Synthesis of rodlike dispiro hydrocarbon skeletons for new liquid crystal compounds

Article abstract of DOI:10.1055/s-1999-3689

A simple synthesis of the dispiro[5.2.5.2]hexadecane skeleton was developed. Starting from the cyclohexanedicarbaldehyde 6 the dispirane was prepared in one step. The synthesised dispirodiketone 4 is a key compound for the preparation of a number of new l

Full text of DOI:10.1055/s-1999-3689

PAPER
117
Synthesis of Rodlike Dispiro Hydrocarbon Skeletons for New Liquid Crystal
Compounds
Nina Feuerbacher,» Fritz Všgtle,*» Jens Windscheidt,» Eike Poetsch,b Martin Niegerc
a
KekulŽ-Institut fŸr Organische Chemie und Biochemie der UniversitŠt Bonn, Gerhard-Domagk-Stra§e 1, D-53121 Bonn, Germany
Tel +49(228)7334956, Fax +49(228)735662; E-mail: voegtle@uni-bonn.de
Merck KG, Liquid Crystal Research, Frankfurter Str. 250, D-64271 Darmstadt, Germany
Institut fŸr Anorganische Chemie der UniversitŠt Bonn, Gerhard-Domagk-Stra§e 1, D-53121 Bonn, Germany
b
c
Received 2 June 1998
Abstract: A simple synthesis of the dispiro[5.2.5.2]hexadecane
skeleton was developed. Starting from the cyclohexanedicarbalde-
hyde 6 the dispirane was prepared in one step. The synthesised
dispirodiketone 4 is a key compound for the preparation of a num-
ber of new liquid crystalline compounds, as its linear molecular
shape is proved by an x-ray structural analysis of the corresponding
diketal 10. Additionally the synthesis of the first dispirane 4 with a
Additionally the synthesis of an alkyl substituted
dispirotetradecane 5 which would be the first dispirane
with a [5.2.3.2]-linkage allows further examinations of the
influence of the molecule geometry on liquid crystal be-
haviour.
[5.2.3.2]-linkage is described.
Keywords: Cyclobutane, Cyclohexane, Ketals, Liquid crystals,
Spiro compounds
Carbocyclic spiro compounds1 are not only part of natural
products such as sesquiterpenes, but can also be used as
building blocks in thermotropic liquid crystals.2 The re-
quired and characteristic molecular shape3 of a calamitic
liquid crystal4 is a linear elongated structure as it is
achieved by the bicyclohexyl compounds 1 synthesised
by Eidenschinck et al5 which show remarkable me-
sophases. The interest in new rodlike liquid crystals is due
to their broad applicability in optical displays and screens.
In search of novel nematogenic compounds we synthe-
sised several dispiranes and spiranes and investigated the
influence of their molecular shape on the liquid crystalline
behaviour.6 We showed that the spiro linkage of cyclo-
hexyl units only retain their required linearity if an even
number of carbon atoms in the middle ring is given (cf. 2).
In this contribution we have reported the synthesis of ter-
minally substituted dispiro[5.1.5.1]tetradecanes 3, which
show enantiotopic mesophases over a large temperature
range of more than 100¡C.6b,c
Various methods of preparing polyspiro compounds con-
sisting of cyclohexane rings are described in the litera-
ture.7 However, to our knowledge, no preparation of a
dispirohexadecane which can be twice terminally substi-
tuted has been discovered and the known syntheses of
dispiro[5.2.5.2]hexadecanes are still very complex.8 For
this reason a simple and efficient synthesis is desirable.
Following the acid-catalysed annelation of a-alkyl alde-
hydes and a,b-unsaturated ketones found by Flaugh et al.9
we succeeded in performing a one-pot synthesis of cyclo-
hexanedicarbaldehyde 7.10 Treatment of 6 with methyl vi-
nyl ketone yields the desired dispirodiketenones 7 and 8
respectively. The synthesis was carried out by treating a
mixture of the dialdehyde and methyl vinyl ketone in tol-
uene with a catalytic amount of sulfuric acid and direct
azeotropic removal of water.
Scheme 1
Now we report the facile synthesis of a dispiro-
[5.2.5.2]hexadecane 2 (n = 2) as an excellent precursor for
new liquid crystal compounds. The dispirodiketone 4 is a
key intermediate which provides the possibility to inves-
tigate the consequences of different terminal substitution
patterns on its physical properties.
The dialdehyde 6 was prepared by a convenient TEMPO-
catalysed oxidation of cyclohexanedimethanol with sodi-
um hypochlorite.11 Subsequent hydrogenation of the di-
enones 7 and 8 afforded the dispirodiketone 4 in an overall
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118
N. Feuerbacher et al.
PAPER
yield of 13%. In order to achieve further successive sub-
stitution with typical end groups the protection of one ke-
tone group was necessary. We have experienced that
protection of diketones with butanediol facilitates the col-
umn chromatographic separation of the mono- and diket-
als.12 As expected the Rf-values differed sufficiently so
that the separation of the formed mono- and diketals could
be achieved easily.
Terminal substitution of the dispirotetradecanone oxygen
in 5 leads to two diastereomers in the same way as they
would occur when substituting the two ketone groups of
the dispirohexadecandione 4. In the case of a trans-substi-
tution the linear shape of the system is preserved. The
dispirane 14 provided with suitable groups typical for an
application in liquid crystal displays are currently under
further investigation.16
Scheme 2
Solvents were purified by standard methods and dried with appro-
priate drying agents prior to use. Mps are uncorrected. Microscope
1
heating unit (Reichert, Vienna). H and 13C NMR spectra: Bruker
The tetraspiro[6.2.2.2.6.2.2.2]-1,6,17,22-tetraoxaoctacos-
ane 10 crystallised in the form of colourless prisms from
a mixture of dichloromethane and methanol. The x-ray
structure13 shows a molecule with nearly linear shape
obeying the necessary form anisotropy. The synthesised
diketone 4 therefore is a promising key precursor for new
liquid crystal compounds with a dispiro[5.2.5.2]hexade-
cane building block.
AM 250 (250 and 62,9 MHz, respectively), 13C NMR data were ver-
ified by DEPT 135 experiments. MS (EI): A.E.I. MS-50 spectrom-
eter, Manchester, GB. GC-MS: Hewlett Packard HP 5980, Series 2
with mass spectrometer HP 5989. Microanalyses: Mikroanalytische
Abteilung der UniversitŠt Bonn. Thin-layer chromatography
(TLC): Silica gel 60 F254 (Merck), detection of the aliphatic com-
pounds was achieved by treatment with a solution of rhodamine 6G
in ethanol. Column chromatography (CC) on silica gel 60, mesh
size 63-100 mm (Merck, Darmstadt, Germany). FTIR: Spectrometer
1600, Perkin-Elmer, on KBr [Abbreviations: (w): weak, (m): medi-
um, (s): strong, (vs): very strong, EE: ethyl acetate].
cis,trans-Cyclohexane-1,4-dicarbaldehyde (6)
cis,trans-1,4-Bis(hydroxymethyl)cyclohexanes (28.4 g, 0.2 mol)
were dissolved in CH2Cl2 (300 mL). 2,2,6,6-Tetramethylpiperidine
1-oxide (1.2 g, 7.6 mmol) and KBr (1.2 g, 7.6 mmol) dissolved in
H2O (40 mL) were added. A solution of sodium hypochlorite
(396 mL, 13% chlorine-active), NaHCO3 (15.0 g) and H2O
(490 mL) was added dropwise in such a way that slight reflux could
be observed. The mixture was stirred for 1 h. Subsequently the
phases were separated. The aqueous phase was extracted twice with
dichloromethane (50 mL). The combined organic phases were
treated with a solution of KI (2.65 g) dissolved in 10% HCl (150
mL). The excess iodine was destroyed by sat. aq Na2S2O3. The or-
ganic phase was washed with H2O and dried (Na2SO4). After re-
moval of the solvent the residue was purified by column
chromatography and gave 14.0 g (50%) of a colorless oil. Rf = 0.51
[cyclohexane/EE 3:1].
Figure. First x-ray structure analysis of the dispiro[5.2.5.2]hexade-
cane skeleton
With regard to our investigations on the dispiro-
[5.1.5.1]tetradecanes we set out to synthesize the first
dispiro[5.2.3.2]tetradecane 5a which is already substitut-
ed in position 10. Starting with a Wittig-alkenation14 of
the pentane substituted spiro[5.5]undecanone 116e the
dispiro[5.2.3.2]tetradecanone 13 could be obtained by in
situ cycloaddition of dichloroketene with the alkene 12.15
The reductive removal of the chlorine was carried out by
treating the dihalogenide 13 with zinc, affording the de-
sired dispiroketone 5a in an overall yield of 54%.
GC-MS (EI, 70 eV, 200¡C): m/z (%): 140 (10) [M+], 112 (23) [M+Ð
CO], 94 (98), 79 (90), 55 (100).
1H NMR (250 MHz, CDCl3, 25¡C): d = 1.31Ð1.37 (m, 4 H, 2 CH2),
1.74Ð1.80 (m, 2 H, CH2), 2.10Ð2.20 (m, 4 H, 2 CH2), 9.60 (d, 3J =
1 Hz, CHO), 9.63 (d, 3J = 1 Hz, CHO).
13C NMR (62.9 MHz, CDCl3): d = 23.31 (2 CH2), 24.90 (2 CH2),
47.98 (CH), 49.65 (CH), 204.04 (CHO), 204.51 (CHO).
IR (KBr, cmÐ1): n = 1722 (vs), 2714 (m), 2858 (s), 2933 (s).
Dispiro[5.2.5.2]hexadecane-1,10-diene-3,12-dione (7) and
Dispiro-[5.2.5.2]hexadecane-1,13-diene-3,12-dione (8)
To a stirred suspension of cis,trans-cyclohexane-1,4-dicarbalde-
hyde (12.5 g, 89 mmol, 6) and methyl vinyl ketone (15 mL,
178 mmol) in toluene (75 mL) was added slowly conc. H2SO4 (0.1
mL) and the mixture was stirred for 0.5 h at r.t. The solution was
cautiously heated to reflux and stirred at this temperature for 6 h
with constant removal of the H2O. After cooling to r.t. the mixture
Scheme 3
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PAPER
Synthesis of Rodlike Dispiro Hydrocarbon Skeletons
119
was treated with 1 M aq NaHCO3 (50 mL). The phases were sepa-
rated and the aqueous phase was extracted with toluene (2 × 50 mL).
The combined organic phases were washed subsequently with brine
and H2O. After drying (Na2SO4) and removal of the solvent the res-
idue was purified by column chromatography to yield 5.1 g (15%)
of a colourless solid (mixture of the two isomers), mp 192Ð196¡C.
Rf = 0.51 [CH2Cl2/EE 15:1].
Tetraspiro[6.2.2.6.2.2]-1,6,17,22-tetraoxooctacosane (10)
The above experimental procedure also yielded 230 mg (21%) of
the diketal 10 as a colourless solid, mp 224¡C.
Rf = 0.75 (cyclohexane/acetone 4:1).
GC-MS (EI, 70 eV, 200¡C): m/z (%): 392 (10) [M+], 320 (2) [M+Ð
C4H8O], 248 (2) [M+Ð2 C4H8O], 127 (100).
1H NMR (250 MHz, CDCl3, 25¡C): d = 1.25 (br, 8 H, CH2), 1.30Ð
1.45 (m, 8 H, CH2), 1.50Ð1.65 (m, 16 H, CH2), 3.66 (m, 8 H, OCH2).
13C NMR (100.6 MHz, CDCl3): d = 29.74 (6 CH2), 30.10 (6 CH2),
32.53 (2 Cq), 37.66 (4 CH2) 61.85 (4 OCH2), 101.86 (2 CO2).
GC-MS (EI, 70 eV, 200¡C): m/z (%): 244 (100) [M+], 202 (72)
[M+ÐC2H2O], 160 (24) [M+Ð2C2H2O], 79 (78).
1H NMR (250 MHz, CDCl3, 25¡C): d = 1.42Ð1.51 (m, 16 H, CH2),
1.82Ð2.00 (m, 8 H, CH2), 2.40 (t, 3J = 6.3 Hz, 8 H, CH2), 5.85 (d, 3J
= 10.2 Hz, 2 H, CH), 5.90 (d, 3J = 10.2 Hz, 2 H, CH), 6.75 (d, 3J =
10.2 Hz, 2 H, CH), 6.88 (d, 3J = 10.2 Hz, 2 H, CH).
3-Methylene-9-pentylspiro[5.5]undecane (12)
To a suspension of methylenetriphenylphosphonium bromide
(4.50 g, 12.6 mmol) and anhyd THF (120 mL) was added BuLi
(9.75 mL, 1.5 molar solution in hexane) dropwise at r.t. The mixture
was stirred for 0.5 h. Subsequently 9-pentylspiro[5.5]undecan-3-
one6e (1.0 g, 4.2 mmol, 11) dissolved in anhyd THF (50 mL) was
added and the mixture stirred for 10 h. The excess of BuLi was hy-
drolised with H2O (10 mL). The solvent was removed under re-
duced pressure. The aqeuous phase was extracted with Et2O (2 ×
50 mL) and the combined organic layers were washed with diluted
HCl and H2O. Subsequently the solution was dried (with Na2SO4)
and the Et2O removed. The crude product was purified by column
chromatography: 612 mg (62%) of a colourless oil were obtained.
13C NMR (62.9 MHz, CDCl3): d = 30.8 (4 CH2), 31.18 (8 CH2),
33.60 (4 CH2), 34.87 (4 Cq), 127.10 (2 CH), 128.06 (2 CH), 157.17
(2 CH), 158.00 (2 CH), 199.48 (2 CO), 199.56 (2 CO).
IR (KBr, cmÐ1): n = 1663 (vs), 2848 (m), 2899 (m), 2943 (m).
HRMS: [M+] (C16H20O2), calcd. 244.1463, found 244.1459.
Dispiro[5.2.5.2]hexadecane-3,12-dione (4)
Dispiro[5.2.5.2]hexadecanedienedione (3.40 g, 14 mmol, 7, 8: a
mixture of the two isomers) were dissolved in 500 mL toluene. Af-
ter addition of Pd/C (700 mg) the solution is stirred at r.t. under H2
(pressure: 3.0 bar). Subsequently the catalyst is filtered off and the
solvent is removed to afford the crude product which can be crys-
tallized from MeOH to yield 3.0 g (86%) of colourless crystals, mp
208¡C.
Rf = 0.84 (hexane).
MS (EI, 70 eV, 200¡C): m/z (%): 234 (48) [M+], 206 (100) [M+Ð
C2H4], 163 (84).
1H NMR (250 MHz, CDCl3, 25¡C): d = 0.87 (t, 3J = 6.9 Hz, 3 H,
CH3), 0.92Ð1.38 (m, 15 H, CH2, CH), 1.40Ð1.52 (m, 4 H, CH2),
1.60Ð1.70 (m, 2 H, CH2), 2.08 (t, 3J = 7 Hz, 2 H, CH2), 2.13 (t, 3J =
6.8 Hz, 2 H, CH2), 4.55 (s, 2 H, =CH2).
GC-MS (EI, 70 eV, 200¡C): m/z (%): 248 (100) [M+], 192 (23)
[M+Ð2CO], 175 (69).
1H NMR (250 MHz, CDCl3, 25¡C): d = 1.47 (s, 8 H, CH2), 1.70 (t,
3J = 6.9 Hz, 8 H, CH2), 2.28 (t, 3J = 6.9 Hz, 8 H, CH2).
13C NMR (62.9 MHz, CDCl3): d = 31.16 (8 CH2), 32.28 (2 Cq),
13C NMR (62.9 MHz, CDCl3): d = 14.30 (CH3), 22.91 (CH2), 26.9
(CH2), 28.57 (2 CH2), 30.59 (CH2), 30.82 (CH2), 32.33 (CH2),
32.45 (Cq), 33.51 (CH2), 36.28 (2 CH2), 37.36 (CH2), 38.30 (CH),
42.90 (CH2), 106.28 (=CH2), 150.79 (Cq).
37.25 (4 CH2), 212.5 (2 Cq, CO).
IR (KBr, cmÐ1): n = 1718 (vs), 2852 (m), 2917 (m).
HRMS: [M+] C16H24O2: calcd. 248.1776, found 248.1774 (MS). Ð
(248.36) C 77.38, H 9.74, found C 76.97 H 9.69.
C17H30: (234.43) calcd. C 87.09 H 12.91 found C 87.06 H 12.94.
1,1-Dichloro-10-pentyldispiro[3.2.5.2]tetradecan-2-one (13)
To a solution of alkene (600 mg, 2.6 mmol, 11) in anhyd Et2O
(50 mL) was added Zn (280 mg) and cupric acetate (16 mg). Subse-
quently trichloroacetyl chloride (0.45 mL, 4 mmol) was added
dropwise. The mixture was heated to 70¡C and stirred at that tem-
perature overnight. After cooling to r.t. the inorganic residues were
filtered off and the crude product was purified by column chroma-
tography to yield 605 mg (67%) of a colourless liquid.
Trispiro[6.2.2.5.2.2]-1,6-dioxadocosane-16-one (9)
To a solution of dispiro[5.2.5.2]hexadecane-3,12-dione (700 mg,
2.8 mmol, 4) and butan-1,4-diol (260 mg, 2.8 mmol)17 in toluene
(200 mL) was added p-toluenesulfonic acid (40 mg). The solution
was refluxed with direct azeotropic removal of the H2O. When the
H2O removal ceased, the mixture was cooled to r.t. and 1 M
NaHCO3 (100 mL) was added. The phases were separated and the
aqueous phase was extracted with toluene (2 × 100 mL). The com-
bined organic phases were washed with H2O and dried (Na2SO4).
The solvent was evaporated and the crude residue subjected to col-
umn chromotography to yield 300 mg (33%) monoketal 9 as a co-
lourless solid which can be recrystallised from MeOH, mp 161¡C.
Rf = 0.46 (cyclohexane/acetone 4:1).
Rf = 0.68 (hexane/toluene 1:1).
GC-MS (EI, 70 eV, 200¡C): m/z (%): 302 (100) [M+ÐCH2CO], 267
(26) [302ÐCl], 232 (38) [302Ð2Cl], 137 (23).
1H NMR (250 MHz, CDCl3, 25¡C): d = 0.86 (t, 3J = 6.7 Hz, 3 H,
3
CH3), 0.96 (d, J = 9.3 Hz, 2 H, CH2), 1.10Ð1.46 (m, 14 H, CH2),
GC-MS (EI, 70 eV, 200¡C): m/z (%): 320 (10) [M+], 248 (2) [M+Ð
C4H8O], 127 (100).
1.47Ð1.65 (m, 5 H, CH2, CH), 1.72Ð2.10 (m, 4 H, CH2), 3.0 (s, 2 H,
CH2Ðcyclobutane).
13C NMR (62.9 MHz, CDCl3): d = 14.27 (CH3), 22.85 (CH2), 26.80
(2 CH2), 28.34 (CH2), 28.44 (CH2), 29.12 (2 CH2), 31.64 (Cq), 31.99
(CH2), 32.35 (CH2), 37.19 (CH2), 38.13 (CH), 38.19 (CH2), 40.20
(CH2), 46.67 (Cq), 52.22 (CH2), 93.17 (Cq), 193.74 (Cq).
1H NMR (250 MHz, CDCl3, 25¡C): d = 1.22Ð1.42 (m, 8 H, CH2),
1.45Ð1.60 (m, 8 H, CH2), 1.65Ð1.80 (m, 8 H, CH2), 2.28 (t, 3J = 6.9
Hz, 4 H, CH2), 3.62 (br, 4 H, OCH2).
13C NMR (62.9 MHz, CDCl3): d = 29.06 (4 CH2), 30.21 (6 CH2),
31.45 (2 CH2), 32.37 (2 Cq), 37.42 (2 CH2), 61.85 (2 OCH2), 101.63
(CO2), 213.10 (CO).
HRMS: [M+ÐCH2CO] C17H28Cl2 calcd. 302.1568 found 302.1567.
IR (KBr, cmÐ1): n = 1716 (vs), 2851 (m), 2916 (m).
10-Pentyldispiro[3.2.5.2]tetradecan-2-one (5a)
1,1-Dichloro-10-pentyldispiro[3.2.5.2]tetradecan-2-one (600 mg,
1.8 mmol, 13) were dissolved in HOAc (5 mL). Zn powder (0.45 g,
¥
C20H32O3 (320.47): calcd. C 73.17, H 10.18 for C20H32O3 1/2
CH3OH; found C 73.33, H 10.14.
Synthesis 1999, No. 1, 117–120 ISSN 0039-7881 © Thieme Stuttgart · New York

120
N. Feuerbacher et al.
PAPER
6.5 mmol) was added and the mixture was stirred for 6 h at 70¡C.
After cooling to r.t. the inorganic residues were filtered off. The
crude residue was purified by colomn chromatography and afforded
410 mg (85%) of a colourless solid, mp 46Ð47¡C.
(b) Calaminus, W.; Všgtle, F.; Eidenschink, R. Z. Natur-
forsch. 1986, 41b, 1011.
(c) Calaminus, W.; Všgtle, F.; Eidenschink, R. German
Patent P 3543997.1 1985, CAS 107: 96503t
(d) Boettcher, J.; Hartmann, R.; Všgtle, F. Chem. Ber. 1992,
125, 1865.
(e) Schmidt, W.; Všgtle, F.; Poetsch, E. Liebigs Ann. 1995,
1319.
Rf = 0.75 (CH2Cl2).
GC-MS (EI, 70 eV, 200¡C): m/z (%): 276 (20) [M+], 232 (72) [M+Ð
C2H4O], 206 (100).
1H NMR (250 MHz, CDCl3, 25¡C): d = 0.85 (t, 3J = 6.7 Hz, 3 H,
(7) Dreiding, A. S. Helv. Chim. Acta 1957, 40, 1812.
Dreiding, A. S. Helv. Chim. Acta 1967, 50, 23.
de Jongh, H. A. P.; Wynberg, H. Recl. Trav. Chim. Pay-Bas
1963, 82, 202.
3
CH3), 1.20 (d, J = 9.1 Hz, 4 H, CH2), 1.10Ð1.40 (m, 15 H, CH2,
CH), 1.47Ð1.64 (m, 6 H, CH2), 2.68 (s, 4 H, 2 CH2Ðcyclobutane).
13C NMR (62.9 MHz, CDCl3): d = 14.26 (CH3), 22.84 (CH2), 26.60
(2 CH2), 28.38 (2 CH2), 29.57 (CH2), 30.86 (Cq), 31.79 (Cq), 32.07
(2 CH2), 32.34 (CH2), 32.82 (CH2), 32.91 (CH2), 36.27 (CH2),
38.17 (CH), 57.08 (2 CH2), 209.00 (Cq).
de Jongh, H. A. P.; Wynberg, H. Tetrahedron, 1964,20, 2553.
Rice, L. M.; Geschickter, C. F.; Grogan, C. H. J. Med. Chem.
1963, 6, 388.
(8) Rice, L. M.; Scott, K. R. J. Med. Soc. 1968, 378.
(9) Flaugh, M. E.; Crowell, T. A.; Farlow, D. S. J. Org. Chem.
1980, 45, 5399.
C19H32O (276.46): calcd. C 82.55 H 11.67, found C 82.43 H 11.98.
Hamata, M. personal communication, 1996.
(10) Herwig, W.; Soomer, S.; Erbes, K. Ger. Patent 1,173,449 (cl.
Acknowledgement
C 07c), 4.7 1964 CAS 61: 9414d
(11) Anelli, P. L.; Montanari, F.; Qiunci, S. Org. Synth. 1990, 45,
5399.
We thank Merck KG, Darmstadt for support of this work.
(12) Herold, D. Ph. D. Thesis University of Bonn, 1996.
(13) Crystal data: C24H40O4, colourless crystals, dimension 0.90 *
0.50 * 0.40 mm, triclinic, space group: P-1 (No. 2), a =
6.632(1), b = 7.854(1), c = 10.580(2) •, a = 80.73(1), b =
78.93(1)¡, g = 84.78(1), V = 532.7(2) •3, F(000) = 216, Z = 1,
wR(F2) = 0.217 [R1 = 0.079 for I>2s(I)] m(Cu-Kα) =
0.638 mmÐ1. A total of 2101 reflections were recorded on
an MACH3-Diffractometer at K = 293K [graphite monochro-
mator, l(Cu-Kα = 1,54178 •)]. Of these 1930 independent re-
flexions were used for structure solution (SHELXTL-Plus)
and refinement (128 parameters, SHELXL-93). Crystallogra-
phic data (excluding structure factors) for the structure repor-
ted in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
no. CCDC-102294. Copies of the data can be obtained free of
charge on application to: CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (+44)1223-336-033; e-mail: depo-
sit@ccdc.cam.ac.uk).
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Redloff, H.; Všgtle, F.; Puff, H.; Reuter, H.; Woller, P.
J. Chem. Res. (M) 1984, 2910.
(17) Higher yields of the product 10 may be achieved by the use of
5.6 mmol (2 eq.) butane-1,4-diol.
Synthesis 1999, No. 1, 117–120 ISSN 0039-7881 © Thieme Stuttgart · New York