Synthesis of the C29-C37 segment of spongistatin 1

Article abstract of DOI:10.1016/S0957-4166(99)00148-2

Starting from racemic 2α-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one the spongistatin E segment has been prepared in nine steps (2.3 steps per stereogenic center) with umpolung of anomeric reactivity at C37. This 3,5- syndiol sequence completes our methodolo

Full text of DOI:10.1016/S0957-4166(99)00148-2

Pergamon
Tetrahedron: Asymmetry 10 (1999) 1539–1549
Synthesis of the C29–C37 segment of spongistatin 1
Ralf Dunkel, Jens Treu † and H. Martin R. Hoffmann ∗
Department of Organic Chemistry, University of Hannover, Schneiderberg 1B, D-30167 Hannover, Germany
Received 23 March 1999; accepted 19 April 1999
Abstract
Starting from racemic 2α-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one the spongistatin E segment has been pre-
pared in nine steps (2.3 steps per stereogenic center) with umpolung of anomeric reactivity at C37. This 3,5-syn-
diol sequence completes our methodology to all stereoisomers of 3,5,7-trihydroxy heptanoic ester building blocks
functionalized for α-oxyanion chemistry. © 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
Tetrahydropyrans and their open chain analogs are of enormous interest in polyketide and in natural
product chemistry in general.1 In a previous paper we have described the synthesis of open-chain seven
carbon based building blocks of the polyacetate aldol type. Each of the stereogenic centers was built
Figure 1.
∗
†
Corresponding author. E-mail: hoffmann@mbox.oci.uni-hannover.de
New address: Product Development cosmed, Cleansing Products, Beiersdorf AG, Unnastr. 48, D-20245 Hamburg, Germany.
0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00148-2

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Scheme 1.
up diastereo- and enantioselectively. The functionalization with carbanion stabilizing π-acceptors at the
terminal carbon was described in full detail for one of the 3,5-anti diols, yielding the C17–C23 fragment
of spongistatin.2,3 In tackling the synthesis of segment E we now extend our anomeric oxabicyclic lactone
concept to methyl substituted bicyclic ketone rac-1. Our sequence affords the C29–C37 fragment of
spongistatin (Fig. 1).
2. Results
Starting from 2α-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one rac-1, SmI2 mediated reduction4 gave the
equatorial alcohol rac-2. exo-Orientation of the hydroxy group provided the equivalent of the syn-3,5-
diol enantiomeric pair. Protection yielded benzyl ether rac-3 quantitatively. Asymmetric hydroboration5
and oxidation of the corresponding regioisomeric alcohols allowed separation of the almost enantiopure
(ee 93%) ketones (−)-4 and (+)-4 by simple column chromatography. Baeyer–Villiger oxidation of (−)-
4 furnished anomeric oxabicyclic lactone (−)-5, which was opened to monocyclic anomers 6 by acidic
methanolysis.

R. Dunkel et al. / Tetrahedron: Asymmetry 10 (1999) 1539–1549
1541
Preparation of the desired sulfone 10 (Scheme 1) required the introduction of thiophenol to afford the
anomeric sulfides 7. However, thiophenol introduction via boron trifluoride etherate at the acetalic center
led to deprotection of the benzyl ether. Instead of changing the sequence to (i) ester reduction followed by
(ii) protection of the corresponding alcohol, we used milder conditions for the acetal functionalization.
Reaction of the acetals 6 with (phenylthio)trimethylsilane Me3SiSPh in the presence of zinc iodide
and tetrabutylammonium iodide6 afforded anomeric sulfides 7. Diisobutylaluminum hydride reduction
and silylation of the resulting alcohol (8 -→ 9) was straightforward and furnished anomeric sulfides 9.
Oxidation with m-chloroperoxybenzoic acid yielded the sulfones (+)-10 eq and (+)-10 ax which could
easily be separated by column chromatography. A building block equivalent to 10 has already been
coupled in Evans’ total synthesis of spongistatin.3a
The synthesis of the triphenylphosphonium tetrafluoroborate 16 (Scheme 2) started again from methyl
acetal (−)-6.7 Reduction of the ester function and tosylation afforded (−)-12 in very good yield.
Elongation via allyl group introduction by Grignard reaction, subsequent dihydroxylation and sodium
periodate cleavage resulted, after reduction, in the C2-elongated acetal (−)-14. Protection of the alcohol
and reaction with triphenylphosphonium tetrafluoroborate furnished 16 as an alternative building block
of the spongistatin C29–C37 segment.
Scheme 2.
In summary, three stereogenic centers and one anomeric center have been installed de novo in
nine steps from racemic 2α-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one. Asymmetric hydroboration gave
single enantiomers. The anomeric center was subjected to umpolung with different π-acceptors. Our
methodology provides enantiopure anti-1,3-aldols8 and syn-1,3-aldols with chemodifferentiated 1,7-
functionality (Scheme 1) and 1,9-functionality (Scheme 2).
3. Experimental
3.1. General
Infrared spectra were recorded on a Perkin–Elmer 1710 infrared spectrometer. 1H NMR and 13C NMR
spectra were recorded on a Bruker AM 400 spectrometer in deuterated chloroform unless otherwise
stated, with tetramethylsilane as an internal standard. Mass spectra were recorded on a Finnigan MAT
312 (70 eV) or a VG Autospec spectrometer at room temperature unless otherwise stated. Preparative
column chromatography was performed on J. T. Baker silica gel (particle size 30–60 µm). Analytical

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TLC was carried out on aluminum-backed 0.2 mm silica gel 60 F254 plates (E. Merck). Diethyl ether (E)
and THF were distilled over sodium and benzophenone before use. CH2Cl2 (DCM) was distilled over
CaH2 before use. DMF was dried over BaO and distilled over CaH2 before use. Methyl t-butyl ether
(MTBE), ethyl acetate (EA), cyclohexane (CH) and light petroleum (PE, bp 40–60°C) were distilled
before use. For the preparation of compounds rac-1 and rac-2 see Treu and Hoffmann. 4
3.2. 2α-Methyl-3β-benzyloxy-8-oxabicyclo[3.2.1]oct-6-ene rac-3
To a solution of alcohol rac-2 (3.96 g, 28.3 mmol) in THF (40 ml) was added NaH (1.70 g, 56.5 mmol,
80% in mineral oil) under N2. The mixture was heated to reflux for 45 min. To the resulting mixture was
added benzyl bromide (6.70 ml, 56.5 mmol) and Bu4NI (30 mg, 0.07 mmol) in THF (5 ml) at room
temperature. The mixture was heated to reflux for 3 h and then stirred at room temperature overnight.
Water was added and the aqueous layer was extracted with E. The combined organic layer was dried
(MgSO4), the solvent removed and the crude product was purified by chromatography (E/PE) to afford
1
rac-3 (6.45 g, 99%) as yellow crystals, mp 35°C. H NMR (400 MHz, CDCl3, TMS) δ 7.39–7.22 (m,
5H, Ph), 6.14 (s, 2H, H-7, H-6), 4.81 (d, J=3 Hz, 1H, H-5), 4.57 (d, J=12 Hz, 1H, CHHPh), 4.55 (d, J=5
Hz, 1H, H-1), 4.35 (d, J=12 Hz, 1H, CHHPh), 3.20 (ddd, J=9 Hz, J=9 Hz, J=6 Hz, 1H, H-3), 1.98 (m,
1H, H-4eq), 1.99 (m, 1H, H-4ax), 1.66 (m, 1H, H-2), 0.92 (d, J=7 Hz, 3H, CH3); 13C NMR (100 MHz,
CDCl3, TMS) δ 138.83 (C, CPh), 132.26 (CH, C-7), 129.64 (CH, C-6), 128.34 (CH, o-CPh), 127.71 (CH,
m-CPh), 127.54 (CH, p-CPh), 82.30 (CH, C-5), 78.44 (CH, C-1), 77.95 (CH, C-3), 70.74 (CH2, CH2Ph),
38.58 (CH, C-2), 31.62 (CH2, C-4), 14.56 (CH3, CH3); νmax (CHCl3)/cm−1 3000, 2956, 2872, 1496,
1356, 1252, 1116, 1088, 1072; MS: 230 (M+, 1), 175 (4), 124 (30), 92 (11), 91 (100), 81 (17), 65 (6).
Anal. calcd for C15H18O2: C, 78.23; H, 7.88. Found: C, 78.20; H, 7.86.
3.3. (1S,3R,4S,5R)-3-Benzyloxy-4-methyl-8-oxabicyclo[3.2.1]octan-6-one (+)-4 and diastereomeric
(1R,2R,3S,5R)-3-benzyloxy-4-methyl-8-oxabicyclo[3.2.1]octan-6-one (−)-4
To a solution of (+)-α-pinene (12.8 ml, 80.5 mmol) in THF (8.6 ml) was added BH3·DMS (3.20
ml, 32.0 mmol, 10 M solution) at rt. Stirring was stopped after 5 min and after a short time (−)-(Ipc)2BH
crystallized. Crystallization was completed overnight. The mixture was cooled to 0°C and the supernatant
liquid was removed with a syringe. The crystals were cooled to −20°C and washed with ice-cold E. The
solvent was removed with a syringe and the crystals were dried for 15 min (oil pump vacuum). To the
resulting (−)-(Ipc)2BH was added THF (2 ml) at −20°C followed by rac-3 (5.24 g, 23.0 mmol) in THF (1
ml). The mixture was stored for 8 days at −15°C and 6 days at −3°C, then MeOH (5.2 ml) was added at
0°C, followed by 3 N NaOH (14.3 ml, 43.2 mmol) and 30% H2O2 (14.3 ml, 141 mmol). The mixture was
stirred for 1.5 h at 0°C and 2 h at rt. The aqueous layer was saturated with NaCl and extracted with EA.
The combined organic phase was dried (MgSO4), the solvent evaporated, and the crude product purified
by column chromatography to afford a mixture of alcohols (4.59 g, 80%), yellowish oil. To a suspension
of PCC on silica gel (18.4 g, 36.8 mmol, ca. 2 mmol/g) in DCM (50 ml) was added a mixture of alcohols
(4.52 g, 18.4 mmol) in DCM (25 ml) at 0°C. The mixture was stirred for 2 h at 0°C and overnight at rt
and then filtered through silica gel (E). After removal of the solvent, the crude product was purified by
column chromatography (E/PE) to afford (+)-4 and (−)-4. Data for (+)-4, yield 1.68 g (37%), crystals, mp
73°C, [α]D20=+67.0 (c=1, CHCl3). H NMR (400 MHz, CDCl3, TMS) δ 7.38–7.23 (m, 5H, Ph), 4.60
1
(d, J=12 Hz, 1H, CHHPh), 4.51 (d, J=4 Hz, 1H, H-5), 4.36 (d, J=12 Hz, 1H, CHHPh), 4.18–4.12 (m,
1H, H-1), 3.25 (ddd, J=11 Hz, J=10 Hz, J=6 Hz, 1H, H-3), 2.53 (dd, J=15 Hz, J=8 Hz, 1H, H-7exo), 2.30
(d, J=15 Hz, 1H, H-7endo), 2.26 (m, 1H, H-2eq), 2.16 (m, 1H, H-4), 1.80 (m, 1H, H-2ax), 0.97 (d, J=7 Hz,
3H, CH3); 13C NMR (100 MHz, CDCl3, TMS) δ 215.12 (C, C-6), 138.09 (C, CPh), 128.44 (CH, o-CPh,
p-CPh), 127.71 (CH, m-CPh), 78.12 (CH, C-5), 77.05 (CH, C-1), 75.49 (CH, C-3), 70.9 (CH2, CH2Ph),

R. Dunkel et al. / Tetrahedron: Asymmetry 10 (1999) 1539–1549
1543
40.11 (CH, C-4), 38.29 (CH2, C-7), 31.43 (CH2, C-2), 14.18 (CH3, CH3); νmax (KBr)/cm−1 3032, 2980,
2944, 2916, 1752, 1452, 1352, 1176, 1108, 1084, 1024; MS (50°C): 246 (M+, 3), 218 (5), 163 (25), 155
(33), 140 (100); HR-MS calcd for C15H18O3 (M+) 246.1256, found 246.1256. Data for (−)-4, 1.825 g,
(40%), light-yellow oil, [α]D20=−31.4 (c=1, CHCl3). H NMR (400 MHz, CDCl3, TMS) δ 7.40–7.20
1
(m, 5H, Ph), 4.82 (m, 1H, H-5), 4.61 (d, J=12 Hz, 1H, CHHPh), 4.42 (d, J=12 Hz, 1H, CHHPh), 3.85
(d, J=4 Hz, 1H, H-1), 3.30 (ddd, J=11 Hz, J=11 Hz, J=5 Hz, 1H, H-3), 2.63 (dd, J=18 Hz, J=8 Hz, 1H,
H-7exo), 2.17 (d, J=18 Hz, 1H, H-7endo), 2.14 (m, 1H, H-4eq) 2.07 (m, 1H, H-2), 1.91 (m, 1H, H-4ax),
1.08 (d, J=7 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3, TMS) δ 213.53 (C, C-6), 138.02 (C, CPh),
128.37 (CH, o-CPh, p-CPh), 127.42 (CH, m-CPh), 80.37 (CH, C-5), 75.77 (CH, C-1), 73.86 (CH, C-3),
70.93 (CH2, CH2Ph), 41.95 (CH2, C-7), 41.55 (CH, C-2), 35.62 (CH2, C-4), 12.27 (CH3, CH3); νmax
(film)/cm−1 3028, 2964, 2896, 2876, 1752, 1496, 1452, 1364, 1112, 1076; MS (50°C): 246 (M+, 4), 190
(3), 177 (33), 161 (2), 155 (17), 140 (100); HR-MS calcd for C15H18O3 (M+) 246.1256, found 246.1256.
3.4. (−)-(1S,5R,6R,7S)-7-Benzyloxy-6-methyl-2,9-dioxabicyclo[3.3.1]nonan-3-one (−)-5
To a solution of ketone (−)-4 (1.6 g, 6.5 mmol) in DCM (40 ml) was added a mixture of KHCO3 (1.3
g, 13 mmol) and m-CPBA (3.2 g, 13 mmol, 70%) portionwise at 0°C. The mixture was stirred overnight
at rt, then 2 N NaOH was added to dissolve the precipitate. The aqueous layer was extracted with DCM
and the combined organic phase dried (MgSO4). After removal of the solvent the residue was purified
by column chromatography (E/PE) to afford (−)-5, 1.47 g (87%), crystals, mp 81°C, [α]D20=−5.0 (c=1,
CHCl3). 1H NMR (400 MHz, CDCl3, TMS) δ 7.40–7.24 (m, 5H, Ph), 5.86 (s, 1H, H-1), 4.61 (d, J=12
Hz, 1H, CHHPh), 4.42 (d, J=12 Hz, 1H, CHHPh), 4.28 (dd, J=8 Hz, J=4 Hz, 1H, H-5), 3.47 (ddd, J=11
Hz, J=10 Hz, J=5 Hz, 1H, H-7), 2.87 (dd, J=18, J=8 Hz, 1H, H-4exo), 2.62 (d, J=18 Hz, 1H, H-4endo),
2.55 (m, 1H, H-8eq), 2.20 (m, 1H, H-6), 1.78 (ddd, J=13 Hz, J=11 Hz, J=3 Hz, 1H, H-8ax), 1.04 (d,
J=7 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3, TMS) δ 166.46 (C, C-3), 137.88 (C, CPh), 128.51
(CH, o-CPh), 127.61 (CH, p-CPh), 127.56 (CH, m-CPh), 99.55 (CH, C-1), 72.48 (CH, C-5), 72.4 (CH,
C-7), 71.31 (CH2, CH2Ph), 40.13 (CH, C-6), 36.78 (CH2, C-8), 29.88 (CH2, C-4), 13.74 (CH3, CH3);
νmax (KBr)/cm−1 2984, 2900, 1740, 1720, 1496, 1376, 1244, 1100, 1068; MS: 190 (1), 172 (2), 171
(M+−C7H7, 17), 130 (5), 92 (1), 91 (100), 77 (2), 65 (7); HR-MS calcd for C15H18O4 (M+) 262.1205,
found 262.1201.
3.5. (−)-(2R,3R,4S,6R)-4-Benzyloxy-6-methoxy-3-methyl-tetrahydropyran-2-acetic acid methyl ester
[(−)-6]
To a solution of lactone (−)-5 (1.33 g, 5.09 mmol) in MeOH was added concentrated HCl (a few drops)
and the mixture was stirred overnight at rt, then DCM was added. The mixture was neutralized with sat.
aqueous NaHCO3 solution. The aqueous layer was extracted with DCM, the combined organic phase
dried (MgSO4), and the solvent evaporated. Purification by column chromatography afforded (−)-6 (93%
1
ee, H NMR shift experiment with (+)-Eu(hfc)3), 1.36 g (86%), as a colorless oil, [α]D20=−17.4 (c=1,
CHCl3). Alternatively, methanolysis in the presence of trimethyl orthoformate (1 equiv.) and catalytic
1
H2SO4 gave 6 (99% yield) as an anomeric mixture, ax:eq=1:3. H NMR (400 MHz, CDCl3, TMS) δ
7.40–7.30 (m, 5H, Ph), 4.71 (dd, J=10 Hz, J=3 Hz, 1H, H-6), 4.58 (d, J=12 Hz, 1H, CHHPh), 4.52 (d,
J=12 Hz, 1H, CHHPh), 4.45 (m, 1H, H-2), 3.68 (s, 3H, OCH3), 3.63 (dd, J=10 Hz, J=3 Hz, 1H, H-4),
3.46 (s, 3H, OCH3), 2.66 (dd, J=15 Hz, J=9 Hz, 1H, H-7a), 2.39 (dd, J=15 Hz, J=5 Hz, 1H, H-7b), 1.90
(m, 2H, H-5eq, H-3), 1.64 (ddd, J=13 Hz, J=10 Hz, J=3 Hz, 1H, H-5ax), 0.95 (d, J=7 Hz, 3H, CH3); 13
C
NMR (100 MHz, CDCl3, TMS) δ 171.8 (C, C-8), 138.54 (C, CPh), 128.42 (CH, o-CPh), 127.58 (CH,
p-CPh), 127.4 (CH, m-CPh), 100.4 (CH, C-6), 78.38 (CH, C-2), 70.44 (CH2, CH2Ph), 69.6 (CH, C-4),
56.24 (CH3, OCH3), 51.63 (CH3, OCH3), 37.52 (CH2, C-7), 34.35 (CH, C-3), 31.38 (CH2, C-5), 10.94

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(CH3, CH3); νmax (film)/cm−1 3028, 2956, 2936, 1740, 1496, 1436, 1300, 1192, 1144, 1040; MS: 308
(M+, 5), 230 (1), 185 (4), 170 (5), 91 (100), 77 (2), 65 (6); HR-MS calcd for C17H24O5 (M+) 308.1624,
found 308.1613.
3.6. (2R,3R,4S)-(4-Benzyloxy-3-methyl-6-phenylsulfanyl-tetrahydro-pyran-2-yl)-acetic acid methyl es-
ter 7
A suspension of 198.0 mg (0.6 mmol) of acetal 6, 382.5 mg (1.2 mmol) of zinc iodide, 255.3 mg
(0.7 mmol) of tetra-n-butylammonium iodide and 220.0 µl (1.2 mmol) of (phenylthio)trimethylsilane
in 3 ml of abs. 1,2-dichloroethane was heated to 60°C for 5 h. The reaction mixture was poured into
sodium hydrogen carbonate solution, extracted with DCM, dried over Na2SO4 and concentrated in vacuo.
Column chromatography (CH:EA=1:0 to 10:1) afforded 231.2 mg (0.6 mmol, 93%) of 7 as anomeric
mixture (ax:eq=1:3). Spectroscopic data for the major anomer were determined from the anomeric
mixture. 1H NMR (400 MHz, CDCl3, TMS) δ 7.47–7.16 (10H, Ph, SPh), 5.26 (dd, J=12.2 Hz, J=2.3 Hz,
1H, H-6), 4.55 (ddd, J=9.5 Hz, J=4.3 Hz, J=2.4 Hz, 1H, H-2), 4.54 (2H, CH2Ph), 3.64 (s, 3H, OCH3),
3.60 (1H, H-4), 2.66 (dd, J=15.4 Hz, J=9.5 Hz, 1H, H-7a), 3.24 (dd, J=15.4 Hz, J=4.3 Hz, 1H, H-7b),
2.02 (dm, J=14.4 Hz, H-5ax), 1.90 (2H, H-5eq, H-3), 0.96 (d, J=7.2 Hz, 3H, CH3); 13C NMR (100 MHz,
CDCl3, TMS) δ 171.69 (C, C-8), 138.36 (C, CSPh), 135.02 (C, CPh), 129.98 (CH, m-CPh), 128.67 (CH,
o-CPh), 128.40 (CH, o-CSPh), 127.60 (CH, p-CPh), 127.38 (CH, m-CSPh), 126.57 (CH, p-CSPh), 83.91
(CH, C-6), 80.79 (CH, C-2), 72.19 (CH, C-4), 70.41 (CH2, CH2Ph), 51.67 (CH3, OCH3), 37.93 (CH2,
C-7), 34.35 (CH, C-3), 30.81 (CH2, C-5), 10.89 (CH3, CH3); νmax (CHCl3)/cm−1 3000, 2956, 2928,
2872, 1732, 1600, 1480, 1452, 1436, 1384, 1352, 1292, 1276, 1192, 1176, 1140, 1092, 1072, 1040, 988,
944; MS (100°C): 386 (M+, 0.68), 361 (0.5), 355 (1.0), 321 (0.8), 308 (7.5), 278 (9.5), 169 (48.7), 167
(18.0), 149 (48.5), 115 (8.3), 111 (9.5), 95 (13.1), 91 (100.0), 85 (5.4), 83 (5.2), 71 (10.6); HR-MS calcd
for C22H26O4S (M+) 386.1552, found 386.1552.
3.7. (2R,3R,4S)-2-(4-Benzyloxy-3-methyl-6-phenylsulfanyl-tetrahydro-pyran-2-yl)-ethanol 8
At −78°C 2.4 ml (2.4 mmol) of a 1 M diisobutylaluminum hydride solution in hexane were added to
a solution of 195.0 mg (0.5 mmol) of ester 7 in abs. THF (3 ml). The reaction mixture was allowed to
warm up to rt over 5 h. After an additional hour at rt 6 ml of a 2 M potassium sodium tartrate solution
was added and stirred overnight. The aqueous layer was extracted with MTBE, dried over Na2SO4 and
concentrated in vacuo. Column chromatography (CH:EA=2:1) yielded 165.2 mg (0.5 mmol, >99%) of
1
alcohol 8. Spectroscopic data for the major anomer were determined from the anomeric mixture. H
NMR (400 MHz, CDCl3, TMS) δ 7.46 (m, 2H, o-Ar), 7.36–7.20 (m, 8H, Ph, m-Ar, p-Ar), 5.21 (dd,
J=12.0 Hz, J=2.3 Hz, 1H, H-6), 4.54 (d, J=12.0 Hz, 1H, CHHPh), 4.52 (d, J=12.0 Hz, 1H, CHHPh),
4.16 (ddd, J=10.4 Hz, J=2.5 Hz, J=2.4 Hz, 1H, H-4), 3.71 (ddd, J=15.7 Hz, J=10.3 Hz, J=7.5 Hz, 1H,
H-8a), 3.69 (ddd, J=15.7 Hz, J=11.0 Hz, J=8.1 Hz, 1H, H-8b), 3.58 (dd, J=5.7 Hz, J=2.8 Hz, 1H, H-2),
2.03 (m, 1H, H-7a), 2.00 (m, 1H, H-7b), 1.91 (m, 1H, H-5eq), 1.87 (ddd, J=14.8 Hz, J=12.0 Hz, J=2.5
Hz, 1H, H-5ax), 1.79 (m, 1H, H-3), 0.93 (d, J=7.2 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3, TMS) δ
138.40 (C, CAr), 133.63 (C, CPh), 131.65 (CH, m-CPh), 128.89 (CH, o-CPh), 128.45 (CH, o-CAr), 127.64
(CH, p-CPh), 127.38 (CH, m-CAr), 125.37 (CH, p-CAr), 80.77 (CH, C-6), 77.78 (CH, C-2), 75.56 (CH,
C-4), 70.44 (CH2, CH2Ph), 61.53 (CH2, C-8), 35.29 (CH, C-3), 34.95 (CH2, C-7), 11.07 (CH3, CH3);
νmax (CHCl3)/cm−1 3452, 3000, 2968, 2928, 2880, 1600, 1480, 1452, 1440, 1384, 1352, 1304, 1236,
1092, 1072, 1040, 1004, 960, 900, 868, 836; FAB: 381 (M++23 (Na), 30), 359 (20), 249 (100), 177 (28);
HR-MS calcd for C21H26O3S (M+) 358.1603, found 358.1606.

R. Dunkel et al. / Tetrahedron: Asymmetry 10 (1999) 1539–1549
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3.8. (2R,3R,4S)-4-Benzyloxy-2-(2-triethylsilyloxy-ethyl)-3-methyl-6-phenylsulfanyl-tetrahydro-pyran 9
At 0°C a solution of 126.0 mg (0.4 mmol) of alcohol 8 in abs. DMF (0.5 ml) was added to a
solution of 78.0 mg (1.2 mmol) of imidazole and 200.0 µl (1.2 mmol) of triethylsilyl chloride in abs.
DMF (0.3 ml). After 10 min the reaction mixture was warmed to rt and stirred for 3 h. The solution
was poured into sodium hydrogen carbonate solution, extracted with MTBE, dried over Na2SO4 and
concentrated in vacuo. Column chromatography (CH:MTBE=5:1) afforded 167.1 mg (0.4 mmol, 92%)
of 9. Spectroscopic data for the major anomer was determined from the anomeric mixture. 1H NMR (400
MHz, CDCl3, TMS) δ 7.49 (m, 2H, o-SPh), 7.33–7.20 (m, 8H, m-SPh, p-SPh, Ph), 5.18 (dd, J=12.0
Hz, J=2.5 Hz, 1H, H-6), 4.54 (s, 3H, OCH3), 4.14 (ddd, J=9.2 Hz, J=3.0 Hz, J=2.5 Hz, 1H, H-4), 3.72
(ddd, J=14.8 Hz, J=10.0 Hz, J=5.3 Hz, 1H, H-8a), 3.65 (m, 1H, H-8b), 3.59 (dd, J=5.7 Hz, J=2.8 Hz,
1H, H-2), 2.01 (dm, J=13.3 Hz, 1H, H-7a), 1.85 (m, 4H, H-7b, H-5eq, H-5ax, H-3), 0.94 (t, J=8.0 Hz,
9H, Si(CH2CH3)3), 0.93 (d, J=7.2 Hz, 3H, CH3), 0.57 (q, J=8.0 Hz, 6H, Si(CH2CH3)3); 13C NMR (100
MHz, CDCl3, TMS) δ 138.62 (C, CSPh), 134.81 (C, CPh), 130.97 (CH, m-CPh), 128.61 (CH, o-CPh),
128.33 (CH, o-CSPh), 127.51 (CH, p-CPh), 127.39 (m-CSPh), 126.86 (CH, p-CSPh), 80.85 (CH, C-6),
78.05 (CH, C-2), 72.35 (CH, C-4), 70.31 (CH2, CH2Ph), 59.88 (CH2, C-8), 36.20 (CH2, C-5), 35.03
(CH, C-3), 31.31 (CH2, C-7), 10.98 (CH3, CH3), 6.81 (CH3, Si(CH2CH3)3), 4.40 (CH2, Si(CH2CH3)3);
νmax (CHCl3)/cm−1 3064, 3000, 2956, 2912, 2876, 1584, 1480, 1456, 1440, 1416, 1384, 1352, 1308,
1288, 1236, 1188, 1096, 1060, 1040, 964, 880; MS (130°C): 364 (M+−108, 0.6), 363 (1.9), 333 (1.8),
257 (12.2), 256 (56.1), 225 (4.7), 199 (2.2), 171 (5.0), 159 (15.9), 145 (2.4), 123 (13.7), 117 (17.8), 115
(9.7), 105 (4.8), 97 (12.7), 91 (100.0), 87 (8.6), 69 (4.8); HR-MS calcd for C21H35O3Si (M+−109 (SPh))
363.2355, found 363.2354.
3.9. (2R,3R,4S,6R)-6-Benzenesulfonyl-4-benzyloxy-2-(2-triethylsilyloxy-ethyl)-3-methyl-tetrahydro-
pyran (+)-10 eq
At 0°C 165.0 mg (2.0 mmol) of sodium hydrogen carbonate and 207.0 mg (0.8 mmol) of m-
chloroperoxybenzoic acid (70%) were added successively to a solution of 99.0 mg (0.2 mmol) of 9
in 7 ml of abs. DCM. After 15 min the reaction was quenched with sodium hydrogen carbonate solution.
The organic layer was washed with ice cooled 2 N sodium hydroxide. The combined aqueous layers
were extracted with DCM, dried over Na2SO4 and concentrated in vacuo. Column chromatography
(CH:EA=5:1) allowed separation of the anomeric sulfones (99.0 mg, 0.2 mmol, >99%, eq:ax=4:1).
1
[α]D20=+63.7 (c=1.0, CHCl3); H NMR (400 MHz, CDCl3, TMS) δ 7.93 (dd, J=7.9 Hz, J=1.4 Hz,
2H, o-Ar), 7.65 (ddd, J=7.5 Hz, J=1.6 Hz, J=1.4 Hz, 1H, p-Ar), 7.54 (ddd, J=7.9 Hz, J=7.5 Hz, J=1.6
Hz, 2H, m-Ar), 7.36–7.29 (m, 5H, Ph), 4.72 (dd, J=12.0 Hz, J=2.5 Hz, 1H, H-6), 4.57 (d, J=11.9 Hz,
1H, CHHPh), 4.52 (d, J=11.9 Hz, 1H, CHHPh), 4.00 (ddd, J=9.8 Hz, J=2.8 Hz, J=2.5 Hz, 1H, H-4),
3.72 (dd, J=5.8 Hz, J=2.9 Hz, 1H, H-2), 3.46 (ddd, J=8.0 Hz, J=6.9 Hz, J=4.5 Hz, 1H, H-8a), 3.30 (ddd,
J=9.9 Hz, J=8.4 Hz, J=5.8 Hz, 1H, H-8b), 2.24 (ddd, J=13.8 Hz, J=2.5 Hz, J=2.2 Hz, 1H, H-5eq), 2.03
(ddd, J=13.8 Hz, J=12.0 Hz, J=2.8 Hz, 1H, H-5ax), 1.80 (m, 1H, H-3), 1.71 (ddd, J=14.1 Hz, J=5.8 Hz,
J=4.5 Hz, 1H, H-7a), 1.45 (dddd, J=14.1 Hz, J=8.4 Hz, J=6.9 Hz, J=2.9 Hz, 1H, H-7b), 0.88 (d, J=7.2
Hz, 3H, CH3), 0.86 (t, J=8.0 Hz, 9H, Si(CH2CH3)3), 0.42 (q, J=8.0 Hz, 6H, Si(CH2CH3)3); 13C NMR
(100 MHz, CDCl3, TMS) δ 138.20 (C, CAr), 136.71 (C, CPh), 133.71 (CH, p-CAr), 129.61 (CH, m-CAr),
128.66 (CH, m-CPh), 128.41 (CH, o-CAr), 127.66 (CH, p-CPh), 127.35 (CH, o-CPh), 88.04 (CH, C-6),
76.52 (CH, C-4), 72.52 (CH, C-2), 70.45 (CH2, CH2Ph), 59.07 (CH2, C-8), 35.74 (CH2, C-7), 35.25
(CH, C-3), 22.92 (CH2, C-5), 10.67 (CH3, CH3), 6.74 (CH3, Si(CH2CH3)3), 4.16 (CH2, Si(CH2CH3)3);
ν
max (CHCl3)/cm−1 2956, 2912, 2876, 1496, 1448, 1412, 1384, 1320, 1288, 1152, 1068, 1016, 968, 884,
588, 548; FAB: 505 (M++1, 9), 367 (8), 255 (100), 225 (29), 197 (6), 171 (6), 154 (12), 137 (16).

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R. Dunkel et al. / Tetrahedron: Asymmetry 10 (1999) 1539–1549
3.10. (2R,3R,4S,6S)-6-Benzenesulfonyl-4-benzyloxy-2-(2-triethylsilyloxy-ethyl)-3-methyl-tetrahydro-
pyran (+)-10 ax
[α]D20=+63.2 (c=0.5, CHCl3); 1H NMR (400 MHz, CDCl3, TMS) δ 7.92 (m, 2H, o-Ar), 7.65 (m, 1H,
p-Ar), 7.55 (m, 2H, m-Ar), 7.36–7.29 (m, 5H, Bn), 4.72 (d, J=11.5 Hz, 1H, CHHPh), 4.55 (dd, J=10.5
Hz, J=3.7 Hz, 1H, H-6), 4.45 (d, J=11.5 Hz, 1H, CHHPh), 4.28 (ddd, J=11.3 Hz, J=4.5 Hz, J=4.2 Hz,
1H, H-4), 3.41 (ddd, J=9.3 Hz, J=9.2 Hz, J=4.4 Hz, 1H, H-2), 3.30 (m, 2H, H-8), 2.59 (ddd, J =13.1 Hz,
J=4.2 Hz, J=4.0 Hz, 1H, H-5eq), 1.94 (m, 1H, H-3), 1.58 (m, 3H, H-5ax, H-7), 0.92 (d, J=6.7 Hz, 3H,
CH3), 0.90 (t, J=8.0 Hz, 9H, Si(CH2CH3)3), 0.50 (q, J=8.0 Hz, 6H, Si(CH2CH3)3).
3.11. (−)-(2R,3R,4S,6R)-2-(4-Benzyloxy-6-methoxy-3-methyl-tetrahydro-pyran-2-yl)-ethanol (−)-11
To a suspension of LiAlH4 (114 mg, 3 mmol) in E (10 ml) was added dropwise a solution of ester
(−)-6 (842 mg, 2.73 mmol) in E (5 ml) at rt and the mixture was stirred for 2 h. Water was added and
the precipitate was dissolved by addition of 2 N HCl. The aqueous layer was saturated with NaCl and
extracted with EA. The combined organic phase was dried (MgSO4) evaporated and purified by column
chromatography (E/PE) to afford (−)-11, 740 mg (97%), as a colorless oil, [α]D20=−7.9 (c=1, CHCl3).
1H NMR (400 MHz, CDCl3, TMS) δ 7.40–7.23 (m, 5H, Ph), 4.52 (dd, J=10 Hz, J=2 Hz, 1H, H-6), 4.54
(s, 2H, CH2Ph), 4.17 (ddd, J=10 Hz, J=3 Hz, J=2 Hz, 1H, H-4), 3.80 (m, 2H, H-8), 3.62 (dd, J=6 Hz,
J=3 Hz, 1H, H-2), 3.48 (s, 3H, OCH3), 2.4 (br. s, 1H, OH), 1.95 (m, 2H, H-7), 1.79 (m, 1H, H-3), 1.66
(ddd, J=13 Hz, J=10 Hz, J=3 Hz, 1H, H-5ax), 1.59–1.50 (m, 1H, H-5eq), 0.98 (d, J=7 Hz, 3H, CH3); 13
C
NMR (100 MHz, CDCl3, TMS) δ 138.55 (C, CPh), 128.43 (CH, o-CPh), 127.61 (C, p-CPh), 127.36 (CH,
m-CPh), 100.49 (CH, C-6), 78.53 (CH, C-2), 72.75 (CH, C-4), 70.49 (CH2, CH2Ph), 61.66 (CH2, C-8),
56.38 (CH3, OCH3), 35.42 (CH, C-3), 34.69 (CH2, C-7), 31.27 (CH2, C-5), 11.09 (CH3, CH3); νmax
(film)/cm−1 3420, 3028, 2960, 2936, 1496, 1388, 1192, 1144, 1092, 1044; MS: 280 (M+, 1), 177 (4), 148
(13), 119 (7), 91 (100), 81 (3), 65 (5); HR-MS calcd for C16H24O4 (M+) 280.1675, found 280.1686.
3.12. (−)-(2R,3R,4S,6R)-2-(4-Benzyloxy-6-methoxy-3-methyl-tetrahydropyran-2-yl)-ethyl-40 toluene-
sulfonic ester (−)-12
To a solution of alcohol (−)-11 (612 mg, 2.18 mmol) in DCM (6.5 ml) was added NEt3 (0.33 ml, 2.4
mmol) at rt and the mixture was stirred for 10 min. Then tosyl chloride (873 mg, 4.60 mmol) was added
in portions under a stream of N2. The reaction mixture was stirred overnight and then diluted with H2O
and acidified (dilute H2SO4). The aqueous layer was extracted with DCM, the combined organic phase
dried (MgSO4) and the solvent removed. The crude product was purified by column chromatography
1
(E/PE) to give (−)-12 (877 mg, 93%), crystals, mp 69°C, [α]D20=−6.67 (c=1, CHCl3). H NMR (400
MHz, CDCl3, TMS) δ 7.79 (d, J=5 Hz, 2H, Ar), 7.42–7.21 (m, 7H, Ar), 4.51 (m, 3H, CH2Ph, H-6),
4.27–4.09 (m, 2H, H-8), 4.01 (dd, J=11 Hz, J=2 Hz, 1H, H-2), 3.59 (dd, J=6 Hz, J=3 Hz, 1H, H-4), 3.34
(s, 3H, OCH3), 2.42 (s, 3H, Ar–CH3), 1.88 (m, 2H, H-7), 1.72 (m, 2H, H-5), 1.58 (m, 1H, H-3), 0.89
(d, J=7 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3, TMS) δ 144.67 (C, CAr), 138.55 (C, CPh), 133.15
(C, p-CAr), 129.83 (CH, o-CAr), 128.45 (CH, m-CAr), 127.93 (CH, o-CPh), 127.63 (CH, p-CPh), 127.40
(CH, m-CPh), 100.27 (CH, C-6), 78.42 (CH, C-2), 70.47 (CH2, CH2Ph), 68.44 (CH, C-4), 67.58 (CH2,
C-8), 56.2 (CH3, OCH3), 34.87 (CH, C-3), 32.00 (CH2, C-7), 31.43 (CH2, C-5), 21.60 (CH3, Ar–CH3),
10.81 (CH3, CH3); νmax (film)/cm−1 2960, 2900, 1496, 1464, 1388, 1356, 1176, 1148, 1096, 1048; MS
(140°C): 434 (M+, 2), 325 (1), 296 (3), 171 (5), 124 (7), 91 (100), 65 (6); HR-MS calcd for C23H30O6S
(M+) 434.1763, found 434.1767.

R. Dunkel et al. / Tetrahedron: Asymmetry 10 (1999) 1539–1549
1547
3.13. (−)-(2R,3R,4S,6R)-4-Benzyloxy-6-methoxy-3-methyl-2-pent-4-enyl-tetrahydropyran (−)-13
To a solution of tosylate (−)-12 (808 mg, 1.86 mmol) and a catalytic amount of HgCl2 in E (15 ml)
was added allylmagnesium bromide (7.44 ml, 7.44 mmol, 1 M solution in E) at −5°C. The mixture
was stirred for 1 h at the same temperature and then allowed to reach 5°C. After complete reaction the
mixture was hydrolyzed by the addition of dilute HCl. The aqueous layer was extracted with E and the
combined organic phase dried (MgSO4). After removal of the solvent the crude product was purified
by column chromatography (E/PE) to afford (−)-13, 437 mg (77%), as a colorless liquid, [α]D20=−10.6
(c=1, CHCl3). 1H NMR (400 MHz, CDCl3, TMS) δ 7.38–7.23 (m, 5H, Ph), 5.81 (m, 1H, H-10), 4.98 (m,
1H, H-11), 4.65 (dd, J=7 Hz, J=1 Hz, 1H, H-6), 4.55 (s, 2H, CH2Ph), 3.88 (m, 1H, H-2), 3.60 (dd, J=6
Hz, J=3 Hz, 1H, H-4), 3.49 (s, 3H, OCH3), 2.08 (m, 2H, H-9), 1.92 (d, J=12 Hz, 1H, H-5ax), 1.78 (m,
1H, H-3), 1.61 (m, 3H, H-7, H-5eq), 1.39 (m, 2H, H-8), 0.92 (d, J=7 Hz, 3H, CH3); 13C NMR (100 MHz,
CDCl3, TMS) δ 138.86 (CH, C-10), 138.74 (C, CPh), 128.41 (CH, m-CPh), 127.54 (CH, p-CPh), 127.32
(CH, m-CPh), 114.49 (CH2, C-11), 100.38 (CH, C-6), 78.92 (CH, C-2), 72.79 (CH, C-4), 70.41 (CH2,
CH2Ph), 56.25 (CH3, OCH3), 34.98 (CH, C-3), 33.78 (CH2, C-9), 31.82 (CH2, C-7), 31.58 (CH2, C-5),
25.53 (CH2, C-8), 10.9 (CH3, CH3); νmax (CHCl3)/cm−1 3064, 3028, 2936, 2860, 1640, 1496, 1452,
1344, 1192, 1096; MS: 304 (M+, 3), 196 (3), 177 (2), 148 (12), 91 (100), 81 (5), 65 (5); HR-MS calcd
for C19H28O3 (M+) 304.2038, found 304.2038.
3.14. (−)-(2R,3R,4S,6R)-4-Benzyloxy-6-methoxy-3-methyl-tetrahydropyran-2-yl)-butan-1-ol (−)-14
To a solution of (−)-13 (420 mg, 1.38 mg) in THF:H2O (12 ml, 3:1) were added a few drops of OsO4
(2.5% in t-BuOH), and the mixture was stirred for 1 h. Then NaIO4 (650 mg, 3.04 mmol) was added
in portions and the resulting mixture was stirred overnight. Water was added and the aqueous layer was
extracted with E. The combined organic phase was dried (MgSO4), and the solvent was removed. The
crude aldehyde was dissolved in E. To this solution was added a solution of NaBH4 (57.4 mg, 1.52 mmol)
in EtOH (3 ml) at −78°C. After 1 h at the same temperature water was added carefully. The aqueous layer
was extracted with EA, the combined organic phase dried (MgSO4) and the solvent evaporated. The crude
product was purified by column chromatography (E/PE) to afford (−)-14 (242 mg, 57%), as a colorless
oil, [α]D20=−11.9 (c=1, CHCl3). 1H NMR (400 MHz, CDCl3, TMS) δ 7.42–7.23 (m, 5H, Ph), 4.65 (dd,
J=9 Hz, J=2 Hz, 1H, H-6), 4.53 (s, 2H, CH2Ph), 3.89 (m, 1H, H-4), 3.65 (m, 2H, H-10), 3.61 (dd, J=6
Hz, J=3 Hz, 1H, H-2), 3.50 (s, 3H, OCH3),1.92 (d, J=12 Hz, 1H, H-5ax), 1.78 (q, J=7 Hz, 1H, H-3),
1.75–1.51 (m, 6H, H-9, H-7, H-5eq, OH), 1.40 (m, 2H, H-8), 0.93 (d, J=7 Hz, 3H, CH3); 13C NMR (100
MHz, CDCl3, TMS) δ 138.72 (C, CPh), 128.41 (CH, o-CPh), 127.55 (CH, p-CPh), 127.33 (CH, m-CPh),
100.42 (CH, C-6), 78.88 (CH, C-2), 72.9 (CH, C-4), 70.42 (CH2, CH2Ph), 62.84 (CH2, C-10), 56.30
(CH2, C-11), 35.01 (CH, C-3), 32.72 (CH2, C-7), 32.06 (CH2, C-9), 31.55 (CH2, C-5), 22.43 (CH2,
C-8), 10.9 (CH3, CH3); νmax (film)/cm−1 3420, 2936, 2864, 1452, 1388, 1192, 1144, 1092, 1048; MS
(60°C): 217 (M+−C7H7, 2), 199 (2), 184 (2), 148 (11), 119 (5), 91 (100), 85 (7), 77 (2), 71 (6), 65 (5);
HR-MS calcd for C18H28O4 (M+) 308.1988, found 308.1983.
3.15. (−)-(2R,3R,4S,6R)-4-Benzyloxy-6-methoxy-2-(4-methoxy-butyl)-3-methyl-tetrahydropyran
(−)-15
To a solution of alcohol (−)-14 (200 mg, 0.65 mmol) in THF (1 ml) was added NaH (58.4 mg, 1.95
mmol, 80% in mineral oil) portionwise under a stream of N2. After 5 min MeI (0.81 ml, 13 mmol)
was added. The mixture was stirred overnight and then diluted with E. The organic phase was washed
with an NaHCO3 solution (twice). The combined aqueous layer was extracted with DCM, and the
combined organic phase dried (MgSO4). After removal of the solvent the crude product was purified

1548
R. Dunkel et al. / Tetrahedron: Asymmetry 10 (1999) 1539–1549
by column chromatography (E/PE) to afford (−)-15 (127 mg, 60%), as a colorless liquid, [α]D20=−13.0
(c=1, CHCl3). 1H NMR (400 MHz, CDCl3, TMS) δ 7.43–7.23 (m, 5H, Ph), 4.65 (dd, J=10 Hz, J=2 Hz,
1H, H-6), 4.55 (s, 2H, CH2Ph), 3.89 (m, 1H, H-2), 3.61 (dd, J=6 Hz, J=3 Hz, 1H, H-4), 3.50 (s, 3H,
OCH3), 3.38 (m, 2H, H-10), 3.33 (s, 3H, OCH3), 1.92 (d, J=10 Hz, 1H, H-5ax), 1.80 (q, J=7 Hz, 1H,
H-3), 1.70–1.48 (m, 5H, H-9, H-7, H-5eq), 1.39 (m, 2H, H-8), 0.93 (d, J=7 Hz, 3H, CH3); 13C NMR (100
MHz, CDCl3, TMS) δ 138.74 (C, CPh), 128.4 (CH, o-CPh), 127.52 (CH, p-CPh), 127.32 (CH, m-CPh),
100.38 (CH, C-6), 78.88 (CH, C-2), 72.86 (CH, C-4), 72.77 (CH2, C-10), 70.39 (CH2, CH2Ph), 58.52
(CH3, OCH3), 56.27 (CH3, OCH3), 34.91 (CH, C-3), 32.16 (CH2, C-7), 31.58 (CH2, C-5), 29.62 (CH2
C-9), 22.75 (CH2, C-8), 10.88 (CH3, CH3); νmax (film)/cm−1 2936, 2864, 2756, 1496, 1452, 1388, 1192,
1144, 1116, 1096, 1048; MS: 322 (M+, 1), 263 (1), 182 (6), 148 (13), 119 (7), 91 (100), 79 (5), 77 (3),
72 (12), 65 (5); HR-MS calcd for C19H30O4 (M+) 322.2144, found 322.2146.
3.16. Triphenylphosphonium tetraflouroborate salt 16
A solution of (−)-15 (50 mg, 0.16 mmol) and Ph3PHBF4 (54.2 mg, 0.16 mmol) in MeCN (1.5
ml) was heated to reflux for 30 min. The mixture was cooled to rt and diluted with E. The solvent
was removed and the residue dried (oil pump). The crude product was dissolved in CHCl3 and then
crystallized by the addition of E. The white precipitate was washed with E and dried (oil pump) to
1
afford 16 (91 mg, 89%), as a white foam, mp 54°C. H NMR (400 MHz, CDCl3, TMS) δ 7.98–7.62
(m, 15H, Ph3P), 7.39–7.16 (m, 5H, Ph), 5.90 (dd, J=10 Hz, J=3 Hz, 1H, H-6), 4.62 (d, J=12 Hz,
1H, CHHPh), 4.33 (d, J=12 Hz. 1H, CHHPh), 4.03–3.84 (m, 2H, H-4, H-2), 3.43–3.17 (m, 5H,
OCH3, H-10), 2.25 (m, 1H, H-5), 2.06 (m, 1H, H-5), 1.90 (m, 1H, H-3), 1.71–1.17 (m, 6H, H-9, H-
8, H-7), 0.96 (d, J=7 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3, TMS) δ 138.56 (C, CPh), 138.09
(C, CBu), 135.18/134.61/134.52/133.84/133.75/130.72/130.69/130.36/130.24/128.53/128.29 (CH, CPh),
81.98 (CH, C-2), 75.43 (CH, C-6), 74.02 (CH, C-4), 72.44 (CH2, CH2Ph), 72.20 (CH2, C-10), 71.98
(CH2, CH2Ph), 58.42 (CH3, OCH3), 40.64 (CH, C-3), 32.41 (CH2, C-7), 31.32 (CH2, C-5), 28.85 (CH2
C-9), 22.98 (CH2, C-8), 13.74 (CH3, CH3); νmax (KBr)/cm−1 2932, 2868, 1440, 1112, 1060; FAB: 553
(M+−BF4, 91), 445 (32), 289 (7), 263 (37), 262 (Ph3P, 34), 183 (16), 133 (100).
Acknowledgements
We thank Deutsche Forschungsgemeinschaft (Graduiertenkolleg Chemische und technische Grundla-
gen der Naturstofftransformation) for a PhD fellowship (R.D.), the Fonds der chemischen Industrie for
financial support and Ulrike Eggert for her help.
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