Synthesis of chiral organotin reagents: Synthesis of diphenyl-{(1S,2R,3S,4R)-3-(alkoxymethyl)bicyclo[2.2.1]heptan-2-yl}tin hydrides. X-Ray crystal structure of (R)-4,4-dimethyl-2-oxotetrahydrofuran-3-yl (1S,2S,3R,4R)-3-triphenylstannylbicyclo[2.2.1]hept-5-ene-2-carboxylate

Article abstract of DOI:10.1039/a706293a

Conditions have been developed for the stereoselective Diels-Alder addition of cyclopentadiene to (R)-4,4-dimethyl-2-oxotetrahydrofuran-3-yl (E)-3-triphenylstannylprop-2-enoate 10 to give the endo-adduct 14 whose structure has been confirmed by X-ray crystallography. The adduct 14 is converted into (1S,2R,3S,4R)-3-hydroxymethylbicyclo[2.2.1]heptan-2-yl(triphenyl)stannane 22 which is shown to have an enantiomeric excess (ee) of 94%. This alcohol has been converted into its methyl ether (-)-3, trityl ether 25, tert-butyldimethylsilyl ether 26 and 1-naphthoate 27 which give the tin hydrides 4, 31-34 on treatment with iodine and sodium borohydride. Aspects of the chemistry of these enantiomerically enriched tin hydrides are briefly discussed.

Full text of DOI:10.1039/a706293a

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Synthesis of chiral organotin reagents: synthesis of diphenyl-
{(1S,2R,3S,4R)-3-(alkoxymethyl)bicyclo[2.2.1]heptan-2-yl}tin
hydrides. X-Ray crystal structure of (R)-4,4-dimethyl-2-oxo-
tetrahydrofuran-3-yl (1S,2S,3R,4R)-3-triphenylstannyl-
bicyclo[2.2.1]hept-5-ene-2-carboxylate
Roy Beddoes, Robert M. Pratt and Eric J. Thomas*
The Department of Chemistry, The University of Manchester, Manchester, UK M13 9PL
Conditions have been developed for the stereoselective Diels–Alder addition of cyclopentadiene to (R)-
4,4-dimethyl-2-oxotetrahydrofuran-3-yl (E)-3-triphenylstannylprop-2-enoate 10 to give the endo-adduct
14 whose structure has been confirmed by X-ray crystallography. The adduct 14 is converted into
(1S,2R,3S,4R)-3-hydroxymethylbicyclo[2.2.1]heptan-2-yl(triphenyl)stannane 22 which is shown to have an
enantiomeric excess (ee) of 94%. This alcohol has been converted into its methyl ether (Ϫ)-3, trityl ether
25, tert-butyldimethylsilyl ether 26 and 1-naphthoate 27 which give the tin hydrides 4, 31–34 on treatment
with iodine and sodium borohydride. Aspects of the chemistry of these enantiomerically enriched tin
hydrides are briefly discussed.
In the preceding paper, a synthesis of the racemic bicyclo-
[2.2.1]heptan-2-yltin hydride 4 is reported.1 The key step in this
synthesis is the Diels–Alder reaction between methyl (E)-3-
(triphenylstannyl)acrylate 1 and cyclopentadiene which gives
the endo-adduct 2 with excellent stereoselectivity. This adduct is
reduced, O-methylated and hydrogenated to give the 2-meth-
oxymethylbicycloheptanyl(triphenyl)stannane 3 which is con-
verted into the tin hydride 4 by treatment with iodine followed
by reduction with sodium borohydride. The tin hydride 4 was
found to reduce alkyl halides and to add to methyl propiolate
under free-radical conditions.1 We now report a synthesis of
enantiomerically enriched tin hydrides including 4 using stereo-
selective Diels–Alder reactions of chiral 3-triphenylstannyl-
acrylates.
unsuccessful, perhaps because the vinylstannane is incompat-
ible with the carboxylic acid functionality, it was decided to
prepare the chiral dienophiles by esterification of propiolic acid
using chiral, non-racemic alcohols followed by conjugate add-
ition of the triphenyltin moiety.4,5
Propiolic acid was esterified using (S)-ethyl lactate and (R)-
pantolactone to give the esters 5 and 9 using N,N-diisopro-
pylcarbodiimide with a catalytic amount of 4-dimethylamino-
pyridine as the coupling reagent.6 Hydrostannation of the ester
5 using triphenyltin hydride under free-radical conditions
initiated by triethylborane7 gave the (E)- and (Z)-3-(triphen-
ylstannyl)acrylates 6 and 7 together with the 3,3-bis(triphenyl-
O
Me
O
Me
Ph3SnH
Et3B
O
CO2Et
O
CO2Et
SnPh3
Ph3Sn
CO2Me
H
5
6
CO2Me
+
Ph3Sn
O
Me
1
2
O
Me
O
SnPh3
8
CO2Et
+
O
CO2Et
Ph3Sn
SnPh3
SnPh2H
SnPh3
7
H
H
OMe
OMe
O
O
O
O
3
4
O
O
Ph3SnH
(see text)
O
O
Me
Me
Results and discussion
Me
Me
Ph3Sn
Many procedures have been developed for the asymmetric syn-
thesis of bicyclo[2.2.1]hept-5-enes by Diels–Alder reactions of
cyclopentadiene and acrylates using both chiral auxiliaries and
chiral, non-racemic Lewis acids as catalysts.2,3 It was decided to
investigate the use of chiral auxiliaries for the asymmetric syn-
thesis of the ester 2 since it was not clear which Lewis acids
would be compatible with the vinylstannane component of
the dienophile. Since attempts to hydrolyse methyl (E)-3-
(triphenylstannyl)propenoate 1 to the corresponding acid were
10
9
+
O
O
O
O
O
O
+
O
O
Me
Me
Me
Me
SnPh3
11
Ph3Sn
SnPh3
12
J. Chem. Soc., Perkin Trans. 1, 1998
717

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stannyl)propanoate 8 which were isolated in yields of 13, 30 and
25% using 1.2 mol equiv. of tin hydride. No attempt was made
to improve this synthesis of the (E)-ester 6. Hydrostannation of
the pantolactone-derived ester 9 under free-radical conditions
gave the (E)- and (Z)-vinylstannanes 10 and 11 in yields of 25
and 32%, respectively, using azoisobutyronitrile as the initiator
in benzene heated under reflux,8 and yields of 23 and 44% using
triethylborane at room temperature.7 The (Z)-isomer 11 is
believed to be the predominant kinetic product in these reac-
tions, partial isomerisation to the more stable (E)-isomer 10
taking place under the free-radical conditions.9 The triphenyltin
cuprate, LiCuBr(Ph3Sn)ؒMe2S, which was prepared using either
Ph3SnCl–Li or Ph3SnH–lithium diisopropylamide to generate
the triphenyltin lithium, reacted with the propiolate 9 to give
modest yields of the (E)- and (Z)-vinylstannanes 10 and 11.10–12
The cuprate reagents prepared from lithium bromide, copper()
bromide, and either 1 or 2 mol equiv. of triphenyltin lithium, i.e.
with no dimethyl sulfide present, gave similar results.13 Better
stereoselectivity, ca. 25:1, in favour of the (E)-vinylstannane 10
was obtained using 2 mol equiv. of the cuprate reagent prepared
from lithium iodide, copper() iodide, and triphenyltin lithium13
if the reaction was quenched by addition to a solution of glacial
acetic acid in tetrahydrofuran at Ϫ78 ЊC. However, the yield
was only modest being ca. 30% for larger scale reactions with
15% of the bis-adduct 12 also being obtained. The use of less
than 2 mol equiv. of the reagent reduced the amount of bis-
adduct 12 but gave a lower yield of the required (E)-
vinylstannane 10.
vinylstannane is unstable in the presence of these strong Lewis
acids. With zinc() chloride or bromide or with tin() chloride
or bromide, only modest conversion into products was
observed at temperatures in the range Ϫ20 to Ϫ55 ЊC. However,
good conversion into products was found using aluminium tri-
chloride or diethylaluminium chloride at temperatures in the
range Ϫ20 to Ϫ78 ЊC.5,14 Optimum results were obtained using
2 mol equiv. of diethylaluminium chloride at Ϫ50 ЊC for 19 h
when the endo:exo selectivity was >98:2 and the ratio of the
separable endo-adducts 13 and 14 was 10:90 leading to an iso-
lated yield of the endo-adduct 14 of 63%. Reactions carried out
at lower temperatures tended not to go to completion and the
use of more than 2 mol equiv. of diethylaluminium chloride led
to lower yields with the formation of a side-product identified
as the pentenoate 17. Note, that within the endo-manifold the
diastereofacial selectivity of addition to the vinylstannane 10
under Lewis acid-promoted conditions is the reverse of that
observed under thermal conditions.
O
O
O
O
O
O
Me
Me
Me
O
Me
O
Me
17
18
Diels–Alder reactions between cyclopentadiene and the
lactate-derived (E)-vinylstannane 6 were carried out in benzene
heated under reflux but gave mixtures of all four endo- and exo-
H
O
1
products which could not be separated. From the H NMR
O
spectra of crude mixtures of products, the endo:exo selectivity
was estimated to be 90:10, with a diastereoisomeric excess in
the endo-manifold of 30%. The Diels–Alder reaction between
the pantolactone-derived (Z)-vinylstannane 11 and cyclopen-
tadiene in benzene heated under reflux similarly gave an
inseparable mixture of all four stereoisomeric products with an
endo:exo ratio of ca. 30:70. However, the endo-products 13
Me
O
Me
O
19
The endo-structures 13 and 14 were assigned to the major
Diels–Alder products from the reactions between the pantolac-
tate 10 and cyclopentadiene by analogy with the reaction of the
methyl ester 1 and cyclopentadiene and were consistent with
spectroscopic data.1 For example, in the 1H NMR spectrum of
the adduct 14, the endo-3-hydrogen showed a 4-bond ‘W’-
coupling to the 7-hydrogen which is syn to the double bond (2
Hz) but was not coupled to the bridgehead 4-hydrogen whereas
the exo-2-hydrogen was coupled to the bridgehead 1-hydrogen
(3.5 Hz) but not to the syn-7-hydrogen. An NOE enhancement
of the exo-2-hydrogen, but not of the endo-3-hydrogen, was
also observed on irradiation of the 7-hydrogen anti to the
double bond, and vice versa. The exo-orientation of the triphen-
ylstannyl moiety in the adducts 13 and 14 was also supported
4
3
SnPh3
SnPh3
H
O
1
+
2
O
O
Me
O
Me
O
Me
O
O
Me
O
10
13
14
(see text)
O
O
by 13C NMR data, specifically by comparison of the 13C-119/117
-
O
O
O
O
Sn coupling constants with those reported for exo- and endo-2-
trimethylstannylbicyclo[2.2.1]heptanes.15,16
O
O
+
+
Me
Me
Full stereochemical assignments were made to the endo-
products 13 and 14 by analogy with the diethylaluminium
chloride-catalysed Diels–Alder reaction between cyclopenta-
diene and the acrylate ester of pantolactone which is known to
give the adducts 18 and 19, ratio 17:83, with an endo–exo stereo-
SnPh3
H
Me
Me
H
SnPh3
15
16
1
and 14 from the Diels–Alder reactions between the (E)-
vinylstannane 10 and cyclopentadiene could be separated and
were isolated in yields of 56 and 19%, respectively, the endo–exo
stereoselectivity being ca. 90:10 in favour of the endo-isomers
13 and 14 over the exo-isomers 15 and 16 which were never
isolated in sufficient quantity to permit their characterisation.
The effect of Lewis acid catalysts on the stereoselectivity of
the Diels–Alder reaction between the vinylstannane 10 and
cyclopentadiene was investigated.5 No product was isolated
from reactions catalysed by titanium() chloride, boron
trifluoride–diethyl ether or boron trichloride. It may be that the
selectivity of 98:2.5 A comparison of the H NMR chemical
shifts of the vinylic protons for the adducts 13 and 14 with
those reported for 18 and 19 was consistent with this assign-
ment. The structure 14 assigned to the major endo-Diels–Alder
adduct obtained from the Lewis acid-catalysed reactions was
also consistent with an X-ray crystal structure determination.
Fig. 1 shows a projection of the major endo-adduct 14 from the
diethylaluminium chloride-catalysed reaction as established by
the X-ray crystal structure determination.
The endo-adduct 14 could, therefore, be conveniently pre-
pared using the diethylaluminium chloride-catalysed reaction
718
J. Chem. Soc., Perkin Trans. 1, 1998

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The alcohol 20 was hydrogenated to give the saturated alco-
hol 22 and the optical purity of this alcohol checked by com-
1
parison of the H and 19F NMR spectra of its (R)- and (S)-
Mosher’s derivatives 23 and 24 which were prepared in yields
of у98%.17 The optical purity of the alcohol 22 was found to
correspond to an enantiomeric excess of 94% since in the 19F
spectra of 23 and 24 signals were observed at δ Ϫ73.19 and
Ϫ73.29, ratio 98:2, and at δ Ϫ73.21 and Ϫ73.31, ratio 4:96,
respectively.
The alcohol 22 was now converted into several derivatives
which had groups on oxygen with different steric and electronic
requirements. These were to be taken through to provide a
series of enantiomerically enriched tin hydrides for provisional
evaluation as chiral reagents for asymmetric synthesis.
The alcohol 22 was converted into its methyl ether (Ϫ)-3,
trityl ether 25, tert-butyldimethylsilyl ether 26 and 1-
naphthoate 27 using standard techniques. The hydroxyalkyl-
(triphenyl)stannane 22 and each of its derivatives (Ϫ)-3 and 25–
27 were then converted into tin hydrides using the procedures
developed for the synthesis of the racemic tin hydride 4, i.e.
treatment with 1 mol equiv. of iodine to remove one of the
phenyl groups from the tin to generate an alkyl(diphenyl)tin
iodide which gave the tin hydride on reduction using sodium
borohydride.1 The tin iodides 28, 29 and 30 from the alcohol 22,
trityl ether 25, and naphthoate 27, were isolated and character-
ised before reduction to the tin hydrides 31–33. However, the
iodides from the methyl and tert-butyldimethylsilyl ethers (Ϫ)-3
and 26 were not purified being, instead, reduced directly to the
corresponding tin hydrides 4 and 34. All the tin hydrides were
fully characterised.
Fig. 1 A projection of a molecule of the Diels–Alder adduct 14 as
The structures of the tin iodides and hydrides were consistent
with their spectroscopic data. Of interest is the possibility of
coordination of the tin atoms in these compounds by the hetero-
atom functionality, particularly for the tin iodides 28–30.18,19
The one-bond, Sn–C(2) coupling constants as measured in the
13C NMR spectra of the trityl and naphthoyl tin iodides 29 and
30 were found to be similar to those of the parent triphenyltin
compounds 25 and 27, i.e. the one-bond coupling constants
established by X-ray diffraction
between the pantolactate 10 and cyclopentadiene. The adduct
14 is the predominant diastereoisomer from these reactions and
can be isolated in yields in the range 60–65%.
Several procedures were investigated for removing the chiral
auxiliary from the adduct 14. Reduction using diisobutyl-
aluminium hydride gave the alcohol 20 and treatment with
an excess of sodium methoxide effected efficient trans-
esterification and gave the laevorotatory enantiomer of the
methyl ester 2.1 However, saponification using lithium hydrox-
ide in aqueous tetrahydrofuran gave only a low yield of the
carboxylic acid 21. Once again a triphenylstannyl group would
appear to be incompatible with a carboxylic acid functionality
in the same molecule.
1J
for 29 and 30 were 422/404 and 415/393 Hz cf.
13C(2)119/117Sn
424/406 and 418/399 Hz, respectively, for the triphenylstan-
nanes 25 and 27. These data suggest that the oxygen atoms of
the heteroatom substituents in the tin iodides 29 and 30 are not
coordinated to the tin atom since an increase in the coordin-
ation number at the tin from four to five would be expected to
result in a significant increase in this one-bond coupling.16,18
Moreover, the X-ray crystal structure of the Diels–Alder
adduct 14, see Fig. 1, shows that in the solid state the tin is
tetrahedral and not coordinated by any of the oxygens.
For the hydroxyalkyltin iodide 28 the one-bond tin–carbon
coupling constants 1J
at 440/418 Hz are slightly
SnPh3
SnPh3
13C(2)119/117Sn
H
H
larger than those of the parent triphenylstannane 22 at 421/403
Hz. However, this increase is very small and may be due to fast
equilibration of the hydroxyalkyltin iodide 28 with a small
amount of a dimeric, five-coordinated tin species in solution.
This lack of coordination of the tin by the oxygenated func-
tional groups in the tin iodides 28–30 may be a consequence of
the trans-disposition of the stannyl and alkoxymethyl substitu-
ents about the bicycloheptyl framework.18,19 A comparison with
their cis-substituted stereoisomers would be of interest.
R
OR
20 R = CH2OH
(–)-2 R = CO2Me
21 R = CO2H
22 R = H
23 R = (R)-Ph(CF3)C(OMe)CO
24 R = (S)-Ph(CF3)C(OMe)CO
(–)-3 R = Me
25 R = CPh3
26 R = SiMe2But
27 R = 1-C10H9CO
Coordination of the tin by the ester and alkoxy groups is less
likely for the tin hydrides.18,19 The one-bond, tin–carbon coup-
ling constants 1J
measured for the 3-(hydroxy-
SnPh2H
H
13C(2)119/117Sn
SnPh2I
methyl)- and 3-(methoxymethyl)-bicycloheptyltin hydrides 31
and 4 at 430/410 and 427/408 Hz are indeed consistent with
four-coordinated tin in these compounds. In their IR spectra,
H
OR
OR
the C᎐O stretching frequencies of the naphthoate esters 27, 30
᎐
31 R = H
28 R = H
and 33 were all in the range 1713–1714 cmϪ1 consistent with no
significant coordination of the tin by the carbonyl oxygen in
these compounds.
32 R = CPh3
33 R = 1-C10H9CO
4 R = Me
29 R = CPh3
30 R = 1-C10H9CO
34 R = SiMe2But
The phenyl groups attached to the tin in the iodides 28–30
J. Chem. Soc., Perkin Trans. 1, 1998
719

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and the hydrides 4, 31–34 are diastereotopic. However, tri-
organotin halides are known to be configurationally unstable
on the NMR timescale,20 and only one set of peaks was
observed for the aromatic carbons in the 13C NMR spectra of
the iodides 28–30. In contrast, the two phenyl rings in the tin
hydrides 31, 34 and 4, for which 13C NMR data are available,
did give rise to different resonances for the ipso carbons of the
phenyl substituents at δ 138.7/138.8, 138.6/138.65 and 138.8/
138.9, respectively. It would appear that the chiral tin atoms of
these tin hydrides are configurationally stable on the NMR
timescale.20,21 The one-bond, tin–hydrogen coupling constants,
an effective tin hydride for the stereoselective transfer of a
hydrogen atom to a prochiral radical may well require a tin
hydride with more bulky substituents than those reported here
since steric factors will have to be instrumental in controlling
the stereoselectivity. For the catalytic asymmetric reduction of
ketones, tin hydrides in which the tin is trigonal bipyramidal,
at least in the transition structure for hydride transfer, due
to coordination of a heteroatom, may be preferred since the
direction of hydride transfer will be predictable.25 Approaches
to the synthesis of enantiomerically enriched tin hydrides con-
taining suitably positioned functional groups based on the
bicyclo[2.2.1]heptane framework are reported in the following
paper.26
1JH Sn, were measured for the tin hydrides 4, 31–33 using
119/117
the tin satellites in the 1H NMR spectra, and were in the range
1763–1791/1681–1711 Hz as expected.22
Experimental
X
Ph
For general experimental details see the first paper in this series.
Me
Ph
CO2Me
Br
O
(S)-1-(Ethoxycarbonyl)ethyl propiolate 5
O
A solution of dicyclohexylcarbodiimide (5.60 g, 27.1 mmol)
and 4-dimethylaminopyridine (220 mg, 1.8 mmol) in dichloro-
methane (15 cm3) was added to a solution of propiolic acid
(1.85 g, 26.4 mmol) and ethyl (S)-lactate (2.84 g, 24 mmol) in
dichloromethane (15 cm3) at Ϫ25 ЊC. The mixture was stirred
at Ϫ25 ЊC for 1 h and then at room temperature for 17 h, after
which it was filtered. The filter was washed with dichloro-
methane (4 × 15 cm3) and filtrate concentrated under reduced
pressure. Chromatography of the residue using ether–light
35 X = I
37
36 X = H
Ph
Sn
Ph
Ph
Ph
Ph
Sn
)
2
H
H
OR
OMe
38 R = H
39 R = Ac
OMe
40
petroleum (1:3) as eluent gave the title compound 5 (1.97 g,
ϩ
48%) as an oil, [α]D Ϫ23.9 (c 0.8, CH2Cl2) (Found: M ϩ NH4
,
188.0925. C8H14NO4 requires M, 188.0923); νmax/cmϪ1 3262,
2121, 1723, 1451, 1096 and 760; δH 1.26 (3 H, t, J 7, OCH2CH3),
1.50 (3 H, d, J 7, 2Ј-H3), 2.96 (1 H, s, 3-H), 4.20 (2 H, q, J 7,
OCH2CH3) and 5.14 (1 H, q, J 7, 1Ј-H); δC 61.7, 61.8, 70.2, 70.3,
74.1, 75.1, 151.7 and 169.3; m/z 188 (Mϩ ϩ 18, 100%).
Preliminary investigations were carried out into the chem-
istry of the tin hydrides 4, 31–34. The 5-iodomethyl-
butyrolactone 35 was reduced to the 5-methylbutyrolactone 36
using catalytic quantities (20 mol%) of the hydroxy- and
methoxy-alkyltin hydrides 31 and
4 with triethylborane
initiation23 in the presence of sodium borohydride24 as the
stoicheiometric reducing agent (60–70%). However, triethyl-
borane-initiated reduction of methyl 2-bromo-2-phenylpro-
panoate 37 using catalytic amounts (20 mol%) of the bicyclo-
heptanyl(diphenyl)tin iodides 28–30 with sodium borohydride
as the stoicheiometric reducing agent gave only racemic methyl
2-phenylpropanoate (41–65%). Reduction of the bromo ester
37 using catalytic quantities of the tin hydrides 4 and 34 gave
only racemic 2-phenylpropanol after reduction of the ester
using lithium aluminium hydride. The addition of the lithiated
stannane formed by deprotonation of the methoxyalkyltin
hydride 4 by lithium diisopropylamide to benzaldehyde was not
stereoselective and gave a 60% yield of a 1:1 mixture of the
adducts 38, characterised as their acetates 39, together with a
small amount of the distananne 40.
(R)-4,4-Dimethyl-2-oxotetrahydrofuran-3-yl propiolate 9
A solution of diisopropylcarbodiimide (15.58 g, 123.5 mmol)
and 4-dimethylaminopyridine (1.01 g, 8.27 mmol) in dichloro-
methane (270 cm3) was added to a solution of propiolic acid
(8.46 g, 120.7 mmol) and (R)-pantolactone (14.29 g, 109.8
mmol) in dichloromethane (52 cm3) at Ϫ25 ЊC over a period of
1.5 h. The mixture was stirred at Ϫ25 ЊC for 2 h and at ambient
temperature for 16 h, after which it was filtered and the filter
washed with dichloromethane–hexane (4:1; 4 × 30 cm3). The
filtrate was concentrated under reduced pressure. Chromatog-
raphy of the residue using dichloromethane–hexane (4:1) as
eluent gave the title compound 9 (17.39 g, 87%) as an oil which
crystallised slowly with time, mp 49–51 ЊC; [α]D ϩ11.2 (c 2.15 in
CH2Cl2) (Found: M ϩ NH4ϩ, 200.0920. C9H14NO4 requires M,
200.0923); νmax/cmϪ1 3269, 2125, 1795, 1727, 1591, 1225, 1162,
1074 and 999; δH 1.19 and 1.28 (each 3 H, s, CH3), 3.10 (1 H, s,
3-H), 4.05 and 4.13 (each 1 H, d, J 8, 5Ј-H) and 5.45 (1 H, s, 3Ј-
H); δC 19.9, 23.0, 40.3, 73.4, 76.2, 76.5, 77.5, 151.4 and 171.1;
m/z (CI) 200 (Mϩ ϩ 18, 100%).
Conclusions
This work has resulted in an asymmetric synthesis of
bicyclo[2.2.1]heptan-2-yltin hydrides using Diels–Alder chem-
istry and confirms that the selective cleavage of a (triphenyl)-
stannane by iodine followed by reduction of the tin iodide so
obtained using sodium borohydride provides a reliable route to
structurally complex tin hydrides. The most difficult step in this
synthesis is the conjugate addition of the triphenylstannyl
moiety to the propiolate 9, and this, at present, restricts the
amount of material which can be prepared. The bicycloalkyltin
hydrides reported in this paper would appear to act as reducing
agents for alkyl halides with only catalytic quantities of the tin
hydrides being required. However the products obtained to date
from the chiral bromide 37 were found to be racemic, although
it may be that racemisation of the initially formed product
under the free-radical conditions of the reactions is at least
partially responsible for this. Nevertheless, the development of
Addition of triphenyltin hydride to (S)-1-(ethoxycarbonyl)ethyl
propiolate 5
Triethylborane (1.0  in hexane; 0.02 mmol) was added to a
solution of triphenyltin hydride (84 mg, 0.24 mmol) and the
propiolate 5 (34 mg, 0.20 mmol) in toluene. The mixture was
stirred at 20 ЊC for 1.5 h and then concentrated under reduced
pressure. Chromatography of the residue using dichlorometh-
ane–light petroleum (1:1) as eluent gave (S)-(ethoxycarbonyl)-
ethyl (Z)-3-triphenylstannylpropenoate 7 (30 mg, 30%) as an
oil (Found: Mϩ Ϫ C6H5, 445.0467. C20H21O4Sn requires M,
445.0461); νmax/cmϪ1 3064, 1752, 1709, 1430, 1356, 1201, 1096,
1075, 823, 729 and 699; δH 1.17 (3 H, t, J 7, CH3CH2O), 1.96 (3
H, d, J 7, 2Ј-H3), 4.10 (2 H, m, OCH2CH3), 5.12 (1 H, q, J 7, 1Ј-
H), 7.13 (1 H, d, J 12, 2-H), 7.40–7.70 (15 H, m, ArH) and 7.60
720
J. Chem. Soc., Perkin Trans. 1, 1998

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(1 H, d, J 12, 3-H); δC 14.0, 16.9, 53.5, 61.4, 69.5, 77.2, 128.3,
136.2, 140.0, 154.4, 167.1 and 170.4; m/z 540 (Mϩ ϩ 18, 63%)
and 445 (80). Further elution gave (S)-(ethoxycarbonyl)ethyl
3,3-bis(triphenylstannyl)propanoate 8 (43 mg, 25%) as an oil,
[α]D Ϫ18.0 (c 1.4, CH2Cl2) (Found: Mϩ Ϫ C6H5, 797.0729.
C38H37O4Sn requires M, 797.0736); νmax/cmϪ1 3064, 1750, 1736,
1481, 1429, 1191, 1097, 1074, 727 and 699; δH 1.14 (3 H, d, J
7.5, 2Ј-H3), 1.24 (3 H, t, J 7.5, CH3CH2O), 2.28 (1 H, dd, J 7.5,
5.5, 3-H), 3.26 (2 H, m, 2-H2), 4.15 (2 H, m, CH3CH2O), 4.50 (1
H, q, J 7.5, 1Ј-H) and 7.32 (30 H, m, ArH); δC 2.7, 14.1, 15.3,
16.7, 61.2, 65.9, 68.8, 128.4, 137.4, 139.3, 170.6 and 174.6; δSn
Ϫ83.7 and Ϫ84.9; m/z 795 (Mϩ Ϫ 77, 5%). Further elution gave
mmol) and azoisobutyronitrile (5 mg, 0.03 mmol) in benzene (6
cm3) were added dropwise to a degassed solution of the propiol-
ate 9 (1.0 g, 5.49 mmol) in benzene (20 cm3). The mixture was
heated cautiously to 80 ЊC for 17 h, cooled to room temperature
and concentrated under reduced pressure. Chromatography of
the residue using chloroform as the eluent gave the (R)-4,4-
dimethyl-2-oxotetrahydrofuran-3-yl (Z)-3-triphenylstannylprop-
enoate 11 (936 mg, 32%) as a white solid, mp 112–114 ЊC; [α]D
Ϫ13.7 (c 2.03 in CH2Cl2) (Found: C, 60.85; H, 5.2. C27H26O4Sn
requires C, 60.8; H, 4.9%; Found: Mϩ Ϫ C6H5, 457.0458.
C21H21O4Sn requires M, 457.0462); νmax/cmϪ1 3065, 1796, 1718,
1430, 1260, 1075, 998, 911, 821, 730 and 700; δH 1.01 and 1.09
(each 3 H, s, CH3), 3.99 and 4.06 (each 1 H, d, J 9, 5Ј-CH), 5.44
(1 H, s, 3Ј-H), 7.22 (1 H, d, J 12.5, 3JHSn 144/138, 2-H), 7.64 (1
(S)-(ethoxycarbonyl)ethyl (E)-3-triphenylstannylpropenoate
6
(13 mg, 13%) as an oil (Found: Mϩ Ϫ C6H5, 445.0462.
C20H21O4Sn requires M, 445.0461); νmax/cmϪ1 3065, 1750, 1728,
1430, 1202, 1154, 1098, 998, 730 and 699; δH 1.28 (3 H, t, J 7.5,
CH3CH2O), 1.52 (3 H, d, J 7.5, 2Ј-H3), 4.20 (2 H, q, J 7.5,
OCH2CH3), 5.15 (1 H, q, J 7.5, 1Ј-H), 6.56 (1 H, d, J 19, 2-H),
7.30–7.70 (15 H, m, ArH) and 8.05 (1 H, d, J 19, 3-H); δC 14.2,
17.1, 61.5, 69.0, 128.8, 129.4, 136.9, 138.1, 148.9, 168.6 and
170.6; m/z (EI) 521 (Mϩ Ϫ 1, 4%), 445 (88) and 351 (42).
2
H, d, J 12.5, JHSn 72.0/68.0, 3-H) and 7.35–7.75 (15 H, m,
ArH); δC 19.9, 22.8, 40.5, 75.8, 76.2, 128.5, 128.9, 135.6 (2JCSn
12.5), 137.0 (2JCSn 39.0), 139.5 (1JCSn 575/549), 156.4 (1JCSn 461/
441), 166.89 (3JCSn 34.5) and 172.2; m/z 552 (Mϩ ϩ 18, 20%)
and 457 (35). Further elution gave the (E)-isomer 10 (726 mg,
25%).
(R)-4,4-Dimethyl-2-oxotetrahydrofuran-3-yl (1R,2R,3S,4S)- and
(1S,2S,3R,4R)-3-triphenylstannylbicyclo[2.2.1]hept-5-ene-2-
carboxylates 13 and 14
Addition of triphenyltin hydride to (R)-4,4-dimethyl-2-oxotetra-
hydrofuran-3-yl propiolate 9
Cuprate addition. A solution of triphenyltin chloride (56.3 g,
146 mmol) in tetrahydrofuran (THF) (120 cm3) was added to a
suspension of lithium shavings (10.1 g, 1.46 mol) in THF (120
cm3) at ambient temperature over 30 min. The mixture was
stirred for 20 h before being added over a period of 30 min to a
solution of copper() iodide (27.80 g, 146 mmol) and lithium
iodide (19.54 g, 146 mmol) in THF (290 cm3) at Ϫ60 ЊC. The
mixture was stirred for 30 min before the dropwise addition
of the propiolate 9 (13.3 g, 73 mmol) in THF (70 cm3). The
mixture was stirred at Ϫ65 ЊC for 1.5 h before being added to a
cold (Ϫ78 ЊC) solution of glacial acetic acid (17 cm3) in tetrahy-
drofuran (50 cm3); the mixture was then warmed to ambient
temperature. The mixture was washed with saturated aqueous
ammonium chloride containing ammonium hydroxide (pH 8;
5 × 100 cm3), water (5 × 100 cm3) and then brine (2 × 100
cm3). The aqueous extracts were washed with dichloromethane
(2 × 100 cm3) and the combined organic extracts dried (MgSO4)
and concentrated under reduced pressure. Repeated chroma-
tography of the residue using chloroform then dichloro-
methane–hexane (3:2) as eluent gave (R)-4,4-dimethyl-2-
oxotetrahydrofuran-3-yl (E)-3-triphenylstannylpropenoate 10
(11.48 g, 29%) which crystallised slowly on standing, mp 118–
120 ЊC; [α]D ϩ7.43 (c 1.36 in CH2Cl2) (Found: Mϩ Ϫ C6H5,
457.0458. C21H21O4Sn requires M, 457.0462); νmax/cmϪ1 3065,
1800, 1733, 1430, 1200, 1148, 1076, 998, 730 and 699; δH 1.17
Lewis acid-catalysed Diels–Alder reaction. Diethylaluminium
chloride (1 mol dmϪ3 in hexanes; 43.54 cm3) was added drop-
wise to a cooled (Ϫ50 ЊC) solution of the (E)-vinylstannane 10
(11.61 g, 21.77 mmol) in dichloromethane–hexane (1:1; 120
cm3). After 1 h, freshly distilled cyclopentadiene (17.9 cm3,
217.7 mmol) was added dropwise the pale green colour of the
solution being gradually discharged on addition of the diene.
After stirring for 16 h, powdered hydrated sodium carbonate
(62.0 g, 217.7 mmol) was added and the mixture warmed to
ambient temperature and filtered. The filter was washed with
dichloromethane (4 × 50 cm3) and the filtrate concentrated
under reduced pressure. Chromatography of the residue using
dichloromethane–light petroleum (2:1) as eluent gave the
(1S,2S,3R,4R)-isomer of the title compound 14 (8.16 g, 63%),
mp 112–114 ЊC; [α]D Ϫ51.1 (c 2.3 in CHCl3) (Found: C, 64.15;
H, 5.5. C32H32O4Sn requires C, 64.1; H, 5.4%; Found:
Mϩ ϩ NH4, 618.1667. C32H36NO4Sn requires M, 618.1666);
νmax/cmϪ1 1788, 1743, 1429, 1152, 1111, 1075, 1014, 997, 729
and 699; δH 0.97 and 1.12 (each 3 H, s, CH3), 1.27 (1 H, d, J 9, 7-
H), 1.32 (1 H, dd, J 9, 2, 7-HЈ), 1.90 (1 H, dd, J 5.5, 2, 3-H), 3.15
(1 H, m, 4-H), 3.31 (1 H, m, 1-H), 3.47 (1 H, dd, J 5.5, 3.5, 2-H),
3.98 (2 H, s, 5Ј-H2), 5.31 (1 H, s, 3Ј-H), 5.85 (1 H, dd, J 5.5, 3,
vinylic-H), 6.32 (1 H, dd, J 5.5, 3, vinylic-H), 7.32–7.42 (9 H, m,
ArH) and 7.42–7.65 (6 H, m, ArH); δC 19.9, 23.1, 26.8 (1JCSn
394/376), 40.1, 46.1, 46.7, 47.4, 49.4, 74.8, 76.0, 128.7 (3JCSn
48.6), 129.0, 129.9, 137.2 (2JCSn 35.0), 138.0 (1JCSn 485/464),
139.5, 172.1 and 173.5; m/z 618 (Mϩ ϩ 18, 23%), 540 (10) and
523 (48). Further elution gave mixtures of (1S,2S,3R,4R)-
stannane 14 and the (1R,2R,3S,4S)-stannane 13 (5:1; 1.21 g,
9%) and (1:1; 2.27 g, 17%) (combined yield of the Diels–Alder
products; 11.64 g, 90%).
and 1.27 (each 3 H, s, CH3), 4.09 and 4.1 (each 1 H, d, J 9, 5Ј-
3
119/117Sn
H), 5.49 (1 H, s, 3Ј-H), 6.62 (1 H, d, J 19, JH
65.5/63, 2-
2
119/117Sn
H), 7.4–7.7 (15 H, m, ArH) and 8.15 (1 H, d, J 19, JH
73/70, 3-H); δC 20.0, 23.1, 40.5, 75.4, 76.3, 129.0, 129.6, 136.4,
137.1, 138.5, 150.9, 163.2 and 172.4; m/z (EI) 457 (Mϩ Ϫ 77,
50%) and 351 (70). Further elution gave (R)-4,4-dimethyl-2-
oxotetrahydrofuran-3-yl 3,3-bis(triphenylstannyl)propanoate 12
(9.5 g, 15%) which crystallised slowly on standing, mp 125–
127 ЊC; [α]D ϩ1.53 (c 3.67 in CH2Cl2) (Found: C, 60.9; H, 4.8.
C45H42O4Sn2 requires C, 61.1; H, 4.8%); νmax/cmϪ1 3064, 1795,
1743, 1428, 1146, 1074, 998, 910, 728 and 699; δH 0.82 and 0.84
(each 3 H, s, CH3), 2.26 (1 H, dd, J 7.5, 5.0, 3-H), 3.32 (1 H, dd,
J 19, 7.5, 2-H), 3.50 (1 H, dd, J 19, 5, 2-HЈ), 3.90 and 3.95 (each
1 H, d, J 9, 5Ј-H), 5.03 (1 H, s, 3Ј-H) and 7.23–7.50 (30 H, m,
ArH); δC 2.4 (1JCSn 310/296), 19.6, 22.8, 34.4 (2JCSn 23.0), 40.0,
75.4, 75.8, 128.4, 128.8, 137.3 (2JCSn 36.5), 137.4 (2JCSn 36.0),
138.9 (1JCSn 507/494) and 171.7, 174.5 (3JCSn 44, 22); m/z 809
(Mϩ Ϫ 77, 50%). Mixed fractions containing the (E)-vinyl-
stannane 10 (0.26 g) and ca. 4% of the (Z)-vinylstannane 11
and 4% of the bis-stannane 12 were also obtained.
Following this procedure, the dienophile 10 (57 mg, 0.11
mmol) and cyclopentadiene (0.09 cm3, 1.07 mmol) in the pres-
ence of diethylaluminium chloride (1 mol dmϪ3 in hexanes; 0.27
cm3) gave the adducts 13 and 14 (41%, 62% de) after chrom-
atography using dichloromethane as eluent. Further elution
gave (R)-4,4-dimethyl-2-oxotetrahydrofuran-3-yl (E )-pent-2-
enoate 17 (5 mg, 22%) as an oil; νmax/cmϪ1 1789, 1730, 1653,
1289, 1250, 1157, 1124, 1092, 1014 and 997; δH 1.09 (3 H, t, J 7,
5-H3), 1.12 and 1.21 (each 3 H, s, CH3), 2.25 (2 H, m, 4-H2),
4.02 and 4.06 (each 1 H, d, J 9, 5Ј-H), 5.40 (1 H, s, 3Ј-H), 5.90 (1
H, d, J 15, 2-H) and 7.15 (1 H, dt, J 15, 7, 3-H); m/z 230
(Mϩ ϩ 18, 100%).
Thermal Diels–Alder reaction. Cyclopentadiene (60 mg, 1.0
mmol) was added dropwise to a solution of the vinylstannane
10 (48 mg, 0.09 mmol) in dry benzene (1.5 cm3). The mixture
By free-radical addition. Triphenyltin hydride (2.04 g, 5.8
J. Chem. Soc., Perkin Trans. 1, 1998
721

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was heated under reflux for 20 h, cooled to room temperature
and concentrated under reduced pressure. Chromatography of
the residue using dichloromethane–light petroleum (7:3) as
eluent gave the (1S,2S,3R,4R)-isomer of the title compound 14
(10 mg, 19%). Further elution gave the (1R,2R,3S,4S)-isomer
of the title compound 13 (30 mg, 56%) as an oil (Found:
ArH), 7.50–7.72 (6 H, m, ArH) and 11.7 (1 H, br s, CO2H); m/z
428 (100%) and 411 (30).
(1S,2R,3S,4R)-3-Hydroxymethyl-2-triphenylstannylbicyclo-
[2.2.1]heptane 22
Palladium (10% on charcoal; 2.0 g, 1.88 mmol Pd) was added
to a solution of the alkene 20 (7.40 g, 15.64 mmol) in ethanol
(195 cm3) and the suspension stirred vigorously for 22 h under
an atmosphere of hydrogen, filtered through Celite, and the
retained solids washed with ether (5 × 20 cm3). The filtrate was
concentrated under reduced pressure to give the (1S,2R,3S,4R)-
enantiomer of the title compound 22 (6.15 g, 83%) as an oil,
which slowly crystallised on standing, mp 85–87 ЊC; [α]D ϩ7.7
(c 0.7 in CHCl3) (Found: C, 65.5; H, 5.8. C26H28OSn requires C,
65.7; H, 5.95%); δC 22.4, 33.9 (1JCSn 421/403), 34.0 (3JCSn 68.5),
39.1 (3JCSn 18.5), 40.3, 40.8 (2JCSn 8), 48.0 (2JCSn 22.5), 64.9 (3JCSn
21.0), 128.7 (3JCSn 46), 128.9 (4JCSn 9.5), 137.5 (2JCSn 33) and
139.0 (1JCSn 465/444); δSn Ϫ106.54; other spectroscopic data
were identical with those of the racemic compound.1
Mϩ Ϫ C6H5, 523.0920. C26H27O4Sn requires M, 523.0931); νmax
/
cmϪ1 3064, 1790, 1745, 1429, 1152, 1112, 1075, 1014, 997, 730
and 700; δH 0.95 and 1.15 (each 3 H, s, CH3), 1.3 (2 H, m, 7-H2),
1.94 (1 H, dd, J 5.5, 2.5, 3-H), 3.22 (1 H, m, 4-H), 3.42 (2 H, m,
1-H and 2-H), 4.01 (2 H, s, 5Ј-H2), 5.32 (1 H, s, 3Ј-H), 6.04 (1 H,
dd, J 5.5, 2.5, vinylic-H), 6.38 (1 H, dd, J 5.5, 3, vinylic-H),
7.38–7.47 (9 H, m, ArH) and 7.47–7.75 (6 H, m, ArH); δC 19.8,
23.0, 27.3, 40.1, 46.3, 46.6, 47.8, 49.4, 74.9, 76.2, 128.7, 129.1,
130.5, 137.3, 138.1, 138.9, 172.2 and 173.7; m/z (EI) 600 (Mϩ,
1%), 523 (1) and 351 (11).
(1R,2R,3S,4S)-3-Hydroxymethyl-2-triphenylstannylbicyclo-
[2.2.1]hept-5-ene 20
Diisobutylaluminium hydride (1 mol dmϪ3 in dichloromethane;
78.09 cm3) was added dropwise over 1.5 h, to a solution of the
adduct 14 (9.36 g, 15.62 mmol) in dry dichloromethane (150
cm3) at Ϫ78 ЊC. The solution was allowed to warm to 0 ЊC and
stirred for 19 h before methanol (100 cm3) was added and the
mixture allowed to warm to ambient temperature. Saturated
aqueous Rochelle’s salt (200 cm3) was added and the mixture
extracted with dichloromethane (4 × 200 cm3). The organic
extracts were dried (MgSO4) and concentrated under reduced
pressure to give the (1R,2R,3S,4S)-enantiomer of the title
compound 20 (7.40 g, 100%) as an oil, [α]D ϩ19.7 (c 1.2 in
CHCl3), with spectroscopic data identical with those of the
racemic compound.1
Oxalyl chloride (0.1 cm3, 1.11 mmol) followed by dimethyl-
formamide (0.01 cm3, 0.13 mmol) was added to a solution of
(R)-2-methoxy-2-trifluoromethylphenylacetic acid (52 mg, 0.22
mmol) in hexane (1.5 cm3). The solution was stirred for 1 h
then the supernatant was decanted and concentrated under
reduced pressure. A solution of the alcohol 22 (42 mg, 0.09
mmol), triethylamine (0.05 cm3, 0.36 mmol) and 4-dimethyl-
aminopyridine (2.0 mg, 0.015 mmol) in dichloromethane (1
cm3) was added. The solution was stirred for 18 h and then
washed with saturated aqueous sodium hydrogen carbonate
(3 × 10 cm3), dried (MgSO4) and concentrated under reduced
pressure to yield the (R)-Mosher’s ester 23 (60 mg, у98%) as
an oil, [α]D ϩ13.2 (c 0.95 in CHCl3) (Found: Mϩ Ϫ C6H5,
615.1174. C30H30F3O3Sn requires M, 615.1169); νmax/cmϪ1 3064,
1747, 1599, 1569, 1429, 1270, 1170, 1123, 1075, 1021, 998, 728
and 699; δH 1.20 (1 H, dd, J 7, 2, 2-H), 1.23–1.80 (6 H, overlap-
ping m, 5-H2, 6-H2 and 7-H2), 2.23 (1 H, m, 4-H), 2.56 (1 H, m,
1-H), 2.68 (1 H, m, 3-H), 3.54 (3 H, s, OMe), 4.21 (1 H, t, J 11,
3-CH), 4.38 (1 H, dd, J 11, 5, 3-CHЈ) and 7.33 (20 H, m, ArH);
δC 22.1, 32.5, 33.8, 39.3, 40.0, 40.7, 43.8, 55.4, 66.8, 77.2, 127.3,
128.4, 128.6, 129.0, 129.5, 132.4, 137.3, 138.3, 166.3; δF Ϫ73.19
(s, major-CF3) and Ϫ73.29 (s, minor-CF3); m/z (EI) 692 (Mϩ,
0.5%), 615 (3.5) and 351 (100).
Following this procedure, the alcohol 22 (14 mg, 0.03 mmol)
gave the (S)-Mosher’s ester 24 (24 mg, у98%) as an oil, [α]D
Ϫ29.1 (c 1.25 in CHCl3) (Found: Mϩ Ϫ C6H5, 615.1147.
C30H30F3O3Sn requires M, 615.1169); νmax/cmϪ1 3064, 1747,
1428, 1270, 1170, 1123, 1075, 1021, 998, 910, 728 and 699; δH
1.20 (1 H, dd, J 7, 2, 2-H), 1.22–1.76 (6 H, overlapping m, 5-H2,
6-H2 and 7-H2), 2.15 (1 H, m, 4-H), 2.55 (1 H, m, 1-H), 2.67
(1 H, m, 3-H), 3.47 (3 H, s, OMe), 4.26 (2 H, m, 3-CH2) and
7.35–7.70 (20 H, m, ArH); δC 22.2, 32.7, 33.8, 39.2, 40.0, 40.8,
43.9, 55.4, 66.9, 77.2, 127.3, 128.4, 128.6, 129.0, 129.6, 132.4,
137.3, 138.3 and 166.4; δF Ϫ73.21 (s, minor-CF3) and Ϫ73.31 (s,
major-CF3); m/z 615 (Mϩ Ϫ 77, 15%) and 368 (50).
Methyl (1S,2S,3R,4R)-3-triphenylstannylbicyclo[2.2.1]hept-5-
ene-2-carboxylate (؊)-2
A solution of the adduct 14 (8.15 g, 13.60 mmol) in carbon
tetrachloride (40 cm3) was added dropwise to sodium methox-
ide (2.72 mol dmϪ3) in methanol (250 cm3) at ambient temper-
ature. The mixture was stirred for 30 min then saturated aque-
ous ammonium chloride (100 cm3) was added. After concentra-
tion under reduced pressure, the aqueous residue was extracted
with ether (4 × 40 cm3). The organic phase was separated, dried
(MgSO4), and concentrated under reduced pressure, to give
the (1S,2S,3R,4R)-enantiomer of the title compound (Ϫ)-2
(6.54 g, 96%), as an oil, [α]D Ϫ45.7 (c 1.7 in CHCl3) (Found:
Mϩ Ϫ C6H5, 425.0575. C21H21O2Sn requires M, 425.0564);
δC 27.4 (1JCSn 398/381), 46.1, 46.8, 47.1, 49.4, 51.6, 128.5
(3JCSn 47), 128.9, 130.3, 137.2 (2JCSn 34), 138.2 (1JCSn 481/458),
138.8 (3JCSn 54.5) and 174.9; m/z 442 (100%) and 425 (60); other
spectroscopic data were identical with those of the racemic
compound.1
(1S,2S,3R,4R)-3-Triphenylstannylbicyclo[2.2.1]hept-5-ene-2-
carboxylic acid 21
A solution of the Diels–Alder adduct 14 (0.10 g, 0.165 mmol) in
tetrahydrofuran (0.5 cm3) was added to a solution of lithium
hydroxide monohydrate (0.86 mol dmϪ3) in tetrahydrofuran–
water (1:1; 1.7 cm3) at ambient temperature and the mixture
was stirred for 17 h. Solvent was removed under reduced pres-
sure and the residue was suspended in water (2 cm3) which was
then acidified to pH 3 with concentrated aqueous hydrogen
chloride (0.25 cm3) and extracted with hexane–dichloro-
methane (50:1; 3 × 10 cm3). The organic phase was separated,
dried (MgSO4) and concentrated under reduced pressure.
Chromatography of the residue using ether–acetic acid (50:1)
as eluent gave the title compound 21 (17 mg, 20%) as a solid;
νmax/cmϪ1 3500–2500, 3063, 1699, 1428, 1260, 1074, 1022, 728
and 699; δH 1.10–1.40 (2 H, m, 7-H2), 1.88 (1 H, dd, J 5, 2, 3-H),
3.16 (1 H, m, 4-H), 3.31 (2 H, m, 1-H and 2-H), 5.92 (1 H, dd, J
5.5, 2, vinylic-H), 6.32 (1 H, dd, J 5.5, 3, vinylic-H), 7.4 (9 H, m,
(1S,2R,3S,4R)-3-Methoxymethyl-2-triphenylstannylbicyclo-
[2.2.1]heptane (Ϫ)-3
A solution of the alcohol 22 (0.94 g, 1.98 mmol) in tetrahydro-
furan (10 cm3) was added dropwise to a stirred suspension
of sodium hydride (60% in mineral oil; 0.15 g, 3.75 mmol) in
tetrahydrofuran (6 cm3) at ambient temperature. The solution
was stirred for 1.5 h before the addition of methyl iodide
(1 cm3, 15.8 mmol) then stirred at ambient temperature for 18 h.
After concentration under reduced pressure, the residue was
partitioned between dichloromethane (20 cm3) and brine (20
cm3). The organic phase was separated, dried (MgSO4) and
concentrated under reduced pressure to give the (1S,2R,3S,4R)-
enantiomer of the title compound (Ϫ)-3 (0.895 g, 93%) as an
oil, used without further purification (Found: Mϩ Ϫ C6H5,
413.0934. C21H25OSn requires M, 413.0927); [α]D Ϫ20.5 (c 0.8
722
J. Chem. Soc., Perkin Trans. 1, 1998

View Article Online
in CHCl3); the spectroscopic data were identical with those of
the racemic compound.1
ArH), 7.86 (1 H, d, J 8, ArH), 7.92 (1 H, dd, J 7.5, 1.5, ArH),
7.95 (1 H, d, J 8.5) and 8.83 (1 H, d, J 8.5); δC 22.6, 33.6, 33.9
(1JCSn 418/399), 39.9 (3JCSn 17.5), 40.2, 41.0 (2JCSn 8), 43.9 (2JCSn
21), 67.2 (3JCSn 22), 124.4, 125.3, 125.7, 125.8, 126.1, 127.2,
127.6, 128.5 (3JCSn 47.5), 128.8 (4JCSn 11), 131.2, 133.7, 137.3
(2JCSn 33), 138.5 (1JCSn 469/448) and 167.5; m/z (FAB) 553
(Mϩ Ϫ 77, 40%), 445 (40), 351 (95) and 155 (100).
(1S,2R,3S,4R)-3-Triphenylmethoxymethyl-2-triphenylstannyl-
bicyclo[2.2.1]heptane 25
A solution of the alcohol 22 (0.133 g, 0.28 mmol) and triethyl-
amine (0.07 cm3, 0.50 mmol) in dichloromethane (1.5 cm3) was
added to a solution of trityl chloride (86 mg, 0.305 mmol) and
4-dimethylaminopyridine (1.0 mg, 0.008 mmol) in dichloro-
methane (1.5 cm3) at ambient temperature. After 19 h, more
trityl chloride (32 mg, 0.115 mmol) and 4-dimethylamino-
pyridine (3.0 mg, 0.025 mmol) were added. After 20 h the
solution was washed with saturated aqueous ammonium
chloride (3 × 5 cm3) and water (5 cm3). The organic phase was
dried (MgSO4) and concentrated under reduced pressure.
Chromatography of the residue using dichloromethane–hexane
(1:1) as eluent gave the title compound 25 (0.184 g, 92%) as an
oil (Found: Mϩ, 718.2264. C45H42OSn requires M, 718.2258);
νmax/cmϪ1 3062, 1428, 1217, 1073, 760, 728 and 699; δH 1.04
(1 H, dd, J 7.5, 2, 2-H), 1.18–1.38 (4 H, overlapping m), 1.5
(2 H, m), 2.40 (1 H, d, J 4, 1-H), 2.50 (1 H, m, 4-H), 2.71 (1 H,
m, 3-H), 2.86 (1 H, t, J 8.5, 3-CH), 3.25 (1 H, dd, J 8.5, 5, 3-
CHЈ), 7.15–7.39 (24 H, m, ArH) and 7.45 (6 H, m, ArH); δC
22.3, 33.5 (1JCSn 424/406), 33.7, 39.7 (3JCSn 18.5), 40.0, 40.9, 45.5
(2JCSn 21), 64.9 (3JCSn 22), 86.2, 126.7, 127.6, 128.4, 128.7, 137.3,
138.9 (1JCSn 462/441) and 144.3; m/z (EI) 718 (Mϩ, 0.2%), 475
(4) and 351 (60).
Preparation of tin iodides
General procedure: preparation of diphenyl{(1S,2R,3S,4R)-3-
hydroxymethylbicyclo[2.2.1]heptan-2-yl}tin iodide 28. Iodine (61
mg, 0.24 mmol) was added to a solution of the triphenyl-
stannane 22 (0.12 g, 0.25 mmol) in dichloromethane (4 cm3)
and the mixture stirred for 1.5 h at ambient temperature. Con-
centration of the mixture under reduced pressure gave the
title compound 28 (0.11 g, 83%), as an oil, used without further
purification, [α]D Ϫ6.0 (c 1.8 in CHCl3) (Found: Mϩ Ϫ C6H5,
448.9430. C14H18IOSn requires M, 448.9424); νmax/cmϪ1 3397,
3063, 1429, 1070, 1021, 999, 728 and 697; δH 1.2–1.9 (8 H,
overlapping m, 2-H, 5-H2, 6-H2, 7-H2 and OH), 2.43 (1 H, m,
4-H), 2.55 (1 H, m, 3-H), 2.62 (1 H, m, 1-H), 3.71 (2 H, d, J 7.5,
3-CH2), 7.46 (6 H, m, ArH) and 7.54–7.80 (4 H, m, ArH); δC
22.5, 33.5 (3JCSn 89/85), 39.0 (1JCSn 440/418), 39.2, 40.1, 41.4,
48.4 (2JCSn 29.5), 65.0 (3JCSn 25.5), 128.9 (3JCSn 54.5), 129.9 (4JCSn
12), 136.5 (2JCSn 43.5) and 137.7; δSn(CDCl3) Ϫ38.8; m/z 466
(50%), 449 (60) and 399 (70).
Diphenyl{(1S,2R,3S,4R)-3-(triphenylmethoxymethyl)bicyclo-
[2.2.1]heptan-2-yl}tin iodide 29. Following the above procedure,
iodine (62 mg, 0.245 mmol) and the triphenylstannane 25
(0.18 g, 0.26 mmol) gave, after 30 min at ambient temperature,
the title compound 29 (0.19 g, 96%), as an oil, used without
further purification; νmax/cmϪ1 3062, 1448, 1429, 1072, 762, 728
and 697; δH 1.00 (1 H, m, 2-H), 1.20–1.55 (6 H, overlapping m,
5-H2, 6-H2 and 7-H2), 2.48 (1 H, m, 1-H), 2.55 (1 H, m, 4-H),
2.72 (1 H, m, 3-H), 2.92 (1 H, t, J 9, 3-CH), 3.24 (1 H, dd, J 8.5,
6, 3-CHЈ) and 7.20–7.58 (25 H, overlapping m, ArH); δC 22.3,
33.1 (3JCSn 87), 38.4 (1JCSn 422/404), 39.7, 39.8, 41.5, 45.9 (3JCSn
27.5), 64.8 (3JCSn 27.5), 86.4, 126.8, 127.7, 128.7, 128.8, 129.7
(4JCSn 13), 136.4 (3JCSn 44), 137.5 (1JCSn 465/443) and 144.1.
Diphenyl{(1S,2R,3S,4R)-3-(1-naphthoyloxymethyl)bicyclo-
[2.2.1]heptan-2-yl}tin iodide 30. Following the above procedure,
iodine (59 mg, 0.23 mmol) and the triphenylstannane 27
(0.155 g, 0.245 mmol) after 2 h at ambient temperature gave the
title compound 30 (0.167 g, 100%), as an oil, used without
further purification (Found: Mϩ Ϫ C6H5, 602.9828. C25H24-
IO2Sn requires M, 602.9843); νmax/cmϪ1 3063, 3048, 1713, 1429,
1276, 1241, 1195, 1133, 1072, 1010, 782, 728 and 696; δH 1.30–
1.76 (7 H, overlapping m, 2-H, 5-H2, 6-H2 and 7-H2), 2.51 (1 H,
m, 4-H), 2.61 (1 H, d, J 3, 1-H), 2.85 (1 H, m, 3-H), 4.44 (2 H,
m, 3-CH2), 7.20–7.36 (7 H, m, ArH), 7.48–7.64 (6 H, m, ArH),
7.86 (1 H, d, J 8, ArH), 7.95 (1 H, d, J 8, ArH), 7.98 (1 H, dd,
J 7.5, 1, ArH) and 8.83 (1 H, d, J 8.5, ArH); δC 22.7, 33.2 (3JCSn
86.5), 38.4 (1JCSn 415/393), 39.96, 40.02, 41.7, 44.5 (JCSn 25.0),
67.14 (3JCSn 25), 124.4, 125.73, 126.1, 126.9, 127.7, 128.5, 128.8
(3JCSn 56), 129.8 (4JCSn 12), 131.2, 133.7, 136.3 (2JCSn 44) and
167.5; m/z 698 (Mϩ ϩ 18, 12%), 603 (60) and 553 (30).
(1S,2R,3S,4R)-3-(tert-Butyldimethylsilyloxymethyl)-2-triphenyl-
stannylbicyclo[2.2.1]heptane 26
tert-Butyldimethylsilyl chloride (19 mg, 0.125 mmol), triethyl-
amine (0.03 cm3, 0.215 mmol) and 4-dimethylaminopyridine
(1 mg, 0.008 mmol) were added to a solution of the alcohol
22 (50 mg, 0.105 mmol) in dimethylformamide (1 cm3). The
mixture was stirred at 0 ЊC for 5 min then warmed to ambient
temperature and stirred for a further 21 h before the addition of
more tert-butyldimethylsilyl chloride (32 mg, 0.21 mmol)
and triethylamine (0.06 cm3, 0.43 mmol). After stirring for 3 h,
the solution was washed with brine (4 × 10 cm3) and the
organic phase was dried (MgSO4) and concentrated under
reduced pressure to yield the title compound 26 (62 mg, 100%),
an oil, used without further purification (Found: Mϩ Ϫ C6H5,
513.1650. C26H37OSiSn requires M, 513.1636); [α]D Ϫ16.6 (c 0.7
in CHCl3); νmax/cmϪ1 3063, 1428, 1253, 1096, 1075, 836, 776,
727 and 699; δH Ϫ0.08 and Ϫ0.06 (each 3 H, s, SiCH3), 0.83 [9
H, s, Si(CH3)3], 1.25–1.75 (7 H, overlapping m, 2-H, 5-H2, 6-H2
and 7-H2), 2.40 (1 H, m, 4-H), 2.57 (2 H, m, 1-H and 3-H), 3.57
(1 H, t, J 10, 3-CH), 3.69 (1 H, dd, J 10, 6.5, 3-CHЈ), 7.46 (9 H,
m, ArH) and 7.51–7.72 (6 H, m, ArH); δC Ϫ5.45, Ϫ5.35, Ϫ5.4,
18.4, 22.4, 26.0, 33.3, 33.9, 39.4, 40.2, 41.0, 47.8, 64.8, 128.5,
128.8, 137.5 and 139.1; m/z 513 (Mϩ Ϫ 77, 100%) and 368 (60).
(1R,2S,3R,4S)-3-Triphenylstannylbicyclo[2.2.1]heptan-2-
ylmethyl 1-naphthoate 27
A solution of the alcohol 22 (0.238 g, 0.50 mmol) and triethyl-
amine (0.08 cm3, 0.60 mmol) in chloroform (3 cm3) was added
to 1-naphthoyl chloride (0.118 g, 0.62 mmol) in chloroform (2
cm3) at ambient temperature. After 19 h, more 1-naphthoyl
chloride (19 mg, 0.10 mmol) and triethylamine (0.015 cm3, 0.10
mmol) were added. After 23 h, the solution was washed with
saturated aqueous sodium hydrogen carbonate (4 × 10 cm3)
and the organic phase dried (MgSO4) and concentrated under
reduced pressure. Chromatography of the residue using
chloroform–hexane (1:1) as eluent gave title compound 27
(0.254 g, 81%) as an oil (Found: Mϩ Ϫ C6H5, 553.1196.
C25H24O2Sn requires M, 553.1190); νmax/cmϪ1 3062, 1713, 1428,
1241, 1195, 1133, 1073, 1009, 782, 728 and 699; δH 1.36 (2 H,
m), 1.42 (1 H, dd, J 6.5, 2.5, 3Ј-H), 1.5 (2 H, m), 1.71 (2 H, m),
2.44 (1 H, m, 1Ј-H), 2.56 (1 H, d, J 3, 4Ј-H), 2.83 (1 H, m, 2Ј-H),
4.4 (2 H, m, 2Ј-CH2), 7.32 (10 H, m, ArH), 7.42–7.63 (8 H, m,
Preparation of tin hydrides from tin iodides
General procedure: preparation of diphenyl{(1S,2R,3S,4R)-3-
hydroxymethylbicyclo[2.2.1]heptan-2-yl}tin hydride 31. A solu-
tion of sodium borohydride (5.5 mg, 0.145 mmol) in dry ethanol
(1 cm3) was added to a solution of the tin iodide 28 (70 mg,
0.135 mmol) in dry ethanol (1 cm3) at ambient temperature.
After 30 min, the mixture was concentrated under reduced
pressure and the residue partitioned between saturated aqueous
ammonium chloride (5 cm3) and ether (5 cm3). The aqueous
phase was extracted with ether (3 × 10 cm3) and the organic
extracts were dried (MgSO4) and concentrated under reduced
pressure to afford the title compound 311 (54 mg, 100%) as an
oil, used without further purification (Found: Mϩ Ϫ C6H5,
J. Chem. Soc., Perkin Trans. 1, 1998
723

View Article Online
323.0467. C14H19OSn requires M, 323.0458); νmax/cmϪ1 3380,
3063, 1825, 1428, 1330, 1074, 1022, 728 and 699; δH(C6D6) 0.85
(1 H, br, OH), 0.95–1.65 (7 H, overlapping m, 2-H, 5-H2, 6-H2
and 7-H2), 2.25 (1 H, m, 4-H), 2.45 (2 H, m, 1-H and 3-H), 3.42
(2 H, m, 3-CH2), 6.51 (1 H, d, J 2, 1JHSn 1771/1688, SnH), 7.17–
7.32 (6 H, m, ArH) and 7.55–7.76 (4 H, m, ArH); δC 22.6, 33.3
(1JCSn 430/410), 33.9 (3JCSn 70.5), 39.61 (2JCSn 18.5), 40.2, 41.7
(2JCSn 8), 48.9 (3JCSn 23.5), 64.8 (3JCSn 21), 128.9 (3JCSn 47), 129.1
(4JCSn 11), 137.8 (2JCSn 34.5), 137.9 (2JCSn 35), 138.7 (1JCSn 449)
light petroleum–ether (100:1) as eluent, the title compound
34 (24 mg, 42%) (Found: Mϩ Ϫ C6H5, 437.1327. C20H33OSiSn
requires M, 437.1323); νmax/cmϪ1 3050, 1822, 1428, 1405, 1254,
1096, 835, 727 and 699; δH(C6D6) Ϫ0.05 and Ϫ0.07 (each 3 H, s,
SiCH3), 1.00 [9 H, s, Si(CH3)3], 1.05–1.75 (7 H, overlapping m,
2-H, 5-H2, 6-H2 and 7-H2), 2.45 (2 H, m, 1-H and 4-H), 2.61 (1
H, m, 3-H), 3.59 (1 H, dd, J 9.5, 9, 3-CH), 3.70 (1 H, dd, J 10,
6.5, 3-CHЈ), 6.58 (1 H, d, J 2, SnH), 7.20–7.34 (6 H, m, ArH)
and 7.65 (4 H, m, ArH); δC(C6D6) Ϫ5.3, Ϫ5.2, 18.5, 22.7, 26.2,
32.8, 33.9, 39.9, 40.1, 41.7, 49.0, 65.2, 128.8, 129.0, 137.8, 138.6
and 138.65; m/z 513 (Mϩ Ϫ 1, 3%) and 437 (5).
1
and 138.8 (1JCSn 449); δSn(C6D6) Ϫ119 (d, JSnH 1769); m/z 399
(Mϩ Ϫ 1, 10%) and 323 (20).
Diphenyl{(1S,2R,3S,4R)-3-triphenylmethoxymethylbicyclo-
[2.2.1]heptan-2-yl}tin hydride 32. Following the above pro-
cedure, sodium borohydride (12 mg, 0.315 mmol) and the tin
iodide 29 (0.19 g) gave, after chromatography using hexane–
ether (50:1) as eluent, the title compound 32 (64 mg, 40%) as an
oil; νmax/cmϪ1 3060, 1820, 1447, 1072 and 701; δH(C6D6) 0.85
(2 H, m), 1.40 (4 H, m), 1.56 (1 H, d, J 9), 2.32 (1 H, d, J 4, 1-H),
2.45 (1 H, m, 4-H), 2.75 (1 H, m, 3-H), 3.08 (1 H, t, J 8.5,
Reduction of (4RS,5SR)-4,5-dihydro-5-iodomethyl-4-phenyl-
furan-2(3H)-one 35
The tin hydride 4 (8 mg, 0.02 mmol) in ethanol (0.5 cm3) was
added to a solution of the iodo lactone 351 (29 mg, 0.096
mmol) in ethanol (0.5 cm3) at Ϫ20 ЊC. Triethylborane (1 mol
dmϪ3 in hexanes; 0.01 cm3) was added, followed rapidly by a
cooled (Ϫ20 ЊC) solution of sodium borohydride (5 mg, 0.13
mmol) in ethanol (1 cm3) and the mixture stirred at Ϫ20 ЊC for
4 h then concentrated under reduced pressure. The residue was
partitioned between ether (10 cm3) and saturated aqueous
ammonium chloride (10 cm3) and the aqueous phase extracted
with ether (4 × 10 cm3). The ethereal extracts were dried
(MgSO4) and concentrated under reduced pressure. Chroma-
tography of the residue using hexane–ether (3:1) as eluent gave
the 5-methylfuranone 361 (12 mg, 71%). Further elution gave
recovered tin hydride 4 (5 mg, 63% recovery).
1
3-CH), 3.35 (1 H, dd, J 8.5, 5, 3-CHЈ), 6.49 (1 H, d, J 2, JHSn
1781/1701, SnH), 7.00–7.27 (14 H, m, ArH) and 7.38–7.65 (11
H, m, ArH); m/z (EI) 399 (4.5%) and 243 (100).
Diphenyl{(1S,2R,3S,4R)-3-(1-naphthoyloxymethyl)bicyclo-
[2.2.1]heptan-2-yl}tin hydride 33. Following the above pro-
cedure, sodium borohydride (9 mg, 0.24 mmol) and the tin
iodide 30 (0.145 g, 0.215 mmol) in ethanol (5 cm3) gave the title
compound 33 (0.115 g, 97%), as an oil; νmax/cmϪ1 3060, 1821,
1714, 1243, 1195, 1134, 1010, 784 and 700; δH(C6D6) 1.05–1.58
(7 H, overlapping m, 2-H, 5-H2, 6-H2 and 7-H2), 2.21 (1 H, m,
4-H), 2.37 (1 H, d, J 4, 1-H), 2.75 (1 H, m, 3-H), 4.32 (1 H, dd,
J 11, 8, 3-CH), 4.41 (1 H, dd, J 11, 7, 3-CHЈ), 6.50 (1 H, d, J 1.5,
1JHSn 1791/1711, SnH), 7.06–7.16 (7 H, m, ArH), 7.23 (1 H,
ddd, J 8, 7, 1, ArH), 7.40 (1 H, ddd, J 8.5, 7, 1.5, ArH), 7.55
(5 H, m, ArH), 7.61 (1 H, d, J 8, ArH), 8.13 (1 H, dd, J 7.5, 1.5,
ArH) and 9.38 (1 H, dd, J 8.5, 1, ArH); m/z 553 (Mϩ Ϫ 1, 90%),
172 (80) and 155 (100).
Reduction of methyl 2-bromo-2-phenylpropanoate 37
The tin iodide 28 (39 mg, 0.075 mmol) in ethanol (1 cm3) was
added to a solution of the bromo ester 37 (90 mg, 0.37 mmol)
in ethanol (2 cm3) at ambient temperature. Triethylborane
(1 mol dmϪ3 in hexanes; 0.01 cm3) was added, followed rapidly
by a solution of sodium borohydride (22 mg, 0.58 mmol)
in ethanol (1 cm3). The mixture was stirred for 19 h and then
concentrated under reduced pressure and the residue par-
titioned between ether (10 cm3) and saturated aqueous ammo-
nium chloride (10 cm3). Following extraction with ether (4 × 10
cm3), the organic phase was dried (MgSO4) and concentrated
under reduced pressure. Chromatography, of the residue using
hexane–ether (30:1) as eluent gave methyl 2-phenylpropanoate
(33 mg, 54%).
Preparation of tin hydrides from triphenylstannanes without
isolation of the tin iodides
General procedure: diphenyl{(1S,2R,3S,4R)-3-methoxymeth-
ylbicyclo[2.2.1]heptan-2-yl}tin hydride 4. Iodine (0.44 g, 1.74
mmol) was added to a solution of the triphenylstannane (Ϫ)-3
(0.89 g, 1.83 mmol) in dichloromethane (20 cm3) and the
mixture stirred for 1 h at ambient temperature then concen-
trated under reduced pressure. Sodium borohydride (90 mg,
2.38 mmol) in ethanol (5 cm3) was added to a solution of the
residue in ethanol (20 cm3). After 1 h, the mixture was concen-
trated under reduced pressure and the residue partitioned
between saturated aqueous ammonium chloride (20 cm3) and
ether (30 cm3). The aqueous phase was extracted with ether
(3 × 30 cm3) and the organic extracts were dried (MgSO4) and
concentrated under reduced pressure to afford the title com-
pound 41 (0.78 g, 100%) as an oil, used without further purifi-
cation (Found: Mϩ Ϫ H, 413.0930. C21H25OSn requires M,
413.0927); νmax/cmϪ1 3063, 1819, 1428, 1111, 1075, 728 and 699;
δH(C6D6) 1.10–1.65 (7 H, overlapping m, 2-H, 5-H2, 6-H2 and 7-
H2), 2.32 (1 H, m, 4-H), 2.45 (1 H, m, 1-H), 2.69 (1 H, m, 3-H),
3.11 (3 H, s, OMe), 3.36 (2 H, d, J 7.5, 3-CH2), 6.62 (1 H, d, J
1.5, 1JHSn 1763/1681, SnH), 7.26 (6 H, m, ArH) and 7.7 (4 H, m,
ArH); δC(50 MHz, C6D6) 22.8, 33.8 (1JCSn 427/408), 34.0 (3JCSn
71), 40.1, 40.3, 41.8 (JCSn 8), 46.3 (JCSn 22), 58.5, 75.4 (3JCSn
20.5), 128.8, 129.0, 137.8 (2JCSn 40), 138.8 and 138.9; δSn(111
MHz; C6D6) Ϫ118.1 (1JSnH 1762); m/z 413 (Mϩ Ϫ 1, 40%) and
337 (100).
{[(1S,2R,3S,4R)-3-Methoxymethylbicyclo[2.2.1]heptan-2-yl]-
(diphenyl)stannyl}phenylmethanol 38
Butyllithium (1.5 mol dmϪ3 in hexanes; 0.49 cm3) was added
dropwise to a solution of diisopropylamine (0.10 cm3, 0.73
mmol) in tetrahydrofuran (4 cm3) at 0 ЊC. The solution was
stirred for 20 min then cooled to Ϫ78 ЊC. The tin hydride 4 (0.15
g, 0.365 mmol) was added and the solution stirred for 5 min.
Benzaldehyde (0.04 cm3, 0.40 mmol) was then added dropwise
and after stirring at Ϫ78 ЊC for 20 min, saturated aqueous
ammonium chloride (2 cm3) was added and the mixture then
allowed to warm to room temperature. The mixture was
extracted with ether (4 × 15 cm3) and the organic phase dried
(MgSO4) and concentrated under reduced pressure. Chrom-
atography of the residue using hexane–ether (9:1) as eluent
gave the distannane 40 (38 mg, 25%) as an oil (Found:
Mϩ Ϫ C9H15O, 687.0740. C33H35OSn2 requires M, 687.0732); δH
1.09–1.60 (14 H, m, 2-H, 5-H2, 6-H2 and 7-H2), 2.16 (2 H, m, 4-
H), 2.30 (2 H, d, J 3, 1-H), 2.42 (2 H, m, 3-H), 3.03 (6 H, s,
2 × OMe), 3.14 (4 H, m, 3-CH2), 7.29 (12 H, m, ArH) and 7.45
(8 H, m, ArH); m/z 747 (Mϩ Ϫ 77, 4%). Further elution gave
the title compounds 38 (0.112 g, 60%) in a 50:50 ratio; νmax/cmϪ1
3401, 3062, 1428, 1108, 1073, 727 and 698; δH 1.00–1.70 (7 H,
overlapping m, 2-H, 5-H2, 6-H2, 7-H2), 2.25 (1 H, m), 2.35 and
2.4 (each 0.5 H, m), 2.62 (1 H, m, 3-H), 3.35–3.50 (4 H, m,
3-CH and OMe), 3.61 (1 H, m, 3-CHЈ), 4.28, 4.46, 5.57 and 5.61
(each 0.5 H, d, J 5) and 6.95–7.70 (15 H, m, ArH); m/z 503
(10%), 443 (3) and 413 (60).
Diphenyl{(1R,2S,3R,4S)-3-(tert-butyldimethylsilyloxymethyl)-
bicyclo[2.2.1]heptan-2-yl}tin hydride 34. Following the above
procedure, iodine (29 mg, 0.115 mmol) and the triphenylstan-
nane 26 (67 mg, 0.115 mmol) in dry dichloromethane (1 cm3)
followed by reduction using sodium borohydride (5 mg, 0.13
mmol) in dry ethanol (1 cm3) gave, after chromatography using
724
J. Chem. Soc., Perkin Trans. 1, 1998

View Article Online
A solution of the alcohols 38 (82 mg, 0.16 mmol), acetic
anhydride (0.03 cm3, 0.32 mmol), triethylamine (0.09 cm3, 0.63
mmol) and 4-dimethylaminopyridine (1.0 mg, 0.008 mmol) in
dichloromethane (2 cm3) was stirred at ambient temperature for
20 h. The mixture was partitioned between water (10 cm3) and
ether (10 cm3) and the aqueous phase extracted with ether
(4 × 10 cm3). The organic phase was dried (MgSO4) and
concentrated under reduced pressure. Chromatography of the
residue using dichloromethane–hexane (4:1) as eluent gave the
esters 39 (38 mg, 44%) in a 50:50 ratio (Found: Mϩ Ϫ C6H5,
485.1147. C24H29O3Sn requires M, 485.1139); νmax/cmϪ1 3063,
1743, 1719, 1428, 1370, 1244, 1110, 1072, 1020, 728 and 698; δH
1.05–1.70 (7 H, m, 2-H, 5-H2, 6-H2 and 7-H2), 1.97 and 2.0
(each 1.5 H, s, CH3), 2.30 (1 H, m), 2.35 and 2.44 (each 0.5 H, d,
J 3), 2.54 (1 H, m, 3-H), 3.18–3.37 (2 H, m, 3-CH2), 3.22 and
3.27 (each 1.5 H, s, OMe), 6.25 and 6.28 (each 0.5 H, s,
CHOAc) and 7.10–7.48 (15 H, m, ArH); m/z 503 (Mϩ Ϫ 59,
10%) and 485 (100).†
Acknowledgements
We thank the EPSRC and Zeneca Pharmaceuticals for a CASE
Award (to R. M. P.), Dr A. Thomas of Zeneca for helpful
discussions, and Dr M. Helliwell for help in preparing the
X-ray data for publication.
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X-Ray crystal structure for the Diels–Alder adduct 14
A number of attempts at this crystal structure were made since
the structure tends to be disordered. The results of the crystal
structure reported here are from the best crystal that could be
obtained although some disorder was apparent around the oxo-
furanyl moiety as indicated by the relatively high R values, gen-
erally high displacement parameters and some poor bond
lengths for this part of the molecule. Nevertheless the results
are sufficient to support the chemical discussion in particular
the stereochemical assignments made around the bicyclic core.
Crystal data. C32H32O4Sn, M = 599.29, orthorhombic, space
group P212121, a = 10.442(3), b = 29.031(9), c = 9.480(2) Å,
U = 2874(1) Å3 (by least-squares refinement on diffractometer
angles of 25 automatically centred reflections in the 2θ range
29.5–35.0Њ), λ = 1.54178 Å, Z = 4, Dc = 1.385 g cmϪ3, µ = 74.89
cmϪ1, F(000) = 1224, colourless prism, crystal dimensions
0.20 × 0.25 × 0.25 mm.
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Data were collected at 297 K using a Rigaku AFC-5R dif-
fractometer with graphite monochromated Cu-Kα radiation
and a rotating anode generator. A total of 2482 independent
reflections were measured in the ω–2θ scan mode to a 2θmax of
120.1Њ. An empirical absorption correction was applied, using
the program DIFABS (transmission factors: 0.92–1.19).27
A
decay correction (based on the intensities of three standard
reflections, measured every 150 reflections) was also applied
(2.82% decline). The data were corrected for Lorentz and polar-
isation effects. 2047 Reflections had I > 3σ(I).
The structure was solved by direct methods using
SHELXS-8628 and refined using full-matrix least-squares
refinement using TEXSAN.29 The non-hydrogen atoms were
refined anisotropically except for the atoms of the oxofuranyl
ring. For these atoms it was possible to refine the positions,
whilst maintaining a fixed isotropic thermal parameter for all
atoms of this part of the molecule. The hydrogen atoms were
included in calculated positions, with isotropic thermal param-
eters which were 20% greater than the Beq of the atom to which
they were bonded. Refinement of the 272 variables converged
(maximum shift/error <0.01) with R = 0.070, Rw = 0.093 using
the 2047 observed reflections (weighting scheme w = 1/
[σ2Fo ϩ 0.00022 |Fo|2]). Max./min. peaks in the final difference
map 1.17/–2.02 e ÅϪ3. Maximum peak at 0.5908, 0.5030, 0.0541
close to O4. Minimum trough at 0.6839, 0.5061, 0.1347 close to
O4.
21 H. Schumann, B. C. Wassermann and J. Pickardt, Organometallics,
1993, 12, 3051; H. Schumann, B. C. Wassermann and F. E. Hahn,
Organometallics, 1992, 11, 2803.
22 A. G. Davies and P. J. Smith, in Comprehensive Organometallic
Chemistry, ed. G. Wilkinson, F. G. Stone and E. W. Abel,
Pergamon, New York, 1982, vol. 2, p. 519.
† Full crystallographic details, excluding structure factor tables, have
been deposited at the Cambridge Crystallographic Data Centre
(CCDC). For details of the deposition scheme, see ‘Instructions for
Authors’, J. Chem. Soc., Perkin Trans. 1, available via the RSC Web
pages (http://www.rsc.org/authors). Any request to the CCDC for
this material should quote the full literature citation and the reference
number 207/173.
23 K. Miura, Y. Ichinose, K. Nozaki, K. Fugami, K. Oshima and
K. Utimoto, Bull. Chem. Soc. Jpn., 1989, 62, 143.
J. Chem. Soc., Perkin Trans. 1, 1998
725

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25 E. Vedejs, S. M. Duncan and A. R. Haight, J. Org. Chem., 1993, 58,
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29 TEXSAN-TEXRAY Structure Analysis Package, Molecular
Structure Corporation, 1985.
26 R. M. Pratt and E. J. Thomas, J. Chem. Soc., Perkin Trans. 1, 1998,
727.
27 N. Walker and D. Stuart, Acta Cryst., Sect. A, 1983, 39, 158.
28 G. M. Sheldrick, in Crystallographic Computing, G. M. Sheldrick,
C. Kruger and R. Goddard, Oxford University Press, 1985, 3rd
edn., p. 175.
Paper 7/06293A
Received 28th August 1997
Accepted 5th November 1997
726
J. Chem. Soc., Perkin Trans. 1, 1998