Iodine-catalyzed highly diastereoselective synthesis of trans-2,6-disubstituted-3,4-dihydropyrans: Application to concise construction of C28-C37 bicyclic core of (H-)-sorangicin A

Article abstract of DOI:10.1002/chem.200902999

A novel iodine-catalyzed highly diastereoselective synthesis of trans-2,6disubstituted-3,4-dihydropyrans have been achieved from o-hydroxy-unsaturated aldehydes by treating with allyltrimethyl silane in THF at room temperature with good to excellent yields. This methodology has been successfully implemented for a concise asymmetric synthesis of C28-C37 dioxabicyclo[3.2.1]octane ring system of (+)-sorangicin A in 8 steps with 21 % overall yield.

Full text of DOI:10.1002/chem.200902999

DOI: 10.1002/chem.200902999
Iodine-Catalyzed Highly Diastereoselective Synthesis of trans-2,6-
Disubstituted-3,4-Dihydropyrans: Application to Concise Construction of
C28–C37 Bicyclic Core of (+)-Sorangicin A
Debendra K. Mohapatra,*[a] Pragna P. Das,[a] Manas Ranjan Pattanayak,[a, b] and
J. S. Yadav*[a]
Abstract: A novel iodine-catalyzed highly diastereoselective synthesis of trans-2,6-
disubstituted-3,4-dihydropyrans have been achieved from d-hydroxy a,b-unsaturat-
Keywords: asymmetric synthesis ·
ed aldehydes by treating with allyltrimethyl silane in THF at room temperature
iodine · oxygen heterocycles · sor-
with good to excellent yields. This methodology has been successfully implemented
angicin A
for a concise asymmetric synthesis of C28–C37 dioxabicycloACTHNUTRGNEU[GN 3.2.1]octane ring
system of (+)-sorangicin A in 8 steps with 21% overall yield.
Introduction
synthetically useful intermediates in the preparation of poly-
substituted tetrahydropyran ring system such as those found
in the pseudomonic acid.[10] Due to the remarkable rich
array of functionalities and chiral centers that these hetero-
cycles can incorporate, their stereoselective synthesis has
become a continuous challenge for synthetic organic chem-
ists. Several approaches have been reported for the prepara-
tion of dihydropyrans and among them varied methodolo-
gies include electrophile-initiated alkylation of glycals,[11]
hetero-Diels–Alder cycloadditions,[12] ring-closing metathe-
sis,[13] Prins cyclizations,[14] metal halide induced cycliza-
tion,[15] and an intramolecular silyl-modified Sakurai reac-
tion (ISMS).[16]
Many of these methods require long reaction times, stoi-
chiometric use of expensive reagents, harsh reaction condi-
tions, and some time gives poor yield and selectivity. To
avoid the above limitations, we have to search for a catalyst
with high catalytic activity, easy availability, short reaction
time, environment friendly and simple work-up procedure.
Molecular iodine[17] attracted our attention as recently it has
attained considerable importance in organic synthesis be-
cause of low cost, nontoxic nature, ready availability, envi-
ronment-friendly, easy handling, high efficiency for various
organic transformations to the corresponding products in ex-
cellent yields with high diastereoselctivity. Since it has been
used as a mild Lewis acid[18] catalyst for the activation of
carbonyl compounds, including acetalization reactions, we
envisaged that iodine could catalyze the reaction for the for-
mation of 2,6-disubstituted-3,4-dihydropyrans starting from
d-hydroxy a,b-unsaturated aldehydes.
Heterocyclic compounds are broadly distributed in nature,
and constitute an integral component of several polyketides,
adding a significant degree of conformational rigidity in nat-
ural products and thus likely to be critical to the pharmaco-
phore of biological activity. Among them, 2,6-disubstituted
dihydropyrans, are probably one of the most common struc-
tural motifs spread across various natural products, from
simple glucose to structurally complex secondary metabo-
lites such as luminaolide;[1] leucascandrolide A;[2] aspergilli-
de A, B, and C;[3] misakinolides;[4] phorboxazole;[5] laulima-
lide;[6] swinholides;[7] scytophycins;[8] and even more elabo-
rated architectures present in polytoxins, maitotoxins, and
other marine derived natural products[9] (see also Figure 1.
compounds 1–7). 2,6-Disubstituted dihydropyrans are also
[a] Dr. D. K. Mohapatra, P. P. Das, M. R. Pattanayak, Dr. J. S. Yadav
Organic Chemistry Division-I
Indian Institute of Chemical Technology
Council of Scientific & Industrial Research (CSIR)
Habsiguda, Uppal Road, Hyderabad-500007 (India)
Fax : (+91)40-27160512
E-mail: mohapatra@iict.res.in
yadavpub@iict.res.in
[b] M. R. Pattanayak
Indian Institute of Chemical Technology
An Associate Institution of University of Hyderabad
Hyderabad 500 046 (India)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902999.
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Chem. Eur. J. 2010, 16, 2072 – 2078

FULL PAPER
periments. No cis-diastereomer
was detected in the 1H NMR
spectrum of the crude product
obtained from the C-allylation
of d-hydroxy a,b-unsaturated
aldehydes. The reaction was in-
complete even after 48 h of stir-
ring at room temperature. To
optimize the reaction condi-
tions, screening was performed
on several parameters, such as
solvents, temperature, and cata-
lyst concentration. Initially, the
reaction was performed in dif-
ferent solvent systems (CH2Cl2,
TBME, THF) at room tempera-
ture with 5 mol% of iodine;
THF was found to be superior
to other solvents. Next, the re-
action was examined carefully
under reflux conditions which
led to an intractable mixture of
products. The experiment was
also conducted carefully under
the influence of different con-
centrations of the catalyst at
Figure 1. A few natural products bearing 2,6-disubstituted-3,4-dihydropyran moiety.
Herein, we report our research on the use of iodine as a
catalyst for the construction of trans-2,6-disubstituted-3,4-di-
hydropyran under neutral reaction conditions and demon-
strated the application of this protocol for a concise synthe-
sis of C28–C37 bicyclic ether core of (+)-sorangicin A.
room temperature with THF as solvent. The use of
10 mol% molecular iodine (based on d-hydroxy a,b-unsatu-
rated aldehyde) gave the best result with a yield of 90%
after 45 min of reaction. Increasing the iodine concentra-
tions did not help in improving the yield and reduction of
reaction time. However, no reaction was observed in ab-
sence of iodine even after a long time (48 h).
Results and Discussion
To investigate the scope and generality of the present
method, a diverse range of hydroxyl–enals with different
protecting groups afforded corresponding trans-2,6-disubsti-
tuted-3,4-dihydropyrans in good to excellent yields
(Table 1). The formation of compound 11i was reported ear-
lier by Isobe et al.[21a] and Danishefsky et al.[21b] by means of
the Hosomi–Sakurai reaction affording a mixture of a and
b-isomers in 16:1 ratio. In our case we obtained exclusively
one isomer, which was confirmed by spectral and analytical
data. It is worth mentioning here that almost all the protect-
ing groups were compatible to the reaction conditions.
To explain the formation of the trans-2,6-disubstituted-
3,4-dihydropyran following catalytic pathways, we postulat-
ed that the product was generated with activation of alde-
hyde by in-situ formation of TMSI and subsequent forma-
tion of an oxonium intermediate in which the stereoelec-
tronic and/or steric factors dictate the direction of the in-
coming nucleophile (Scheme 2). To test the viability of the
proposed reaction pathways, we conceived that the reaction
of a d-hydroxy a,b-unsaturated aldehyde in presence of cat-
alytic amount of trimethylsilyliodide (TMSI) should gener-
ate the corresponding trans-2,6-disubstituted-3,4-dihydropyr-
an. Pleasingly, when 10 mol% of TMSI was added instead
of molecular iodine at room temperature, the reaction com-
Initially, we investigated the effect of 5 mol% iodine on the
conversion of 10, which was prepared in two steps[19,20] start-
ing from 8 (via intermediate 9) in good yield, with allyltri-
methyl silane in CH3CN at room temperature to obtain 11.
After 12 h at room temperature, the reaction afforded the
expected trans-2,6-disubstituted-3,4-dihydropyran 11 in 42%
1
yield (Scheme 1). The H and 13C NMR of the product re-
vealed a single diastereomer. The stereochemistry of the
product 11 was assigned by comparing the 1H NMR data
with known tetrahydropyran derivatives as well as NOE ex-
Scheme 1. Synthesis of 2,6-disubstituted-3,4-dihydropyran moiety using
iodine as catalyst.
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D. K. Mohapatra, J. S. Yadav et al.
dosuccinimide (NIS)[23] failed to produce the desired
product.
Table 1. Iodine-catalyzed synthesis of trans-2,6-disubstituted-3,4-dihydro-
pyrans.
Product[a]
Solvent
THF
t [min]
Yield [%][b]
96
To demonstrate the applicability and generality of our
method to complex biologically active natural products syn-
theses, we were interested in targeting the C28–C37 bicyclic
ether core 13 of marine macrolactone (+)-sorangicin A
(12).[24] The first elegant synthesis of the novel C28–C37 bi-
cyclic ether fragment of 12 was achieved by Smith et al.[24e]
and later on by Crimmins et al.[24c] As shown in Scheme 3,
we envisioned that 13 would be synthesized from 11j, which
in turn could be prepared from d-hydroxy a,b-unsaturated
aldehyde 17. Compound 17 could be achieved starting com-
mercially available benzyloxyacetaldehyde.
1
2
45
THF
THF
THF
30
60
30
88
94
93
3
4
5
6
7
8
9
THF
THF
THF
THF
THF
45
40
45
30
45
84
91
90
87
90
10
THF
30
92
[a] Single diastereomeric product was confirmed by 1H and 13C NMR
spectroscopy. [b] Isolated yields after purification on silica gel.
Scheme 3. Retrosynthetic analysis of (+)-sorangicin A.
We initiated the synthesis of 13 with a known secondary
alcohol 16, which was obtained through asymmetric crotyla-
tion of commercially available benzyloxyacetaldehyde in
96% ee under conditions originally developed by Brown
and Bhat.[25] In order to obtain the unsaturated aldehyde 17,
a
cross-metathesis (CM)[20] between 16 and acrolein
(6.0 equiv) was achieved using Hoveyda–Grubbs catalyst
16a (10 mol%) in CH2Cl2 at room temperature for 24 h af-
forded the required aldehyde 17 in 84% yield (Scheme 4).
On treatment of 17 with 10 mol% molecular iodine in THF
at room temperature gave the
trans-2,6-disubstituted-3,4-dihy-
dropyran 11j in 90% yield.
One-step conversion of termi-
nal olefin to aldehyde 18 was
Scheme 2. Possible catalytic pathways for the formation of the product.
achieved by modified dihy-
droxylation followed by oxida-
pleted in 10 min, which strongly supported our proposed
tive cleavage of the diol in
mechanism. Other reagents such as NaI/TMSCl[22] and N-io-
80% yield over two steps.[26]
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Chem. Eur. J. 2010, 16, 2072 – 2078

Asymmetric Synthesis
FULL PAPER
Conclusion
In conclusion, we have de-
scribed an efficient protocol for
the synthesis of trans-2,6-disub-
stituted-3,4-dihydropyran,
which is an essential core for a
number of complex natural
products, from d-hydroxy a,b-
unsaturated aldehyde and allyl-
trimethylsilane in
a
highly
regio- and stereoselective
manner. We have also demon-
strated the broad scope of the
protocol to the construction of
C28–C37 fragment of (+)-sor-
angicin A in 8 steps with 21%
overall yield. Further applica-
Scheme 4. Synthesis of C28-C37 fragment of (+)-sorangicin A.
tions and extensions of the
methodology are currently on-
going in our laboratory and will be reported in due time.
Table 2. Iodo-etherification under different reaction conditions.
Reagent[a]
Solvent
T
t [h]
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
I2
I2
I2
I2
I2
I2
CH2Cl2
THF
CH3CN
CH2Cl2
THF
CH3CN
CH2Cl2
THF
CH3CN
CH2Cl2
THF
RT
RT
RT
reflux
reflux
reflux
RT
RT
RT
RT
RT
RT
RT
72
72
72
2
1
1
72
72
72
24
24
24
24
12
10
11
15
decomp
decomp
decomp
15
18
28
21
34
81
0
Experimental Section
General methods: Air and/or moisture sensitive reactions were carried
out in anhydrous solvents under an atmosphere of argon in an oven/
flame-dried glassware. All anhydrous solvents were distilled prior to use:
THF, toluene, and tert-butyl methyl ether from Na and benzophenone;
CH2Cl2, DMSO from CaH2; MeOH from Mg cake. Commercial reagents
were used without purification. Column chromatography was carried out
by using Spectrochem silica gel (60–120 mesh). Specific optical rotations
[a]D are given in 10À1 8cm2 gÀ1. Infrared spectra were recorded in CHCl3/
I2, NaHCO3
I2, NaHCO3
I2, NaHCO3
NIS
NIS
NIS
CH3CN
PMHS
THF
neat (as mentioned) and reported in cmÀ1 1H and 13C NMR chemical
.
NIS
PhSeCl, DIEA
À788C
0
shifts are reported in ppm downfield from tetramethylsilane and coupling
constants (J) are reported in Hz. The following abbreviations are used to
designate signal multiplicity: s=singlet, d=doublet, t=triplet, q=quar-
tet, m=multiplet, br=broad.
[a] Stoichiometric amount was taken. [b] Isolated yields after purification
on silica gel.
General procedure for iodo cyclization: Iodine (0.1 mmol) was added to
a stirred solution of d-hydroxyl a,b-unsaturated aldehyde (1.0 mmol) and
allyltrimethyl silane (2.0 mmol) in THF (3 mL) at 08C and allowed to
come to room temperature. After completion of the reaction (as indicat-
ed by TLC; 30–60 min), the reaction mixture was quenched with saturat-
ed solution of NaHSO3 (3 mL). The reaction mixture was extracted with
tert-butyl methyl ether (TBME) (2ꢂ10 mL), combined organic layer was
dried over anhydrous Na2SO4 and concentrated under reduced pressure
to give a pale yellow oil, which was purified by silica gel column chroma-
tography using 2–5% ethyl acetate/hexane as eluent to obtain 84–96% of
isolated yield of the cyclized product.
Direct catalytic asymmetric a-aminoxylation of the resulting
aldehyde by using enantiopure proline as the catalyst and
nitrosobenzene as the oxygen source and in situ reduction
gave the 1,2-diol 19 in 61% yield over three steps.[27]
Selective protection of the primary hydroxyl group as its
tert-butyldiphenylsilyl (TBDPS) ether yielded 20 in 92%
yield. The C36 stereogenic center was confirmed by modi-
fied Mosherꢁs method.[28] Treatment of 20 with different
iodine source (Table 2) gave unsatisfactory results except
with NIS/CH3CN,[29] which furnished the corresponding
iodo-ether derivative 21 as a single regio-isomer in excellent
yield (95%). De-iodination was achieved smoothly by treat-
ment of 21 with Bu3SnH and azobisisobutyronitrile (AIBN)
in toluene under reflux conditions to obtain 13 in 94%
yield.[30] The product was confirmed by 1H, 13C NMR and
HRMS data. The stereochemistry of the advanced inter-
mediate was ascertained by NOE experiments.
Data for 11: [a]2D5 =+103 (c 0.33 in CHCl3); IR (KBr, neat): n˜ =3450,
2922, 2853, 1640, 1613, 1512, 1461, 1363, 1300, 1247, 1177, 1090, 1036,
913, 821, 772, 709 cmÀ1 1H NMR (300 MHz, CDCl3): d=7.27 (d, J=
;
8.5 Hz, 2H), 6.87 (d, J=8.7 Hz, 2H), 5.94–5.79 (m, 2H), 5.72 (m, 1H),
5.15–5.03 (m, 2H), 4.51 (q, J=11.7, 15.3 Hz, 2H), 4.24 (m, 1H), 3.96 (m,
1H), 3.80 (s, 1H), 3.55 (m, 1H), 3.45 (m, 1H), 2.45 (m, 1H), 2.28 (m,
1H), 2.05–1.98 ppm (m, 2H); 13C NMR (75 MHz, CDCl3): d=156.0,
134.8, 129.2, 129.1, 123.8, 116.9, 113.7, 130.5, 73.0, 72.2, 72.3, 67.2, 55.2,
38.9, 27.1 ppm; ESI-HRMS: m/z calcd for C17H22O3 [M+Na]+: 297.1466;
found: 297.1465.
Data for 11b: [a]2D5 =+14.2 (c 0.8 in CHCl3); IR (KBr, neat): n˜ =3482,
2925, 2857, 1729, 1612, 1513, 1459, 1367, 1300, 1247, 1178, 1091, 1037,
914, 820, 723 cmÀ1 1H NMR (300 MHz, CDCl3): d=7.27 (d, J=8.5 Hz,
;
2H), 6.87 (d, J=8.5 Hz, 2H), 5.86 (m, 1H), 5.70–5.59 (m, 2H), 5.16–5.00
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D. K. Mohapatra, J. S. Yadav et al.
(m, 2H), 4.45–4.38 (m, 2H), 4.16 (m, 1H), 3.81–3.74 (m, 3H), 3.62 (m,
1H), 3.57–3.46 (m, 3H), 3.36–3.26 (m, 3H), 2.41 (m, 1H), 2.26 (m, 1H),
2.00–1.66 (m, 4H), 1.53 (m, 1H), 0.97 ppm (d, J=7.2 Hz, 3H); 13C NMR
(75 MHz, CDCl3): d=159.0, 135.2, 131, 130.6, 129.2, 127.9, 116.7, 113.7,
74.8, 72.6, 71.5, 71.0, 66.5, 57.0, 55.2, 38.8, 38.8, 34.2, 34.0, 18.0 ppm; ESI-
HRMS: m/z calcd for C22H32O4 [M+Na]+: 383.2198; found: 383.2195.
132.8, 123.6, 117.5, 71.3, 69.7, 64.9, 62.8, 37.8, 21.0, 20.7 ppm; ESI-HRMS:
m/z calcd for C13H18O5 [M+H]+: 254.1152; found: 254.1155.
Data for 11j: [a]2D5 =+6.2 (c 0.51 in CHCl3); IR (KBr, neat): n˜ =3448,
2924, 1855, 1729, 1640, 1454, 136, 1100 cmÀ1
;
1H NMR (300 MHz,
CDCl3): d=7.4–7.25 (m, 5H), 5.88 (m, 1H), 5.65 (q, J=10.4, 16.8 Hz,
2H), 5.15–5.04 (m, 2H), 4.59 (q, J=12.3, 18.9 Hz, 2H), 4.23 (m, 1H),
3.60 (d, J=4.3 Hz, 2H), 3.53 (m, 1H), 2.42 (m, 1H), 2.27 (m, 2H),
0.96 ppm (d, J=7.0 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=138.5,
134.9, 130.7, 128.3, 128.0, 127.6, 127.5, 116.9, 74.1, 73.3, 71.7, 70.8, 38.9,
30.2, 17.9 ppm; ESI-HRMS: m/z calcd for C17H22O2 [M+Na]+:
258.16198; found: 258.16208.
Data for 11c: [a]2D5 =+111 (c 0.73 in CHCl3); IR (KBr, neat): n˜ =3500,
2922, 2853, 1641, 1455, 1365, 1104, 997, 738, 697 cmÀ1
;
1H NMR
(300 MHz, CDCl3): d=7.31–7.21 (m, 5H), 5.94–5.85 (m, 2H), 5.78 (m,
1H), 5.11–5.00 (m, 2H), 4.47 (m, 2H), 4.17 (m, 1H), 4.00 (dt, J=3.8,
9.8 Hz, 1H), 3.64–3.43 (m, 5H), 2.34 (m, 1H), 2.19 (m, 1H), 1.96–1.81
(m, 2H), 1.17 ppm (t, J=6.7 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=
138.5, 134.7, 132.6, 128.3, 127.6, 127.5, 124.6, 116.9, 72.9, 71.5, 70.6, 68.5,
67, 64.3, 37.3, 29.9, 15.5 ppm; ESI-HRMS: m/z calcd for C19H26O3
[M+Na]+: 325.1779; found: 325.1772.
Data for 11k: [a]2D5 =À20.4 (c 1.9 in CHCl3); IR (KBr, neat): n˜ =3445,
2920, 2843, 1641, 1610, 1505, 1450, 1358, 1310, 1240, 1172, 1091, 1040,
909, 825, 770, 712 cmÀ1 1H NMR (300 MHz, CDCl3): d 7.22 (d, J=
;
8.5 Hz, 2H), 6.84 (d, J=8.7 Hz, 2H), 5.89–5.75 (m, 2H), 5.68 (m, 1H),
5.11–5.01 (m, 2H), 4.41 (s, 2H), 4.16 (m, 1H), 3.85 (m, 1H), 3.79 (m,
3H), 3.62–3.48 (m, 2H), 2.38 (m, 1H), 2.22 (m, 1H), 1.99–1.91 (m, 2H),
1.8–1.72 ppm (m, 2H); 13C NMR (75 MHz, CDCl3): d=159.2, 135.2,
130.7, 129.3, 129.2, 124.4, 116.7, 113.8, 72.7, 72.3, 66.6, 64.9, 55.2, 38.8,
35.6, 30.7 ppm; ESI-HRMS: m/z calcd for C18H24O3 [M+H]+: 288.1725;
found: 288.1731.
Data for 11d: [a]2D5 =À34.1 (c 0.28 in CHCl3); IR (KBr, neat): n˜ =3450,
2923, 2852, 1726, 1640, 1459, 1375, 1215, 1164, 1084, 1015, 731 cmÀ1
;
1H NMR (300 MHz, CDCl3): d=6.11–6.01 (m, 2H), 5.98 (d, J=3.8 Hz,
1H), 5.84 (m, 1H), 5.18–5.09 (m, 2H), 4.59 (d, J=3.8 Hz, 1H), 4.36 (m,
1H), 4,27 (m, 1H), 4.14 (d, J=2.5 Hz, 1H), 2.14 (m, 1H), 2.29 (m, 1H),
1.52 (s, 3H), 1.33 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d=134.8,
133.9, 120.7, 117.6, 111.4, 105.3, 84.7, 73.5, 72.3, 70.2, 37.0, 26.7, 26.1 ppm;
ESI-HRMS: m/z calcd for C13H18O4 [M+Na]+: 261.1102; found:
261.1105.
AHCTUNGTERG(NNUN 2R,3R)-1-(Benzyloxy)-3-methylpent-4-en-2-ol (16): E-2-Butene (5 mL,
excess) was added through a cannula to a stirred suspension of KOtBu
(2.5 g, 21.85 mmol) in THF (50 mL) at À788C, followed by the drop wise
addition of nBuLi (15.0 mL, 1.45m in hexane, 21.75 mmol). The reaction
suspension was slowly warmed to À458C stirred at this temperature for
15 min and then cooled to À788C. A solution of (+)-B-methoxydiisopi-
nocampheylborane (7.9 g, 24.95 mmol) in diethyl ether (20 mL) was then
added through a cannula over a 15 min period. Stirring was continued for
10 min and boron trifluoride diethyl ether (3.8 mL, 30.0 mmol) added,
followed by addition of a pre-cooled solution of 8 (2.34 mL, 16.65 mmol)
in diethyl ether (15 mL). After completion of the reaction (checked by
TLC), the reaction mixture was warmed to 08C and quenched with 2.5m
aqueous solution of NaOH (14 mL) and aqueous solution of hydrogen
peroxide (3.75 mL, 33.0 mmol). The reaction mass was refluxed for 1 h.
The reaction mixture was then cooled to room temperature, the organic
phase separated and washed with Na2SO3 (75 mL). The aqueous layer
was extracted with ethyl acetate (3ꢂ50 mL), the combined organic layer
dried over Na2SO4 and concentrated under reduced pressure. The crude
product was purified by silica gel column chromatography using 6–8%
ethyl acetate/hexane as eluent to obtain 16 (2.8 g, 82%) as a colorless
liquid. 1H NMR (300 MHz, CDCl3): d=7.34–7.26 (m, 5H), 5.81 (m, 1H),
5.08–4.09 (m, 2H) 4.53 (s, 2H), 3.63 (m, 1H), 3.47 (dd, J=3.2, 9.4 Hz,
1H) 3.37 (dd, J=7.5, 9.2 Hz, 1H), 2.32 (m, 1H), 1.04 ppm (d, J=6.7 Hz,
3H); 13C NMR (75 MHz, CDCl3): d=140.0, 137.9, 129.5, 128.4, 127.7,
115.5, 73.5, 73.3, 72.5, 40.7, 16.1 ppm.
Data for 11e: [a]2D5 =+90.1 (c 0.52 in CHCl3); IR (KBr, neat): n˜ =3480,
2920, 2848, 1645, 1450, 1370, 1112, 997, 739, 702 cmÀ1
;
1H NMR
(300 MHz, CDCl3): d=7.32–7.21 (m, 5H), 5.98–5.85 (m, 2H), 5.79 (m,
1H), 5.11–5.00 (m, 2H), 4.48 (m, 2H), 4.17 (t, J=6.0 Hz, 1H), 4.0 (m,
1H), 3.64–3.50 (m, 3H), 3.35 (s, 3H), 2.35 (m, 1H), 2.20 (m, 1H), 1.93–
1.81 ppm (m, 2H); 13C NMR (75 MHz, CDCl3): d=144.2, 143.7, 138.1,
133, 129.6, 128.4, 127.7, 124.4, 84, 73.2, 71.7, 67.8, 60.6, 57.6, 32.3,
14.2 ppm; ESI-HRMS: m/z calcd for C18H24O3 [M+Na]+: 288.1723;
found: 325.1775.
Data for 11 f: [a]2D5 =À23.7 (c 0.72 in CHCl3); IR (KBr, neat): n˜ =3100,
2922, 2853, 1640, 1731, 1513, 1464, 1429, 1360, 1247, 1120, 1036, 990, 825,
770, 712 cmÀ1 1H NMR (300 MHz, CDCl3): d=7.71–7.67 (m, 4H), 7.42–
;
7.34 (m, 6H), 7.17 (d, J=8.7 Hz, 2H), 6.80 (d, J=8.8 Hz, 2H), 5.91–5.89
(m, 2H), 5.81 (m, 1H), 5.06 (m, 1H), 5.01 (m, 1H), 4.51 (q, J=11.7,
18.5 Hz, 2H), 4.24 (m, 1H), 3.98–3.80 (m, 3H), 3.79 (m, 3H), 2.34 (m,
1H), 2.20 (m, 1H), 1.07 ppm (s, 9H); 13C NMR (75 MHz, CDCl3): d=
166.8, 135.6, 135.2, 134.9, 134.5, 133.7, 129.6, 127.5, 123.6, 117.1, 72.3,
72.1, 69.7, 62.4, 56.6, 37.3, 26.9, 14.3 ppm; ESI-HRMS: m/z calcd for
C33H40O4Si [M+H]+: 528.2690; found: 528.2693.
Data for 11g: [a]2D5 =À24.4 (c 1.5 in CHCl3); IR (KBr, neat): n˜ =3070,
2925, 2855, 1731, 1464, 1429, 1255, 1189, 1107, 998, 830, 740, 702 cmÀ1
;
1H NMR (300 MHz, CDCl3): d=7.73–7.67 (m, 4H), 7.45–7.34 (m, 6H),
6.04 (m, 1H), 5.94 (m, 1H), 5.82 (m, 1H), 5.11–5.01 (m, 2H), 4.25 (m,
1H), 3.95–3.86 (m, 2H), 3.79 (m, 1H), 3.68 (m, 1H), 3.36 (s, 1H), 2.37
(m, 1H), 2.22 (m, 1H), 1.07 ppm (m, 9H); 13C NMR (75 MHz, CDCl3):
d=135.6, 134.9, 134.5, 133.7, 129.6, 127.6, 123.6, 117.1, 72.3, 72.1, 69.7,
62.4, 56.6, 37.3, 26.9,19.3 ppm; ESI-HRMS: m/z calcd for C26H34O3Si
[M+H]+: 422.2275; found: 422.2279.
AHCTUNGERTG(NNUN 4R,5R)-6-(Benzyloxy)-5-hydroxy-4-methylhex-2-enal (17): Hoveyda–
Grubbs catalyst 16a (288 mg, 0.48 mmol) and acrolein (2.80 g,
49.0 mmol) were added to a solution of 16 (1.0 g, 4.85 mmol) in CH2Cl2
(8 mL) and the resulting mixture was stirred at room temperature for
overnight. After concentration, the crude oil was purified by flash chro-
matography on silica gel using 3–5% ethyl acetate: hexane to afford 17
(961 mg, 84%) as a colorless liquid.
Data for 11h: [a]2D5 =À42 (c 0.32 in CHCl3); IR (KBr, neat): n˜ =3110,
2-[(2S,5R,6R)-6-(benzyloxymethyl)-5-methyl-5,6-dihydro-2H-pyran-2-
yl]acetaldehyde (18): 2,6-Lutidine (3.6 mL, 31.0 mmol) was added to a
stirred solution of 11j (2.0 g, 7.75 mmol) in 1,4-dioxane (25 mL). NaIO4
(6.6 g, 31.0 mmol) was dissolved in distilled water (10 mL) and then
added to the reaction mixture. Finally, OsO4 (0.78 mL, 0.78 mmol, 1m so-
lution in toluene) was added and stirring was continued in the dark.
After completion of the reaction (as indicated by TLC), the reaction mix-
ture was quenched with saturated aq. NaHSO3 (10 mL) solution. Organic
solvent was removed under reduced pressure, aqueous layer extracted
with tert-butyl methyl ether (3ꢂ40 mL), the combined organic layer was
washed with 1n HCl (3ꢂ50 mL) to remove excess lutidine. The organic
layer was dried over anhydrous Na2SO4 and concentrated under reduced
pressure to give a colorless oil, which was purified by silica gel column
chromatography using 20% ethyl acetate/hexane as eluent to give alde-
hyde 18 (1.7 g, 80%) as a colorless liquid. [a]2D5 =À9.8 (c 0.39 in CHCl3);
2925, 2853, 1730, 1644, 1460, 1428, 1364, 1255, 1110, 997, 912, 831, 741,
703 cmÀ1 1H NMR (300 MHz, CDCl3): d=7.72–7.67 (dd, J=1.5, 7.7 Hz,
;
4H), 7.44–7.32 (m, 6H), 7.29–7.26 (m, 5H), 5.97–5.90 (m, 2H), 5.83 (m,
1H), 5.11–5.02 (m, 2H), 4.65–4.54 (q, J=11.9, 19.5 Hz, 2H), 4.27 (m,
1H), 4.03–3.83 (m, 4H), 2.36 (m, 1H), 2.22 (m, 1H), 1.08 ppm (s, 9H);
13C NMR (75 MHz, CDCl3): d=135.6, 135.5, 134.5, 133.4, 129.6, 129.5,
128.2, 127.7, 127.6, 127.4, 124.1, 117.1, 115.8, 72.5, 71.9, 70.9, 68.1, 62.5,
37.3, 26.9, 19.2 ppm; ESI-HRMS: m/z calcd for C32H38O3 [M+H]+:
498.2591; found: 498.2589.
Data for 11i: [a]2D5 =+53.5 (c 0.9 in CHCl3); IR (KBr, neat): n˜ =2921,
2851, 1742, 1457, 1371, 1232, 1046, 913, 727 cmÀ1 1H NMR (300 MHz,
;
CDCl3): d=5.97–5.77 (m, 3H), 5.18–5.09 (m, 3H), 4.28 (m, 1H), 4.22 (d,
J=6.6 Hz, 1H), 4.16 (m, 1H), 3.96 (m, 1H), 2.47 (m, 1H), 2.33 (m, 1H),
2.09 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=170.8, 170.4, 133.9,
2076
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 2072 – 2078

Asymmetric Synthesis
FULL PAPER
IR (KBr, neat): n˜ =3434, 3029, 2962, 2871, 1724, 1453, 1365, 1001 cmÀ1
;
19.1, 15.8 ppm; ESI-HRMS: m/z calcd for C32H39O4SiI [M+Na]+:
1H NMR (300 MHz, CDCl3): d=9.80 (s, 1H), 7.39–7.22 ( m, 5H), 5.73–
5.62 (m, 2H), 4.77 (m, 1H), 4.56 (q, J=12.3, 14.9 Hz, 2H), 3.61–3.53 (m,
2H), 3.47 (m, 1H), 2.73 (m, 1H), 2.54 (m, 1H), 2.30 (m, 1H), 0.96 ppm
(d, J=7.0 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=200.9, 138.1, 131.6,
128.2, 127.7, 127.5, 126.6, 74.2, 73.2, 70.2, 67.5, 47.7, 29.8, 17.7 ppm.
665.1560, found: 665.1571.
(1S,3R,4S,5S,7R,8R)-3-(Benzyloxymethyl)-7-ethyl-4-methyl-2,6-
dioxabicycloACTHNUTRGNEUG[N 3.2.1]octane (13): AIBN (5 mg) was added to a stirred solu-
tion of 21 (40 mg, 0.062 mmol) in dry toluene (3 mL), and the resulting
mixture was heated under reflux under a nitrogen atmosphere. Then
Bu3SnH (0.034 mL, 0.124 mmol) was added to the reaction mixture
under refluxed conditions. After completion of the reaction (monitored
by TLC), toluene was removed under reduced pressure and the crude
mass directly loaded on silica gel, which on purification with 5% ethyl
(R)-1-[(2R,5R,6i)-6-(Benzyloxymethyl)-5-methyl-5,6-dihydro-2H-pyran-
2-yl]ethane-1,2-diol (19): Nitrosobenzene (452 mg, 0.423 mmol) followed
by d-proline (128 mg, 1.05 mmol) were added to a stirred solution of al-
dehyde 9 (1.1 g, 4.23 mmol) in dry DMSO (5 mL) under a nitrogen at-
mosphere and the resulting mixture was stirred the solution turned deep
orange. Then the reaction mixture was diluted with methanol (10 mL)
and cooled to 08C. NaBH4 (160 mg, 4.23 mmol) was added in portions
and further stirred for 30 min. At this stage TLC was checked which
showed complete disappearance of the starting material. Methanol was
removed under reduced pressure and diluted with water (30 mL). The
aqueous layer was extracted with ethyl acetate (3ꢂ50 mL), dried over an-
hydrous Na2SO4, and concentrated under reduced pressure to give deep
orange syrup, which was dissolved in methanol and stirred overnight with
excess CuSO4·5H2O at room temperature to get the desired diol com-
pound. Again, methanol was removed, water (20 mL) added and extract-
ed with ethyl acetate (3ꢂ50 mL). The combined organic layer was dried
over anhydrous Na2SO4 and concentrated under reduced pressure to give
a yellow oil which was purified by silica gel column chromatography
using 40% ethyl acetate/hexane as eluent to afford diol 19 (0.72 g, 61%)
as a colorless liquid. [a]2D5 =À10.1 (c 0.42 in CHCl3); IR (KBr, neat): n˜ =
acetate/hexane afforded 13 (31 mg, 95%) as a colorless liquid. [a]D25
À22 (c 0.29 in CHCl3); IR (KBr, neat): n˜ =3463, 2923, 2852, 1644, 1464,
1370, 1262, 1221, 1129, 1091, 1020, 772 cmÀ1 1H NMR (300 MHz,
CDCl3): d=7.77–7.67 (m, 4H), 7.4–7.28 ( m, 11H), 4.63–4.45 (m, 3H),
4.23 (d, J=6.6 Hz, 1H), 4.10 (m, 1H), 4.03–3.9 (m, 2H), 3.53–3.38 (m,
3H), 2.02 (m, 1H), 1.86 (d, J=11.5 Hz, 1H), 1.66 (m, 1H), 1.05 (s, 9H),
0.81 ppm (d, J=6.6 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=135.6,
133.5, 129.6, 128.3, 127.6, 127.6, 127.5, 83.4, 79.2, 77.4, 74.6, 73.2, 71.2,
61.7, 38.2, 37.1, 29.9, 26.8, 19.1, 15.7 ppm; ESI-HRMS: m/z calcd for
C32H40O4Si [M+Na]+: 534.3029; found: 534.3032.
=
;
Acknowledgements
3421, 2923, 2854, 1724, 1854, 1455, 1099 cmÀ1 1H NMR (300 MHz,
;
P.P.D. and M.R.P. thank the Council of Scientific & Industrial Research
(CSIR), New Delhi, India, for financial support in the form of fellow-
ships. D.K.M. thanks the Council of Scientific & Industrial Research
(CSIR), New Delhi, India, for a research grant (INSA Young Scientist
Award).
CDCl3): d=7.4–7.28 (m, 5H), 5.73 (q, J=10.2, 11.9 Hz, 2H), 4.61–4.54
(m, 1H), 4.20 (m, 1H), 3.85–3.48 (m, 6H), 2.2 (m, 1H), 0.96 ppm (d, J=
6.98 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=132.9, 128.4, 127.7, 127.7,
124.1, 75.2, 73.7, 73.4, 72.1, 70.8, 63.3, 30.2, 17.5 ppm; ESI-HRMS: m/z
calcd for C16H23O4 [M+H]+: 278.15181; found: 278.15083.
(R)-1-[(2R,5R,6R)-6-(Benzyloxymethyl)-5-methyl-5,6-dihydro-2H-pyran-
2-yl]-2-(tert-butyldiphenylsilyloxy)ethanol (20): Imidazole (220 mg,
3.2 mmol) and TBDPSCl (450 mg, 1.6 mmol) were added to a stirred so-
lution of diol 19 (450 mg, 1.6 mmol) in CH2Cl2 (15 mL), and the resulting
mixture was stirred for 2 h at room temperature. The reaction mixture
was quenched with water (15 mL) and the water layer was washed with
CH2Cl2 (2ꢂ30 mL). The combined organic layer was dried over anhy-
drous Na2SO4 and concentrated under reduced pressure to give a color-
less oil, which was purified by silica gel column chromatography with 5%
ethyl acetate/hexane as eluent to yield alcohol 20 (750 mg, 92%) as a col-
orless liquid. [a]2D5 =+3.2 (c 0.48 in CHCl3); IR (KBr, neat): n˜ =3440,
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(300 MHz, CDCl3): d=7.72–7.65 (m, 4H), 7.44–7.25 (m, 11H), 5.71–5.66
(m, 2H), 4.58 (q, J=12.1, 21.2 Hz, 2H) 4.29 (m, 1H), 3.86–3.72 (m, 3H),
3.60–3.53 (m, 2H), 2.29 (m, 1H), 1.06 (s, 9H), 0.93 ppm (d, J=7.2 Hz,
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=
;
7.67 (m, 4H), 7.43–7.25 (m, 11H), 4.57 (s, 2H), 4.30–4.25 (m, 2H), 4.21
(m, 1H), 4.12 (brd, J=5.9 Hz, 1H), 4.04 (m, 1H), 3.93 (m, 1H), 3.63 (m,
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Chem. Eur. J. 2010, 16, 2072 – 2078
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: October 30, 2009
ˇ
Pospꢄsil, I. E. Marko, Tetrahedron Lett. 2006, 47, 5933.
Published online: January 22, 2010
2078
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Chem. Eur. J. 2010, 16, 2072 – 2078