The regio- and stereo-selective formation of allylic chlorides during the overman rearrangement of trichloroacetimidates derived from certain brominated conduritols

Article abstract of DOI:10.1071/CH08438

Microwave irradiation of imidate 2 at 165C affords a ～3:1 mixture of the Overman rearrangement product 3 and the allylic chloride 4 (83% combined yield). Under the same conditions the deoxy-conduritol 6 gives a comparable mixture of compounds 7 and 8. The

Full text of DOI:10.1071/CH08438

Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2009, 62, 64–68
www.publish.csiro.au/journals/ajc
The Regio- and Stereo-Selective Formation of Allylic
Chlorides During the Overman Rearrangement
of Trichloroacetimidates Derived from Certain
Brominated Conduritols
Maria Matveenko,A Anthony C. Willis,A and Martin G. BanwellA,B
AResearch School of Chemistry, Institute of Advanced Studies, The Australian
National University, Canberra, ACT 0200, Australia.
BCorresponding author. Email: mgb@rsc.anu.edu.au
Microwave irradiation of imidate 2 at 165◦C affords a ∼3:1 mixture of the Overman rearrangement product 3 and the
allylic chloride 4 (83% combined yield). Under the same conditions the deoxy-conduritol 6 gives a comparable mixture of
compounds 7 and 8. The single-crystal X-ray structure of a derivative of chloride 8 is reported together with a mechanism
that accounts for the selective formation of this compound and congener 4.
Manuscript received: 14 October 2008.
Final version: 20 November 2008.
OMOM
OMOM
OMOM
OMOM
Introduction
Cl3CCN,
DBU
MOMO
MOMO
The Overman or allylic trihaloacetimidate rearrangement pro-
cess is a thermally promoted, suprafacial [3,3]-sigmatropic
process that allows for the stereoselective, three-step conver-
sion of an allylic alcohol into the corresponding (rearranged)
allylic amine.[1] This generally very reliable and robust reaction
sequence has found broad application, including in the synthe-
sis of natural products. Catalytic enantioselective variants have
been introduced in recent years and promise to further enhance
the utility of this important process.[2] By-products are rarely
observed during the Overman rearrangement although the allylic
trihaloacetamide can sometimes undergo a [1,3]-rearrangement
to the corresponding (non-double-bond migrated) trihalo-
acetamide, or ionize to form an allylic cation that then engages
in a range of reactions including proton loss to give a diene.[1a]
The ionization process is catalyzed by acid and so it can be sup-
pressed by adding potassium carbonate to the reaction mixture
and thus ensuring the Overman rearrangement process prevails.
Given this background we are now prompted to describe a hith-
erto unreported process that, under certain conditions, appears
to compete with the trichloroacetimidate variant of the Overman
rearrangement. The products of this process are allylic chlorides
that possess the same regio- and stereo-chemistry as the rear-
ranged trichloroacetamide. Details are presented in the following
section as is a mechanistic rationalization for the formation of
these by-products.
DCM,
4 Å MS
O
OH
Br
Br
CCl3
HN
2
1
o-Cl2C6H4,
K2CO3, 165°C
Microwave irradiation
OMOM
OMOM
OMOM
OMOM
MOMO
MOMO
Cl
ϩ
HN
Br
Br
4 (18% from 1)
CCl3
O
3 (65% from 1)
Scheme 1.
Overman rearrangement reaction. For example, compound
1[3a] was treated with a mixture of trichloroacetonitrile and
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in dichloromethane
(DCM) to afford the trichloroacetimidate 2[3a] (Scheme 1). Sub-
jection of an o-dichlorobenzene solution of this material that
contained anhydrous potassium carbonate to microwave irra-
diation at ∼165◦C resulted in the desired rearrangement taking
place and thus produced the acetamide 3[3a] in 65% yield.∗ How-
ever a by-product, which we now believe to be the allylic chloride
Results and Discussion
In connection with the development of the total synthe-
ses of certain Amaryllidaceae alkaloids[3] we have prepared
various halogenated conduritols and subjected them to an
∗It is worth noting that the conversion 2 → 3 represents a rare example of a microwave-promoted Overman rearrangement[5] and seemingly only the second
example of such a process involving a halogenated alkene.[3]
© CSIRO 2009
10.1071/CH08438
0004-9425/09/010064

Regio- and Stereo-Selective Formation of Allylic Chlorides
65
OMOM
MOMO
HN
Br
CCl3
O
OMOM
OMOM
7 (62% from 5)
o-Cl2C6H4,
K2CO3, 165°C
Cl3CCN,
MOMO
MOMO
DBU
ϩ
DCM,
4 Å MS
Microwave irradiation
O
OH
Br
OMOM
Br
CCl3
HN
MOMO
Cl
6
5
Br
8 (17% from 5)
TMSBr, 4 Å MS,
Ϫ60 to Ϫ40°C
80%
OH
O
O
NO2
O2N
O
O
p-O2NC6H4COCl,
Et3N, DMAP
HO
Cl
O
O
O2N
NO2
30%
O
O
Cl
Cl
Br
Br
Br
10
10
9
Scheme 2.
O20
4 (18%), was also generated. While the structure of compound 3
follows from the single-crystal X-ray analysis of a derivative,[3a]
we had been unable to gain similarly rigorous and direct evidence
for the stereo-structure of congener 4. Now, though, we describe
additional experiments that have led us to assign the illustrated
structure to compound 4.
O19
N18
C15
C16
C14
C13
C17
The critical additional experiments are presented in
Scheme 2 and involved preparing, using standard conditions,
the trichloroacetimidate 6 from the previously reported allylic
alcohol 5.[4] When the former compound was subjected to the
same rearrangement conditions as defined earlier,[3] a chro-
matographically separable mixture of compounds 7 (62% from
5) and 8 (17% from 5) was obtained. The spectroscopic data
acquired on the Overman rearrangement product 7 were in full
accord with the assigned structure and similar to those obtained
on related products that have been converted into various con-
geners of lycoricidine or narciclasine.[3] The analogous data
obtainedonby-product8wereconsistentwiththeassignedstruc-
ture but in order to confirm this the compound was subjected
to treatment with trimethylsilyl bromide so as to effect cleav-
age of the methoxymethyl ether residues and thereby produce
diol 9. Conversion of this last compound into the correspond-
ing bis-p-nitrobenzoate 10 was readily achieved under standard
conditions.
C12
O11
C10
O23
C29
O9
C28
O32
N30
O31
C22
C24
C27
C1
C2
C25
C6
C5
O21
C3
C26
Cl7
C4
Br8
Fig. 1. Molecular structure of compound 10 (C20H14BrClN2O8) with
labelling of selected atoms. Anisotropic displacement ellipsoids show 30%
probability levels. Hydrogen atoms are drawn as circles with small radii.
The crystalline nature of compound 10 allowed an X-ray anal-
ysis to be undertaken and thus confirming its structure and that
of its precursors, particularly by-product 8.The ORTEP diagram
derived from this analysis is shown in Fig. 1.
Clearly compound 8 arises from an allylic rearrangement pro-
cess in which the stereochemistry of the starting imidate 6 is
reflected in the product. On this basis, it is believed that the
by-product from the Overman rearrangement of compound 2
arises from the same type of process and must, therefore,
possess the illustrated structure 4. Interestingly, the Overman
rearrangement of compound 11[6] (Fig. 2), which incorporates a

66
M. Matveenko, A. C. Willis, and M. G. Banwell
OMe
Series FTIR spectrometer. Samples were analyzed as KBr disks
(for solids) or as thin films on NaCl plates (for oils and low-
melting solids). A VG Fisons AutoSpec three-sector (E/B/E)
double focusing mass spectrometer was used to obtain both low-
and high-resolution electron impact (EI) mass spectra. Low- and
high-resolution electrospray (ESI) mass spectra were obtained
on a VG Quattro II triple quadrupole MS instrument operating
in positive ionization mode.
H
N
CCl3
OMe
Cl
OMOM
CCl3
O
O
Cl
OMOM
NH
11
12
Optical rotations were measured at 18◦C, in spectroscopic
grade solvents, with a Perkin–Elmer 241 polarimeter at the
sodium-D line (589 nm) and at the concentrations (c) (g per
100 mL) indicated. The measurements were carried out in a cell
with a path length (l) of 10 cm. Specific rotations {[α]D} were
calculated using the equation [α]D = 100 · a/(c · l) and are given
in 10−1 deg cm2 g−1. Melting points were measured on an Opti-
melt automated melting point system or a Reichert hot-stage
microscope apparatus and are uncorrected.
AnalyticalTLCwasperformedonaluminium-backed0.2 mm
thick silica gel 60 F254 plates as supplied by Merck. Eluted
plates were visualized using a 254 nm UV lamp and/or by
treatment with a suitable dip followed by heating. These
dips included phosphomolybdic acid:ceric sulfate:sulfuric acid
(conc.):water (37.5 g:7.5 g:37.5 g:720 mL) or potassium per-
manganate:potassium carbonate:5% w/v sodium hydroxide
aqueous solution:water (3 g:20 g:5 mL:300 mL). The retarda-
tion factor (RF) was quoted to the nearest 0.1. Flash column
chromatography was performed using silica gel 60 (0.040–
0.0063 mm) as the stationary phase and the analytical reagent
(AR) or HPLC grade solvents indicated.
Starting materials and reagents were generally available
from Sigma–Aldrich, Merck, TCI, Strem, or Lancaster Chem-
ical Companies and were used as supplied. Drying agents
and other inorganic salts were purchased from AJAX, BDH,
or Unilab Chemical Companies. Tetrahydrofuran (THF) and
diethyl ether (ether) were distilled from sodium benzophenone
ketyl. Methanol was distilled from its magnesium alkoxide
salt. Benzene and toluene were distilled from sodium wire.
Dichloromethane was distilled from calcium hydride. Triethyl-
amine was distilled from and stored over potassium hydroxide
pellets.
Fig. 2. Compounds 11 and 12.
chloro- rather than a bromo-cyclohexene residue, proceeds
smoothly to give the trichloroacetamide 12[6] in high yield (88%
from the alcohol precursor to compound 11) and without any evi-
dence of the formation of the sort of allylic chloride by-product
discussed above.
The precise mode of formation of the allylic chloride by-
products 4 and 8 from their trichloroacetimidate precursors 2
and 6, respectively, remains unclear at the present time. That
having been said, given the stereochemical outcomes of the pro-
cesses that lead to these compounds, internal delivery of chloride
seems a distinct possibility and the sort of process illustrated
in structure 13 (Fig. 3), or a related but non-concerted variant,
would appear plausible. If this pathway were indeed operative
then the other primary by-product would be the oxiranimine 14,
although under the reaction conditions involved such a highly
strained species would be expected to hydrolyze to give two
equivalents of carbonic acid. The origin of the seemingly diver-
gent behaviours of the brominated systems 4 and 8 relative to the
chloro-congener 11 remains uncertain but could well be a reflec-
tion of steric factors. The optimization of the processes that lead
to allylic chlorides such as 4 and 8 as well as their exploitation
in synthetic chemistry are the subject of ongoing studies in our
laboratories. Details will be presented in due course.
Br
Cl
Cl
O
Cl
Cl
O
Cl
NH
NH
13
Fig. 3. Compounds 13 and 14.
14
Microwave Irradiation Experiments
All microwave irradiation experiments were carried out in a
CEM Explorer microwave apparatus operating at a frequency
of 2.45 GHz with continuous irradiation power from 0 to 300W
using the standard absorbance level of 300W to represent max-
imum power. The reactions were carried out in 80 mL sealed
Pyrex vessels (working volume of 50 mL) equipped with a
magnetic stirrer. The temperature was measured with a fibre
optic temperature sensor immersed in the reaction vessel. After
the specified irradiation period, the reaction vessel was cooled
rapidly (1–2 min) to ambient temperatures using a nitrogen jet.
Experimental
General Procedures
Unless otherwise specified, proton (1H) and carbon (13C) NMR
spectra were recorded at 18◦C in base-filtered CDCl3 on a Var-
ian Mercury or Inova 300 spectrometer operating at 300 MHz
for proton and 75 MHz for carbon nuclei. In certain cases, a
Varian Inova 500 spectrometer operating, at 500 MHz for pro-
1
ton nuclei, or a Bruker 800 MHz machine were used. For H
NMR spectra, signals arising from residual protio-forms of
the solvent were used as the internal standards. H NMR data
Synthetic Studies
1
Compound 2
are recorded as follows: chemical shift (δH) [multiplicity, cou-
pling constant(s) J (Hz), relative integral] where multiplicity
is defined as: s = singlet, d = doublet, t = triplet, q = quartet,
m = multiplet, or combinations of the above.The residual CHCl3
peak (δH 7.26) was used as a reference for 1H NMR spec-
tra, and the central peak (δC 77.0) of the CDCl3 ‘triplet’ was
used as a reference for proton-decoupled 13C NMR spectra.
Infrared spectra (νmax) were recorded on a Perkin–Elmer 1800
A magnetically stirred solution of compound 1[3a] (210 mg,
0.59 mmol) in CH2Cl2 (3 mL) containing 4 Å molecular sieves
(100 mg) and maintained under an atmosphere of nitrogen was
cooled to 0◦C and then treated, sequentially, with DBU (132 µL,
0.88 mmol) and trichloroacetonitrile (106 µL, 1.06 mmol). The
resulting mixture was warmed to 18◦C over ∼0.5 h, stirred at
this temperature for 1.5 h, and then treated with NH4Cl (5 mL of

Regio- and Stereo-Selective Formation of Allylic Chlorides
67
a saturated aqueous solution). The separated aqueous layer was
extracted with CH2Cl2 (3 × 15 mL) and the combined organic
phases were filtered through a pad comprised of a layer of TLC-
grade silica (1 cm) covered by a layer of anhydrous MgSO4
(2 cm).The pads were then washed with 1:49 v/v MeOH/CH2Cl2
solution (50 mL) and the combined filtrates concentrated under
reduced pressure to afford the previously reported compound
2[3a] (296 mg, ∼100%) as a yellow oil, RF 0.5 (in 1:1 v/v ethyl
acetate/hexane). δH (300 MHz, CDCl3) 8.51 (br s, NH), 6.37 (d,
J 4.2, 1H), 6.00 (d, J 3.6), 4.82–4.64 (complex m, 6H), 4.53–
4.43 (complex m, 2H), 4.20 (dd, J 7.8 and 3.6, 1H), 3.43 (s, 3H),
3.40 (s, 3H), 3.39 (s, 3H). νmax (cm−1) 3344, 2931, 2894, 1669,
1290, 1151, 1118, 1099, 1076, 1041, 917, 794.This material was
used, withoutfurtherpurification, intheOvermanrearrangement
reaction.
extracted with CH2Cl2 (3 × 15 mL) and the combined organic
phases were filtered through a pad comprised of a layer of TLC-
grade silica (1 cm) covered by a layer of anhydrous MgSO4
(2 cm). The pad was washed with MeOH/CH2Cl2 (1 × 50 mL of
a 1:49 v/v mixture) and the combined filtrates were concentrated
under reduced pressure to afford the title compound 6 (420 mg,
∼100%) as a yellow oil, RF 0.5 (in 2:3 v/v ethyl acetate/hexane)
[Found: (M + Na)+ 461.9253. C12H1779Br35Cl3NO5 requires
(M + Na)+ 461.9253]. δH (300 MHz, CDCl3) 8.50 (br s, 1H,
NH), 6.44 (d, J 5.4, 1H), 5.74 (m, 1H), 4.82–4.68 (complex m,
4H), 4.24 (m, 1H), 4.13 (ddd, J 10.8, 3.0 and 3.0, 1H), 3.41 (s,
3H), 3.38 (s, 3H), 2.59–2.50 (complex m, 1H), 2.10 (m, 1H).
m/z (ESI) 468, 467, 466, 465, 464, and 462 [(M + Na)+, 17, 9,
60, 13, 90, and 48%]. This material was used, without further
purification, in the Overman rearrangement reaction.
Compounds 3 and 4
Compounds 7 and 8
Asolutionoftrichloroacetimidate2[3a] (296 mg, ∼0.59 mmol)
in anhydrous o-dichlorobenzene (10 mL) that contained K2CO3
(20 mg, 0.14 mmol) was stirred at 165◦C for 0.25 h in
the microwave reactor. The resulting black reaction mix-
ture was cooled and then loaded directly onto a 2.5 cm ×
12 cm column of silica gel and eluted with hexane then
1:9 → 15:85 → 1:4 → 2:3 v/v ethyl acetate/hexane. In this man-
ner two fractions, A and B, were obtained.
A solution of trichloroacetimidate 6 (420 mg, ∼0.91 mmol)
in anhydrous o-dichlorobenzene (10 mL) that contained anhy-
drous K2CO3 (20 mg, 0.14 mmol) was stirred at 165◦C for
0.25 h in the microwave reactor. The resulting black reac-
tion mixture was cooled and then loaded directly onto a
2.5 cm × 12 cm column of silica gel and eluted with hexane
then 1:9 → 15:85 → 1:4 → 2:3 v/v ethyl acetate/hexane. In this
manner two fractions, A and B, were obtained.
Concentration of fraction A (RF 0.4 in 1:1 v/v ethyl
acetate/hexane) afforded the title compound 3[3a] (192 mg,
65%) as a clear, pale-tan oil, [α]D +9 (c 0.4, CHCl3) [Found:
(M + Na)+ 523.9447. C14H2179Br35Cl237ClNO7 requires
(M + Na)+ 523.9435]. δH (300 MHz, CDCl3) 6.73 (br d, J 8.1,
NH), 6.34 (dd, J 3.9 and 1.2, 1H), 4.83–4.68 (complex m, 7H),
4.26 (dd, J 5.1 and 4.5, 1H), 4.11 (dd, J 6.0 and 2.1, 1H), 3.93
(dd, J 5.7 and 2.1, 1H), 3.41 (s, 6H), 3.38 (s, 3H). δC (75 MHz,
CDCl3) 161.8 (CO), 132.6 (CH), 122.3 (C), 96.8 (CH2), 96.3
(CH2), 96.2 (CH2), 92.2 (CCl3), 75.0 (CH), 74.4 (CH), 74.1
(CH), 56.7 (CH), 55.9 (CH3), 55.8 (CH3), 55.7 (CH3). νmax
(cm−1) 3310, 2930, 2895, 1714, 1642, 1520, 1214, 1151, 1103,
1034, 822. m/z (ESI) 529, 528, 527, 526, 525, 524, 523, and 522
[(M + Na)+, 3, 18, 10, 65, 16, 100, 10, and 52%].
Concentration of fraction A (RF 0.3 in 2:3 v/v ethyl
acetate/hexane) afforded the title compound 7 (247 mg, 62%
from 5) as a clear, colourless oil, [α]D +61 (c 0.4, CHCl3)
[Found: (M + Na)+ 461.9249. C12H1779Br35Cl3NO5 requires
(M + Na)+ 461.9253]. δH (500 MHz, CDCl3) 6.65 (d, J 8.1, 1H,
NH), 6.25 (tm, J 4.5, 1H), 4.83 (d, J 6.9, 1H), 4.78 (d, J 6.9,
1H), 4.75–4.70 (complex m, partially obscured, 1H), 4.73 (d, J
6.9, 1H), 4.67 (d, J 6.9, 1H), 4.06 (dd, J 5.1 and 2.4, 1H), 3.95
(m, 1H), 3.43 (s, 3H), 3.37 (s, 3H), 2.51 (m, 1H), 2.40 (m, 1H).
δC (75 MHz, CDCl3) 161.5, 131.5, 117.5, 96.0, 95.2, 92.2, 75.7,
70.1, 57.5, 55.7, 55.4, 30.5. νmax (cm−1) 3319, 2935, 2894, 1702,
1522, 1151, 1105, 1035, 1009, 917, 822. m/z (ESI) 468, 467, 466,
465, 464, and 462 [(M + Na)+, 20, 8, 60, 13, 100, and 50%].
Concentration of fraction B (RF 0.4 in 3:7 v/v ethyl
acetate/hexane) afforded the title compound 8 (52 mg, 17% from
5) as a clear, colourless oil, [α]D +120 (c 0.6, CHCl3) [Found:
(M + Na)+ 338.9798. C10H1681Br35ClO4 requires (M + Na)+
338.9798]. δH (800 MHz, CDCl3) 6.16 (dd, J 5.6 and 3.2, 1H),
4.83 (d, J 7.2, 1H), 4.76 (d, J 7.2, 1H), 4.73 (d, J 7.2, 1H), 4.69
(d, J 7.2, 1H), 4.63 (d, J 3.2, 1H), 4.23 (ddd, J 9.6, 6.4 and 2.4,
1H), 4.16 (dd, J 3.2 and 2.4, 1H), 3.40 (s, 3H), 3.39 (s, 3H), 2.46
(m, 1H), 2.44 (m, 1H). δC (75 MHz, CDCl3) 132.2, 118.6, 97.2,
95.5, 79.0, 68.9, 61.5, 55.7, 55.6, 30.3. νmax (cm−1) 2946, 2893,
1151, 1109, 1052, 1034, 982, 941, 917, 837, 768. m/z (ESI) 341,
340, 339, 338, and 337 [(M + Na)+, 25, 11, 100, 9, and 77%].
Concentration of fraction B (RF 0.5 in 1:1 v/v ethyl
acetate/hexane) afforded the previously reported, but at that
time configurationally unassigned, chloride 4[3a] (39 mg, 18%)
as a clear, colourless oil, [α]D +53 (c 1.0, CHCl3) [Found:
(M + Na)+ 399.0013. C12H2081Br35ClNO6 requires (M + Na)+
399.0009]. δH (300 MHz, CDCl3) 6.23 (d, J 3.0, 1H), 4.83–4.70
(complex m, 6H), 4.64 (d, J 3.6, 1H), 4.38 (br dd, J 7.8 and 3.0,
1H), 4.21 (dd, J 3.6 and 2.4, 1H), 4.16 (dd, J 7.8 and 2.4, 1H),
3.41 (s, 6H), 3.40 (s, 3H). δC (75 MHz, CDCl3) 133.9 (br, CH),
120.8 (br, C), 97.3 (CH2), 97.1 (CH2), 96.7 (CH2), 79.6 (CH),
75.6 (br, CH), 73.8 (CH), 60.8 (br, CH), 55.8 (CH3), 55.7 (CH3),
55.7 (CH3). νmax (cm−1) 2931, 2891, 1640, 1151, 1108, 1036,
917, 810. m/z (ESI) 401, 400, 399, 398, and 397 [(M + Na)+,
26, 13, 100, 10, and 76%].
Compound 9
A magnetically stirred solution of compound 8 (22 mg,
0.07 mmol) in CH2Cl2 (1 mL) that contained 4 Å molecular
sieves (500 mg) and was maintained under a nitrogen atmo-
sphere at −60◦C was treated with TMS-Br (71 µL, 0.55 mmol).
The reaction was warmed to −40◦C over ∼0.5 h, stirred at this
temperature for 2 h, and then treated with NaHCO3 (3 mL of a
saturated aqueous solution). The ensuing mixture was warmed
to 18◦C, stirred at this temperature for ∼0.25 h, and then diluted
with ethyl acetate (10 mL). The aqueous layer was separated and
extracted with ethyl acetate (4 × 10 mL). The combined organic
phases were dried (MgSO4) and filtered before being treated
Compound 6
A magnetically stirred solution of compound 5[4] (270 mg,
0.91 mmol) in CH2Cl2 (5 mL) that contained 4 Å molecular
sieves (100 mg) and was maintained under an atmosphere of
nitrogen was cooled to 0◦C and then treated with DBU (205 µL,
1.36 mmol) and trichloroacetonitrile (165 µL, 1.63 mmol). The
ensuing mixture was warmed to 18◦C over ∼0.5 h, stirred at this
temperature for 1.5 h, and then treated with NH4Cl (5 mL of a
saturated aqueous solution). The separated aqueous layer was

68
M. Matveenko, A. C. Willis, and M. G. Banwell
with silica (500 mg), and then concentrated under reduced pres-
sure.The resulting white powder was loaded onto a silica column
that was then eluted with CH2Cl2 followed by 1:99 → 1:49 v/v
MeOH/CH2Cl2. Concentration of the appropriate fractions (RF
0.2 in 5% v/v MeOH/CH2Cl2) under reduced pressure afforded
the title compound 9 (12 mg, 80%) as a clear, colourless oil. δH
(300 MHz, CDCl3) 6.14 (dd, J 4.8 and 3.9, 1H), 4.54 (d, J 3.9,
1H), 4.29 (m, 1H), 4.18 (m, 1H), 2.52–2.43 (complex m, 2H),
2.34 (m, 1H), 2.01 (d, J 5.4, 1H, OH).
Structure Determination
Images were measured on a Nonius Kappa CCD diffracto-
meter (MoKα, graphite monochromator, λ 0.71073 Å) and data
extracted using the DENZO package.[7] The structure was solved
by direct methods (SIR92).[8] The structure of the abovemen-
tioned compound was refined using the CRYSTALS program
package.[9]
Atomic coordinates, bond lengths and angles, and displace-
ment parameters have been deposited at the Cambridge Crys-
tallographic Data Centre (CCDC number 704835). These data
can be obtained free-of-charge from www.ccdc.cam.ac.uk/data_
request/cif, by emailing data_request@ccdc.cam.ac.uk, or by
contacting the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Compound 10
Triethylamine (17 µL, 0.12 mmol), 4-(N,N-dimethylamino)
pyridine (DMAP) (2 mg, 0.02 mmol), and then p-nitrobenzoyl
chloride(25 mg, 0.12 mmol)wereaddedtoamagneticallystirred
solution of alcohol 9 (7 mg, 0.03 mmol) in CH2Cl2 (1 mL) main-
tained at 0◦C under an atmosphere of nitrogen. The reaction
was warmed to 18◦C and after 16 h NaHCO3 (5 mL of a sat-
urated aqueous solution) was added. The ensuing mixture was
extracted with CH2Cl2 (3 × 10 mL) and the combined organic
phases were then dried (MgSO4), filtered, and concentrated
under reduced pressure.The resulting orange residue was loaded
onto a silica column that was eluted with hexane and then
1:9 v/v ethyl acetate/hexane.The appropriate fractions (RF 0.3 in
1:4 v/v ethyl acetate/hexane) were concentrated under reduced
pressure to afford the title compound 10 (5 mg, 30%) as a pale-
orange solid, mp 188–194◦C, [α]D +38 (c 0.4, CDCl3) [Found:
(M − Cl•)+ 490.9899 and 488.9933. C20H1481BrClN2O8 and
C20H7194BrClN2O8 require (M − Cl•)+ 490.9913 and 488.9934,
respectively]. δH (300 MHz, CDCl3) 8.35–8.08 (complex m,
8H), 6.36 (dd, J 5.4 and 3.3, 1H), 5.93–5.80 (complex m, 2H),
4.71 (d, J 3.6, 1H), 2.90 (dt, J 18.0 and 5.4, 1H), 2.69 (m,
1H). δC (75 MHz, CDCl3) 163.7, 163.4, 151.1, 150.8, 134.5,
134.2, 131.0, 130.8, 130.6, 123.9, 123.7, 118.4, 73.9, 66.8, 59.3,
29.3. νmax (cm−1) 2924, 2854, 1731, 1608, 1526, 1347, 1271,
1261, 1097, 1014, 872, 835, 717. m/z (EI) 491 and 489 (both
3%, [M − Cl•]+), 192 (36), 150 (100). Recrystallization (ethyl
acetate/hexane) of this material afforded pale-orange needles
suitable for X-ray crystallographic structure determination.
Acknowledgements
The authors thank the Institute of Advanced Studies and the Australian
Research Council for financial support.
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X-Ray Crystallographic Study on Compound 10
Crystal Data
C20H14BrClN2O8, M 525.70, T 200(1) K, orthorhombic,
space group P212121, Z 4, a 6.8298(1), b 14.9660(3), c
20.3511(3) Å, V 2080.18(6) Å3, Dx 1.678 g cm−3, 6060 unique
data (2θmax 60◦); R 0.026 [for 5043 reflections with I > 2.0σ(I)],
Rw 0.030 (all data), S 1.11. Absolute configuration determined
by refinement of the Flack parameter [final value −0.014(5)].
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