A simple approach to 5,5′-bis(1,3-dioxolan-4-ones) of tartaric acids

Article abstract of DOI:10.1016/j.tetasy.2003.12.016

An easy access to acetals of aldehydes and tartaric acid is described. A series of bis(1,3-dioxolan-4-ones) was isolated with a high degree of 2,5-cis-selectivity. Transformations were performed with both (S,S)- and (R,R)-tartaric acid.

Full text of DOI:10.1016/j.tetasy.2003.12.016

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 803–806
A simple approach to 5,50-bis(1,3-dioxolan-4-ones) of tartaric acids
*
€
Morris Markert, Ingo Buchem, Hannes Kruger and Rainer Mahrwald
Institut f€ur Chemie der Humboldt-Universit€at, Brook-Taylor-Str. 2, D-12 489 Berlin, Germany
Received 18 November 2003; accepted 8 December 2003
Abstract—An easy access to acetals of aldehydes and tartaric acid is described. A series of bis(1,3-dioxolan-4-ones) was isolated with
a high degree of 2,5-cis-selectivity. Transformations were performed with both (S,S)- and (R,R)-tartaric acid.
ꢀ 2003 Elsevier Ltd. All rights reserved.
1. Introduction
tartaric acid reported in the literature. Moreover, these
examples only describe the formation of bis(1,3-diox-
olanones) of the activated aldehydes chloral7 and bro-
mal.8 Also the authors had to use large amounts of
concentrated sulfuric acid (up to 10 equiv) in reactions
of chloral with tartaric acid.9
1,3-Dioxolan-4-ones of a-hydroxy acids are important
compounds in the pool of chiral building blocks.1 Since
the pioneering work of Seebach et al.,2 many reported
synthetic methods have been based on these chiral
building blocks. For example, Kellog et al. described an
aldol addition resulting from reacting the acetals of
aldehydes and mandelic acid with enol ethers in the
presence of boron trifluoride etherate,3 with chiral ethers
of aldol adducts and mandelic acid being isolated. By
oxidative cleavage of these ethers, access to chiral aldol
products can be achieved. Diastereoselective proton-
ation of dioxolanones of mandelic acid and aldehydes
has also been reported.4 In conjugate addition of the
anions of dioxolanones derived from a-hydroxy acids to
a,b-unsaturated esters, the corresponding c-oxo-esters
were obtained with up to 86% eeÕs after flash vacuum
pyrolysis.5 Furthermore, highly diastereoselective
Michael additions of lithium enolates of chiral 1,3-di-
oxolan-4-one of mandelic acid with a,b-unsaturated
carbonyl compounds have been described.6 This method
allows, 1,4-dicarbonyl compounds to be obtained with
high enantiomeric excess.
2. Results and discussion
During our investigations of alkylations of aldehydes in
the presence of LiClO4 and tartaric acid, we saw that
from time to time small amounts of acetals of aldehydes
and tartaric acid were produced.10 In order to analyze
and compare these substances we tried to synthesize
acetals from aldehydes and tartaric acid [substituted
bis(1,3-dioxolan)-4-ones]. We found it was not possible
to synthesize these dioxolanones by the classical proce-
dure used for synthesis of dioxolanones of mandelic
acid.4 Upon further investigation, we developed a simple
and useful method for the synthesis of dioxolanones of
tartaric acid. Herein we present the first synthesis of
dioxolanones of unactivated, aliphatic aldehydes and
tartaric acid (Scheme 1).
This easy access to chiral 1,3-dioxolanones (via simple
dehydration methods of aldehydes and a-hydroxy acids)
attracts synthetic chemists time and time again. How-
ever in all the reactions and examples described in the
literature, mostly dioxolanones of mandelic acid, lactic
acid, malic acid or phenyl lactic acid have been
described. To the best of our knowledge there have been
only two examples of 1,3-dioxolan-4-ones derived from
R
OH
O
O
LiClO4, r.t.
COOH
O
R - CHO +
HOOC
O
OH
O
O
R
Scheme 1.
Acetals of tartaric acid and aldehydes were easily pre-
pared by the reaction of tartaric acid and aldehydes in
* Corresponding author. Tel.: +49-30-2093-8397; fax: +49-30-2093-
6940; e-mail: rainer.mahrwald@rz.hu-berlin.de
0957-4166/$ - see front matter ꢀ 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2003.12.016

804
M. Markert et al. / Tetrahedron: Asymmetry 15 (2004) 803–806
(S,S)-tartaric acid
Table 1
(R,R)-tartaric acid
OH
OH
COOH
COOH
HOOC
HOOC
OH
OH
R
R
O
O
O
O
O
O
O
O
O
O
Figure 2. X-ray structure of dimethyl-bis(1,3-dioxolan-4-one) 1b.
O
O
R
R
1a-6a
1b-6b
Entry R
Compound (yield %)a
and 1b–6b in the (S,S)-series, Table 1). The dioxola-
nones of tartaric acid and acetaldehyde were only iso-
lated in the 2,20,5,50-cis-configuration (1a and 1b, Table
1). Using higher aldehydes in these reactions, the 2,5-
cis,20,50-trans-configurated dioxolanones 7–11 were iso-
lated in small amounts as well and described as
byproducts; propionaldehyde ) 7, butyraldehyde ) 8,
isobutyraldehyde ) 9, pivalaldehyde ) 10 and cyclo-
hexancarboxaldehyde ) 11.
Me
Et
1a 43
2a 36
3a 33
4a 28
5a 45
6a 29
1b 46
2b 33
3b 37
4b 23
5b 48
6b 31
n-Pr
i-Pr
t-Bu
c-Hex
a Yields are not optimized.
the presence of equimolar amounts of dry LiClO4.
Several other dry metal salts and the usual Lewis acids
were used but without any success. The same highly
selective behaviour of LiClO4 was observed during
alkylations of aldehydes in the presence of LiClO4 and
tartaric acid.10
The synthesis of dioxolanones of aromatic aldehydes
and tartaric acid failed under these reaction conditions.
No products were detected on using benzaldehyde. We
do not believe that steric reasons are alone responsible
for the failure of this reaction, if one considers the
results with isobutyraldehyde, pivalaldehyde or cyclo-
hexancarboxaldehyde (Table 1, entries 4–6). Electronic
effects may be responsible for this observation. In order
to check this assumption we tested several aromatic
aldehydes with completely different electrophilic behav-
iour, p-tolualdehyde and p-nitrobenzaldehyde, but in
both cases no reaction occurred, even with heating.
There is no explanation for this phenomenon at this
time.
The reactions were performed neat at room temperature
for 24 h with only the bis(1,3-dioxolan-4-ones) being
obtained in good yields (Table 1). Other acetals, as
shown in Figure 1 could not be detected under these
conditions.
R
R
O
R
O
Further investigations of this reaction are currently in
progress.
O
O
O
O
HOOC
COOH
O
O
3. Experimental
Figure 1.
The structures of the 1,3-dioxolan-4-ones were deter-
mined unambiguously by X-ray structure analysis of
compounds 1b and 5a (Fig. 2).11
All reactions were performed using oven dried glassware
under an atmosphere of dry argon. Aldehydes were
distilled before use. Purification of products was
accomplished using flash chromatography. LiClO4 was
dried at 120 ꢁC in vacuo for 10 h.12
For comparison, both forms of chiral tartaric acid were
used in these reactions with the results shown in Table 1.
1H NMR and 13C NMR spectra were recorded at 300
and 75 MHz in CDCl3, respectively, using a AC-300
spectrometer. Chemical shifts are given in ppm. Thin
The dioxolanones were formed with a high degree of
2,20,5,50-cis-stereoselectivity (1a–6a in the (R,R)-series

M. Markert et al. / Tetrahedron: Asymmetry 15 (2004) 803–806
805
0
layer chromatography was performed out using Merck
silica gel 60 F254 TLC plates.
H5 or H5 ), 1.79 (2H, dq, J ¼ 4:9, 7.5 Hz, CH2), 1.61
(2H, dq, J ¼ 4:5, 7.5 Hz, CH2), 0.96 (3H, t, J ¼ 7:5 Hz,
CH3), 0.93 (3H, t, J ¼ 7:5 Hz, CH3); 13C NMR (CDCl3,
0
0
The dioxolanones of the (S,S)-series 1b–6b were
described by the rotatory power only, because there are
the same physical constants (1H NMR, 13C NMR and
MS) as the acetales in the (R,R)-series 1a–6a.
75 MHz): d ¼ 169:4 (C4 or C4 ), 169.0 (C4 or C4 ), 108.3
0 0 0
(C2 or C2 ), 106.0 (C2 or C2 ), 75.0 (C5 or C5 ), 72.9 (C5 or
0
C5 ), 27.9 (CH2), 27.3 (CH2), 6.8 (CH3), 6.4 (CH3).
HRMS: Calcd for C10H14O6Na 253.0681. Found:
253.0680.
3.1. General procedure
3.1.6. (2R,20R,5R,50R)-2,20-Dipropyl-5,50-bis(1,3-dioxo-
10 mmol LiClO4, 10 mmol aldehyde and 5 mmol tartaric
acid were stirred at room temperature in diethyl ether
(ca. 10 mL). The reaction was monitored by thin-layer
chromatography. At the end of the reaction (mostly
24 h) the resulting mixture was extracted by diethyl ether
and saturated aq NaHCO3-solution. The organic layers
were separated, dried (Na2SO4) and the solvent removed
in vacuo. The residue was then purified by column
chromatography.
lane-4,40-dione) 3a. Colourless oil; ½aꢀ ¼ +61 (c 1,
D
CH2Cl2); IR (neat) mmax ¼ 2963, 2877, 1792, 1466, 1404,
1368, 1324, 1254, 1178, 1147, 1102, 1046 cmꢁ1; 1H NMR
0
(CDCl3) d ¼ 5:56 (2H, dd, J ¼ 4:9, 5.3, H2, H2 ), 4.67
0
(2H, s, H5, H5 ), 1.76 (4H, dddd, J ¼ 1:9, 4.9, 5.3,
7.2 Hz, 2 · CH2), 1.45 (4H, ddt, J ¼ 1:9, 7.2, 7.5 Hz,
2 · CH2), 0.91 (6H, t, J ¼ 7:5 Hz, 2 · CH3); 13C NMR
0
0
(CDCl3) d ¼ 169:1 (C4, C4 ), 105.6 (C2, C2 ), 73.3 (C5,
0
C5 ), 36.2, 16.3 (4 · CH2), 13.7 (2 · CH3); HRMS: Calcd
for C12H18O6 258.1103. Found: 258.1104.
3.1.1. (2R,20R,5R,50R)-2,20-Dimethyl-5,50-bis(1,3-dioxo-
lane-4,40-dione) 1a. Colourless solid; mp: 118–120 ꢁC
3.1.7.
(2S,20S,5S,50S)-2,20-Dipropyl-5,50-bis(1,3-dioxo-
(petrolether/ethylacetate); ½aꢀ ¼ +96 (c 1, ethylacetate);
lane-4,40-dione) 3b. Colourless oil; ½aꢀ ¼ )55 (c 1,
D
D
IR (neat) mmax ¼ 2999, 2956, 1788, 1400, 1363, 1182,
CH2Cl2).
1140, 1105, 1077, 1041 cmꢁ1
;
1H NMR (CDCl3)
0
0
d ¼ 5:73 (2H, q, J ¼ 4:9, H2, H2 ), 4.69 (2H, s, H5, H5 ),
1.53 (6H, d, J ¼ 4:9 Hz, 2 · CH3); 13C NMR (CDCl3)
3.1.8. (2S,20R,5R,50R)-2,20-Dipropyl-5,50-bis(1,3-dioxo-
d ¼ 169:1 (C4, C4 ), 103.2 (C2, C2 ), 73.6 (C5, C5 ), 20.6
(2 · CH3); HRMS: Calcd for C8H10O6 202.0477. Found:
202.0459.
lane-4,40-dione) 8. Colourless oil; ½aꢀ ¼ +33 (c 0.04,
0
0
0
D
CH2Cl2); IR (neat) mmax ¼ 2969, 2925, 2852, 1795, 1737,
1483, 1411, 1260, 1216, 1190, 1093, 1054 cmꢁ1; 1H NMR
0
(CDCl3) d ¼ 5:68 (1H, dt, J ¼ 1:1, 4.9 Hz, H2 or H2 ),
0
5.53 (1H, dt, J ¼ 1:1, 4.9 Hz, H2 or H2 ), 4.70 (1H, dd,
3.1.2. (2S,20S,5S,50S)-2,20-Dimethyl-5,50-bis(1,3-dioxo-
lane-4,40-dione) 1b. Colourless solid; mp: 118–120 ꢁC
J ¼ 1:1, 1.5 Hz, H5 or H5 ), 4.64 (1H, dd, J ¼ 1:1,
0
0
1.5 Hz, H5 or H5 ), 1.80–1.69 (4H, m, 2 · CH2), 1.51–
(petrolether/ethylacetate); ½aꢀ ¼ )91 (c 1, CH2Cl2).
1.34 (4H, m, 2 · CH2), 0.92 (3H, t, J ¼ 7:5 Hz, CH3),
D
0.91 (3H, t, J ¼ 7:5 Hz, CH3); 13C NMR (CDCl3)
0
0
0
d ¼ 169:4 (C4 or C4 ), 168.9 (C4 or C4 ), 107.7 (C2 or C2 ),
3.1.3.
(2R,20R,5R,50R)-2,20-Diethyl-5,50-bis(1,3-dioxo-
105.3 (C2 or C2 ), 75.0 (C5 or C5 ), 72.8 (C5 or C5 ), 36.8,
36.1, 16.3, 15.9 (4 · CH2), 13.7, 13.6 (2 · CH3). HRMS:
Calcd for C12H18O6Na 281.1001. Found: 281.0995.
0
0
0
lane-4,40-dione) 2a. Colourless oil; ½aꢀ ¼ +35 (c 0.64,
D
CH2Cl2); IR (CH2Cl2) mmax ¼ 2978, 2939, 2886, 1804,
1466, 1406, 1364, 1326, 1272, 1264, 1218, 1113,
;
1014 cmꢁ1
1H NMR (CDCl3) d ¼ 5:52 (2H, t,
0
0
J ¼ 4:9 Hz, H2, H2 ), 4.69 (2H, s, H5, H5 ), 1.80 (4H, dq,
13
3.1.9. (2R,20R,5R,50R)-2,20-Diisopropyl-5,50-bis(1,3-di-
J ¼ 4:9, 7.5 Hz, 2 · CH2), 0.95 (6H, t, J ¼ 7:5 Hz,
oxolane-4,40-dione) 4a. Colourless oil; ½aꢀ ¼ +43 (c 0.6,
D
0
2 · CH3); C NMR (CDCl3) d ¼ 169:0 (C4, C4 ), 106.2
CH2Cl2); IR (neat) mmax ¼ 3403, 2968, 2929, 1800, 1472,
0
0
(C2, C2 ), 73.2 (C5, C5 ), 27.2 (2 · CH2), 6.7 (2 · CH3).
HRMS: Calcd for C10H14O6 230.0790. Found: 230.0791.
1399, 1371, 1210, 1127, 1115, 1083, 1053 cmꢁ1; 1H NMR
0
(CDCl3) d ¼ 5:48 (2H, d, J ¼ 5:7 Hz, H2, H2 ), 4.90 (2H,
0
s, H5, H5 ), 2.16 (2H, dsp, J ¼ 5:7, 6.8 Hz, 2 · CH), 1.19
(12H, t, J ¼ 6:84 Hz, 4 · CH3); 13C NMR (CDCl3)
3.1.4. (2S,20S,5S,50S)-2,20-Diethyl-5,50-bis(1,3-dioxolane-
d ¼ 169:2 (C4, C4 ), 108.8 (C2, C2 ), 73.3 (C5, C5 ), 32.4
(2 · CH), 16.1, 15.9 (4 · CH3); HRMS: Calcd for
C12H18O6 258.1103. Found: 258.1104.
0
0
0
4,40-dione) 2b. Colourless oil; ½aꢀ ¼ )32 (c 0.84,
D
CH2Cl2).
3.1.5. (2S,20R,5S,50S)-2,20-Diethyl-5,50-bis(1,3-dioxolane-
3.1.10. (2S,20S,5S,50S)-2,20-Diisopropyl-5,50-bis(1,3-di-
4,40-dione) 7. Colourless oil; ½aꢀ ¼ )65 (c 1.04, CH2Cl2);
oxolane-4,40-dione) 4b. Colourless oil; ½aꢀ ¼ )50 (c 0.8,
D
D
IR (neat) mmax ¼ 2978, 2940, 2887, 1794, 1465, 1401,
CH2Cl2).
1365, 1202, 1136, 1113, 1082, 1007 cmꢁ1
;
1H NMR
0
(CDCl3) d ¼ 5:66 (1H, dt, J ¼ 1:1, 4.5 Hz, H2 or H2 ),
3.1.11. (2S,20R,5R,50R)-2,20-Diisopropyl-5,50-bis(1,3-di-
0
5.50 (1H, dt, J ¼ 1:1, 4.9 Hz, H2 or H2 ), 4.72 (1H, t,
oxolane-4,40-dione) 9. Colourless oil; ½aꢀ ¼ +38 (c 0.16,
0
J ¼ 1:1, 1.5 Hz, H5 or H5 ), 4.66 (1H, dt, J ¼ 1:1, 1.5 Hz,
D

806
M. Markert et al. / Tetrahedron: Asymmetry 15 (2004) 803–806
CH2Cl2); IR (neat) mmax ¼ 2962, 2932, 2876, 1796, 1727,
3.1.17. (2S,20R,5R,50R)-2,20-Dicyclohexyl-5,50-bis(1,3-di-
1464, 1367, 1202, 1119, 973 cmꢁ1
;
1H NMR (CDCl3)
oxolane-4,40-dione) 11. Colourless oil; ½aꢀ ¼ +24 (c 0.26,
D
0
d ¼ 5:59 (1H, dd, J ¼ 1:5, 4.5, H2 or H2 ), 5.54 (1H, dd,
CH2Cl2); IR (neat) mmax ¼ 2926, 2854, 1800, 1727, 1451,
J ¼ 1:1, 4.9 Hz, H2 or H2 ), 4.85 (1H, t, J ¼ 1:5 Hz, H5 or
1288, 1241, 1206, 1127, 1070, 1018 cmꢁ1
;
1H NMR
0
0
0
0
H5 ), 4.77 (1H, dd, J ¼ 1:1, 1.5 Hz, H5 or H5 ), 2.14–2.00
(2H, m, 2 · CH), 1.10 (6H, dd, J ¼ 2:3, 6.8 Hz, 2 · CH3),
1.06 (6H, d, J ¼ 7:8 Hz, 2 · CH3); 13C NMR (CDCl3)
(CDCl3) d ¼ 5:42 (1H, dd, J ¼ 1:5, 4.5 Hz, H2 or H2 ),
0
5.24 (1H, dd, J ¼ 1:5, 5.3 Hz, H2 or H2 ), 4.68 (1H, dd,
0
J ¼ 1:1, 1.5 Hz, H5 or H5 ), 4.61 (1H, dd, J ¼ 1:1,
13
0
0
0
0
1.5 Hz, H5 or H5 ), 1.81–1.55 (12H, m), 1.28–0.95 (10H,
d ¼ 169:5 (C4 or C4 ), 169.0 (C4 or C4 ), 110.8 (C2 or C2 ),
0
0
0
0
108.5 (C2 or C2 ), 75.0 (C5 or C5 ), 73.0 (C5 or C5 ), 32.9,
32.2 (2 · CH), 15.8, 15.8, 15.4, 15.3 (4 · CH3). HRMS:
Calcd for C12H18O6Na 281.1001. Found: 281.0996.
m); C NMR (CDCl3) d ¼ 169:5 (C4 or C4 ), 169.1 (C4
0
or C4 ), 110.2 (C2 or C2 ), 107.9 (C2 or C2 ), 74.8 (C5 or
0
0
0
0
C5 ), 72.9 (C5 or C5 ), 42.3, 41.7 (2 · CH), 27.0, 26.5,
26.2, 26.2, 26.0, 25.7, 25.6, 25.3, 25.2, 25.1 (10 · CH2).
HRMS: Calcd for C18H26O6Na 361.1627. Found:
361.1626.
3.1.12. (2R,20R,5R,50R)-2,20-Ditertbutyl-5,50-bis(1,3-di-
oxolane-4,40-dione) 5a. Pale solid; mp: 136–138 ꢁC (hex-
ane/ethylacetate); ½aꢀ ¼ +18 (c 1, Et2O); IR (neat)
D
mmax ¼ 2961, 2928, 1801, 1728, 1483, 1463, 1409, 1366,
Acknowledgements
1
1285, 1203, 1135, 1090, 1073 cmꢁ1; H NMR (CDCl3)
0
0
d ¼ 5:17 (2H, s, H2, H2 ), 4.66 (2H, s, H5, H5 ), 0.93
This research was supported by the Deutsche Fors-
chungsgemeinschaft. The authors thank B. Ziemer and
P. Neubauer for performing the X-ray analysis.
(18H, s, 6 · CH3); 13C NMR (CDCl3) d ¼ 169:5 (C4,
0
0
0
C4 ), 109.7 (C2, C2 ), 72.8 (C5, C5 ), 34.1 (2 · Cq), 23.3
(6 · CH3); HRMS: Calcd for C14H22O6 286.1416.
Found: 286.1417.
References and notes
3.1.13.
(2S,20S,5S,50S)-2,20-Ditertbutyl-5,50-bis(1,3-di-
oxolane-4,40-dione) 5b. Pale solid; ½aꢀ ¼ )13 (c 1,
1. (a) Coppola, G. M.; Schuster, H. F. a-Hydroxy Acids in
Enantioselective Syntheses; Wiley-VCH: Weinheim, 1997;
(b) Gawronski, J. Tartaric and Malic Acids in Synthesis:
A Source Book of Building Blocks, Ligands, Auxiliaries,
and Resolving Agents; Wiley: New York, 1999; (c)
D
CH2Cl2).
3.1.14. (2S,20R,5R,50R)-2,20-Ditertbutyl-5,50-bis(1,3-di-
Seebach, D.; Hungerbuhler, E. In Modern Synthetic
€
€
Methods; Scheffold, R., Ed.; Saale & Sauerlander: Fran-
furt, Aarau, 1980; p 93.
oxolane-4,40-dione) 10. Colourless oil; ½aꢀ ¼ +49 (c
D
0.26, CH2Cl2); IR (neat) mmax ¼ 2960, 2911, 1797, 1482,
2. For reviews of this work see Seebach, D.; Imwinkelried,
R.; Weber, T. In Modern Synthetic Methods; Scheffold, R.,
Ed.; Springer: Berlin, 1986; p 125; Seebach, D.; Sting,
A. R.; Hoffmann, M. Angew. Chem., Int. Ed. 1996, 35,
2708.
3. Mashraqui, S. H.; Kellog, R. M. J. Org. Chem. 1984, 49,
2513.
4. Gerlach, U.; Haubenreich, T.; Huenig, S. Chem. Ber. 1994,
127, 1981, and references cited therein.
1411, 1366, 1325, 1286, 1214, 1197, 1139, 1056,
1038 cmꢁ1; H NMR (CDCl3) d ¼ 5:38 (1H, d, J ¼ 1:5,
1
0
0
H2 or H2 ), 5.21 (1H, d, J ¼ 1:5, H2 or H2 ), 4.80 (1H, t,
0
0
J ¼ 1:5, H4 or H4 ), 4.67 (1H, t, J ¼ 1:5, H4 or H4 ), 1.00
(9H, s, 3 · CH3), 0.96 (9H, s, 3 · CH3); 13C NMR
0
(CDCl3) d ¼ 169:7, 169.2 (C4, C4 ), 112.7, 109.3 (C2,
0
0
C2 ), 75.2, 73.1 (C5, C5 ), 35.6, 34.3 (2 · Cq), 23.4, 23.0
(6 · CH3). HRMS: Calcd for C14H22O6Na 309.1314.
Found: 309.1308.
5. Aitken, R. A.; Thomas, A. W. Synlett 1998, 102.
6. Blay, G.; Fernandez, I.; Monje, B.; Pedro, J. R.; Ruiz, R.
Tetrahedron Lett. 2002, 43, 8463.
7. (a) Uray, G.; Lindner, W.; Reiter, F. Synthesis 1989, 194;
(b) Uray, G.; Lindner, W.; Keller, W.; Fabian, W. Chem.
Ber. 1989, 122, 1203.
8. Czerny, P.; Epperlein, J.; Mischock, G.; Wieck, S. Ger.
(East.), DD 130508, 1978.
9. Shah, N. M.; Alimchandani, R. L. J. Indian Chem. 1934,
11, 545.
10. (a) Mahrwald, R. Angew. Chem., Int. Ed. 2002, 41, 1361;
(b) Mahrwald, R. Angew. Chem., Int. Ed. 2003, 42, 2443;
3.1.15. (2R,20R,5R,50R)-2,20-Dicyclohexyl-5,50-bis(1,3-di-
oxolane-4,40-dione) 6a. Pale solid; mp: 155–158 ꢁC (hex-
ane/ethylacetate); ½aꢀ ¼ +43 (c 1, CH2Cl2); IR (neat)
D
mmax ¼ 2923, 2855, 1796, 1452, 1319, 1251, 1219, 1201,
1145, 1068, 1039 cmꢁ1; 1H NMR (CDCl3) d ¼ 5:25 (2H,
0
0
d, J ¼ 6:0 Hz, H2, H2 ), 4.65 (2H, s, H5, H5 ), 1.85–1.58
(12H, m), 1.26–0.95 (10H, m); 13C NMR (CDCl3)
0
0
0
d ¼ 169:2 (C4, C4 ), 108.1 (C2, C2 ), 73.1 (C5, C5 ), 41.9
(2 · CH), 26.5, 26.1, 26.0, 25.2, 25.1 (10 · CH2); HRMS:
Calcd for C18H26O6 338.1729. Found: 338.1729.
€
(c) Markert, M.; Buchem, I.; Kruger, H.; Mahrwald, R.
Tetrahedron 2004, 60, 993.
11. The crystal structures have been deposited at the Cam-
bridge Crystallographic Data Centre and have been
allocated the deposition numbers CCDC 219 740 for 1b
and CCDC 219 741 for 5a.
12. For comments of safety see Armarego, W. L. F.; Perrin,
D. D. Purification of Laboratory Chemicals; Butterworth-
Heinemann: Oxford, 1997.
3.1.16. (2S,20S,5S,50S)-2,20-Dicyclohexyl-5,50-bis(1,3-di-
oxolane-4,40-dione) 6b. Pale solid; ½aꢀ ¼ )46 (c 1,
D
CH2Cl2).