A chemoenzymatic-RCM strategy for the enantioselective synthesis of new dihydroxylated 5-hydroxymethyl-indolizidines and 6-hydroxymethyl-quinolizidines

Article abstract of DOI:10.1016/j.tetasy.2007.07.017

A direct method for the synthesis of new azasugars-like compounds has been developed, which involves a new biocatalytic protocol based on the use of a lipase from Candida Cylindracea and of a ionic liquid as reaction medium, to prepare the key C₁

Full text of DOI:10.1016/j.tetasy.2007.07.017

Tetrahedron: Asymmetry 18 (2007) 1948–1954
A chemoenzymatic-RCM strategy for the enantioselective
synthesis of new dihydroxylated 5-hydroxymethyl-indolizidines
and 6-hydroxymethyl-quinolizidines
Giordano Lesma,* Alessia Colombo, Nicola Landoni,
Alessandro Sacchetti and Alessandra Silvani*
`
Dipartimento di Chimica Organica e Industriale, Universita degli Studi di Milano, via G. Venezian 21, 20133 Milano, Italy
Received 10 July 2007; accepted 18 July 2007
Available online 24 August 2007
Abstract—A direct method for the synthesis of new azasugars-like compounds has been developed, which involves a new biocatalytic
protocol based on the use of a lipase from Candida Cylindracea and of a ionic liquid as reaction medium, to prepare the key C1-sym-
metric piperidine precursor. By subsequent application of RCM reactions and OsO4-catalyzed double bond syn-dihydroxylation, the syn-
thesis of the target compounds could be accomplished in a straightforward and stereocontrolled manner.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
We have recently demonstrated how chemoenzymatically
derived chiral synthons can be successfully employed, in
combination with metathesis reactions, to readily access
various classes of naturally occurring piperidine, pyrrol-
idine and quinolizidine alkaloids.6
Azabicyclic ring skeletons, such as quinolizidines and ind-
olizidines, are important structural subunits present in
numerous biologically active natural products.1 In this
family, polyhydroxylated alkaloids have attracted much
attention due to the ability of some of them to act as selec-
tive glycosidase inhibitors.2 Glycosidases are involved in
several metabolic pathways and the development of inhib-
itors is an important challenge towards the treatment of
diseases, such as diabetes, cancer and viral infections,
including AIDS.3 The high therapeutic potential of these
alkaloids, also called azasugars, has prompted considerable
efforts towards their structural modification and towards
the design of new stereocontrolled synthetic routes to these
compounds, or to their unnatural isomers,4 which might be
of interest for SAR studies. In fact, small structural modi-
fications have often been proven to induce very significant
changes in terms of inhibiting potency and selectivity of the
glycosidase enzymes. On the basis of these considerations,
the development of novel synthetic strategies to expand
upon the repertoire of available analogues constitutes as
an area of considerable current interest.5
Herein, we report a non-carbohydrate based approach
to dihydroxylated 5-hydroxymethyl-indolizidines 1 and 6-
hydroxymethyl-quinolizidines 2, starting from the key
building block N-carbobenzyloxy-cis-(2S)-acetoxymethyl-
(6R)-hydroxymethylpiperidine 3, already described by
Chenevert (Fig. 1).7,8 An improved access to 3 has been
secured by means of a new biocatalytic protocol based on
the use of lipase from Candida Cylindracea and the ionic
H
H
OH HO
HO
OH
HO
N
N
1
2
HO
HO
OAc
N
Cbz
3
*
Corresponding authors. Tel.: +39 0250314080; fax: +39 0250314078;
e-mail: alessandra.silvani@unimi.it
Figure 1.
0957-4166/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2007.07.017

G. Lesma et al. / Tetrahedron: Asymmetry 18 (2007) 1948–1954
1949
liquid [BMIM]PF6 as a reaction medium. From 3, obtained
on a multigram scale in high ee, we developed a versatile
RCM-based strategy for constructing the second hetero-
cyclic ring, found in the aforementioned hydroxylated azabi-
cyclic compounds, which are not naturally occurring, to
the best of our knowledge.
are simple and inexpensive to manufacture, environmen-
tally benign and easy to recycle; their properties can be
fine-tuned by changing the anion or the R group of the cat-
ion. A number of publications10 have recently shown the
potential of carrying out enzymatic bioconversions in ionic
liquids, but, no examples of desymmetrization of CS-sym-
metric compounds have been reported until now.
Two ionic liquids, [EMIM]–[BF4] ([EMIM]+ = 1-ethyl-3-
methylimidazolium) and [BMIM]–[PF6] ([BMIM]+ = 1-but-
yl-3-methylimidazolium), were tested as media for lipase-
catalyzed transesterification and two different enzymes
were chosen, namely a lipase from Candida Antarctica
and a lipase from C. Cylindracea, in order to compare their
activity and enantioselectivity.
2. Result and discussion
The requisite substrate 4 (Scheme 1) for the enzymatic
desymmetrization was easily prepared from commercial
pyridine-2,6-dicarboxylic acid, according to the litera-
ture.7b Diol 4 is known8 to undergo enzyme-catalyzed
transesterification by treatment with Candida Antarctica
lipase in vinyl acetate to give optically active ester 3 in
80% yield and 95% ee. As part of our ongoing project on
the enzyme-mediated asymmetric synthesis of nitrogen
compounds, we became interested in ionic liquids9 as alter-
native solvents for biotransformations using cell-free
enzymes. Room-temperature ionic liquids, are attracting
growing interest as novel replacements for volatile organic
solvents in industrial organic synthesis and are particularly
promising as solvents for catalysis. Moreover, ionic liquids
Under identical conditions, the acylation of 4 in [BMIM]–
[PF6] with vinyl acetate, proceeded promptly with both
enzymes, but not in [EMIM]–[BF4]. In particular, when
lipase from C. Cylindracea was employed in [BMIM]–
[PF6], the best result of 90% yield and 98% ee11 was
achieved in around an half of the time with respect to the
standard acylation conditions.
With the common precursor 3 in hand on a multigram
scale, we pursued the synthetic sequence reported in
Scheme 2. Swern oxidation of 3 gave the corresponding
1
ref. 7b
aldehyde, which, after work up and H NMR verification
HO
OH
of the lack of epimerisation, was immediately added to
the methyl Wittig ylide to give alkene 5 in good yield. By
treatment with KOH 1 M in MeOH at reflux, amino alco-
hol 6 was achieved in high yield and after which it was
selectively N-acylated to give 7, by reaction with acryloyl
chloride in aqueous acetone, in the presence of Na2CO3.
HO2C
N
CO2H
OAc
N
Cbz
4
CCL,
HO
OAc
[BMIM]-[PF6]
40 °C, 24 h
N
Cbz
90% yield
We next examined ring-closing metathesis (RCM) condi-
tions in order to prepare bicyclic compound 8. Unlike first
generation Grubbs’s ruthenium catalyst, the second gener-
(2S,6R)-3 98% ee
Scheme 1.
OH
c
a, b
d
h
HO
N
OAc
OAc
OH
N
OH
N
Cbz
5
N
H
Cbz
(2S,6R)-3
O
7
6
H
H
OH
(1R,2S,5S,8aR)-1
N
N
HO
HO
O
O
O
9a
O
10a
HO
O
H
e
f
g
OH
N
H
H
O
OH
10b
OH
N
N
8
O
O
O
9b
HO
9a : 9b = 4.5 : 1
Scheme 2. Reagents and conditions: (a) (COCl)2, DMSO, TEA, DCM, 94%; (b) Ph3PCH3Br, t-BuOK, toluene, 77%; (c) KOH 1 M, MeOH, 86%; (d)
acryloyl chloride, Na2CO3, acetone/water, 73%; (e) 2nd generation Grubbs’s ruthenium catalyst, toluene, MW irradiation, 180 ꢁC, 72%; (f) OsO4,
trimethylamine N-oxide, t-BuOH, 70%; (g) (i) ADA, Dowex 50W · 8 (H+ form); (ii) chromatographic separation, 64% for 10a and 14% for 10b; (h)
(i) Me2SÆBH3, THF; (ii) 3 M HCl, 50 ꢁC, 10 h, 85%.

1950
G. Lesma et al. / Tetrahedron: Asymmetry 18 (2007) 1948–1954
ation one proved to be very suitable for RCM reaction of
a,b-unsaturated amide 7. Moreover, the use of microwave
irradiation12 in this step allowed us to complete the reac-
tion in 30 min compared with the 20 hrs required under
conventional oil bath heating. The presence of a carbonyl
group and a double bond in the five-membered ring adds
versatility to the chiral building block 8. In our plan,
dihydroxylation of olefin 8 was then easily achieved by
oxidation with catalytic OsO4 and trimethylamine N-oxide,
affording the desired products 9a and 9b in good yield as an
inseparable diastereoisomeric mixture. The reaction took
place with good diastereoselectivity and 9a and 9b were
ble mixture of 13a and 13b in a 3:1 diastereoisomeric ratio,
as determined by 1H NMR. After chromatographic separa-
tion, the exo-configuration of the diol moiety was attrib-
uted to the major diastereoisomer 13a, by means of
NOESY analysis (Fig. 2). Compound 13a was then reacted
with borane dimethylsulfide complex, affording the final
product (1R,2S,6S,9aR)-2 in good yield.
For both 8 and 12 molecular modelling calculations13 show
the endo-face to be effectively more sterically hindered
when compared to the exo one, thus precluding an efficient,
high scale preparation of the 1,2-di-epi isomers of 1 and 2.
1
obtained in a 4.5:1 ratio, as determined by H NMR. In
order to separate the two diastereoisomers, 9a and 9b were
converted into the respective acetonide derivatives, which
could be easily separated by usual flash chromatography.
The exo-configuration of the diol formed was unambigu-
ously assigned to the major diastereoisomer 10a, by means
of NOESY analysis, as outlined in Figure 2. Compound
10a was then submitted to the reduction of the amide func-
tion by treatment with borane dimethylsulfide complex,
followed by deprotection of the acetonide, to afford the
desired final product (1R,2S,5S,8aR)-1.
3. Conclusion
In conclusion, this work provides a straightforward proce-
dure to prepare enantiopure dihydroxylated 5-hydroxy-
methyl-indolizidines and 6-hydroxymethyl-quinolizidines,
by means of a chemoenzymatic-RCM approach. Aiming
to give a synthetic contribution in gaining more insights
about the mechanism by which these unnatural alkaloids
act on glycosidase enzymes, further application of this
strategy is currently under investigation, particularly for
the synthesis of pyrrolizidine-based compounds.
H
H6ax
H
H9ax
O
H
OH
N
H2
H
H1
H2
H8ax
H
O
OH
N
4. Experimental
4.1. General
H
H
H
H8ax
H
OH
O
H7ax
H5ax
H6ax
H
H8a
O
All solvents were distilled and properly dried, when neces-
sary, prior to use. All chemicals were purchased from com-
mercial sources and used directly, unless indicated
otherwise. All reactions were monitored by thin layer chro-
matography (TLC) on precoated silica gel 60 F254
(Merck); spots were visualized with UV light or by treat-
ment with 1% aqueous KMnO4 solution. Products were
purified by flash chromatography on Merck silica gel 60
H9a
OH
10a
Figure 2. Diagnostic NOE contacts in 10a and 13a.
13a
The intermediate 6 was also used as a starting material for
the synthesis of the quinolizidine derivative 2 (Scheme 3).
Acylation with 3-butenoic acid in the presence of 1-ethyl-
3-(3-dimethylaminopropyl)carbodiimide (EDC) cleanly
afforded amide 11, which was cyclised by RCM in the pre-
viously described reaction conditions (2nd generation
Grubbs’s ruthenium catalyst, toluene, microwave irradia-
tion). Bicyclic olefin 12 was then dihydroxylated with the
OsO4/trimethylamine N-oxide system to produce a separa-
1
(230–400 mesh). H and 13C NMR spectra were recorded
with Bruker AC 300 (1H, 300 MHz; 13C, 75.4 MHz) and
400 MHz Avance (1H, 400 MHz; 13C, 100 MHz) NMR
spectrometers. Chemical shifts are reported in parts per
million downfield from SiMe4 (d = 0.0). HRMS spectra
were measured on a Jeol SX 102 instrument equipped with
its standard sources. Optical rotations were measured with
a Perkin–Elmer 241 polarimeter.
H
HO
HO
OH
e
N
(1R,2S,6S,9aR) - 2
O
13a
H
c,d
a
OH
b
OH
6
N
N
O
O
H
HO
HO
OH
11
12
N
13a : 13b = 3 : 1
O
13b
Scheme 3. Reagents and conditions: (a) 3-butenoic acid, EDC, DMAP, DMF, 79%; (b) 2nd generation Grubbs’s ruthenium catalysts, toluene, MW
irradiation, 180 ꢁC, 87%; (c) (i) OsO4, trimethylamine N-oxide, t-BuOH; (ii) chromatographic separation, 48% for 13a and 16% for 13b; (d) Me2SÆBH3,
THF, 85%.

G. Lesma et al. / Tetrahedron: Asymmetry 18 (2007) 1948–1954
1951
25
4.2. Synthesis
2:1). ½aꢁD ¼ ꢀ2:3 ðc 1; CHCl3Þ. 1H NMR (CDCl3,
1
400 MHz): H NMR (400 MHz, CDCl3) d 7.35 (m, 5H),
4.2.1.
dine-1-carboxylic acid benzyl ester 3. Compound
(2S,6R)-2-Acetoxymethyl-6-hydroxymethyl-piperi-
4
5.88 (ddd, 1H, J = 17.5, 10.7, 4.8), 5.17 (m, 4H), 4.86
(m, 1H), 4.56 (dd, 1H, J = 12.3, 6.6), 4.20 (dd, 1H,
J = 10.8, 8.1), 4.00 (dd, 1H, J = 10.8, 7.2), 1.98 (s, 3H),
1.95 (m, 1H), 1.77–1.65 (m, 5H), 1.52 (m, 1H). 13C NMR
(CDCl3, 75 MHz): d 171.2, 156.7, 139.9, 137.6, 129.1
(5C), 116.2, 67.9, 64.7, 52.2, 49.8, 28.2, 25.8, 21.3, 15.4.
HRMS-FAB m/z calcd 317.1627. Found: 317.1628. Anal.
Calcd for C18H23NO: C, 68.12; H, 7.30; N, 4.41; O,
20.16. Found: C, 68.17; H, 7.27; N, 4.39.
(100 mg, 0.4 mmol), vinyl acetate (110 lL, 1.2 mmol), and
lipase from C. Cylindracea (10 mg) were mixed with 1 mL
of ionic liquid [BMIM]–[PF6] ([BMIM]+ = 1-butyl-3-
methylimidazolium), and the resulting heterogeneous mix-
ture was stirred at 40 ꢁC for 24 h. The reaction was diluted
with 3 mL of water and the enzyme was filtered through a
pad of Celite. The aqueous phase was extracted three times
with AcOEt and the combined organic fractions were dried
and evaporated. The crude product was purified by flash
chromatography (hexane/ethyl acetate, 3:4) to yield 3 as
a colorless oil (115 mg, 90% yield). Spectroscopical data
are in agreement with the previously reported ones (see
Ref. 8).
4.2.3. ((2S,6R)-6-Vinyl-piperidin-2-yl)-methanol 6. To a
solution of 5 (600 mg, 3.59 mmol) in MeOH (30 mL) were
added KOH 2 M (18 mL, 36 mmol). The resulting mixture
was stirred at 80 ꢁC for 40 h and the aqueous phase
extracted 3 times with CH2Cl2. The combined organic
phases were dried and evaporated to yield product 6 pure
without other purification (440 mg, 86% yield). Rf = 0.21
4.2.2. (2S,6R)-2-Acetoxymethyl-6-vinyl-piperidine-1-carb-
oxylic acid benzyl ester 5. To a stirred solution of oxalyl
chloride (0.105 mL, 1.24 mmol) in 1.8 mL of anhydrous
CH2Cl2 at ꢀ78 ꢁC under N2, was added DMSO
(0.130 mL, 1.42 mmol) in 1 mL of anhydrous CH2Cl2
dropwise and the mixture allowed to react for 5 min at
ꢀ78 ꢁC. Alcohol 3 (200 mg, 0.62 mmol) in 1 mL of anhy-
drous CH2Cl2 was added, and the reaction mixture was
stirred for 1 h at ꢀ78 ꢁC. On addition of anhydrous Et3N
(0.345 mL, 2.48 mmol), the dry ice/acetone bath was
removed, and the reaction temperature left to go to rt. The
reaction was diluted with 4 mL of CH2Cl2 and then poured
into 10 mL of CH2Cl2 and 10 mL of 5% H3PO4 solution.
The aqueous phase was extracted twice with CH2Cl2 and
the combined CH2Cl2 fractions were dried and evaporated
to give the crude aldehyde (2S,6R)-2-acetoxymethyl-6-
formyl-piperidine-1-carboxylic acid benzyl ester (185 mg,
94% yield) sufficiently pure to proceed to the next synthetic
25
1
(hexane/ethyl acetate, 1:2). ½aꢁD ¼ ꢀ3:3 ðc 1; CHCl3Þ. H
NMR (CDCl3, 400 MHz): d 5.87 (ddd, J = 17.1, 10.4,
6.5 Hz, 1H), 5.19 (dt, J = 17.1, 1.5 Hz, 1H), 5.06 (ddd,
J = 10.4, 1.5, 1.0 Hz, 1H), 3.66 (dd, J = 10.6, 3.6 Hz,
1H), 3.48 (dd, J = 10.6, 7.6 Hz, 1H), 3.16 (m, 1H), 2.79
(m, 1H), 1.98 (br s, 2H), 1.87 (m, 1H), 1.72 (m, 1H), 1.56
(m, 1H), 1.45 (m, 1H), 1.20 (m, 1H), 1.15 (m, 1H). 13C
NMR (CDCl3, 75 MHz): d 141.6, 114.3, 66.3, 59.4, 57.9,
32.1, 27.9, 24.0. HRMS-FAB m/z calcd 141.1154. Found:
141.1157. Anal. Calcd for C8H15NO: C, 68.04; H, 10.71;
N, 9.92; O, 11.33. Found: C, 68.05; H, 10.72; N, 9.89.
4.2.4. 1-((2S,6R)-2-Hydroxymethyl-6-vinyl-piperidin-1-yl)-
propenone 7. To a solution of 6 (600 mg, 4.25 mmol) in
acetone (20 mL) was added 9 mL of a saturated Na2CO3
aqueous solution and acryloyl chloride (0.6 mL,
7.43 mmol). The resulting mixture was stirred for 4 h and
the aqueous phase was extracted 3 times with CH2Cl2.
The combined organic phases were dried and evaporated
to yield the product 7 pure without further purification
(590 mg, 73% yield). Rf = 0.49 (ethyl acetate).
step without purification. Rf = 0.72 (hexane/ethyl acetate,
25
1:3). ½aꢁD ¼ ꢀ20:9 ðc 1; CHCl3Þ. 1H NMR (CDCl3,
300 MHz): d 9.6 (s, 1H) 7.40–7.32 (m, 5H), 5.12 (s, 2H),
4.58–4.50 (m, 1H), 4.40–4.30 (m, 1H), 4.13 (dd, J = 10.9,
8.0 Hz, 1H), 3.95 (dd, J = 10.9, 6.9 Hz, 1H), 1.93 (s, 3H),
1.81–1.45 (m, 6H). 13C NMR (CDCl3, 75 MHz): d 201.2,
170.6, 158.7, 137.6, 128.5–128.0 (5C), 67.61, 63.9, 59.5,
48.9, 24.6, 22.4, 20.7, 17.5. HRMS-FAB m/z calcd
319.1420. Found: 319.1424. Anal. Calcd for C17H21NO5:
C, 63.94; H, 6.63; N, 4.39; O, 25.05. Found: C, 63.89; H,
6.64; N, 4.38.
25
1
½aꢁD ¼ þ10:4 ðc 1; CHCl3Þ. H NMR (CDCl3, 400 MHz):
d 6.65 (dd, J = 16.6, 10.7 Hz, 1H), 6.30 (dd, J = 16.6,
1.6 Hz, 1H), 5.93 (ddd, J = 17.3, 10.9, 4.4 Hz, 1H), 5.67
(dd, J = 10.7, 1.6 Hz, 1H), 5.35 (d, J = 17.3, 1H), 5.21 (d,
J = 10.9, 1.5 Hz, 1H), 4.88–4.55 (br m 2H), 3.75 (t,
J = 9.9 Hz, 1H), 3.65 (dd, J = 9.9, 7.2 Hz, 1H), 2.43 (br
s, 1H), 1.95 (br d, J = 11.9 Hz, 1H), 1.85–1.50 (m, 5H).
13C NMR (CDCl3, 100 MHz): d 167.8, 140.1, 129.5,
128.0, 116.8, 65.7, 52.4, 50.2, 29.7, 25.9, 16.0. HRMS-
FAB m/z calcd 195.1259. Found: 195.1257. Anal. Calcd
for C11H17NO2: C, 67.66; H, 8.78; N, 7.17; O, 16.39.
Found: C, 67.64; H, 8.75; N, 7.13.
Anhydrous toluene (4 mL) and t-BuOK (107 mg,
0.952 mmol) were mixed at rt under N2, and Ph3P(CH3)Br
(340 mg, 0.952 mmol) was added to the mixture. After the
mixture was stirred for 1.5 h, (2S,6R)-2-acetoxymethyl-6-
formyl-piperidine-1-carboxylic acid benzyl ester (100 mg,
0.313 mmol) was added with 2 mL of anhydrous toluene
to the reaction mixture, and it was refluxed for 3 h. The
reaction mixture was then partitioned between 10 mL of
AcOEt and 6 mL of 10% Na2S2O3 solution, and the
aqueous phase was extracted 3 times with AcOEt. The
organic fractions were dried and evaporated. The crude
product was purified by flash chromatography (hexane/
ethyl acetate, 2:1) to yield compound 5 as a colorless
oil (76 mg, 77% yield). Rf = 0.55 (hexane/ethyl acetate,
4.2.5. (5S,8aR)-5-Hydroxymethyl-6,7,8,8a-tetrahydro-5H-
indolizin-3-one 8. To a stirred solution of 7 (300 mg,
1.54 mmol) in 50 mL of toluene was added the Grubbs cat-
alyst 2nd generation (65 mg, 0.076 mmol). The reaction
mixture was heated by microwave irradiation at 180 ꢁC
for 300 and the solvent was removed under reduced pres-
sure. The resulting oil was purified by column chromato-
graphy (ethyl acetate) to afford 8 (185 mg, 72%). Rf =
25
1
0.31 (ethyl acetate). ½aꢁD ¼ ꢀ4:5 ðc 1; CHCl3Þ. H NMR

1952
G. Lesma et al. / Tetrahedron: Asymmetry 18 (2007) 1948–1954
(CDCl3, 400 MHz): d 7.05 (dd, J = 6.0, 1.0 Hz, 1H), 6.12
(dd, 6.0, 1.0 Hz, 1H), 5.24 (t, J = 7.8 Hz, 1H), 3.97 (m,
1H), 3.85 (br d, J = 12.4 Hz, 1H), 3.72 (br s, 1H), 3.41
(ddt, J = 13.4, 6.5, 3.4 Hz 1H), 2.12 (dqd, J = 12.8, 3.4,
1.0 Hz, 1H), 2.09 (dt, J = 13.5, 3.3 Hz, 1H), 1.70 (m, 1H),
1.60 (dt, J = 13.5, 3.3 Hz, 1H), 1.37 (qd, J = 12.8, 4.2 Hz,
1H), 1.09 (qd, J = 12.8, 4.2 Hz, 1H). 13C NMR (CDCl3,
100 MHz): d 174.6, 147.7, 128.8, 64.9, 63.9, 60.9, 31.0,
30.4, 24.4. HRMS-FAB m/z calcd 167.0946. Found:
167.0941. Anal. Calcd for C9H13NO2: C, 64.65; H, 7.84;
N, 8.38; O, 19.14. Found: C, 64.69; H, 7.81; N, 8.32.
4.6 Hz, 1H). 13C NMR (CDCl3, 100 MHz): d 169.8,
112.7, 78.1, 77.1, 64.6, 62.7, 61.3, 30.6, 29.7, 27.6, 26.7,
23.8. HRMS-FAB m/z calcd 241.1314. Found: 241.1318.
Anal. Calcd for C12H19NO4: C, 59.73; H, 7.94; N, 5.81;
O, 26.52. Found: C, 59.69; H, 7.91; N, 5.72.
25
Compound 10b: Rf = 0.14 (ethyl acetate). ½aꢁD
¼
1
ꢀ2:0 ðc 1; CHCl3Þ. H NMR (CDCl3, 400 MHz): d ppm
4.97 (br s, 1H), 4.66 (br s, 2H), 3.92 (dd, J = 12.9, 6.9
Hz, 1H), 3.85 (dd, J = 12.9, 2.4 Hz, 1H), 3.50 (m, 1H),
3.19 (m, 1H), 2.00 (m, 1H), 1.84–1.61 (m, 2H), 1.54 (m,
1H), 1.49 (s, 3H), 1.42 (s, 3H), 1.40 (m, 1H), 1.28 (m,
1H). 13C NMR (CDCl3, 100 MHz): d 171.5, 112.7, 78.3,
74.1, 63.7, 61.1, 60.1, 27.9, 27.0, 26.0, 25.4, 23.1. HRMS-
FAB m/z calcd 241.1314. Found: 241.1313. Anal. Calcd
for C12H19NO4: C, 59.73; H, 7.94; N, 5.81; O, 26.52.
Found: C, 59.66; H, 7.58; N, 5.82.
4.2.6.
hexahydro-indolizin-3-one 9a and (1R,2R,5S,8aR)-1,2-di-
hydroxy-5-hydroxymethyl-hexahydro-indolizin-3-one 9b.
(1S,2S,5S,8aR)-1,2-Dihydroxy-5-hydroxymethyl-
A
2.5% solution of osmium tetraoxide in tert-butyl alcohol
(0.350 mL, 6.86 mg, 0.027 mmol) was added to a solution
of 90 mg (0.539 mmol) of indolizidinone 8 and 100 mg
(0.875 mmol) of trimethylamine N-oxide dihydrate in
2.5 mL of tert-butyl alcohol–water (3:1). The resulting solu-
tion was stirred at 35–40 ꢁC for 3.5 h. After being allowed
to cool to 25 ꢁC, the reaction mixture was treated with
sodium bisulfite (181 mg, 1.74 mmol), and the resulting
mixture was stirred for 30 min, partially concentrated under
reduced pressure, and then filtered through Celite with ethyl
acetate. The filtrate was dried over sodium sulfate and
concentrated under reduced pressure to afford the crude
product, which was purified by column chromatography
(dichloromethane/methanol, 95:5) to afford 75 mg (70%
yield) of a 4.5:1 inseparable mixture of 9a and 9b. 1H
NMR (CDCl3, 400 MHz, major diastereoisomer 9a): d
7.05 (dd, J = 6.0, 1.0 Hz, 1H), 6.12 (dd, 6.0, 1.0 Hz, 1H),
5.24 (t, J = 7.8 Hz, 1H), 3.97 (m, 1H), 3.85 (br d,
J = 12.4 Hz, 1H), 3.41 (ddt, J = 13.4, 6.5, 3.4 Hz 1H),
2.12 (dqd, J = 12.8, 3.4, 1.0 Hz, 1H), 2.09 (dt, J = 13.5,
3.3 Hz, 1H), 1.70 (m, 1H), 1.60 (qt, J = 13.5, 3.3 Hz, 1H),
1.37 (qd, J = 12.8, 4.2 Hz, 1H), 1.09 (qd, J = 12.8, 4.2 Hz,
1H). 13C NMR (CDCl3, 100 MHz): d 172.4, 147.7, 128.8,
64.9, 63.9, 60.9, 31.0, 30.4, 24.4. HRMS-FAB m/z calcd
201.1001. Found: 201.1004. Anal. Calcd for C9H15NO4:
C, 53.72; H, 7.51; N, 6.96; O, 31.80. Found: C, 53.75; H,
7.56; N, 7.00.
4.2.8. (1R,2S,5S,8aR)-5-Hydroxymethyl-octahydro-indol-
izine-1,2-diol 1. Lactam 10a (20 mg, 0.084 mmol) in dry
THF (3.8 mL) was treated with a solution of Me2SÆBH3
(2 M in THF, 0.39 mL, 0.78 mmol) under N2. After 2 h
at RT and 1 h at reflux conditions, the excess reducing
reagent was decomposed by the careful addition of EtOH
(0.77 mL) at ꢀ5 ꢁC. After evaporation, the resulting resi-
due was stirred in 5 mL of 1M aqueous HCl at reflux for
1 h. The reaction mixture was then concentrated under
reduced pressure, and the resulting residue was passed
through a column of 5 g of Dowex 1 · 8-200 resin (OHꢀ
form) with water. The oil obtained was purified by flash
column chromatography on silica gel (methanol/ethyl ace-
tate/triethylamine, 10:89:1) to give 1 (13 mg, 85% yield).
25
Rf = 0.35 (dichloromethane/methanol, 95:5). ½aꢁD
¼
1
ꢀ5:1 ðc 1; MeOHÞ. H NMR (CDCl3, 400 MHz): d ppm
4.08 (m, 1H), 3.72 (br s, 3H), 3.59 (m, 2H), 3.41 (m, 1H),
3.19 (m, 1H), 3.02 (m, 1H), 2.65–2.20 (m, 2H), 1.99 (m,
2H), 1.80–1.65 (m, 3H), 1.33 (m, 1H). 13C NMR (CDCl3,
100 MHz): d 83.7, 77.1, 68.8, 63.7, 63.2, 56.2, 27.9, 26.8,
23.5. HRMS-FAB m/z calcd 187.1208. Found: 187.1205.
Anal. Calcd for C9H17NO3: C, 57.73; H, 9.15; N, 7.48;
O, 25.64. Found: C, 57.69; H, 9.11; N, 7.51.
4.2.9. 1-((2S,6R)-2-Hydroxymethyl-6-vinyl-piperidin-1-yl)-
but-3-en-1-one 11. To an ice cooled solution of EDC
(150 lL, 0.85 mmol) in 4 mL of dry DMF under N2, 6
(100 mg, 0.71 mmol), 3-butenoic acid (67 lL, 0.78 mmol)
and DMAP (104 mg, 1.78 mmol) were added with stirring.
The cooling bath was removed and the solution stirred at
room temperature for 11 h. After evaporation of the sol-
vent, the residue was dissolved in 10 mL of AcOEt and
washed with 15 mL of solution. The aqueous phase was
extracted twice with AcOEt (10 mL). The combined organic
phases were washed with 5% aqueous HCl (10 mL), satu-
rated aqueous NaHCO3(10 mL) and then brine (10 mL).
The organic phase was dried and evaporated to yield
4.2.7.
(3aR,6S,9aR,9bR)-6-Hydroxymethyl-2,2-dimethyl-
hexahydro-[1,3]dioxolo[4,5-a]indolizin-4-one 10a and (3aS,6S,
9aR,9bS)-6-hydroxymethyl-2,2-dimethyl-hexahydro-[1,3]di-
oxolo[4,5-a]indolizin-4-one 10b.
A mixture of 35 mg
(0.174 mmol) of the 9a and 9b and 103 mg of Dowex
50W · 8 (H+ form) in 5 mL of 2,2-dimethoxypropane
(ADA) was stirred at 40 ꢁC for 3.5 h, after which it was
partially concentrated, filtered through Celite, and evapo-
rated to dryness. Purification of the resulting crude prod-
uct by column chromatography (hexane/ethyl acetate,
2:1) gave 31 mg (64% yield) of 10a and 7 mg (14% yield)
of 10b.
the product 11 (117 mg, 79% yield) pure without
25
25
Compound 10a: Rf = 0.25 (ethyl acetate). ½aꢁD
¼
further purification. Rf = 0.44 (ethyl acetate). ½aꢁD ¼
1
1
þ6:4 ðc 1; CHCl3Þ. H NMR (CDCl3, 400 MHz): d 4.72
(br s, 1H), 4.66 (d, J = 6.4 Hz, 1H), 4.37 (d, J = 6.4 Hz,
1H), 3.92 (m, 2H), 3.46 (dd, J = 12.9, 2.6 Hz, 1H), 3.25
(m, 1H), 2.00 (m, 1H), 1.65 (m, 2H), 1.57 (m, 1H), 1.49
(s, 3H), 1.44 (m, 1H), 1.39 (s, 3H), 1.16 (dq, J = 13.1,
ꢀ2:5 ðc 1; CHCl3Þ. H NMR (CDCl3, 400 MHz): d ppm
5.86 (m, 2H), 5.20 (m, 4H), 4.82 (br m, 1H), 4.49 (br m,
1H), 4.09 (br s, 1H), 3.65 (m, 2H), 3.21 (m, 2H), 1.98–
1.43 (br m, 6H). 13C NMR (CDCl3, 100 MHz): d 168.3,
139.2, 131.7, 117.6, 116.2, 65.0, 53.9, 50.6, 38.8, 29.3,

G. Lesma et al. / Tetrahedron: Asymmetry 18 (2007) 1948–1954
1953
24.9, 15.1. HRMS-FAB m/z calcd 209.1416. Found:
209.1421. Anal. Calcd for C12H19NO2: C, 68.87; H, 9.15;
N, 6.69; O, 15.29. Found: C, 68.83; H, 9.14; N, 6.66.
70.3, 66.9, 66.8, 62.5, 55.4, 36.9, 24.5, 23.0, 16.8. HRMS-
FAB m/z calcd 215.1158. Found 215.1151. Anal. Calcd
for C10H17NO4: C, 55.80; H, 7.96; N, 6.51; O, 29.73.
Found: C, 55.77; H, 7.98; N, 6.48.
4.2.10. (6S,9aR)-6-Hydroxymethyl-3,6,7,8,9,9a-hexahydro-
quinolizin-4-one 12. To a stirring solution of 11 (80 mg,
0.38 mmol) in 12 mL of dry toluene was added the Grubbs
catalyst 2nd generation (16 mg, 0.088 mmol). The reaction
mixture was heated by microwave irradiation at 180 ꢁC for
30 min and the solvent was removed under reduced pres-
sure. The resulting oil was purified by column chromato-
graphy (ethyl acetate) to afford 12 (59 mg, 87%). Rf =
0.31 (ethyl acetate). ½aꢁD ¼ ꢀ4:5 ðc 1; CHCl3Þ. H NMR
(CDCl3, 400 MHz): d 5.66 (m, 2H), 3.95 (dd, J = 12.0,
3.0 Hz, 1H), 3.81 (m, 2H), 3.14 (m, 1H), 2.94 (m, 2H,
H3), 2.61 (br s, 1H), 1.98 (m, 1H), 1.89 (m, 1H), 1.71 (m,
1H), 1.67 (m, 1H), 1.63 (m, 1H), 1.32 (m, 1H). 13C NMR
(CDCl3, 100 MHz): d 167.7, 125.8, 120.9, 65.3, 63.7, 60.3,
34.1, 33.2, 30.4, 24.4. HRMS-FAB m/z calcd 181.1103.
Found: 181.1109. Anal. Calcd for C10H15NO2: C, 66.27;
H, 8.34; N, 7.73; O, 17.66. Found: C, 66.29; H, 7.77; N,
8.28.
4.2.12. (1S,2R,6S,9aR)-6-Hydroxymethyl-octahydro-quin-
olizine-1,2-diol 2. Lactam 13a (40 mg, 0.186 mmol) in
dry THF (6 mL) was treated with a solution of Me2S.BH3
(2 M in THF, 0.930 mL, 1.86 mmol) under N2. After 2 h at
rt and 1 h under reflux conditions, the excess reducing
reagent was decomposed by careful addition of EtOH
(2 mL) at ꢀ5 ꢁC. After evaporation, the residue was puri-
fied by flash column chromatography on silica gel (metha-
nol/ethyl acetate/triethylamine, 10:89:1) to give 2 (31 mg,
25
1
85% yield). Rf = 0.37 (methanol/ethyl acetate/triethyl-
25
amine, 10:89:1). ½aꢁD ¼ ꢀ7:9 ðc 1; MeOHÞ. 1H NMR
(CDCl3, 400 MHz): d ppm 4.03 (m, 1H), 3.94 (dd,
J = 11.2, 3.7 Hz, 1H), 3.40 (m, 2H), 2.98 (m, 1H), 2.47–
2.27 (m, 3H), 1.83 (m, 2H), 1.79–1.90 (m, 6H), 1.35 (m,
1H), 1.23 (m, 2H). 13C NMR (CDCl3, 100 MHz): d 73.9,
66.8, 62.8, 62.5, 61.3, 43.9, 30.1 (2C), 29.0, 23.4. HRMS-
FAB m/z calcd 201.1365. Found: 201.1361. Anal. Calcd
for C10H19NO3: C, 59.68; H, 9.52; N, 6.96; O, 23.85.
Found: C, 59.61; H, 9.41; N, 6.82.
4.2.11.
(1R,2S,6S,9aR)-1,2-Dihydroxy-6-hydroxymethyl-
octahydro-quinolizin-4-one 13a and (1S,2R,6S,9aR)-1,2-
dihydroxy-6-hydroxymethyl-octahydro-quinolizin-4-one 13b.
A 2.5% solution of osmium tetraoxide in tert-butyl alcohol
(0.700 mL, 13.7 mg, 0.054 mmol) was added to a solution
of 180 mg (1.0 mmol) of 12 and trimethylamine N-oxide
dihydrate (180 mg, 1.62 mmol) in 2.5 mL of tert-butyl alco-
hol/water (3:1). The resulting solution was stirred at 40 ꢁC
for 3 h. After cooling to 25 ꢁC, the reaction mixture was
treated with sodium bisulfite (400 mg, 3.84 mmol), and
the resulting mixture was stirred for 30 min, partially con-
centrated under reduced pressure, and then filtered through
Celite with ethyl acetate. The filtrate was dried over sodium
sulfate and concentrated under reduced pressure to
afford the crude product, which was purified by silica gel
column chromatography with 5% methanol in dichloro-
methane to afford 13a (104 mg, 48% yield) and 13b
(34 mg, 16% yield).
References
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Compound 13a: Rf = 0.44 (dichloromethane/methanol,
25
95:5). ½aꢁD ¼ þ8:6 ðc 1; MeOHÞ. 1H NMR (CDCl3,
400 MHz): d ppm 4.13 (m, 1H), 3.89 (dd, J = 12.2,
2.7 Hz, 1H), 3.77 (dd, J = 12.2, 6.6 Hz, 1H), 3.73 (m,
1H), 3.48 (m, 2H), 2.72 (dd, J = 17.4, 7.3 Hz, 1H), 2.63
(dd, J = 17.4, 5.3 Hz, 1H), 2.39 (br s, 1H), 2.01 (m, 1H),
1.91 (m, 1H), 1.75–1.60 (m, 3H), 1.38–1.25 (m, 3H), 0.86
(m, 1H). 13C NMR (CDCl3, 100 MHz): d 170.2, 71.5,
65.7, 64.8, 62.7, 60.9, 37.6, 29.7, 26.3, 21.9. HRMS-FAB
m/z calcd 215.1158. Found: 215.1149. Anal. Calcd for
C10H17NO4: C, 55.80; H, 7.96; N, 6.51; O, 29.73. Found:
C, 55.86; H, 7.94; N, 6.53.
Compound 13b: Rf = 0.25 (dichloromethane/methanol,
25
95:5). ½aꢁD ¼ ꢀ6:6 ðc 1; MeOHÞ. 1H NMR (CDCl3,
400 MHz): d ppm 4.21 (m, 1H), 3.91 (dd, J = 12.3,
2.8 Hz,1H), 3.81 (dd, J = 12.4, 6.8 Hz, 1H), 3.78 (m, 1H),
0
3.57 (m, 1H, H9a ), 3.49 (m, 1H), 2.71 (m, 2H), 2.11 (m,
3H), 2.07 (m, 1H), 1.88 (m, 2H), 1.79 (m, 1H), 1.76 (m,
1H), 1.64 (m, 1H). 13C NMR (CDCl3, 100 MHz): d 171.6,

1954
G. Lesma et al. / Tetrahedron: Asymmetry 18 (2007) 1948–1954
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