Synthesis of an A'B' precursor to angelmicin B: Product diversification in the Suarez lactol fragmentation

Article abstract of DOI:10.1002/ejoc.201100815

We describe a synthetic strategy for the angelimicin family of anthraquinoid natural products that involves converting a central highly oxygenated decalin intermediate to the AB and A'B' subunits. Herein, we report the synthesis of the bicyclic A'B' subun

Full text of DOI:10.1002/ejoc.201100815

FULL PAPER
DOI: 10.1002/ejoc.201100815
Synthesis of an AЈBЈ Precursor to Angelmicin B: Product Diversification in the
Suárez Lactol Fragmentation
Jialiang Li,[a] Louis Todaro,[a] and David R. Mootoo*[a]
Keywords: Synthesis design / Natural products / Cyclitols / Carbohydrates / Radical fragmentation
We describe a synthetic strategy for the angelimicin family
of anthraquinoid natural products that involves converting a
central highly oxygenated decalin intermediate to the AB
and AЈBЈ subunits. Herein, we report the synthesis of the bi-
cyclic AЈBЈ subunit that complements our earlier route to the
tricyclic AB framework. The differentiating tact in the two
syntheses focused on controlling the Suárez radical fragmen-
tation of lactol precursors by modulating the substrate’s
structural rigidity. A more flexible lactol gave the tricyclic AB
framework, whereas a more rigid substrate led to the bicyclic
AЈBЈ precursor, presumably through divergent pathways
from the radical produced in the initial fragmentation step.
These results establish a versatile advanced synthetic precur-
sor for the angelimicins, and on a more general note, illus-
trate strategies for applying the Suárez fragmentation to di-
verse and complex molecular frameworks.
on human myeloid leukemia (HL-60) cell lines (IC50
=
Introduction
0.10 μg/mL or 57 nm).[6–13] The pseudodimeric aglycon of
angelmicin B is comprised of similar anthraquinoid-derived
cyclitol segments ABCD and AЈBЈCЈDЈ connected through
a D–DЈ biaryl bond. Biosynthetically, this core structure
originates as a polyketide precursor that was initially con-
verted to a half unit. It has been suggested that dimeriza-
tion of this half unit gives HMP-Y1 (2), and subsequent
Angelmicin B (1, hibarimicin B) is a polyketide-derived
microbial metabolite (Figure 1)[1–5] that has attracted syn-
thetic attention because of its structural complexity and po-
tent growth-inhibiting and differentiation-inducing activity
Figure 1. Angelmicin B and HMP-Y1.
[a] Chemistry Department, Hunter College, City University of
New York,
695 Park Avenue, New York, NY 10065, USA
Fax: +1-212-772-5332
E-mail: dmootoo@hunter.cuny.edu
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100815.
Scheme 1. Unified strategy for AB and AЈBЈ enone precursors.
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J. Li, L. Todaro, D. R. Mootoo
FULL PAPER
desymmetrization and glycosylation lead to 1. Thus, be-
cause of its symmetric structure, HMP-Y1 is an attractive
precursor in the biomimetic synthesis of 1.
We have reported a synthesis for enone 7, which is a po-
tential precursor for the AB segment of angelmicin B
(Scheme 1).[14] The key step involved the transformation of
the complex decalin 3 to tricyclic ether 5, which is a precur-
sor to 7. Importantly, bicyclic iodide 6 was a minor product
in this step and could be converted to enone 8 for use as a
precursor to the AЈBЈ subunit of angelmicin B. Enone 8 can
also be used in the synthesis of HMP-Y1. Given the rele-
vance of 8 to the syntheses of both HMP-Y1 and angel-
micin B, we sought a more selective synthesis for a precur-
sor such as 6, and towards this end, we envisaged a straight-
forward modification of the original route. However, it was
necessary to rework the strategy with new tactics for the
application of the Suárez radical fragmentation, and this
was nontrivial. The results are described herein.
Results and Discussion
We speculated that the reaction of lactol 3 with iodoso-
benzene diacetate proceeded through a radical fragmenta-
tion to give intermediate 4, which led to the tricyclic THF
product 5 and iodide 6.[15–18] Suppression of the pathway
to 5 could bias the reaction to give 6 and/or the epimeric
iodo derivative. Towards this end, we decided to perform
the fragmentation reaction on a lactol substrate that is more
rigid than 3 and, therefore, less prone to the cycloetherifi-
cation. Alkene-lactol 10b was considered as a suitable sub-
strate (Scheme 2). This material was prepared by a re-
duction of lactone 9 by using DIBALH (diisobutylalumi-
num hydride), which was also utilized for 3. However, the
1H NMR spectroscopic data suggested that 10b existed pri-
marily as hydroxy aldehyde 10a, and this raised questions
about the feasibility of the planned radical fragmentation
reaction. Indeed, exposure of 10a and 10b to iodosobenzene
diacetate and iodine led to a complex mixture of intractable
products. Instead, epimeric lactol 11 was examined as a
candidate for the radical reaction, because of the expecta-
tion that lower strain in the 1,3-syn-bridged framework
would lead to a higher proportion of lactol tautomer 11b
(compared to the case for 10). Accordingly, DBU-promoted
(1,8-diazabicyclo[5.4.0]undec-7-ene) epimerization of lac-
tone 9 followed by reduction of the product provided 11,
Scheme 2. Radical fragmentation reactions.
Next, the mixture of epimeric iodides 12 was elaborated
to the AЈBЈ enone target (Scheme 3). Under standard deio-
dination conditions, 12 was treated with nBu3SnH and
1
which – within the limits of H NMR detection – existed
entirely as 11b. Exposure of this material to the conditions
for radical fragmentation afforded a 2:1 mixture of iodo
formates 12 in 96% yield. Thus, the framework presented
for 11 is delicately balanced in terms of the strain require-
ments for the two key elements in the radical reaction.
Strain effects are sufficiently low to allow formation of lac-
tol 11b, which is required to trigger the fragmentation step,
and are adequate to channel this pathway to the desired
bicyclic product by working against the competing cyclo-
etherification process.
Scheme 3. nBu3SnH reduction of iodo formate 12.
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Synthesis of an AЈBЈ Precursor to Angelmicin B
AIBN [azobis(isobutyronitrile)] and heated to reflux in ben-
zene to afford the expected formate 13 in 90% yield to-
gether with bridged lactone 14 (7%). A possible mechanism
for producing 14 begins with an intramolecular hydrogen
transfer within initially formed radical 15 to give alkoxycar-
bonyl radical 16. A 5-exo-trig cyclization step followed by
a hydrogen transfer to the resulting carbon radical 17 gives
14.[19,20] This transformation may be of wider interest as
14, with a synthetically formidable bridgehead quaternary
center, bears a resemblance to a variety of naturally occur-
ring terpenoid natural products.[21,22]
The use of standard protecting-group procedures with
formate 13 provided silyl ether 18 in 95% overall yield
(Scheme 4). The stereoselective dihydroxylation of 18 af-
forded the expected triol 19 (50%) and a minor amount of
ketone 20 (15%).[23] The stereochemistry of 19 was con-
firmed by X-ray crystal structure determination (see Sup-
porting Information). At 100 K, the unit cell of 19 contains
two independent molecules that are not related by crystallo-
graphic symmetry (Figure 2). The tert-butyldimethylsilyl
(TBDMS) group of one independent molecule has con-
siderable disorder, and the occupancies of the two rotamers
are approximately the same. Treatment of 19 with IBX (2-
iodoxybenzoic acid) gave 20,[24] and the overall yield of 20
from 18 was approximately 63%. The transformation of
ketone 20 into the AЈBЈ enone 8 was accomplished by ap-
plying the Sharpless–Reich protocol, which was also used
for the preparation of the AB enone 7.[25–27]
Scheme 4. End games for the AЈBЈ enone 8.
Conclusions
The readily accessible carbohydrate-derived Diels–Alder
adduct 9 was transformed into bicyclic enone 8, a potential
precursor to the bicyclic AЈBЈ cyclitol segment in the angeli-
micin family of anthraquinoid natural products. This result
complements our earlier synthesis of the tricyclic THF-
bridged AB segment from 9, and the underlying chemical
transformations illustrate the versatility of 9 in the synthesis
of polyhydroxylated decalin frameworks. Within the specific
context of the angelimicins, the preparation of both AB and
AЈBЈ precursors from a central relay intermediate paves the
way to the synthesis of advanced and diverse analogues
from a relatively underinvestigated family of biologically
interesting natural products. The differentiating ploy in
these syntheses focuses on controlling the outcome of the
Suárez radical fragmentation by varying the rigidity of the
lactol substrate. Given the compatibility of the Suárez frag-
mentation with highly functionalized substrates, such as
employed here, this tactic opens up new strategies for the
synthesis of complex molecular frameworks.
Experimental Section
General Methods: Unless otherwise noted, all reactions were per-
formed in anhydrous organic solvents under argon with oven-dried
glassware by using standard syringe and septa techniques. Thin
layer chromatography was performed by using Whatman silica gel
Figure 2. X-ray crystal structure of triol 19.
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J. Li, L. Todaro, D. R. Mootoo
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HF254 plates or Selecto Scientific alumina B F254 plates, and chro-
matograms were developed by using UV light, 12-molybdophos-
phoric acid (PMA), or potassium permanganate (KMnO4). Flash
column chromatography (FCC) was performed by using silica gel
60 (230–400 mesh). Optical rotations were measured with a Ru-
dolph Autopol III polarimeter. IR spectra were recorded with a
Thermo Nicolet IR100 spectrometer, and the vibrations are re-
8.8 Hz, 1 H, 8-H), 3.48 (d, J = 8.8 Hz, 1 H, 7-H), 3.04–2.97 (m, 2
H, 2a-H and 2a -H), 2.84 (s, 1 H, 6-OH), 2.11–2.09 (m, 3 H, 3-HA
1
and 4-CH2), 1.67–1.48 (m, 3 H, 3-HB and 1Ј-CH2), 1.31–1.27 (m,
1 H, 2Ј-HA), 1.22–1.12 (m, 1 H, 2Ј-HB), 0.84 (t, J = 7.3 Hz, 3 H,
CH3) ppm. 13C NMR (CDCl3): δ = 177.5 (C=O), 138.2, 137.8,
132.7 (2 C, Ph and C-5a), 128.7, 128.6, 128.5, 128.3, 128.0 (6 C,
Ph), 126.6 (CH-5), 83.1 (C-8a), 79.7 (C-7), 78.9 (C-8), 75.0
(CH2Ph), 74.8 (C-6), 73.5 (CH2Ph), 41.7 (C-1Ј), 39.0, 35.6 (C-2a
1
ported in wavenumbers (cm–1). H NMR spectroscopic data were
1
recorded with a Bruker 500 MHz spectrometer in CDCl3 or C6D6,
and the chemical shifts are reported in parts per million (ppm)
relative to the signal for the protonated solvent [CD(H)Cl3: δ =
7.27 ppm]. 13C NMR spectroscopic data were recorded with a
Bruker 125 MHz spectrometer in CDCl3, and the chemical shifts
are reported in parts per million (ppm) relative to the solvent peak
(CDCl3: δ = 77.23 ppm). High-resolution mass spectra were ob-
tained with an Ultima Micromass Q-TOF Mass Spectrometer at
the Mass Spectrometry Laboratory of Hunter College, CUNY.
CCDC-828273 (for 19) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
and C-2a ), 20.6 (C-4), 19.2 (C-3), 16.8 (C-2Ј), 14.6 (CH3) ppm.
HRMS (ESI): calcd. for C28H32O5Na [M + Na]+ 471.2142; found
471.2142. To a solution of C-8-epi-9 (520 mg, 1.16 mmol) in
CH2Cl2 (7 mL) at –78 °C was added DIBALH (1.0 m in hexane,
2.68 mL, 2.68 mmol). After the TLC results showed complete dis-
appearance of starting material, the reaction mixture was quenched
with an aqueous saturated solution of potassium sodium tartrate
and diluted with Et2O. The mixture was stirred at room temp. for
30 min and then extracted with Et2O. The combined organic phases
were washed with brine and water, dried with Na2SO4, and filtered.
The resulting mixture was concentrated in vacuo, and the residue
was purified by FCC to afford 11 (495 mg, 94%); Rf = 0.12 (15%
1
EtOAc/petroleum ether). H NMR (CDCl3): δ = 7.39–7.28 (m, 10
H, Ph), 6.02 (m, 1 H, 5-H), 5.29 (m, 1 H, 2-H), 4.89 (d, J = 11.2 Hz,
1 H, CHAPh), 4.79 (d, J = 11.6 Hz, 1 H, CHCPh), 4.66 (d, J =
11.6 Hz, 1 H, CHDPh), 4.60 (d, J = 11.2 Hz, 1 H, CHBPh), 4.43
(dd, J = 5.7, 6.4 Hz, 1 H, 8a-H), 3.68 (dd, J = 5.5, 8.0 Hz, 1 H, 8-
H), 3.51 (br., 1 H, 2-OH), 3.42 (d, J = 8.0 Hz, 1 H, 7-H), 3.01 (s,
(1S,5S,6R,7S,8R,8aR)-6,7-Bis(benzyloxy)-5,8-dihydroxy-5-propyl-
1,2,3,5,6,7,8,8a-octahydronaphthalene-1-carbaldehyde (10): To a
solution of 9 (85 mg, 0.190 mmol) in CH2Cl2 (1.5 mL) at –78 °C
was added DIBALH (1.0 m in hexane, 0.57 mL, 0.57 mmol). After
the TLC results showed complete disappearance of starting mate-
rial, the reaction mixture was quenched with an aqueous saturated
solution of potassium sodium tartrate and then diluted with Et2O.
The mixture was stirred at room temp. for 30 min and then ex-
tracted with Et2O. The combined organic phases were washed with
brine and water, dried with Na2SO4, and filtered. The resulting
mixture was concentrated in vacuo, and the residue was purified
by FCC to afford 10 (44 mg, 50%); Rf = 0.13 (15% EtOAc/petro-
leum ether). 1H NMR (CDCl3): δ = 9.71 (d, J = 0.7 Hz, 1 H,
CHO), 7.40–7.33 (m, 8 H, Ph), 7.27–7.24 (m, 2 H, Ph), 6.10 (m, 1
H, 4-H), 4.68 (d, J = 12.0 Hz, 1 H, CHAPh), 4.60 (d, J = 10.9 Hz,
1 H, CHCPh), 4.57 (d, J = 12.0 Hz, 1 H, CHBPh), 4.43 (d, J =
10.9 Hz, 1 H, CHDPh), 3.94 (t, J = 2.8 Hz, 1 H, 7-H), 3.87 (qd, J
= 1.8, 11.9 Hz, 1 H, 8-H), 3.57 (dd, J = 1.8, 2.6 Hz, 1 H, 6-H),
2.99 (m, 1 H, 8a-H), 2.92 (d, J = 11.9 Hz, 1 H, 8-OH), 2.88–2.84
(m, 1 H, 1-H), 2.66 (d, J = 1.1 Hz, 1 H, 5-OH), 2.11 (m, 3 H, 2-
HA and 3-CH2), 2.07–2.01 (m, 1 H, 1Ј-HA of propyl), 1.58–1.51
(m, 2 H, 2-HB and 1Ј-HB), 1.38–1.29 (m, 1 H, 2Ј-HA of propyl),
1
1 H, 6-OH), 2.78 (m, 1 H, 2a -H), 2.45 (m, 1 H, 2a-H), 2.07 (m, 2
H, 4-CH2), 1.74–1.68 (m, 1 H, 3-HA), 1.66–1.58 (m, 2 H, 3-HB and
1Ј-HA), 1.50 (ddd, J = 4.5, 12.0, 13.1 Hz, 1 H, 1Ј-HB), 1.40–1.31
(m, 1 H, 2Ј-HA), 1.24–1.15 (m, 1 H, 2Ј-HB), 0.86 (t, J = 7.3 Hz, 3
H, CH3) ppm. 13C NMR (CDCl3): δ = 139.0, 138.2, 135.3 (2 C, Ph
and C-5a), 128.8, 128.6, 128.5, 128.2, 127.9, 127.8 (6 C, Ph), 123.8
(CH-5), 101.6 (C-2), 81.6 (C-8a), 81.5 (C-7), 80.7 (C-8), 75.1
(CH2Ph), 75.0 (C-6), 73.4 (CH2Ph), 45.4, 42.4, 38.1, 21.6, 21.5 (C-
1
2a , C-2a, C-3, C-4, and C-1Ј), 16.9 (C-2Ј), 14.7 (CH3) ppm. HRMS
(ESI): calcd. for C28H34O5Na [M + Na]+ 473.2298; found 473.2299.
(1R,2S,3R,4S,8aR)-2,3-Bis(benzyloxy)-4-hydroxy-8-iodo-4-propyl-
1,2,3,4,6,7,8,8a-octahydronaphthalen-1-yl formate (12a and 12b): To
a solution of lactol 11 (490 mg, 1.09 mmol) in cyclohexane (0.03 m,
36 mL) was added diacetoxyiodobenzene (456 mg, 1.42 mmol) and
I2 (331 mg, 1.30 mmoL). After the TLC results showed complete
disappearance of starting material, the reaction mixture was
quenched with 10% Na2S2O3 in a saturated aqueous solution of
NaHCO3. The mixture was extracted with Et2O, and the combined
organic phases were washed with brine and water, dried with
Na2SO4, and filtered. The resulting mixture was concentrated, and
the residue was purified by FCC to give a mixture of iodides 12a
and 12b (596 mg, 95%) in approximately a 2:1 ratio. 12a: Rf = 0.20
(15% EtOAc/petroleum ether). 1H NMR (CDCl3): δ = 8.02 (s, 1
H, HCO2), 7.41–7.30 (m, 8 H, Ph), 7.17–7.14 (m, 2 H, Ph), 6.19
(m, 1 H, 5-H), 5.40 (br., 1 H, 1-H), 4.71 (d, J = 12.0 Hz, 1 H,
CHAPh), 4.56 (d, J = 12.0 Hz, 1 H, CHBPh), 4.41–4.33 (m, 3 H,
CH2Ph and 8-H), 3.92 (t, J = 2.6 Hz, 1 H, 2-H), 3.40 (dd, J = 1.1,
2.4 Hz, 1 H, 3-H), 3.04 (d, J = 7.0 Hz, 1 H, 8a-H), 2.79 (d, J =
0.6 Hz, 1 H, 4-OH), 2.35–2.23 (m, 2 H, 6-HA and 7-HA), 2.20–2.11
(m, 2 H, 7-HB and 6-HB), 1.90–1.84 (m, 1 H, 1Ј-HA), 1.55–1.49 (m,
1 H, 1Ј-HB), 1.40–1.30 (m, 1 H, 2Ј-HA), 1.28–1.21 (m, 1 H, 2Ј-HB),
0.87 (t, J = 7.3 Hz, 3 H, CH3) ppm. 13C NMR (CDCl3): δ = 160.6
(C=O), 137.7, 137.1, 135.9 (2 C, Ph and C-4a), 128.8, 128.7, 128.6,
128.5, 128.2, 128.1 (6 C, Ph), 124.0 (CH-5), 81.6 (C-3), 74.6 (C-4),
73.6 (CH2Ph), 73.0 (CH2Ph), 72.9 (C-2), 72.5 (C-1), 45.4 (C-8a),
39.8 (C-1Ј), 35.3 (C-6), 29.5 (C-8), 26.5 (C-7), 16.5 (C-2Ј), 14.6
(CH3) ppm. HRMS (ESI): calcd. for C28H33IO5Na [M + Na]+
1.26–1.19 (m, 1 H, 2Ј-HB), 0.87 (t, J = 7.3 Hz, 3 H, CH3) ppm. 13
C
NMR (CDCl3): δ = 203.9 (CH=O), 138.0, 136.6, 135.7 (2 C, Ph
and C-4a), 129.0, 128.9, 128.8, 128.7, 128.1, 127.9 (6 C, Ph), 125.6
(CH-4), 83.5 (C-6), 75.6 (C-5), 75.4 (C-7), 74.1 (CH2Ph), 72.5
(CH2Ph), 71.9 (C-8), 48.3 (C-1), 39.0 (C-2), 35.0 (C-8a), 23.8 (C-
3), 21.7 (C-1Ј), 16.5 (C-2Ј), 14.7 (CH3) ppm. HRMS (ESI): calcd.
for C28H34O5Na [M + Na]+ 473.2298; found 473.2302.
(2R,2aR,2a1R,6S,7R,8S,8aR)-7,8-Bis(benzyloxy)-6-propyl-
2a,2a1,3,4,6,7,8,8a-octahydro-2H-naphtho[1,8-bc]furan-2,6-diol (11):
A solution of lactone 9 (680 mg, 1.51 mmol) and DBU (0.25 mL,
1.68 mmol) in toluene (35 mL) was heated at reflux until the TLC
results showed less than 5% of the starting material remained, at
which time the solution was cooled to room temp. The solvent was
then removed in vacuo, and the residue was purified by FCC to
give the C-8 epimeric lactone (C-8-epi-9) as a white solid (650 mg,
1
96%). Rf = 0.30 (15% EtOAc/petroleum ether); m.p. 93–96 °C. H
NMR (CDCl3): δ = 7.38–7.28 (m, 10 H, Ph), 6.10 (m, 1 H, 5-H),
4.95 (d, J = 11.2 Hz, 1 H, CHAPh), 4.77 (d, J = 11.5 Hz, 1 H,
CHCPh), 4.67 (d, J = 11.5 Hz, 1 H, CHDPh), 4.61 (t, J = 5.5 Hz,
1 H, 8a-H), 4.58 (d, J = 11.2 Hz, 1 H, CHBPh), 3.84 (dd, J = 4.8,
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Synthesis of an AЈBЈ Precursor to Angelmicin B
599.1265; found 599.1252. 12b: Rf = 0.17 (10% EtOAc/petroleum
(1S,2R,3R,4R,4aR)-2,3-Bis(benzyloxy)-4-[(tert-butyldimethylsilyl)-
1
ether). H NMR (CDCl3): δ = 8.01 (s, 1 H, HCO2), 7.41–7.31 (m, oxy]-1-propyl-1,2,3,4,4a,5,6,7-octahydronaphthalen-1-ol (18): To a
8 H, Ph), 7.17–7.13 (m, 2 H, Ph), 6.09 (d, J = 5.1 Hz, 1 H, 5-H), solution of 13 (415 mg, 0.922 mmol) in MeOH (8.1 mL) and
5.58 (m, 1 H, 1-H), 4.71 (d, J = 12.0 Hz, 1 H, CHAPh), 4.60–4.55 CH2Cl2 (0.9 mL) at 0 °C was added K2CO3 (127 mg, 0.922 mmol).
(m, 2 H, 8-H and CHBPh), 4.37 (d, J = 11.8 Hz, 1 H, CHCPh),
After the TLC results showed complete disappearance of starting
4.32 (d, J = 11.8 Hz, 1 H, CHDPh), 3.92 (t, J = 2.4 Hz, 1 H, 2-H), material, the reaction mixture was diluted with water and extracted
3.32 (br., 1 H, 3-H), 2.87 (d, J = 1.4 Hz, 1 H, 4-OH), 2.78 (d, J = with Et2O. The combined organic phases were dried with MgSO4
6.5 Hz, 1 H, 8a-H), 2.57–2.46 (m, 1 H, 7-HA), 2.31–2.21 (m, 2 H, and concentrated in vacuo, and the resulting residue was purified
7-HB and 16-HA), 2.15–2.08 (m, 1 H, 16-HB), 1.98–1.92 (m, 1 H,
1Ј-HA), 1.50–1.44 (m, 1 H, 1Ј-HB), 1.40–1.32 (m, 1 H, 2Ј-HA), 1.15– EtOAc/petroleum ether). 1H NMR (CDCl3): δ = 7.39–7.31 (m, 8
1.08 (m, 1 H, 2Ј-HB), 0.87 (t, J = 7.3 Hz, 3 H, CH3) ppm. 13C
H, Ph), 7.28–7.26 (m, 2 H, Ph), 6.10 (br. s, 1 H, 8-H), 4.64–4.57
by FCC to afford the derived diol (375 mg, 96%); Rf = 0.36 (15%
NMR (CDCl3): δ = 160.5 (C=O), 137.8, 137.2, 135.6 (2 C, Ph and (m, 3 H, CH2Ph), 4.45 (d, J = 11.0 Hz, 1 H, CHAPh), 3.93 (t, J =
C-4a), 128.8, 128.7, 128.6, 128.5, 128.2 (6 C, Ph), 123.2 (CH-5), 2.7 Hz, 1 H, 3-H), 3.74 (qd, J = 0.4, 11.8 Hz, 1 H, 4-H), 3.57 (br.,
82.3 (C-3), 77.1 (C-1), 75.4 (C-4), 73.8 (C-2), 73.5, 72.9 (2 CH2Ph), 1 H, 2-H), 2.82 (d, J = 11.8 Hz, 1 H, 4-OH), 2.63 (s, 1 H, 1-OH),
38.9 (C-1Ј), 37.8 (C-8a), 33.3 (C-7), 31.4 (C-8), 28.0 (C-6), 16.8 (C- 2.54 (br., 1 H, 4a-H), 2.04–1.96 (m, 3 H, 7-CH2 and 1Ј-HA), 1.87–
2Ј), 14.6 (CH3) ppm. HRMS (ESI): calcd. for C28H33IO5Na [M +
1.68 (m, 3 H, 5-CH2 and 6-HA), 1.58–1.54 (m, 1 H, 1Ј-HA), 1.48–
1.41 (m, 1 H, 6-HB), 1.39–1.30 (m, 1 H, 2Ј-HA), 1.28–1.19 (m, 1
H, 2Ј-HB), 0.87 (t, J = 7.3 Hz, 3 H, CH3) ppm. 13C NMR (CDCl3):
δ = 138.1, 137.9, 136.5 (2 C, Ph and C-8a), 128.9, 128.8, 128.7,
128.6, 128.1, 127.8 (6 CH, Ph), 126.4 (CH-8), 83.4 (C-2), 76.4 (C-
3), 75.6 (C-1), 74.0 (CH2Ph), 73.8 (C-4), 72.5 (CH2Ph), 39.2 (C-1Ј),
35.5 (C-4a), 25.8 (C-5), 25.4 (C-7), 21.6 (C-6), 16.6 (C-2Ј), 14.7
(CH3) ppm. To a solution of the diol (375 mg, 0.889 mmol) in
DMF (dimethylformamide, 8.0 mL) was added imidazole (294 mg,
4.32 mmol), TBAI (tetrabutylammonium iodide, 320 mg,
0.865 mmol) and tert-butyldimethylsilyl chloride (651 mg,
4.32 mmol). After the TLC results showed complete disappearance
of starting material, the reaction mixture was quenched with water
and extracted with Et2O, and the combined organic phases were
dried with MgSO4 and concentrated in vacuo. The residue was
purified by FCC to afford 18 (470 mg, 99%). Rf = 0.50 (5% EtOAc/
Na]+ 599.1265; found 599.1263.
(1R,2S,3R,4S,8aR)-2,3-Bis(benzyloxy)-4-hydroxy-4-propyl-
1,2,3,4,6,7,8,8a-octahydronaphthalen-1-yl formate (13) and
(1R,2S,3R,4S,4aS,8aR)-2,3-Bis(benzyloxy)-4-hydroxy-4-propyl-
octahydro-1H-1,4a-(epoxymethano)naphthalen-9-one (14): To a
flask containing the mixture of 12a and 12b (614 mg, 1.066 mmol)
in benzene (35 mL) heated at reflux was added dropwise a solution
of tributyltin hydride (0.423 mL, 1.60 mmol) and AIBN (17.4 mg,
0.106 mmol) in benzene (23 mL). After the TLC results showed
complete disappearance of starting material, the reaction mixture
was cooled to room temp. and diluted with brine (20 mL). The
mixture was extracted with Et2O, and the combined organic phases
were washed with brine and water, dried with Na2SO4, and filtered.
The resulting mixture was concentrated, and the residue was puri-
fied by FCC to give formate 13 (430 mg, 90%) and carbonate 14
(33 mg, 7 %). 13: Rf = 0.23 (10 % EtOAc/petroleum ether). 1H
NMR (CDCl3): δ = 8.08 (s, 1 H, HCO2), 7.39–7.30 (m, 8 H, Ph),
7.22–7.20 (m, 2 H, Ph), 6.13 (br., 1 H, 5-H), 5.09 (br., 1 H, 1-H),
4.60 (d, J = 11.9 Hz, 1 H, CHAPh), 4.52 (d, J = 11.9 Hz, 1 H,
CHBPh), 4.47 (d, J = 11.9 Hz, 1 H, CHCPh), 4.44 (d, J = 11.9 Hz,
1 H, CHDPh), 3.79 (t, J = 2.5 Hz, 1 H, 2-H), 3.45 (d, J = 1.5 Hz,
1 H, 3-H), 2.76 (d, J = 0.8 Hz, 1 H, 4-OH), 2.66 (br., 1 H, 8a-H),
2.17 (m, 1 H, 6-HA), 2.09–2.01 (m, 1 H, 6-HB), 1.94 (ddd, J = 1.3,
4.6, 14.7 Hz, 1 H, 1Ј-HA), 1.77–1.69 (m, 2 H, 7-HA and 8-HA),
1.60–1.42 (m, 3 H, 8-HB, 1Ј-HB, and 7-HB), 1.40–1.29 (m, 1 H, 2Ј-
HA), 1.24–1.14 (m, 1 H, 2Ј-HB), 0.87 (t, J = 7.3 Hz, 3 H, CH3)
ppm. 13C NMR (CDCl3): δ = 161.2 (C=O), 137.9, 137.4, 136.7 (2
C, Ph and C-4a), 128.8, 128.7, 128.6, 128.4, 128.1, 127.9 (6 C, Ph),
124.9 (CH-5), 81.5 (C-3), 74.9 (C-4), 74.6 (C-2), 74.0 (C-1), 73.7,
72.7 (2 CH2Ph), 39.9 (C-1Ј), 33.0 (C-8a), 25.5 (C-8), 25.2 (C-6),
21.3 (C-7), 16.7 (C-2Ј), 14.6 (CH3) ppm. HRMS (ESI): calcd. for
C28H34O5Na [M + Na]+ 473.2298; found 473.2302. Data for 14: Rf
= 0.40 (15% EtOAc/petroleum ether). [α]2D9 = –15.0 (c = 0.20,
petroleum ether); [α]2D8 = –6.2 (c = 0.85, CHCl ). IR (neat): ν =
˜
3
3546, 3030, 2928, 2857, 1454, 1254, 1071 cm–1. 1H NMR (CDCl3):
δ = 7.42–7.27 (m, 10 H, Ph), 6.07 (br., 1 H, 8-H), 4.83 (d, J =
11.7 Hz, 1 H, CHAPh), 4.69–4.60 (m, 3 H, CH2Ph), 3.86 (br., 1 H,
4-H), 3.83 (d, J = 5.0 Hz, 1 H, 3-H), 3.68 (s, 1 H, 1-OH), 3.54 (d,
J = 5.0 Hz, 1 H, 2-H), 2.47 (br., 1 H, 4a-H), 2.13–2.02 (m, 3 H, 1Ј-
HA and 7-CH2), 1.85–1.80 (m, 1 H, 6-HA), 1.69–1.59 (m, 3 H, 1Ј-
HB and 5-CH2), 1.52–1.42 (m, 1 H, 6-HB), 1.22–1.13 (m, 1 H, 2Ј-
H), 1.04–0.94 (m, 1 H, 2Ј-H), 0.91 (s, 9 H, SiCMe3), 0.86 (t, J =
7.3 Hz, 3 H, CH3), 0.15 (s, 3 H, SiMeA), 0.14 (s, 3 H, SiMeB) ppm.
13C NMR (CDCl3): δ = 138.8, 138.3, 137.3 (2 C, Ph and C-8a),
128.7, 128.4, 128.1, 127.8, 127.7 (6 CH, Ph), 125.9 (CH-8), 84.5 (C-
3), 81.6 (C-2), 75.1 (C-1), 73.9 (CH2Ph), 73.7 (C-4), 72.2 (CH2Ph),
38.1 (C-1Ј), 36.8 (C-4a), 26.7 (C-5), 26.1 (SiCMe3), 25.6 (C-7), 22.0
(C-6), 18.3 (SiCMe3), 17.6 (C-2Ј), 14.7 (CH3), –3.6 (SiMeA), –4.7
(SiMeB) ppm. HRMS (ESI): calcd. for C33H48O4NaSi [M + Na]+
559.3214; found 559.3217.
(1R,2R,3R,4R,4aS,8R,8aS)-2,3-Bis(benzyloxy)-4-[(tert-butyldi-
methylsilyl)oxy]-1-propyldecahydronaphthalene-1,8,8a-triol (19): To
CHCl ). IR (neat): ν = 3534, 2934, 2863, 1776, 1453, 1099, 1075,
˜
3
1
1027 cm–1. H NMR (CDCl3): δ = 7.40–7.30 (m, 8 H, Ph), 7.23– a flask containing alkene 18 (465 mg, 0.867 mmol) in acetone
7.20 (m, 2 H, Ph), 4.57 (s, 2 H, CH2Ph), 4.37 (d, J = 11.8 Hz, 1 H, (8 mL) at 0 °C was added OsO4 (2.5 % in tBuOH, 0.44 mL,
CHAPh), 4.29 (d, J = 11.8 Hz, 1 H, CHBPh), 4.15 (d, J = 4.2 Hz, 0.043 mmol) and N-methylmorpholine oxide (50 % in water,
1 H, 1-H), 3.87 (dd, J = 1.0, 4.2 Hz, 1 H, 2-H), 3.67 (s, 1 H, 3-H),
2.97 (d, J = 1.5 Hz, 1 H, 4-OH), 2.54 (dd, J = 6.0, 11.7 Hz, 1 H,
8a-H), 2.20 (md, J = 14.3 Hz, 1 H), 1.81–1.63 (m, 5 H), 1.55–1.46
(m, 2 H), 1.24–1.04 (m, 4 H), 0.92 (t, J = 7.3 Hz, 3 H, CH3) ppm.
13C NMR (CDCl3): δ = 178.6 (C=O), 137.5, 137.3 (2 C, Ph), 128.8,
128.7, 128.4, 128.3, 128.2, 127.9 (6 CH, Ph), 79.0 (C-1), 76.8 (C-
0.539 mL, 2.60 mmol). After 24 h, an aqueous solution of Na2SO3
(2 m) was added. The mixture was extracted with EtOAc, and the
combined organic phases were washed with brine and water and
then dried with Na2SO4. The resulting mixture was concentrated
in vacuo, and the residue was purified by FCC to afford triol 19
(247 mg, 50%) and dihydroxy ketone 20 (74 mg, 15%). 19: Rf =
3), 75.3 (C-4), 74.9 (C-2), 73.5, 72.7 (2 CH2Ph), 53.1 (C-4a), 38.6 0.60 (15% EtOAc/petroleum ether); m.p. 149–151 °C. [α]2D7 = +4.7
(C-8a), 35.6 (C-1Ј), 26.5, 23.7, 22.9, 22.8 (C-5, C-6, C-7, and C-8),
17.0 (C-2Ј), 14.8 (CH3) ppm. HRMS (ESI): calcd. for C28H34O5Na
[M + Na]+ 473.2298; found 473.2304.
(c = 0.45, CHCl ). IR (film): ν = 3500, 3030, 2954, 2928, 2856,
˜
3
1454, 1253, 1115, 1056, 873, 836, 775, 735, 698 cm–1. 1H NMR
(CDCl3): δ = 7.35 (m, 2 H, Ph), 7.31–7.23 (m, 6 H, Ph), 7.16 (m,
Eur. J. Org. Chem. 2011, 6281–6287
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6285

J. Li, L. Todaro, D. R. Mootoo
FULL PAPER
1
2 H, Ph), 5.00 (d, J = 10.7 Hz, 1 H, CHAPh), 4.96 (d, J = 11.6 Hz,
1 H, CHCPh), 4.74 (d, J = 11.6 Hz, 1 H, CHDPh), 4.59 (d, J =
10.7 Hz, 1 H, CHBPh), 4.24 (dd, J = 5.8, 9.7 Hz, 1 H, 4-H), 4.05
(td, J = 2.7, 5.3 Hz, 1 H, 8-H), 3.79 (t, J = 9.5 Hz, 1 H, 3-H), 3.72
(d, J = 9.1 Hz, 1 H, 2-H), 2.77 (s, 1 H, OH), 2.38 (s, 1 H, OH),
2.30 (ddt, J = 2.9, 4.8, 14.1 Hz, 1 H), 1.96–1.91 (m, 1 H, 4a-H),
1.87–1.80 (m, 3 H), 1.78–1.72 (m, 2 H), 1.67–1.53 (m, 3 H), 1.47–
leum ether). H NMR (CDCl3): δ = 7.40–7.29 (m, 10 H, Ph), 7.12
(md, J = 10.2 Hz, 1 H, 3-H), 6.23 (dd, J = 2.3, 10.2 Hz, 1 H, 2-H),
5.01 (d, J = 10.6 Hz, 1 H, CHAPh), 4.99 (d, J = 11.2 Hz, 1 H,
CHCPh), 4.76 (d, J = 11. 2 Hz, 1 H, CHDPh), 4.68 (d, J = 10.6 Hz,
1 H, CHBPh), 4.13 (m, 1 H, 5-H), 4.01 (s, 1 H, OH), 3.99 (t, J =
9.8 Hz, 1 H, 6-H), 3.81 (d, J = 9.1 Hz, 1 H, 7-H), 2.91–2.83 (m, 1
H, 4-HA), 2.60–2.52 (m, 2 H, 4-HB and 4a-H), 2.22 (d, J = 2.5 Hz,
1.30 (m, 2 H), 0.91 (s, 9 H, SiCMe3), 0.87 (t, J = 7.3 Hz, 3 H, 1 H, OH), 2.09 (s, 1 H, OH), 1.64 (ddd, J = 4.5, 12.3, 14.3 Hz, 1
CH3), 0.09 (s, 3 H, SiMeA), 0.05 (s, 3 H, SiMeB) ppm. 13C NMR
(CDCl3): δ = 139.7, 138.8 (2 C, Ph), 128.5, 128.3, 128.1, 127.8,
127.2, 127.1 (6 CH, Ph), 84.2 (C-2), 82.6 (C-3), 79.0 (C-8a), 76.1
H, 1Ј-HA), 1.54–1.50 (m, 1 H, 1Ј-HB), 1.45–1.35 (m, 1 H, 2Ј-HA),
1.26–1.16 (m, 1 H, 2-HB), 0.83 (t, J = 7.2 Hz, 3 H, CH3) ppm. 13C
NMR (CDCl3): δ = 201.0 (C=O), 154.1 (C-3), 138.7, 138.2 (2 C,
(CH2Ph), 75.8 (C-1), 75.2 (CH2Ph), 72.3 (C-4), 70.0 (C-8), 46.9 (C- Ph), 128.9, 128.8, 128.2, 128.1, 128.0, 127.8, 127.7, (6 CH, Ph and
4a), 38.5, 31.0, 26.2 (SiCMe3), 21.5, 19.2, 19.1, 18.3 (SiCMe3), 15.3
(CH3), –4.2 (SiMeA), –4.3 (SiMeB) ppm. HRMS (ESI): calcd. for
C33H50O6NaSi [M + Na]+ 593.3269; found 593.3273. 20: For data,
see below.
C-2) 83.6 (C-7), 82.8 (C-6), 80.2, 77.6 (C-13 and C-14), 76.1, 75.8
(2 CH2Ph), 70.3 (C-5), 46.0 (C-4a), 36.9 (C-1Ј), 27.1 (C-4), 18.0 (C-
2Ј), 15.2 (CH3) ppm. HRMS (ESI): calcd. for C27H32O6Na [M +
Na]+ 475.2091; found 475.2097.
(4aS,5R,6R,7R,8R,8aR)-6,7-Bis(benzyloxy)-5-[(tert-butyldimethyl-
silyl)oxy]-8,8a-dihydroxy-8-propyloctahydronaphthalen-1(2H)-one
(20): Triol 19 (30 mg, 0.0526 mmol) was dissolved in DMSO (di-
methyl sulfoxide, 0.240 mL), and iodoxybenzoic acid (38 mg,
0.137 mmol) was added. The mixture was stirred at 75 °C for 20 h,
cooled to room temp., and then quenched with saturated aqueous
NaHCO3. The mixture was extracted with Et2O, and the combined
organic phases were washed with brine and water, dried with
MgSO4, and filtered. The resulting mixture was concentrated in
vacuo, and the residue was purified by FCC to afford ketone 20
Supporting Information (see footnote on the first page of this arti-
1
cle): H and 13C NMR spectroscopic data for all new compounds.
Acknowledgments
This investigation was supported by a grant from the National In-
stitutes of Health (NIH) (R01GM57865). A “Research Centers in
Minority Institutions” award is also acknowledged from the
National Center for Research Resources of the NIH (RR-03037),
which supports the infrastructure and instrumentation of the
Chemistry Department at Hunter College.
1
(28 mg, 95%); Rf = 0.66 (10% EtOAc/petroleum ether). H NMR
(CDCl3): δ = 7.36–7.24 (m, 8 H, Ph), 7.16 (m, 2 H, Ph), 5.00 (d, J
= 10.9 Hz, 2 H, CH2Ph), 4.80 (d, J = 11.5 Hz, 1 H, CHAPh), 4.57
(d, J = 11.5 Hz, 1 H, CHBPh), 4.32 (s, 1 H, OH), 4.14 (dd, J = 5.8,
10.0 Hz, 1 H, 5-H), 3.91 (t, J = 9.7 Hz, 1 H, 6-H), 3.63 (d, J =
9.2 Hz, 1 H, 7-H), 3.23 (dt, J = 6.8, 13.2 Hz, 1 H, 2-HA), 2.55 (md,
J = 14.6 Hz, 1 H, 2-HB), 2.53 (s, 1 H, OH), 2.32 (dq, J = 4.1,
13.5 Hz, 1 H, 4-HA), 2.17 (m, 1 H, 3-HA), 1.94 (md, J = 13.5 Hz,
1 H, 4-HB), 1.86 (td, J = 5.0, 13.7 Hz, 1 H, 4a-H), 1.65–1.42 (m, 3
H, 1Ј-CH2 and 3-HB), 1.33–1.25 (m, 1 H, 2Ј-HA), 1.11–1.01 (m, 1
H, 2Ј-HB), 0.89 (s, 9 H, SiCMe3), 0.78 (t, J = 7.3 Hz, 3 H, CH3),
0.05 (s, 3 H, SiMeA), 0.04 (s, 3 H, SiMeB) ppm. 13C NMR (CDCl3):
δ = 214.9 (C=O), 139.5, 138.5 (2 C, Ph), 128.6, 128.4, 128.1, 128.0,
127.3, 127.2 (6 CH, Ph), 84.3 (C-7), 82.3 (C-6), 80.9, 79.3 (C-8 and
C-8a), 76.4, 75.5 (2 CH2Ph), 72.2 (C-5), 55.7 (C-4a), 40.8 (C-2),
38.0 (C-1Ј), 27.6 (C-3), 26.2 (SiCMe3), 21.3 (C-4), 18.3 (SiCMe3),
17.1 (C-2Ј), 15.2 (CH3), –4.3 (SiMeA), –4.4 (SiMeB) ppm. HRMS
(ESI): calcd. for C33H48O6NaSi [M + Na]+ 591.3112; found
591.3119.
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Received: June 7, 2011
Published Online: September 7, 2011
Eur. J. Org. Chem. 2011, 6281–6287
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6287