Synthesis and crystal structure of chiral hydroquinoxaline derivatives

Article abstract of DOI:10.1016/j.mencom.2008.05.014

The addition of dialkyl acetylenedicarboxylate and 1,2-dibenzoylacetylene to trans-(1R,2R)-diaminocyclohexane afforded quinoxaline derivatives. The reaction of trans-(1R,2R)-N,N'-diisopropyldiaminocyclohexane with dimethyl acetylenedicarboxylate gave a new chiral compound.

Full text of DOI:10.1016/j.mencom.2008.05.014

Mendeleev
Communications
Mendeleev Commun., 2008, 18, 153–155
Synthesis and crystal structure
of chiral hydroquinoxaline derivatives
Navabeh Nami,*a Bernhard Neumuller,b Majid M. Heravic and Mina Haghdadid
a Department of Chemistry, Islamic Azad University, Ghaemshahr, 47631–35953 Mazandaran, Iran.
Fax: +98 111 226 7163; e-mail: Navabehnami@yahoo.com
b Fachbereich Chemie der Universitat Marburg, D-35032 Marburg, Germany
c Department of Chemistry, School of Sciences Azzahra University, Vanak, 34149–16818 Tehran, Iran
d Department of Chemistry, Islamic Azad University, Babol, 47189–38346 Mazandaran, Iran
DOI: 10.1016/j.mencom.2008.05.014
The addition of dialkyl acetylenedicarboxylate and 1,2-dibenzoylacetylene to trans-(1R,2R)-diaminocyclohexane afforded
quinoxaline derivatives. The reaction of trans-(1R,2R)-N,N'-diisopropyldiaminocyclohexane with dimethyl acetylenedicarboxylate
gave a new chiral compound.
Quinoxalines serve as a source of pharmaceutical agents.1–4
These nitrogen heterocycles are useful intermediates in organic
syntheses.5
An ORTEP diagram of 2a is shown in Figure 1. [The absolute
configuration of the reagent used trans-(1R,2R)-DACH was
determined in another context.8]
Acetylenic esters are versatile reagents for heterocyclization,
and many products can be prepared from the addition of these
compounds to nitrogen-, oxygen- and sulfur-containing com-
pounds.6,7
trans-(1R,2R)-Diaminocyclohexane (DACH)8 derivatives are
now well established as anticancer drugs.9 The enantiomeric
pairs of this compound exhibit different biological activities. For
example, the 1R,2R isomers of DACH derivatives have some-
what higher antitumor activity than that of the 1S,2S isomer.10
Compound 2a in the solid state shows dimers linked by
hydrogen bonds [N(1)–H(1)···O(4) and N(3)–H(3)···O(1)]. In
addition, there are intramolecular hydrogen bonds [N(2)–H(2)···O(3)
and N(4)–H(4)···O(6)] which fix the α,β-unsaturated sequences
†
trans-(1R,2R)-DACH was purchased from Aldrich. The other chemicals
and solvents were purchased from Merck. 1,2-Dibenzoylacetylene was
prepared by the published method.11 The melting points were obtained
using an Electrothermal IA 9100 Digital melting point apparatus. The IR
spectra were recorded on a Bruker IFS-88 instrument (the samples as
1
KBr disks for the range 4000–400 cm–1). The H and 13C NMR spectra
O
OR
were recorded on a Bruker AC-300 spectrometer (1H, 300.134 MHz;
13C, 75.469 MHz) using TMS as an internal standard. Mass-spectrometric
measurements were made on an Agilent 6890 N Network GC system.
The C, H, N analyses were performed by the microanalytical service of
the N.I.O.C. Research Institute of Petroleum Industry.
H
N
NH2
NH2
H
ROOC
ROOC
COOR
COOR
N
H
O
Synthesis of 3-(methoxycarbonylmethylene)-1,4,4aR,5,6,7,8,8aR-octa-
hydroquinoxalin-2-one 2a: trans-(1R,2R)-DACH (10 mmol, 1.14 g) and
dimethyl acetylenedicarboxylate (10 mmol, 1.42 g) in 40 ml of MeOH
was heated at reflux for 30 min. The solution was cooled and the reaction
vessel set aside overnight. The crystals formed were separated. Colourless
prism crystals from methanol. Yield 65%, mp 187–188 °C. [a]D25 –248.4
(c 0.40, CHCl3). FT-IR (n/cm–1): 3314, 3188 (NH), 1691, 1659 (CO),
2a,b
1
+
O
OR
H
H
N
COOR
2 ROOC
COOR
1
1615 (C=C), 1214 (C–O), 1153 (C–N). H NMR (CDCl3) d: 1.31 (m,
4H, CH2), 1.83 (m, 4H, CH2), 3.02 (m, 1H, CH), 3.04 (m, 1H, CH), 3.62
(s, 3H, OMe), 5.54 (s, 1H, =CH), 6.52 (s, 1H, NH), 8.02 (br. s, 1H, NH).
13C NMR (CDCl3) d: 23.5 (CH2), 23.8 (CH2), 29.5 (CH2), 29.8 (CH2),
50.7 (CH), 55.2 (CH), 55.6 (OMe), 86.4 (=CH), 149.1 (C=), 161.2 (CO),
170.9 (CO2). MS, m/z (%): 224 (100) (M+), 193 (53) (C10H13N2O2+), 165 (15)
(C9H13N2O+), 136 (8) (C8H12N2+), 149 (22) (C9H13N+2). Found (%): C, 58.87;
H, 7.69; N, 12.36. Calc. for C11H16N2O3 (%): C, 58.93; H, 7.14; N, 12.5.
3-(Ethoxycarbonylmethylene)-1,4,4aR,5,6,7,8,8aR-octahydroquinoxalin-
2-one 2b was synthesised analogously to 2a. Colourless plate crystals from
ethanol. Yield 68%, mp 194–195 °C, [a]D25 –210.2 (c 0.36, CHCl3). FT-IR
(n/cm–1): 3321, 3172 (NH), 1692, 1657 (CO), 1602 (C=C), 1211 (C–O),
N
H
O
COOR
3a,b
a R = Me
b R = Et
Scheme 1
We are interested in the chemistry of heterocyclic com-
pounds containing nitrogen and sulfur atoms.11 We first carried
out the reaction of dimethyl acetylenedicarboxylate12 with trans-
(1R,2R)-DACH 1 (1:1) in methanol to obtain a single com-
pound, which was characterized to be 3-(methoxycarbonyl-
methylene)-1,4,4aR,5,6,7,8,8aR-octahydroquinoxalin-2-one 2a, in
65% yield. The structure of 2a was determined by NMR and IR
spectroscopy, mass spectrometry and microanalysis (Scheme 1).†
Compound 2a exhibited two broad lines at d 6.52 and
8.02 ppm arising from NH protons along with a sharp signal
from the C=CH proton at about d 5.54 ppm. Further, we obtained
a single crystal suitable for an X-ray diffraction study to confirm
the structure.‡
1
1132 (C–N). H NMR (CDCl3) d: 1.22 (t, 3H, Me, J 7.5 Hz), 1.35 (m,
4H, CH2), 1.94 (m, 4H, CH2), 2.96 (m, 1H, CH), 3.11 (m, 1H, CH), 4.13
(q, 2H, OCH2, J 7.5 Hz), 5.66 (s, 1H, =CH), 6.58 (s, 1H, NH), 8.12
(br. s, 1H, NH). 13C NMR (CDCl3) d: 14.9 (Me), 24.2 (CH2), 24.8
(CH2), 29.1 (CH2), 30.4 (CH2), 50.8 (CH), 55.1 (CH), 55.0 (OCH2), 86.8
(=CH), 149.1 (C=), 162.4 (CO), 169.7 (CO2). MS, m/z (%): 238 (M+), 193
(48) (C10H13N2O+2), 165 (20) (C9H13N2O+), 136 (5) (C8H12N+2), 73 (38)
(C3H5O+2). Found (%): C, 60.11; H, 7.59; N, 11.75. Calc. for C12H18N2O3
(%): C, 60.05; H, 7.56; N, 11.76.
– 153 –
© 2008 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2008, 18, 153–155
O(3)
C(11)
N
C(10)
O(2)
C(9)
H(2)
N(2)
PhOC
COPh
C(3)
N
H
1
C(4)
C(8)
C(7)
C(2)
O
N(1)
C(1)
O(1)
C(5)
4
C(6)
H(1)
H(3)
C(17)
N(3)
O(4)
N
C(16)
C(12)
C(18)
C(19)
C(13)
C(15)
C(14)
N
H
C(20)
C(21)
N(4)
H(4)
O
O(5)
C(22)
O(6)
Scheme 2
controlled the reaction. This reaction was directed to other face
of the diene by the C-4aR, C-8aR and NH···O=C hydrogen bond
in compound 2 to give compound 3.
Figure 1 ORTEP drawing of 2a dimer. Selected bond lengths (Å):
O(1)–C(7) 1.243(2), O(3)–C(10) 1.222(2), N(1)–C(1) 1.471(2), N(1)–C(7)
1.327(2), N(2)–C(8) 1.354(2), N(2)–H(2) 0.82(2), O(5)–C(22) 1.446(2),
N(4)–C(13) 1.461(2), N(4)–C(19) 1.345(2), N(3)–H(3) 0.86(2). Selected
bond angles (°): C(1)–N(1)–C(7) 122.9(2), C(2)–N(2)–C(8) 123.7(2), N(1)–
C(1)–C(2) 108.7(1), N(1)–C(1)–C(6) 112.0(1), N(2)–C(8)–C(7) 116.3(2),
N(2)–C(8)–C(9) 124.8(2), O(2)–C(10)–O(3) 121.5(2), C(1)–N(1)–H(1)
121.(1), N(4)–C(19)–C(18) 116.9(2), C(12)–N(3)–H(3) 120.(1), C(18)–
N(3)–H(3) 116.(1), C(19)–N(4)–H(4) 114.(1). Selected hydrogen bonding
dimensions (Å): [N(1)···O(4) 2.840(2), N(3)···O(1) 2.912(2), N(2)···O(3)
2.722(2), N(4)···O(6) 2.767(2)].
The reaction of 1 with 1,2-dibenzoylacetylene15 gave
3-(2-hydroxy-2-phenylvinyl)-2-phenyl-4aR,5,6,7,8,8aR-hexa-
1
hydroquinoxaline 4 in 73% yield. The H NMR spectra of 4¶
COOMe
Pri
Pri
N
H
NH
MeOOC
COOMe
COOMe
NH
Pri
N
COOMe
in the plane of the six-membered heterocyclic ring. The dihedral
angle between the ‘best planes’ of the two molecules in the
dimer of 2a is 15°.
The reaction of compound 2 with dialkyl acetylenedicar-
boxylate (1:1) or the reaction of trans-(1R,2R)-DACH with
dialkyl acetylenedicarboxylate (1:2) afforded trialkyl-4S,5aR,
9aR-4H-pyrano[2,3-b]-1,4,4a,5,6,7,8,8a-octahydroquinoxaline-
2,3,4-tricarboxylate 3 (Scheme 1).§
Because of the NH···O=C intramolecular hydrogen bond,
the 1H NMR spectra of 3a exhibited one NH proton (br. s,
d 9.08 ppm) more deshielded than the other (br. s, d 6.18 ppm).
Compound 3 contains three centers of chirality and two dia-
stereomers are possible but TLC and NMR spectra of this
compound exhibited only a single, pure structure. These
data indicated that a Michael type addition and Diels–Alder
[4 + 2] cycloaddition reaction have occurred to afford 2 and 3,
respectively. As the Diels–Alder transition state involves the
diene and dienophile, if one or both of these components are
chiral, an asymmetric synthesis becomes possible. The reaction
of chiral diene 2 with DMAD afforded chiral compound 3.
In compound 3, the absolute configuration at C-4 depends on
which face of the diene was attacked. The NH···O=C hydrogen
bond in compound 2 blocked one face of the diene and
Pri
MeOOC
H
5
6
Scheme 3
§
Synthesis of trimethyl-4S,5aR,9aR-4H-pyrano[2,3-b]-1,4,4a,5,6,7,8,8a-
octahydroquinoxaline-2,3,4-tricarboxylate 3a: compound 2a (10 mmol,
2.24 g) and dimethyl acetylenedicarboxylate (10 mmol, 1.42 g) or com-
pound 1 (10 mmol, 1.14 g) and dimethyl acetylenedicarboxylate (20 mmol,
2.84 g) in 40 ml of MeOH were heated at reflux for 1 h. The progress of
reaction was monitored by TLC using n-hexane–ethyl acetate (4:1). The
solvent was removed on a rotary evaporator. The crude product was
subjected to column chromatography on silica gel using n-hexane–ethyl
acetate (4:1) as an eluent affording pure compound 3a as yellow powder.
Yield 82%, mp 137–138 °C, [a]D25 –357.9 (c 0.17, CHCl3). FT-IR (n/cm–1):
3290, 3182 (NH), 1722 (CO), 1589, 1435 (C=C), 1208 (C–O), 1158 (C–N).
1H NMR (CDCl3) d: 1.31 (m, 4H, CH2), 1.94 (m, 4H, CH2), 3.05 (m,
1H, CH), 3.17 (m, 1H, CH), 3.56 (s, 3H, OMe), 3.58 (s, 3H, OMe), 3.62
(s, 3H, OMe), 6.18 (s, 1H, NH), 6.58 (s, 1H, CH), 9.08 (br. s, 1H, NH).
13C NMR (CDCl3) d: 23.4 (CH2), 23.7 (CH2), 28.7 (CH2), 29.5 (CH2),
39.2 (CH), 51.4 (CH), 53.6 (OMe), 54.5 (CH), 54.8 (OMe), 55.2 (OMe),
96.4 (C=C), 112.7 (C=C), 130.9 (C=C), 152.1 (C=C), 164.2 (CO2),
165.9 (CO2), 169.2 (CO2). MS, m/z (%): 366 (19) (M+), 307 (100)
(C15H19N2O+5), 224 (4) (C11H16N2O3+), 275 (83) (C14H15N2O+4), 59 (38)
(C2H3O+2). Found (%): C, 55.79; H, 6.08; N, 7.69. Calc. for C17H22N2O7
(%): C, 55.74; H, 6.01; N, 7.65.
Triethyl-4S,5aR,9aR-4H-pyrano[2,3-b]-1,4,4a,5,6,7,8,8a-octahydro-
quinoxaline-2,3,4-tricarboxylate 3b was synthesised analogously to 3a.
Yellow powder. Yield 88%, mp 155–156 °C, [a]D25 –218.4 (c 0.57,
CHCl3). FT-IR (n/cm–1): 3285, 3180 (NH), 1718 (CO), 1593, 1482
(C=C), 1211 (C–O), 1142 (C–N). 1H NMR (CDCl3) d: 1.25 (t, 3H, Me,
J 7.5 Hz), 1.29 (m, 4H, CH2), 1.79 (m, 2H, CH2), 1.83 (m, 2H, CH2),
3.04 (m, 1H, CH), 3.07 (m, 1H, CH), 3.95 (q, 2H, OCH2, J 7.5 Hz), 6.05
(s, 1H, NH), 6.51 (s, 1H, CH), 8.99 (br. s, 1H, NH). 13C NMR (CDCl3)
d: 14.3 (Me), 15.5 (Me), 15.7 (Me), 23.1 (CH2), 23.8 (CH2), 28.3 (CH2),
29.4 (CH2), 39.8 (CH), 50.6 (CH), 54.5 (CH), 58.9 (OCH2), 59.2
(OCH2), 59.7 (OCH2), 95.0 (C=C), 110.5 (C=C), 130.3 (C=C), 151.7
(C=C), 162.4 (CO2), 165.8 (CO2), 170.1 (CO2). MS, m/z (%): 408 (9)
(M+), 335 (100) (C17H23N2O5+), 238 (6) (C12H18N2O+3), 290 (13)
(C15H18N2O+4), 73 (41) (C3H5O+2). Found (%): C, 58.78; H, 6.88; N, 6.86.
Calc. for C20H28N2O7 (%): C, 58.82; H, 6.86; N, 6.86.
‡
X-ray diffraction analysis: at 193 K crystals of 2a (C11H16N2O3)
are monoclinic, space group P21(4),13 a = 10.663(1), b = 9.928(1) and
c = 11.318(2) Å, b = 106.19(1)°, V = 1150.6(3) Å3, Z = 4, M = 224.26,
dcalc = 1.295 g cm–3, m = 0.9 cm–1, 2qmax = 51.93°, –13 £ h £ 13,
–12 £ k £ 12, –13 £ l £ 13, 16273 measured reflections, 4460 unique,
Rint = 0.0437 [F0 > 4s(F0) = 3221], number of parameter, 307. The structure
was solved by a directed method using SHELXS-97 program14 and refined
against F2 (SHELXL-97).14 H atoms = free refinement, Flack-parameter
= 0.1(7), R1 = 0.0279 [F0 > 4s(F0)], R1 = 0.0439 (all data), wR2 = 0.0526
(all data), w = 1/[s2(F02) + (0.0256P)2]; P = [max(F02, 0) + 2Fc2]/3, max.
residual electron density 0.14 eÅ–3.
CCDC 635031 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
For details, see ‘Notice to Authors’, Mendeleev Commun., Issue 1, 2008.
– 154 –

Mendeleev Commun., 2008, 18, 153–155
exhibited one proton (s, d 10.82 ppm), and the FT-IR spectra
1H and 13C NMR spectra. The mass spectra of this compound
displayed a molecular ion peak at m/z 482. Any initial
fragmentation involves loss from or complete loss of the side
chain and section of the diaminocyclohexyl ring system.
In summary, the presented reactions carried the advantage of
being performed under neutral conditions and occurred under
mild conditions to provide high levels of stereoselectivity.
exhibited a broad vibration bond at 3434 cm–1 (not the C=O
bond). It was concluded that there is proton transfer across
the N···OH hydrogen bond, a tautomeric enaminone structure
(Scheme 2).
We expected that the reaction of trans-(1R,2R)-N,N'-diiso-
propyldiaminocyclohexane 5 with dimethyl acetylenedicar-
boxylate gives a product with a structure analogous to that
of 2, but the reaction of these compounds afforded a pure
trans-(1R,2R)-N,N'-diisopropyl-N,N'-bis{(E)-dimethyl but-2-ene-
dioate}DACH 6 (Scheme 3). The 1H NMR spectra of 6¶
exhibited a sharp signal at d 4.91 ppm for the two olefinic
protons of C=CH in (E) geometrical isomer. The structure of
compound 6 was deduced from its elemental analyses and IR,
This work was supported by the Islamic Azad University in
Ghaemshahr.
References
1
2
3
C. F. Turk, J. Krapecho, I. M. Michael and I. Weinryb, J. Med. Chem.,
1977, 20, 729.
G. Thuiler, J. Laforest, P. Bessim and J. Thuillier, Eur. J. Med. Chem.,
1975, 10, 37.
A. S. Bourlot, I. Sanchez, G. Dureng, G. Guillaumeat, R. Masingham,
A. Monteil, E. Winslow, M. D. Pujol and J. Y. Merour, J. Med. Chem.,
1998, 41, 3142.
¶
Synthesis of 3-(2-hydroxy-2-phenylvinyl)-2-phenyl-4aR,5,6,7,8,8aR-
hexahydroquinoxaline 4: trans-(1R,2R)-DACH (10 mmol, 1.14 g) and 1,2-di-
benzoylacetylene (10 mmol, 2.34 g) in 40 ml of MeOH were heated at
reflux for 3 h. The solution was cooled and the reaction vessel set aside
overnight. Compound 4 was separated as yellow needles crystals from
methanol, yield 73%, mp 187–188 °C, [a]D25 –477.6 (c 0.12, CHCl3). FT-IR
(n/cm–1): 3434 (OH), 1612 (C=N), 1565, 1538 (C=C). 1H NMR (CDCl3)
d: 1.54 (m, 4H, CH2), 1.91 (m, 2H, CH2), 2.20 (m, 1H, CH2), 2.48 (m,
1H, CH2), 2.99 (m, 1H, CH), 3.19 (m, 1H, CH), 5.81 (s, 1H, =CH), 7.51
(m, 6H, HAr), 7.51 (m, 4H, HAr), 10.82 (s, 1H, NH). 13C NMR (CDCl3)
d: 22.5 (CH2), 22.8 (CH2), 28.6 (CH2), 28.8 (CH2), 53.6 (CH), 55.4
(CH), 75.9 (=CH), 125.3 (CAr), 125.8 (CAr), 126.4 (CAr), 127.7 (CAr),
128.8 (CAr), 129.3 (CAr), 134.9 (CAr), 136.7 (CAr), 163.8 (HOC=), 163.3
(C=N), 164.9 (C=N). MS, m/z (%): 330 (94) (M+), 314 (78) (C22H22N2+),
225 (100) (C15H17N+2), 147 (98) (C9H11N2+), 77 (69) (Ph+). Found (%): C,
80.05; H, 6.69; N, 8.46. Calc. for C22H22N2O (%): C, 80.00; H, 6.67; N, 8.48.
Synthesis of trans-(1R,2R)-N,N'-diisopropyl-N,N'-bis{(E)-dimethyl but-
2-enedioate}-DACH 6: trans-(1R,2R)-N,N'-diisopropyldiaminocyclohexane
5 (10 mmol, 1.98 g) and dimethyl acetylenedicarboxylate (20 mmol, 2.84 g)
in 40 ml of MeOH were heated at reflux for 3 h. The solution was cooled
and the reaction vessel set aside overnight. Compound 6 was separated as
yellow crystals from methanol, yield 85%, mp 166–167 °C, [a]D25 +132.3
(c 0.46, CHCl3). FT-IR (n/cm–1): 1742, 1697 (CO), 1573 (C=C), 1214
4
A. P. Kozikowski, K. Sugiyama and J. P. Springer, J. Org. Chem.,
1981, 46, 2428.
5
6
R. M. Acheson and N. F. Elmor, Adv. Heterocycl. Chem., 1978, 23, 263.
I. Yavari, M. T. Maghsoodlu and A. Pourmossavi, J. Chem. Res., 1997,
5, 212.
7
8
F. Barka and B. Batanero, Synthesis, 1994, 5, 55.
(a) T. Mukaiyama, Aldrichim. Acta, 1996, 29, 59; (b) P. J. Chenier,
Tetrahedron Lett., 1997, 38, 7341.
9
P. M. Vivienne and J. S. Peter, Chem. Commun., 2004, 1788.
10 Y. Kidani and K. Inagaki, J. Med. Chem., 1978, 21, 1315.
11 (a) M. M. Heravi, N. Nami, H. A. Oskooie and R. Hekmatshoar,
Phosphorus Sulfur Silicon Relat. Elem., 2006, 181, 87; (b) H. A.
Oskooie, M. M. Heravi, N. Nami and A. Nazari, Heterocycl. Commun.,
2005, 11, 101.
12 (a) M. M. Heravi, Y. Sh. Beheshtiha, N. Nami and M. Ghassemzadeh,
Phosphorus Sulfur Silicon Relat. Elem., 2000, 161, 7; (b) M. M. Heravi,
Y. Sh. Beheshtiha, N. Nami and R. Hekmatshoar, Phosphorus Sulfur
Silicon Relat. Elem., 2000, 165, 285.
13 International Tables for Crystallography, 2nd edn., Kluwer Academic
Publisher, Dordrecht, 1989, vol. A.
1
(C–O), 1156 (C–N). H NMR (CDCl3) d: 0.90 (d, 6H, 2Me, J 7.0 Hz),
14 G. M. Sheldrick, SHELX-97, Göttingen, 1997.
0.95 (d, 6H, 2Me, J 7.0 Hz), 1.15 (m, 2H, CH2), 1.25 (m, 4H, 2CH2),
1.62 (m, 2H, CH2), 3.07 (m, 2H, 2CH), 3.09 (m, 2H, 2CH), 3.23 (s, 6H,
2OMe), 3.47 (s, 6H, 2OMe), 4.91 (s, 2H, =CH). 13C NMR (CDCl3) d:
14.2 (Me), 31.5 (CH2), 46.5 (CH2), 48.8 (CH), 50.9 (CH), 64.5 (OMe),
87.2 (OMe), 136.4 (C=), 151.8 (=CH), 165.0 (CO2), 166.0 (CO2). MS,
m/z (%): 482 (2) (M+), 423 (1) (C22H35N2O6+), 266 (2) (C15H24NO+3), 216
(100) (C10H18NO+4), 81 (21) (C6H9+), 43 (22) (C3H7+). Found (%): C, 59.87;
H, 7.89; N, 5.78. Calc. for C24H38N2O8 (%): C, 59.75; H, 7.88; N, 5.81.
15 (a) K. Bowden and E. R. H. Jones, J. Chem. Soc., 1946, 39;
(b) I. Skattebol, E. R. H. Jones and M. C. Whiting, Org. Synth., 1963,
4, 39.
Received: 31st August 2007; Com. 07/3003
– 155 –