained
allylic alcohol 1d the threo-selectivity is very high (as
large as with Ti(OiPr)4). As for the other metal-catalyzed
epoxidations, the effect of the alkyl group R4 (Scheme 1) is
almost negligible, slightly favouring the threo isomer.
In a recent work,4 Adam et al. resumed a concept,
previously proposed by Sharpless, according to which,
given a key intermediate such as 4, the diastereoselectivity
depends on the O±C±CvC dihedral angle value of the
allylic frame in the transition state.
In the vanadium-catalyzed epoxidations the angle value is
40±508; this implies a strong A1,2 strain and a weak A1,3
strain. When substrates 1 with A1,2 strain are used (Scheme
1: R1, R2ˆalkyl; R3ˆH) excellent erythro-selectivity is
gained whereas with substrates with A1,3 strain (Scheme 1:
R1, R3ˆalkyl; R2ˆH) only poor threo-selectivity is
observed. In the peracid epoxidations the O±C±CvC
dihedral angle value is estimated about 1208C and so the
It should be pointed out that good yields can be obtained in
the presence of really reduced amounts of catalyst (0.1%
mol) although a slightly lower diastereoselectivity is usually
observed (cf. entries 8±9 and 10±11, Table 3).
Reaction times can be shortened by performing the
oxidation under microwave irradiation (Table 4);
under these conditions, less reactive alcohols, such as
Table 4. MW-assisted epoxidation of allylic alcohols 1 by TBHP catalyzed by Cp2TiCl2 (6) (in all entries 1/TBHP/catalyst 1/1/0.02 molar ratio was used. MW
power: 250 W)
Entry
1
Substrate
Reaction time (cycles £ min)
Yield (%)a
60
Amount of ketone (%)b
erythro/threo d.r.
c
1£15
2£20
±
±
d
2
3
1£15
2£20
.95
±
83/17
80/20
1£15
1£20
90
6
c
4
5
1£15
1£20
82
68
±
8/92
c
8£15
±
±
a All the yields of 2 were determined by 1H NMR analysis (400 MHz) on the crude reaction mixture.
b Determined by 1H NMR analysis (400 MHz) on the crude reaction mixture.
c Amount of ketone not measured.
d Amount of ketone not detected.

G. Della Sala et al. / Tetrahedron 56 (2000) 3567±3573
3571
trans-2-hexen-1-ol (1f), are transformed into the related
epoxide with noticeably improved yields (Table 4, entry 5).
In summary, the previously unreported titanocene- and
zirconocene-catalyzed epoxidations of allylic alcohols
were accomplished in hydrocarbon solvents under mild
conditions with good yields and diastereoselectivity. Two
convenient aspects of the procedure are the cheapness of
the catalysts and the easy work-up (only ®ltration of the
insoluble catalyst is needed). The nucleophilicity of the
substrates and the dependence of the erythro±threo ratios
on the substitution pattern suggest a Sharpless-type mechan-
ism involving a transition state in which the allylic alcohol
and the hydroperoxide are simultaneously coordinated to
the metal.
Zirconocene compounds 8±9 proved to be good catalysts,
too. As expected, the activity is somewhat lower than that of
titanocenes 5±7 and a larger amount of catalyst (8% mol) is
often required. The epoxidations were carried out at 608C in
n-hexane. The yields are moderate, usually lower than for
titanocene-catalyzed epoxidations and reaction times are
longer (Table 5). Analogously to the related titanium
compounds, the catalytic activity of bis-cyclopentadienyl
derivative 9 is higher than that of the mono-cyclopenta-
dienyl one 8.
No great difference of diastereoselectivity is observed
between 8 and 9 catalysts; this is somewhat dependent on
amounts of zirconocene 9 (cf. entries 5±6, 8±9, 11±12, 14±
15, Table 5). The erythro±threo ratios, however, are as large
as or even better than those of titanocene-promoted oxida-
tions. Once again, for the A1,3 strained compound 1d the
threo isomer prevails whereas for the A1,2 strained ones 1b,c
the erythro is more abundant. The effect of group R4 is now
reversed, being moderately erythro-directing.
Experimental
General remarks
All reactions were carried out under a dry nitrogen
atmosphere. Glassware was ¯ame-dried (0.05 Torr) before
use. Cyclopentadienyltitanium trichloride (5), cyclopenta-
dienylzirconium trichloride (8), zirconocene dichloride
(9), TiCl4 and Ti(OiPr)4 were all purchased from Aldrich
Table 5. Epoxidation of allylic alcohols 1 by TBHP promoted by zirconocenes 8±9. (Unless otherwise noted 1/TBHP/catalyst 1/1/0.08 molar ratio was used.
Solvent: n-hexane (similar results have been obtained in light petroleum); temperature: 608C)
Entry
Substrate
Catalyst
Reaction
time (h)
Yield
(%)a
Amount of
ketone (%)b
erythro/
threo d.r.
c
1
2
3
8
9
9d
7.0
7.0
43
40
71
70
±
±
±
±
c
±
c
±
c
4
5
8
9
7.0
6.5
73
84
±
±
88/12
92/8
c
6
7
9d
8
22
82
80
18
c
±
94/6
91/9
8.0
c
8
9
9d
8
7.5
20
23
77
90
26
±
94/6
86/14
9/91
9
10
c
10
±
c
11
12
9
9d
29
30
48
58
±
11/89
12/88
5
13
14
8
9
25
22
59
70
5
67/33
66/34
10
15
16
9d
8
46
20
55
18
f
60/40
±
54e
±
f
17
18
9
28
46
69e
59e
±
±
±
9d
±
f
a Unless otherwise noted all the yields of 2 refer to isolated pure compound.
b Unless otherwise noted the amount of ketone was determined by isolation of the pure compound.
c Amount of ketone not detected.
d 2% mol of catalyst was used.
1
e Yields determined by H NMR analysis (400 MHz) on the crude reaction mixture.
f Amount of ketone not measured.

3572
G. Della Sala et al. / Tetrahedron 56 (2000) 3567±3573
and used without further puri®cations. Titanocene di-
chloride (6) was prepared according to the procedure of
Cardoso et al.;12 the known catalyst (7)13 was prepared as
described below. Geraniol (1a) and trans-2-hexen-1-ol (1f)
were purchased from Aldrich. Secondary allylic alcohols
1b±e were prepared, according to the Grignard method,14
from n-pentyl magnesium bromide and the corresponding
aldehydes. All the solvents employed in the organometallic
reactions were freshly distilled and dried: n-hexane and
diethyl ether were distilled from calcium hydride and THF
was distilled from sodium/benzophenone.
General procedure for the epoxidation of allylic alcohols
1 catalyzed by 5±9
A mixture of allylic alcohol 1 (2 mmol), TBHP (2 mmol)
and the appropriate metallocene (see Tables for the amount)
in n-hexane (2.5 ml) was stirred in a screw-cap bottle under
the conditions reported in Tables 1±3 and 5. After comple-
tion of the reaction, the solid catalyst was removed by ®ltra-
tion under reduced pressure and the crude product obtained
after the removal of the organic solvent was, unless other-
wise noted, puri®ed by ¯ash-chromatography (eluent: light
petroleum/ethyl acetate mixtures).
Epoxidations promoted by microwave irradiation were
performed in an Ace pressure tube (Aldrich) which was
General procedure for the MW-assisted epoxidation of
allylic alcohols 1 catalyzed by 5
placed inside
(2450 MHz).
a
conventional MW kitchen oven
A mixture of alcohol 1 (2 mmol), TBHP (2 mmol) and the
catalyst 5 (0.04 mmol) in n-hexane (2.5 ml) was placed in
the MW oven and irradiated until completion of the reac-
tion. Then the reaction mixture was subjected to the usual
work-up.
Reactions were monitored by thin layer chromatography
(TLC) on Merck silica gel plates (0.25 mm) and visualized
by UV light or by 10% H2SO4/ethanol spray test. Reaction
temperatures were measured externally. Flash chromatog-
raphy was performed on Merck silica gel (60, particle
size: 0.040±0.063 mm). NMR spectra were recorded in
CDCl3 solutions on a Bruker DRX 400 spectrometer
(400 MHz) at room temperature. Chemical shifts are
reported relative to the residual solvent peak (CHCl3:
dHˆ7.26). EIMS spectra were performed on VG TRIO
2000 spectrometer.
1-(3-Ethyl-2-methyl-oxiranyl)-hexan-1-ol (2b). (erythro
isomer): [Found: C, 70.9; H, 11.6. C11H22O2 requires C,
70.92; H, 11.90%]; Rf (25% Et2O/light petroleum) 0.39;
dH (400 MHz, CDCl3) 3.61 (1H, dd, Jˆ6.8, 2.6 Hz,
CHOH), 2.99 (1H, dd, Jˆ6.5, 6.5 Hz, CH3CH2CHO), 2.28
(1H, bs, OH), 1.70±1.25 (13H, m), 1.03 (3H, t, Jˆ7.6 Hz,
CH3CH2CHO), 0.90 (3H, t, Jˆ6.7 Hz, (CH2)4CH3); dC
(100.6 MHz, CDCl3) 72.5, 62.9, 60.4, 32.6, 31.8, 25.1,
22.5, 21.3, 14.0, 13.9, 10.3; m/z (EIMS) 186 (M1). (threo
isomer): [Found: C, 70.8; H, 12.0. C11H22O2 requires C,
70.92; H, 11.90%]; Rf (25% Et2O/light petroleum) 0.19;
dH (400 MHz, CDCl3) 3.21 (1H, m, CHOH), 2.79 (1H,
dd, Jˆ6.5, 6.5 Hz, CH3CH2CHO), 1.97 (1H, bs, OH),
1.70±1.25 (13H, m), 1.03 (3H, t, Jˆ7.6 Hz, CH3CH2CHO),
0.90 (3H, t, Jˆ6.7 Hz, (CH2)4CH3); dC (100.6 MHz, CDCl3)
77.0, 63.7, 63.4, 33.0, 31.8, 25.2, 22.5, 21.4, 13.9, 10.9,
10.4; m/z (EIMS) 186 (M1).
Yields of products 2 refer to isolated pure compounds or
were determined by 1H NMR analysis on the crude reaction
mixtures. Products 2 were identi®ed by comparison with the
1
data reported in literature15 and with H NMR spectra of
authentic samples prepared by an alternative procedure.16
erythro/threo Ratios of epoxy alcohols 2b±e were deter-
mined by integrating the characteristic peaks of the two
diastereomers in the 1H NMR spectra of the crude reaction
mixtures.
Preparation of catalyst 7
1-(2,3-Dimethyl-oxiranyl)-hexan-1-ol (2c). (erythro isomer):
[Found: C, 69.9; H, 11.3. C10H20O2 requires C, 69.72; H,
11.70%]; Rf (25% Et2O/light petroleum) 0.39; dH
(400 MHz, CDCl3) 3.62 (1H, dd, Jˆ7.9, 3.0 Hz, CHOH),
3.15 (1H, q, Jˆ5.6 Hz, CH3CHO), 2.10 (1H, s, OH), 1.54±
1.16 (14H, m), 0.89 (3H, t, Jˆ7.7 Hz, (CH2)4CH3); dC
(100.6 MHz, CDCl3) 72.6, 62.7, 54.9, 32.6, 31.8, 25.2,
22.5, 14.1, 14.0, 13.5; m/z (EIMS) 172 (M1). (threo
isomer): [Found: C, 69.8; H, 11.2. C10H20O2 requires C,
69.72; H, 11.70%]; Rf (25% Et2O/light petroleum) 0.30;
dH (400 MHz, CDCl3) 3.20 (1H, m, CHOH), 2.97 (1H, q,
Jˆ5.5 Hz, CH3CHO), 2.13 (1H, s, OH), 1.54±1.15 (14H,
m), 0.89 (3H, t, Jˆ7.7 Hz, (CH2)4CH3); dC (100.6 MHz,
CDCl3) 76.9, 63.6, 57.7, 33.0, 31.8, 25.3, 22.5, 14.1, 14.0,
13.5; m/z (EIMS) 172 (M1).
Cyclopentadiene (41 ml, 0.5 mol) was added dropwise to a
vigorously stirred suspension of powdered NaOH (50 g,
1.2 mol) and triethyl benzyl ammonium chloride (2.5 g,
0.011 mol) in dry THF (20 ml). Stirring was prolonged for
2 h. Then dry acetone (18 ml, 0.24 mol) was added and after
3 h the reaction was quenched by addition of brine (100 ml).
After the usual work-up the solvent was removed. The crude
oily residue was puri®ed by distillation under reduced
pressure to give 2,2-bis-cyclopentadienyl propane (23.0 g,
54% yield).
2.5N (n-hexane) n-butyllithium (14 ml, 0.035 mol) was
slowly added at 08C to a solution of 2,2-bis-cyclopenta-
dienyl propane (3.0 g, 0.017 mol) in dry THF (180 ml).
The solution was stirred at 608C for 3 h. Then, at 2788C,
a solution of TiCl4(THF)2 (5.8 g, 0.014 mol) in THF
(150 ml) was added and stirring was prolonged overnight.
After additional re¯uxing for 3 h, the solvent was removed
under reduced pressure. The crude solid was extracted with
dichloromethane (400 ml) and the organic phase was cooled
at 2208C. After 16 h the catalyst 713 was obtained as a dark
green solid (2.3 g, 43% yield).
1-(3,3-Dimethyl-oxiranyl)-hexan-1-ol (2d). (Major isomer:
threo): [Found: C, 70.0; H, 11.6. C10H20O2 requires C,
69.72; H, 11.70%]; Rf (50% Et2O/light petroleum) 0.37;
dH (400 MHz, CDCl3) 3.47 (1H, dt, Jˆ7.9, 5.2 Hz,
CHOH), 2.70 (1H, d, Jˆ7.9 Hz, CHOCHOH), 2.16 (1H, s,
OH), 1.75±1.16 (14H, m), 0.89 (3H, t, Jˆ7.4 Hz,
(CH2)4CH3); dC (100.6 MHz, CDCl3) 70.2, 68.0, 59.6,

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Á
We are grateful to Ministero dell'Universita e Ricerca
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