A mild access to chiral syn 1,2-diaryl glycols by stereoselective ring opening of ortho substituted trans 2,3-diaryl-oxiranes using Amberlyst 15 in H2O/THF system

Article abstract of DOI:10.1016/j.tet.2015.06.039

Amberlyst 15 was an efficient and green catalyst for the reaction of 2,3-diaryloxiranes with H₂O in organic co-solvent to prepare glycols in high yield. Ortho substituted trans 2,3-diaryloxiranes afforded the corresponding syn glycols stereo- and enantiospecifically. Stereoselectivity appeared related to the coordination ability of the substituents, irrespective of their electronic properties. Indeed o-OCH₃ and o-OBn substituted syn glycols were obtained in high stereochemical ratios (6/1 and 10/1, respectively), and o-OTIPS and o-NO₂ substituted ones were obtained as exclusive products, with the same ee of the parent epoxides.

Full text of DOI:10.1016/j.tet.2015.06.039

Tetrahedron 71 (2015) 5662e5668
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A mild access to chiral syn 1,2-diaryl glycols by stereoselective ring
opening of ortho substituted trans 2,3-diaryl-oxiranes using
Amberlyst 15 in H2O/THF system
,
a
a
a
Paolo Lupattelli a , Lucia Chiummiento , Maria Funicello , Francesco Tramutola ,
*
Antonella Marmo a, Natascia Gliubizzi a, Daniela Tofani b
Dipartimento di Scienze, Universita degli studi della Basilicata, via dell’Ateneo Lucano 10, 85100, Potenza, Italy
a
ꢀ
b
ꢀ
Dipartimento di Scienze, Sezione di Nanoscienze e Nanotecnologie, Universita di Roma 3, via della Vasca Navale 79, 00146, Roma, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Amberlyst 15 was an efficient and green catalyst for the reaction of 2,3-diaryloxiranes with H2O in or-
ganic co-solvent to prepare glycols in high yield. Ortho substituted trans 2,3-diaryloxiranes afforded the
corresponding syn glycols stereo- and enantiospecifically. Stereoselectivity appeared related to the
coordination ability of the substituents, irrespective of their electronic properties. Indeed o-OCH3 and
o-OBn substituted syn glycols were obtained in high stereochemical ratios (6/1 and 10/1, respectively),
and o-OTIPS and o-NO2 substituted ones were obtained as exclusive products, with the same ee of the
parent epoxides.
Received 3 March 2015
Received in revised form 25 May 2015
Accepted 9 June 2015
Available online 17 June 2015
Keywords:
Diaryloxiranes
Amberlyst 15
Ring opening
Green chemistry
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
2,3-Diaryloxiranes can be considered non-conventional epox-
ides in terms of their synthesis and, above all, their reactivity. If
Epoxides are among the most intriguing and challenging moi-
eties in organic synthesis because they are not only significant
synthetic endpoints, but also highly useful synthetic
intermediates.1
Utility and convenience of their use can be enhanced by the
modulation of their reactivity with the help of Lewis acids co-
ordinating to the oxygen atom. Thus, ring-openings of epoxides
have been applied on an industrial scale for the synthesis of bulk
chemicals, and in the synthesis of natural products and
pharmaceuticals.
A wide range of nucleophiles are described to react efficiently
with epoxides and the regioselectivity of the opening is usually
predicted by the different electrophilicity of the two oxiranyl car-
bons and/or the formation of chelates in the presence of other
coordinating moieties in the molecule. The stereochemistry in the
opening reaction is mostly assured by the SN2 pathway and there is
usually low, if any, epimerization at the electrophilic oxiranyl
carbon.
compared to alkyl ones, they usually show lower reactivity towards
nucleophiles and they need some activation by Lewis acids. Due to
the characteristic chemical behaviour of benzyl type carbons in
neutral or acidic medium they appear challenging substrates due to
the small reactivity differences of the two oxiranyl carbons and the
possible side reactions such as eliminations or rearrangements.2
The so-called ‘Meinwald rearrangement’ of epoxides to carbonyl
compounds represents a key topic of a rich literature and a number
of inorganic and organometallic Lewis acids have been employed,
ranging from the classical lithium salts or BF3∙Et2O3 to the more
recent copper tetrafluoroborate4 or mixed-valent iron tri-
fluoroacetate.5 Concerning the Brønsted acid-catalysed rearrange-
ment, acidic zeolite HZSM-5,6 Nafion-H7 and nanoporous alumino-
and borosilicates8 are efficient for isomerization of styrene oxide
and stilbene oxide.
Epoxide ring-opening reactions by hydrolysis and alcoholysis
are in general practical and widely employed strategies in synthe-
sis9 although, in most cases, they deal with the handling of toxic
and/or expensive reagents, intolerance to highly sensitive groups
and the formation of unwanted byproducts. In this respect, new
‘green’ methods under solvent free conditions have been recently
developed.10
* Corresponding author. Tel.: þ39 0971 205495; fax: þ39 0971 205503; e-mail
address: paolo.lupattelli@unibas.it (P. Lupattelli).
http://dx.doi.org/10.1016/j.tet.2015.06.039
0040-4020/Ó 2015 Elsevier Ltd. All rights reserved.

P. Lupattelli et al. / Tetrahedron 71 (2015) 5662e5668
5663
Epoxide hydrolysis usually occurs through
a
general SN2
performed at 65 ꢀC, affording the syn diol as the main reaction
product. These results were then compared to those obtained with
p-TsOH, which can be considered the homogenous counterpart of
Amberlyst 15.
mechanism, with inversion of configuration at the oxiranyl carbon
approached by the water molecule. Thus, simple trans-symmetrical
2,3-disubstituted oxiranes lead invariably to meso-diols as the main
reaction product (Scheme 1).
Using p-TsOH (20% mol) as acidic catalyst, at room temperature,
the conversion was<5% after 48 h while at 65 ꢀC the reaction was
complete within 12 h. Encouraged by the higher reaction rates
using Amberlyst 15 and the positive effect of the temperature on
the efficiency and the stereochemical outcome of the reaction, we
extended our procedure to substituted trans 2,3-diaryloxiranes. In
this way, we could evaluate the effect of different substituents and
their position, to achieve diols bearing an extra coordinating group.
Chiral diols are frequently used ligands in asymmetric trans-
formations.17 They have been successfully employed as enantiose-
lective hydrogen-bonding organocatalysts in hetero-DielseAlder
reactions,18 in various asymmetric cycloaddition reactions,19,20 in
asymmetric N-nitroso aldol reactions of enamines21 and in enan-
tioselective, vinylogous Mukaiyama aldol reactions,22 as well as
additives in direct aldol reaction catalysed by Proline.23 Also the
substitution pattern of the chiral diol unit may have a great in-
fluence on the enantioselectivity of the reaction. 17a
The catalytic asymmetric dihydroxylation of olefins is by far the
most used method for their synthesis.24 Despite its widespread
application, the high cost, hazardous toxicity, volatility and con-
tamination of products with osmium are the main drawbacks,
notably in the field of green chemistry. This is highly pointed out by
the literature on immobilization of the catalyst on suitable in-
organic or organic supports as polymers,25 dendrimers,26 ion-
exchange resins,27 silica gels,28 hydroxyapatites,29 fullerenes,30
mesoporous and microporous solids.31 In particular, substituted
stilbene derivatives are rarely encountered.32
Scheme 1. Hydrolysis of trans symmetrical epoxides through SN2 mechanism.
In the case of certain tertiary mono-aryl substituted oxiranes
consistent amounts of syn adducts in the acid hydrolysis were
justified by means of an ion-dipole pair mechanism.11
Herein we report the direct conversion of different 2,3-
diaryloxiranes into the corresponding 1,2-diols (or vic-diols) by
water in the presence of the acid resin Amberlyst 15.
In the last twenty years the chemistry of Amberlyst 15 has ex-
perienced a rapid development. Such growing interest is mainly
due to its mild and highly selective properties, combined with its
environmentally benign character and commercial availability at
low cost and it is testified by a recent review, which only partially
covered all its wide applicability.12
During our studies on oxiranyl ring opening reactions on diaryl
epoxides we noted a general stereoretention at the reacting carbon
using different nucleophiles, in the presence of Amberlyst 15 as
acidic promoter. Thus ortho-methoxy and ortho-nitro trans 2,3-
diaryloxiranes were stereoselectively converted to the syn-bro-
mohydrins by LiBr/Amb. 15 system,13 while trans 4,5-diaryl-2,2-
dimethyl-1,3-dioxolanes were obtained stereospecifically by ace-
tone/Amb. 15 system.14 This last reaction was successfully applied
to a calix[4]arene bis-epoxide15 and to the synthesis of Com-
bretastatine derivatives.16
Thus a series of new enantioenriched 2-aryl-3-phenyloxiranes
was prepared by asymmetric sulfur ylide mediated epoxidation of
aldehydes,33 using Isothiocineole as chiral precursor, which is
readily available in both enantiomeric forms and has been recently
shown to be highly efficient in epoxidation and aziridination re-
actions, with high levels of enantioselectivity.34
These resultsprompted us toinvestigatewateras the nucleophile
in the presence of Amberlyst 15 with a variety of 2,3-diaryloxiranes.
Reactions of the corresponding benzyl sulfonium salt35 with
aromatic aldehydes in presence of KOH as a base, in either H2O/
CH3CN or t-BuOH/CH3CN solvent mixtures, worked smoothly well
in all cases, furnishing good yields and very high levels of diastereo-
and enantioselectivity (Table 1).
The method confirmed its wide applicability with aromatic al-
dehydes. Isothiocineole was always recovered at the end of the
purification in 75e85% yield, thus underlining the practical value of
this stoichiometric enantioselective epoxidation.
Epoxides were then tested in different hydrolytic conditions in
the presence of Amberlyst 15 and the results are collected in Table 2.
The relative stereochemistry (syn vs anti) of diols was de-
termined by stereospecific formation of the corresponding 2,2-
dimethyl-1,3-dioxolanes (Scheme 3) and determination of the
trans/cis ratio of the products.36
2. Results and discussion
We first tested the chemoselectivity of the method, with respect
to competitive rearrangement reactions. Thus, we studied the be-
haviour of the model trans stilbene oxide at different reaction
temperatures and solvents. The use of an organic water-miscible
solvent was required to dissolve the substrate, so H2O/THF 1:9
mixture was used (Scheme 2).
Scheme 2. Hydrolysis of trans stilbene oxide by Amberlyst 15.
The reaction ran slowly at room temperature and, after 24 h,
afforded an equimolar mixture of syn and anti diols, diphenylace-
taldehyde and unreacted epoxide. On the other hand, the substrate
was completely converted within 2 h 30 min when the reaction was
Scheme 3. Formation of 2,2-dimethyl-1,3-dioxolanes from the parent diols.

5664
P. Lupattelli et al. / Tetrahedron 71 (2015) 5662e5668
Table 1
Preparation of enantioenriched trans 2-aryl-3-phenyloxiranes
Entry
Ar
Method
Prod., yield (%)a
d.r.b (trans/cis)
e.r.(trans)c
1
2
3
4
5
6
7
8
9
o-Br-C6H4
o-Cl-C6H4
B
B
A
B
B
B
B
A
A
2a, 60d
2b, 60d
2c, 80
2d, 88
2e, 68
2f, 65d
2g, 80
2h, 78
2i, 70
95/5
95/5
97/3
96/4
o-NO2-C6H4
o-CH3OeC6H4
o-TsO-C6H4
o-TIPSO-C6H4
o-BnO-C6H4
30,50-di-CH3O-C6H3
p-NO2-C6H4
only trans
only trans
only trans
only trans
only trans
only trans
only trans
>99/1
>99/1
95/5
>99/1
>99/1
95/5
95/5
a
Isolated Yield.
trans/cis.
b
c
Determined by chiral HPLC; see Experimental Section for details.
The main product was isolated by preparative TLC.
d
Table 2
Hydrolysis of 2-aryl-3-phenyloxiranes by Amberlyst 15
Entry
Ar
Methoda
Time (h)
Yield (%)b
syn/anti (3/4)
1
2
3
4
5
6
7
8
o-Br-C6H4 (2a)
o-Br-C6H4 (2a)
o-Cl-C6H4 (2b)
o-Cl-C6H4 (2b)
o-NO2-C6H4 (2c)
o-CH3OeC6H4 (2d)
o-TsO-C6H4 (2e)
o-TsO-C6H4 (2e)
o-TIPSO-C6H4 (2f)
o-BnO-C6H4 (2g)
30,50-di-CH3O-C6H3 (2h)
p-NO2-C6H4 (2i)
A
B
A
B
A
A
A
B
A
A
A
A
20
2
20
2
11
2
24
3
2
2
4
24
63
55
65
57
75
70
60
55
70
65
80
80
(3a/4a) 3/1
(3a/4a) 3/1
(3b/4b) 3/1
(3b/4b) 3/1
only syn (3c)
(3d/4d) 6/1
(3e/4e) 3/1
(3e/4e) 3/1
only syn (3f)
(3g/4g) 10/1
(3h/4h) 3/2
(3i/4i) 1/1
9
10
11
12
a
All the reactions were performed with 660 mg Amb. 15 per mmol of the substrate in 0.1 M H2O/org. solv. 1:9 solution.
Isolated yield.
b
As it can be noted in Table 2, the diols were obtained in good
the same results), the coordination ability of the heteroatoms in the
substituent can be invoked to explain the observed stereochemical
outcome. Cationic chelates of type A and B can be proposed, in
which the substituent hinders the anti position to the approaching
nucleophile (Fig. 1). Five-membered chelates A, in which the pos-
itive charge is partially released to the X group, are more favoured
in the case of highly coordinating OCH3, OTIPS and OBn sub-
stituents (entries 6, 9 and 10) than in the case of Br, Cl and OTs
(entries 1e4, 7e8). In the case of o-NO2 derivative the six member
chelate B or a neighbouring group inversion can explain the com-
plete stereoselectivity toward the syn diol.
yield within acceptable reaction time. In certain cases (entries 2, 4
and 8) the use of the higher boiling dioxane allowed the reaction
time to be considerably reduced. Comparing the results of ortho-
versus para-substituted substrates the stereoselectivity of the re-
action was deeply affected by the position of the substituent. In the
presence of an ortho-substituent the syn isomer was always the
main product, the stereoisomeric ratio ranging between 3/1 for o-
Br, o-Cl and o-OTs derivatives, to 10/1 in the case of o-OBn ones and
complete stereoselectivity in the case of o-NO2 and o-OTIPS diols. If
no ortho-substituent is present, as in the case of 30,50-dimethoxy
and p-NO2 derivatives, syn/anti ratio dropped to 3/2 and 1/1,
respectively.
From a deeper analysis of the results obtained for ortho-
substituted epoxides, the type of substituent played a decisive role
in boosting the stereoselectivity from moderate ratios (o-Br, o-Cl, o-
OTs derivatives) to synthetically useful ones (o-NO2, o-OCH3, o-OBn,
o-OTIPS37), which afforded syn diols in >60% chemical yield. While
electronic properties of the substituents seem to have no effect on
the stereoselectivity (o-NO2, and o-OTIPS epoxides 2c and 2f gave
Fig. 1. Proposed cationic intermediates.

P. Lupattelli et al. / Tetrahedron 71 (2015) 5662e5668
5665
Apart from mechanistic considerations, the synthetic value of
the procedure is unquestionable, considering, at least, the synthetic
versatility of o-NO2- and o-OTIPS substituted syn diols 3c and 3f
and their optical purity, which remained the same of the parent
epoxides.
(6 mL). Then the aldehyde (2 equiv) was added. The solution was
then placed in a 0 ꢀC bath and freshly ground KOH (62 mg,
1.1 equiv) was added. The solution was stirred at 0 ꢀC overnight.
Acetonitrile and tert-butanol were then evaporated under re-
duced pressure and dichloromethane (15 mL) and water (15 mL)
was added. The organic layer was separated and the aqueous
layer was extracted with dichloromethane (2ꢁ15 mL). The or-
ganic phases were then combined, dried with MgSO4 and the
solvent evaporated under reduced pressure. Products were puri-
fied by chromatography on silica gel at atmospheric pressure
(unless stated otherwise).
3. Conclusions
In conclusion, Amberlyst 15, THF/H2O system proved to be ef-
ficient for the stereoselective conversion of enantioenriched ortho
substituted trans 2-aryl-3-phenyl-oxiranes to corresponding chiral
1,2-diols, which are useful intermediates to polydentate organo-
catalysts and ligands.
In each case the chiral-phase HPLC Rt given is for the major
enantiomer obtained using salts derived from (R)-1.
4. Experimental section
4.1. General
4.2.3. trans (2R,3R)-2-(2-Bromo-phenyl)-3-phenyl-oxirane 2a. trans
(2R,3R)-2-(2-Bromo-phenyl)-3-phenyl-oxirane 2a was obtained
(165 mg, 60%) as a pale yellow oil after chromatografic purification
on preparative thin layer silica gel plate (2% Et2O/PE). [Found: C,
60.85; H, 4.10. C14H11BrO requires C, 61.11; H, 4.03%]; Rf (2% Et2O/PE)
All solvents or reagents were purified according to literature
procedures. IR data were collected on a PerkineElmer Model 2000
FTIR spectrometer. 1H NMR spectra were recorded on a high field
NMR spectrometer (at 500 or 400 MHz) and are reported relative to
CDCl3 signal. Data for 1H NMR spectra are reported as follows:
0.60; [
a
]
D
25 þ48 (c¼1.2, CH2Cl2); ee 94%. HPLC conditions: Chiralcel
OD column, 5% iPrOH/n-hexane, 1 mL/min tR¼7.87 min; IR (neat),
nmax 2962, 2924, 1472, 1456, 1260, 1091, 1024, 798, 696, 612 cmꢂ1
;
dH (400 MHz, CDCl3) 3.68 (d, 1H, J¼1.6 Hz), 4.10 (d, 1H, J¼1.6 Hz),
7.30e7.34 (m, 8H), 7.49 (d, 1H, J¼8.4 Hz); dC (100 MHz, CDCl3); 62.1,
62.2,122.5,125.7,126.2,127.6,128.4,128.6,129.3,132.3,136.6,136.8.
MS (m/z, %): 274 (28) [M]þ, 276 (28) [Mþ2]þ, 245 (38), 247 (37), 183
(26), 185 (25), 89 (100).
chemical shift (d ppm), multiplicity, coupling constant (Hz) and
integration. Splitting patterns are designated as follows: s, singlet;
d, doublet; t, triplet; q, quartet; m, multiplet; and b, broad. 13C NMR
spectra were recorded on a high field NMR spectrometer (at 125 or
100 MHz). Data for 13C NMR spectra are reported in terms of
(2S,3S)-enantiomer was prepared from sulfonium salt derived
25
chemical shift and are reported in parts per million (ppm,
d). Thin-
from (þ)-isothiocineole. tR¼4.97 min ee 94%. [
a
]
D
ꢂ49 (c¼0.5,
layer chromatography (TLC) was carried out using pre-coated silica
gel sheets (Merck 60 F254). Visual detection was performed using
UV light at 254 nm and phosphomolybdic acid. Column chroma-
tography was carried out on Merck silica gel (0.063e0.200 mm
particle size) by progressive elution with suitable solvent mixtures.
MS spectra were recorded on a gas-chromatograph equipped
CH2Cl2).
4.2.4. trans (2R,3R)-2-(2-Chloro-phenyl)-3-phenyl-oxirane 2b. trans
(2R,3R)-2-(2-Chloro-phenyl)-3-phenyl-oxirane 2b was obtained
(138 mg, 60%) as a pale yellow oil after chromatografic purification
on preparative thin layer silica gel plate (Rf 0.45, 2% Et2O/PE):
with an MS capillary column (30 mꢁ0.25 mm i.d.ꢁ0.25
m
m film
[Found: C, 72.75; H, 4.90. C14H11ClO requires C, 72.89; H, 4.81%]; Rf
25
thickness; injection temperature: 250 ꢀC, column temperature
program: 100 ꢀC for 3 min, then 10 ꢀC minꢂ1 until 250 ꢀC) and
a mass selective detector (mass range: 15e800 amu; scan rate: 1.9
scans sꢂ1; EM voltage: 1435). Enantiomeric excess was determined
by HPLC analysis performed on a JASCO PU-1580 pump with
a Varian 2550 UV detector and Daicel CHIRALCELÒ columns (in-
ternal diameter 4.6 mm, column length 250 mm, particle size
(2% Et2O/PE) 0.45; [
a
]
þ56 (c¼0.6, CHCl3); ee 92%. HPLC condi-
D
tions: Chiralcel OD column, 5% iPrOH/n-hexane, 0.5 ml/min;
tR¼17.29 min; IR (neat), nmax 3064, 2925, 1456, 1051, 885, 700,
612 cmꢂ1
;
dH (500 MHz, CDCl3) 4.25 (d, 1H, J¼2.0 Hz), 3.78 (d, 1H,
J¼2.0 Hz), 7.20e7.40 (m, 9H); dC (125 MHz, CDCl3) 59.9, 62.2, 125.7,
125.8,127.1, 128.4,128.6, 129.0,129.1, 133.2, 135.1, 137.6. MS (m/z, %):
230 (43) [M]þ, 232 (14) [Mþ2]þ, 201 (78) [Mꢂ29]þ, 203 (26)
[Mꢂ27]þ, 139 (41) [Mꢂ91]þ, 141 (13) [Mꢂ89]þ, 89 (100).
10 mm). The optical rotation was evaluated by using a JASCO Mod
Dip-370 polarimeter.
(1R,4R,5R,6R)-6-Benzyl-4,7,7-trimethyl-6-thioniabicyclo[3.2.1]
octane trifluoromethanesulfonate was prepared according to lit-
erature procedure.18
(2S,3S)-enantiomer was prepared from sulfonium salt derived
25
from (þ)-isothiocineole ee 92%. tR¼10.32 min [
a
]
ꢂ60 (c¼0.8,
D
CHCl3).
4.2.5. trans (2R,3R)-4-Methyl-benzenesulfinic acid 2-(3-phenyl-ox-
iranyl)-phenyl ester 2e. trans (2R,3R)-4-Methyl-benzenesulfinic
acid 2-(3-phenyl-oxiranyl)-phenyl ester 2e was obtained (249 mg,
68%) as colourless oil after purification by column chromatography
at atmospheric pressure (30% Et2O/EP); [Found: C, 72.1; H, 5.0; S,
9.1. C21H18O3S requires C, 71.98; H, 5.18; S, 9.15%]; Rf (30% Et2O/EP)
4.2. General epoxidation
4.2.1. Method A. Sulfonium salt (820 mg, 2.0 mmol, 1 equiv) was
dissolved in a 9:1 mixture of acetonitrile and water (10 mL). Then
the aldehyde (1.1 equiv) was added. The solution was then placed in
a 0 ꢀC bath and freshly ground KOH (123 mg, 1.1 equiv) was added.
The solution was stirred at 0 ꢀC overnight. Acetonitrile was then
evaporated under reduced pressure and dichloromethane (20 mL)
and water (20 mL) were added. The organic layer was separated
and the aqueous layer was extracted with dichloromethane
(2ꢁ20 mL). The organic phases were then combined, dried with
MgSO4 and the solvent evaporated under reduced pressure. Prod-
ucts were purified by chromatography on silica gel at atmospheric
pressure (unless stated otherwise).
0.6; [
a
]
25 þ59 (c 0.8, CHCl3); ee 90%. HPLC Chiralcel OD, n-hexane/
D
2-propanol 90/10, 1.0 mL/min; tR¼8.97 min; IR (neat), nmax 3033,
2925, 1494, 1455, 1361, 1291, 1178, 850, 800, 650 cmꢂ1
; dH
(500 MHz, CDCl3) 2.35 (s, 3H), 3.98 (br s, 1H), 3.72 (br s, 1H), 7.08
(d, J¼8.5 Hz, 2H), 7.19e7.41 (m, 9H), 7.54 (d, J¼8.5 Hz, 2H); dC
(125 MHz, CDCl3) 21.7, 57.6, 62.5, 122.7, 125.9, 125.9, 127.6, 128.2,
128.5, 128.6, 129.1, 129.9, 131.1, 132.3, 136.6, 145.6, 147.9. MS (m/z,
%): 366 (1) [Mþ], 337 (20) [Mꢂ29]þ, 275 (35) [Mꢂ91]þ, 207 (18),
183 (100).
(2S,3S)-enantiomer was prepared from sulfonium salt derived
25
4.2.2. Method B. Sulfonium salt (410 mg, 1 mmol, 1 equiv) was
dissolved in a 15:1 mixture of acetonitrile and tert-butanol
from (þ)-isothiocineole. ee 90%. tR¼11.98 min [
a
]
ꢂ60 (c¼0.8,
D
CHCl3).

5666
P. Lupattelli et al. / Tetrahedron 71 (2015) 5662e5668
4.2.6. trans (2R,3R)-3-phenyl-2-(2-triisopropylsilyloxy-phenyl)-oxir-
ane 2f. trans (2R,3R)-3-Phenyl-2-(2-triisopropylsilyloxy-phenyl)-
oxirane 2f was obtained (239 mg, 65%) as pale yellow oil after
chromatografic purification on preparative thin layer plate (2%
NMR and used as substrate for the formation of the corre-
sponding acetals.
4.2.9.1. syn (1R,2R)-1-(2-Nitro-phenyl)-2-phenyl-ethane-1,2-diol
3c. syn (1R,2R)-1-(2-Nitro-phenyl)-2-phenyl-ethane-1,2-diol 3c
was obtained (194 mg, 75%, method A) as pale yellow oil after
chromatographic purification (50% E2O/EP); [Found: C, 64.7; H, 5.1.
Et2O/PE); [Found: C, 74.8; H, 8.9; Si, 7.5. C23H32O2Si requires C,
25
74.95; H, 8.75; Si, 7.62%]; Rf (2% Et2O/EP) 0.5; [
a]
þ32 (c 1.2,
D
CHCl3); ee 99%. HPLC Chiralcel OD, n-hexane/2-propanol 99/1,
0.5 mL/min; IR (neat), nmax 3050, 2965, 1465, 1405, 752, 696,
C
14H13NO4: C, 64.86; H, 5.05]; Rf (50% E2O/EP) 0.4; [
a
]
25 ꢂ16 (c 1.0,
D
614 cmꢂ1
;
dH (400 MHz, CDCl3) 0.54 (d, J¼8.6 Hz, 9H), 0.76 (d,
CHCl3) ee 99%;38 IR (neat), nmax 3600e3200 (br s), 2950, 1524, 1345,
J¼8.6 Hz, 9H), 3.74 (br s, 1H), 4.28 (br s, 1H), 6.83 (d, J¼8.8 Hz, 1H),
6.99 (dd, J1¼J2¼8.8 Hz, 1H), 7.18 (dd, J1¼J2¼8.8 Hz, 1H), 7.22e7.40
(m, 6H). dC (100 MHz, CDCl3) 17.8, 29.7, 59.4, 62.4, 118.2, 121.1, 124.9,
125.4, 127.7, 128.1, 128.3, 128.6, 137.3, 154.6. MS (m/z, %): 368 (6)
[Mþ], 327 (7), 325 (100), 237 (8), 165 (9).
758, 700 cmꢂ1
; dH (500 MHz, CDCl3) 2.67e3.05 (br s, 2H), 4.94 (d,
J¼4.0 Hz, 1H), 5.51 (d, J¼4.0 Hz, 1H), 7.29e7.36 (m, 5H), 7.44 (dd,
J1¼J2¼7.8 Hz, 1H), 7.64 (dd, J1¼J2¼7.8 Hz, 1H), 7.80 (d, J¼7.8 Hz, 1H),
7.89 (d, J¼7.8 Hz, 1H); dC (125 MHz, CDCl3) 73.1, 76.4, 124.5, 126.2,
128.0, 128.5, 128.5, 129.3, 133.1, 136.2, 140.1, 147.9.
(2S,3S)-enantiomer was prepared from sulfonium salt derived
from (þ)-isothiocineole.
(S,S)-syn diol was prepared from the parent (S,S)-epoxide.
25
ee 99%21
[
a]
þ15 (c 1.0, CHCl3).
D
ee 99%. [
a]
25 ꢂ31 (c¼1.2, CHCl3).
D
4.2.9.2. (R,R)-syn
2-phenyl-1-(2-Triisopropylsilyloxy-phenyl)-
4.2.7. trans
(2R,3R)-2-(2-Benzyloxy-phenyl)-3-phenyl-oxirane
ethane-1,2-diol 3f. (R,R)-syn 2-phenyl-1-(2-Triisopropylsilyloxy-
phenyl)-ethane-1,2-diol 3f was obtained (270 mg, 70% by method
A) as colourless oil after chromatographic purification (5% Et2O/
CHCl3). [Found: C, 71.5; H, 8.7. C23H34O3Si requires C, 71.46; H,
2g. trans (2R,3R)-2-(2-Benzyloxy-phenyl)-3-phenyl-oxirane 2g
was obtained (242 mg, 80%) as colourless oil after purification
by column chromatography at atmospheric pressure (20% Et2O/
EP); [Found: C, 83.3; H, 6.1. C21H18O2 requires C, 83.42; H,
6.00%]; Rf (20% Et2O/EP) 0.4; [
8.86]; [
a
]
D
25 þ37 (c 1.3, CHCl3); ee 99%;21 IR (neat), nmax 3500e3200
25
a
]
þ34 (c 1.05, CHCl3); ee 99%.
(br s), 3030, 2980, 1450, 1405, 750, 700 cmꢂ1
;
dH (500 MHz, CDCl3)
D
HPLC Chiralcel OD, n-hexane/2-propanol 98/2, 0.5 mL/min;
tR¼12.87 min; IR (neat), nmax 3013, 3005, 1497, 1452, 1253, 1216,
1.12 (d, J¼7.6 Hz, 18H), 1.30e1.40 (m, 3H), 3.15 (br s, 1H, OH), 3.29 (d,
J¼6.5 Hz, 1H, OH), 4.90 (d, J¼6.8 Hz, 1H), 4.93 (dd, J1¼6.8 Hz,
J2¼6.5 Hz, 1H), 6.77 (d, J¼8.1 Hz, 1H), 6.84 (dd, J1¼J2¼8.1 Hz, 1H),
7.01 (dd, J1¼8.0 Hz, J2¼1.6 Hz,1H), 7.11 (ddd, J1¼J2¼8.1 Hz, J3¼1.6 Hz,
1H), 7.19e7.39 (m, 5H). dC (125 MHz, CDCl3) 13.1, 18.1, 76.1, 76.7,
117.8, 120.8, 126.8, 127.3, 127.6, 128.0, 128.6, 129.2, 140.2, 153.3.
(S,S)-syn diol was prepared from the corresponding (S,S)-
epoxide.
859, 761, 696 cmꢂ1
;
dH (500 MHz, CDCl3) 3.81 (d, J¼1.5 Hz, 1H),
4.30 (d, J¼1.5 Hz, 1H), 5.08 (br s, 2H), 6.92 (d, J¼8.2 Hz, 1H),
6.99 (dd, J1¼J2¼7.2 Hz, 1H), 7.24e7.35 (m, 12H); dC (125 MHz,
CDCl3) 58.4, 62.1, 70.0, 111.8, 121.1, 125.2, 125.7, 126.3, 126.8,
127.7, 128.1, 128.4, 128.4, 128.8, 136.8, 137.3, 157.1; MS (m/z, %):
302 [Mþ] (1), 273 (10), 212 (10), 211 (67), 183 (29), 181 (19), 167
(14), 91 (100).
ee 99%.21
[a
]
25 ꢂ35 (c 1.0, CHCl3).
D
(2S,3S)-enantiomer was prepared from sulfonium salt derived
from (þ)-isothiocineole. tR¼10.64 min [
25
a
]
ꢂ34 (c 0.75, CHCl3).
4.2.9.3. syn and anti 1-(2-Benzyloxy-phenyl)-2-phenyl-ethane-
1,2-diols 3g and 4g. syn and anti 1-(2-Benzyloxy-phenyl)-2-phenyl-
ethane-1,2-diols 3g and 4g were obtained (208 mg, 65%) as syn/anti
10:1 mixture after chromatographic purification (5% CH3OH/
CH2Cl2); dH (500 MHz, CDCl3) 2.70 (br s, 1H, OH, anti), 2.92 (br s, 1H,
OH, anti), 3.10 (br s, 1H, OH, syn), 3.19 (br s, 1H, OH, syn), 4.86 (m,1H,
CHOH, syn and anti), 4.89 (d, J¼11.2 Hz, 1H, CHOH, syn and anti),
4.95 (m, 1H, CHOH, syn and anti), 5.00 (d, J¼11.2 Hz, 1H, CHOH, syn
and anti), 6.88 (m, 2H, syn and anti), 7.08e7.22 (m, 7H), 7.33e7.39
(m, 5H).
D
4.2.8. trans
(2R,3R)-2-(3,5-Dimethoxy-phenyl)-3-phenyl-oxirane
2h. trans (2R,3R)-2-(3,5-Dimethoxy-phenyl)-3-phenyl-oxirane 2h
was obtained (200 mg, 78%) as colourless oil after purification by
column chromatography at atmospheric pressure (15% Et2O/EP);
[Found: C, 74.8; H, 6.4. C16H16O3 requires C, 74.98; H, 6.29%]; Rf (15%
Et2O/EP) 0.5; [
a
]
25 þ38 (c 1.2, CH2Cl2); ee 90%, HPLC Chiralcel OD, n-
D
hexane/2-propanol 98/2, 0.5 mL/min tR¼10.23 min; IR (neat), nmax
3014, 2939, 1607, 1463, 1353, 1215, 1156, 1065, 837, 754, 700 cmꢂ1
;
dH (400 MHz, CDCl3) 3.82 (s, 3H), 3.85 (br s, 2H), 6.45 (dd,
J1¼J2¼2.3 Hz, 1H), 6.54 (d, J¼2.4 Hz, 2H), 7.35e7.42 (m, 5H). dC
(100 MHz, CDCl3) 55.4, 62.6, 62.8, 100.5, 103.1, 125.5, 128.3, 128.5,
136.9, 139.6, 161.1; MS (m/z, %): 256 (45) [Mþ], 228 (60), 227 (100),
212 (37), 197 (22), 196 (35).
4.2.10. Conversion of the diols to acetals: general procedure. A so-
lution of diols (1 mmol), 2,2-dimethoxypropane (0.2 mL), cam-
phorsulfonic acid (CSA, 20 mg) in acetone (20 mL) was kept stirring
at room temperature till completion of the reaction (ca. 1e2 h). The
mixture was cooled to 0 ꢀC and NaHCO3 s.s (20 mL) was poured into
the solution. The organic solvent was then evaporated and the
aqueous layer was extracted with Et2O (3ꢁ10 mL). The combined
organic layers were dried with Na2SO4 and the solvent was re-
moved. The crude product was purified by silica gel chromatogra-
(2S,3S)-enantiomer was prepared from sulfonium salt derived
from (þ)-isothiocineole. tR¼9.61 min [
a
]
25 ꢂ192 (c 1.1, CHCl3).
D
4.2.9. General hydrolysis method. Amberlyst 15 (660 mg) was
added in one portion to a solution of diaryl oxirane (1 mmol) in
the appropriate solvent mixture (THF/H2O 9:1, Method A, 1,4-
dioxane/H2O 9:1, Method B) (10 mL) and the mixture was kept
stirring at reflux temperature till completion of the reaction (by
TLC and GC analysis). The mixture was cooled to rt, the Amber-
lyst was filtered off and NaHCO3 s.s (10 mL) was poured into the
solution. The organic solvent was then evaporated and the
aqueous layer was extracted with Et2O (3ꢁ10 mL). The combined
organic layers were dried with Na2SO4 and the solvent was re-
moved. The crude product was purified by silica gel chroma-
tography to give the mixture of diols, which was analysed by 1H
phy to give the corresponding acetals, which were analysed by 1
NMR.
H
4.2.10.1. trans (R,R) 4-(2-Bromo-phenyl)-2,2-dimethyl-5-phenyl-
[1,3]dioxolane 5a. trans (R,R) 4-(2-Bromo-phenyl)-2,2-dimethyl-5-
phenyl-[1,3]dioxolane 5a was obtained (232 mg, 70%) from the
parent syn/anti mixture of diols after chromatographic purification
(5% Et2O/EP). [Found: C, 61.4; H, 5.1. C17H17BrO2 requires C, 61.28; H,
5.14]; [
a
]
25 þ9 (c 1.0 CH2Cl2); ee 94%. HPLC Chiralcel OD, n-hexane/
D
2-propanol 95/5, 0.5 mL/min tR¼11.78 min; IR (neat), nmax 2955,

P. Lupattelli et al. / Tetrahedron 71 (2015) 5662e5668
5667
2910, 1490, 1450, 1260, 1030, 800, 705, 630 cmꢂ1
;dH (400 MHz,
4.2.10.6. trans and cis 2,2-Dimethyl-4-(4-nitro-phenyl)-5-phenyl-
[1,3]dioxolanes 5i and 6i. trans and cis 2,2-Dimethyl-4-(4-nitro-
phenyl)-5-phenyl-[1,3]dioxolanes 5i and 6i were obtained (284 mg,
95%) as trans/cis¼45:55 mixture after chromatographic purification
(50% Et2O/EP). dH (400 MHz, CDCl3) 1.64 (s, 3H, cis), 1.70 (s, 3H,
trans), 1.72 (s, 3H, trans), 1.85 (s, 3H, cis), 4.66 (d, J¼8.3 Hz,1H, trans),
4.86 (d, J¼8.3 Hz, 1H, trans), 5.58 (A of AB system, JAB¼7.8 Hz, 1H,
cis), 5.61 (A of AB system, JAB¼7.8 Hz, 1H, cis), 6.99e7.37 (m, 5H),
7.92 (d, J¼8.7 Hz, 2H, cisþtrans), 8.18 (d, J¼8.7 Hz, 2H, cisþtrans).
CDCl3) 1.71 (s, 3H), 1.72 (s, 3H), 4.74 (d, J¼8.8 Hz, 1H), 5.27 (d,
J¼8.8 Hz, 1H), 7.17 (ddd, J1¼J2¼7.8 Hz, J3¼1.8 Hz, 1H), 7.24e7.40 (m,
6H), 7.43 (dd, J1¼J2¼7.8 Hz, 1H), 7.70 (dd, J1¼7.8 Hz, J2¼1.8 Hz, 1H);
dC (100 MHz, CDCl3) 27.2, 27.2, 83.3, 85.8, 109.5, 126.7, 127.1, 127.7,
128.3, 128.4, 128.6, 129.6, 132.9, 135.8, 136.1; MS (m/z, %): 334
[Mþ2]þ (0.2), 332 [Mþ] (0.2), 277 (7), 275 (7), 259 (6), 257 (6), 228
(80), 226 (80), 147 (100).
(S,S)-trans dioxolane was prepared from the corresponding
(S,S)-diol. ee 94%. tR¼10.73 min [
a]
25 ꢂ9 (c 1.0 CH2Cl2).
D
Acknowledgements
4.2.10.2. cis 4-(2-Bromo-phenyl)-2,2-dimethyl-5-phenyl-[1,3]di-
oxolane 6a. cis 4-(2-Bromo-phenyl)-2,2-dimethyl-5-phenyl-[1,3]
dioxolane 6a was obtained (93 mg, 28%) after chromatographic
purification (5% Et2O/EP); [Found: C, 61.2; H, 5.2. C17H17BrO2 re-
quires C, 61.28; H, 5.14; IR (neat), nmax 2962, 2924, 1472, 1460, 1260,
This material is based upon work supported by Ministero del-
ꢀ
l’Istruzione
e
dell’ Universita
e
Ricerca (MIUR) (PRIN
20109Z2XRJ_009), University of Basilicata. We also thank Consorzio
Interuniversitario Nazionale ‘Metodologie e Processi Innovativi di
Sintesi’ for a grant to A.M (n. 21/1 2014).
1100, 1025, 797, 690, 620 cmꢂ1
;dH (400 MHz, CDCl3) characteristic
signals 1.65 (s, 3H), 1.86 (s, 3H), 5.67 (d, J¼7.2 Hz, 1H), 5.89 (d,
J¼7.2 Hz, 1H), 6.89e7.63 (aromatics); MS (m/z, %): 334 [Mþ2]þ
(0.2), 332 [Mþ] (0.2), 277 (6), 275 (6), 259 (5), 257 (5), 228 (83), 226
(83), 185 (13), 183 (13), 171 (28), 169 (28), 148 (83), 147 (100).
Supplementary data
Supplementary data (Characterizations of epoxides 2c, 2d, 2i,
diols 3a, 4a, 3b, 4b, 3d, 4d, 3e, 4e, 3h, 4h, 3i, 4i, dioxolanes 5c, 5d,
6d, 5e, 6e, 5g, 6g, 5h, 6h) related to this article can be found in the
online version, at http://dx.doi.org/10.1016/j.tet.2015.06.039.
4.2.10.3. trans (R,R)-4-(2-Chloro-phenyl)-2,2-dimethyl-5-phenyl-
[1,3]dioxolane 5b. trans (R,R)-4-(2-Chloro-phenyl)-2,2-dimethyl-5-
phenyl-[1,3]dioxolane 5b was obtained (202 mg, 70%) from the
parent syn/anti 3:1 mixture of diols after chromatographic purifi-
cation (5% Et2O/EP). [Found: C, 70.8; H, 5.9. C17H17ClO2 C, 70.71; H,
References and notes
25 þ8 (c 0.5 CH2Cl2); ee 92% HPLC Chiralcel OD, n-hexane/
1. Aziridines and Epoxides in Organic Synthesis; Yudin, A., Ed.; Wiley-VCH: Wein-
heim, 2006.
5.93]. [
a
]
D
2-propanol 95/5, 0.5 mL/min tR¼11.02 min; IR (neat), nmax 3060,
2. Jamalian, A.; Rathman, B.; Borosky, G. L.; Laali, K. K. Appl. Catal., A 2014, 486,
1e11 Bonini, C.; Lupattelli, P. ARKIVOC 2008, (viii), 150e182.
3. Rickborn, B. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon:
Oxford, 1991; Vol. 3, Chapter 3.3, pp 733e775 and references cited therein.
4. Robinson, M. W. C.; Pillinger, K. S.; Mabbett, I.; Timms, D. A.; Graham, A. E.
Tetrahedron 2010, 66, 8377e8382.
2940, 1450, 1035, 880, 705, 602 cmꢂ1
;dH (500 MHz, CDCl3) 1.69 (s,
6H) 4.75 (d, J¼8.5 Hz, 1H), 5.30 (d, J¼8.5 Hz, 1H), 6.90e7.36 (m, 8H),
7.70 (d, J¼7.5 Hz, 1H); dC (100 MHz, CDCl3) 27.2, 27.2, 81.1, 85.6,
103.6, 126.6, 127.1, 128.3, 128.4, 128.6, 129.1, 129.2, 129.6, 130.0,
136.2, 145.2; MS (m/z, %): 286 [Mþ], 288 [Mþ2]þ, 213 (8), 215 (3),
125 (43), 127 (15), 182 (100).
€
€ €
5. Erturk, E.; Gollu, M.; Demir, A. S. Tetrahedron 2010, 66, 2373e2377.
6. Smith, K.; El-Hiti, G. A.; Al-Shamali, M. Catal. Lett. 2006, 109, 77e82.
7. Prakash, G. K. S.; Mathew, T.; Krishnaraj, S.; Marinez, E. R.; Olah, G. A. Appl. Catal.
, A 1999, 181, 283e288.
(S,S)-trans dioxolane was prepared from the corresponding
(S,S)-diol. ee 92%. tR¼7.41 min [
a
]
25 ꢂ8 (c 1.0 CH2Cl2).
8. Davies, T. E.; Kondrat, S. A.; Nowicka, E.; Kean, J. L.; Harris, C. M.; Socci, J. M.;
Apperley, D. C.; Taylor, S. H.; Graham, A. E. Appl. Catal., A 2015, 493, 17e24.
9. See among others: (a) Machida, S.; Isoda, Y.; Kunieda, M.; Tamiaki, H. Tetra-
hedron Lett. 2012, 53, 6277e6279; (b) Sengul, M. E.; Menzek, A.; Sahin, E.; Arik,
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D
4.2.10.4. cis 4-(2-Chloro-phenyl)-2,2-dimethyl-5-phenyl-[1,3]di-
oxolane 6b. cis 4-(2-Chloro-phenyl)-2,2-dimethyl-5-phenyl-[1,3]
dioxolane 6b was obtained (81 mg, 27%) after chromatographic
purification (5% Et2O/EP). [Found: C, 70.6; H, 6.0. C17H17ClO2 re-
quires C, 70.71; H, 5.93]. IR (neat), nmax 3064, 2925, 1456, 1060, 880,
700, 610 cmꢂ1
;dH (500 MHz, CDCl3) 1.62 (s, 3H), 1.83 (s, 3H), 5.61 (d,
J¼7.0 Hz, 1H), 5.90 (d, J¼7.0 Hz, 1H), 7.03e6.89 (m, 8H), 7.26 (d,
J¼9.5 Hz,1H); dC (125 MHz, CDCl3) 24.2, 26.6, 78.0, 80.4,108.7,126.1,
127.1, 127.3, 127.3, 128.0, 128.2, 128.4, 128.4, 131.6, 135.6, 137.8; MS
(m/z, %): 286 [M]þ, 288 [Mþ2]þ, 213 (7), 215 (2), 182 (94), 184 (31),
125 (45), 127 (14), 147 (100).
12. Pal, R.; Sarkar, T.; Khasnobis, S. Arkivoc 2012, I, 570e609.
ꢁ
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yl)-phenoxy]-triisopropyl-silane 5f. trans (R,R) [2-(2,2-Dimethyl-5-
phenyl-[1,3]dioxolan-4-yl)-phenoxy]-triisopropyl-silane 5f was
obtained (405 mg, 95%) as colourless oil after chromatographic
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purification (20% Et2O/EP). [Found C, 73.2; H, 9.0. C26H38O3Si re-
25
quires C, 73.19; H, 8.98]. [
a
]
D
¼þ23 (c 1.1, CHCl3); ee 99%. HPLC
Chiralcel OD, n-hexane/2-propanol 98/2, 0.5 mL/min tR¼4.45 min;
IR (neat), nmax 3030, 2980, 1452, 1412, 758, 691, 605 cmꢂ1
;
dH
(500 MHz, CDCl3) 0.90 (d, J¼7.3 Hz, 18H), 1.05e1.07 (m, 3H), 1.64 (s,
3H), 1.68 (s, 3H), 4.86 (d, J¼8.7 Hz, 1H), 5.40 (d, J¼8.7 Hz, 1H), 6.72
(d, J¼8.2 Hz, 1H), 7.03 (dd, J1¼J2¼8.2 Hz, 1H), 7.15 (dd, J1¼J2¼8.2 Hz,
1H), 7.24e7.60 (m, 5H), 7.61 (d, J¼8.2 Hz, 1H); dC (125 MHz, CDCl3)
12.8, 17.9, 27.0, 27.5, 77.7, 84.9, 108.7, 118.2, 121.1, 126.1, 126.9, 127.7,
128.2, 128.4, 129.0, 137.2, 154.4.
(S,S)-trans dioxolane was prepared from the corresponding
28. Huang, K.; Liu, H.-W.; Dou, X.; Huang, M.-Y.; Juang, Y. Y. Polym. Adv. Technol.
2003, 14, 366e370.
25
(S,S)-diol. ee 99%. tR¼3.18 min [
a
]
¼þ21 (c 0.7, CHCl3)
D

5668
P. Lupattelli et al. / Tetrahedron 71 (2015) 5662e5668
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34. Illa, O.; Arshad, M.; Ros, A.; McGarrigle, E. M.; Aggarwal, V. K. J. Am. Chem. Soc.
2010, 132, 1828e1830.
€
€
€
35. This was prepared in high yield by alkylation of the sulfide with BnBr and
U. Green. Chem. 2012, 14, 1488e1492.
required 24 h at 20 ꢀC.
32. Periasamy, M.; Kumar, S. S.; Kumar, N. S. Tetrahedron Lett. 2008, 49, 4416e4419.
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36. The stereochemistry of the dioxolanes was easily determined by characteristic
1H NMR signal pattern of the two gem methyl groups: in the trans isomers,
possessing a pseudo-C2 symmetry, the two singlets’ shifts differed less than 0.
05 ppm, while in the cis isomers they split up more than 0.2 ppm.
37. Given the steric encumbrance of OTIPS group, also an influence of such effect
can not be excluded.
38. Calculated by ee of the corresponding 2,2-dimethyl-1,3-dioxolane