α-Alkoxystannanes as masked oxonium ions: application to the synthesis of furo[2,3-b]pyrans

Article abstract of DOI:10.1016/j.tetlet.2006.02.161

α-Alkoxystannanes undergo oxidation upon treatment with cerium ammonium nitrate generating oxonium ions, which can be trapped in an intramolecular fashion affording furo[2,3-b]pyrans.

Full text of DOI:10.1016/j.tetlet.2006.02.161

Tetrahedron Letters 47 (2006) 3607–3611
a-Alkoxystannanes as masked oxonium ions: application
to the synthesis of furo[2,3-b]pyrans
a
b
b
c
b,
*
Michael R. Attwood, Philip S. Gilbert, Mark L. Lewis, Keith Mills, Peter Quayle,
b
d
Simon P. Thompson and Shouming Wang
a
Roche Products Ltd, Broadwater Road, Welwyn Garden City, Herts AL7 3AY, UK
b
School of Chemistry, The University of Manchester, Manchester M13 9PL, UK
Chemical Development, GlaxoSmithKline Medicines Research Centre, Gunnels Wood Road, Stevenage, Herts SG1 2NY, UK
c
d
Xenova Ltd, Slough SL1 4EF, UK
Received 19 January 2006; revised 10 February 2006; accepted 14 February 2006
Abstract—a-Alkoxystannanes undergo oxidation upon treatment with cerium ammonium nitrate generating oxonium ions, which
can be trapped in an intramolecular fashion affording furo[2,3-b]pyrans.
ꢀ
2006 Elsevier Ltd. All rights reserved.
The generation and interception of oxonium (oxacarb-
enium) and iminium ions play a pivotal role in many
synthetic and biological processes. Although these
The oxidation of organometallic species has been stud-
ied extensively and given our interest in the use of
5
6,7
1
a-alkoxystannanes in synthesis we were aware of the
8
reactions have broad synthetic utility, there are cases
where functionality sensitive to Lewis acids necessitates
the development of alternate methods for oxonium ion
generation. An attractive alternative to this scenario
seminal investigations from Yoshida’s group concern-
ing the electrochemical oxidation of group 14 organo-
metallics. These workers have demonstrated that the
oxidation potential of a-heterosubstituted organosilanes
and organostannanes are significantly reduced due to a
rM-C–nX: interaction such that their oxidation in solu-
tion becomes relatively facile (Fig. 1).
2
involves the use of SET reactions. Here the key step
involves fragmentation of a radical cation to a carb-
enium ion and a stable radical, for example, Scheme 1,
3
sequences which have been realized both in solution
and supported phases.
4
Ed (V vs Ag/AgCl)
X
R'
R'
OR
SET
1.36
Sn
4
OR
MeO
PhS
Sn(n-Bu)3
0.98
0.72
Sn(n-Bu)3
N Sn(n-Bu)3
X
MeO C
2
Nu
R'
R'
OR
Nu
0.77
C12H25
OR
1.39
3
Scheme 1. SET approach to oxonium ion generation.
SiMe Ph
O
2
Keywords: SET; CAN; Stannane; Oxidation; Oxonium; Acetal.
Me Si
2.19
3
*
Corresponding author. Tel.: +44 161 275 4619; fax: +44 161 275
598; e-mail: peter.quayle@manchester.ac.uk
11
4
Figure 1. Decomposition potentials of organostannanes/silanes.
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.02.161

3608
M. R. Attwood et al. / Tetrahedron Letters 47 (2006) 3607–3611
CAN (2 eq), CH CN,
Table 1. CAN-mediated oxidative acetal forming reactions
CO Me
3
CO Me
2
2
-
20 o
C
a
a
Entry Substrate
Product
Yield (%)
Ph
Ph
O
1
SnBu3
O
4
50%
MeO C
2
MeO C
2
1
2
OH
OH
54
CAN, CH CN
3
H+
O
O
-
O
SnBu3
-
e-
O
H
H
5
6
CO Me
H
CO Me
2
2
MeO C
2
MeO C
2
74
O
2
SnBu3
O
O
SnBu3
O
3
7
8
Scheme 2. Oxidative destannylation using CAN.
Ph
Ph
Ph
MeO C
2
MeO C
2
7
OH
OH
3
4
67
68
In earlier work, we demonstrated that SET fragmenta-
Ph
Ph
9
O
O
tion of a-alkoxysilanes could also be effected by chem-
O
SnBu3
O
H
H
ical oxidants such as CAN,10 albeit under relatively
forcing conditions (CAN, AcOH, 70 ꢁC), thereby
providing an alternate to Yoshida’s electrochemical
9
1
0
Ph
Ph
Ph
MeO C
2
MeO C
2
1
1
procedures. The electrochemical data suggest that
oxidation of the analogous a-alkoxystannanes should
be more facile (Fig. 1) and it was with this thought in
mind that the oxidation of the readily available stannane
O
11
SnBu3
O
12
O
O
1
was undertaken.
MeO C
The exposure of 1 to CAN (2 equiv, 20 ꢁC) in dry aceto-
nitrile afforded the unsaturated ester 4 in 50% yield. We
reasoned that 4 arose via the intermediacy of the oxo-
nium ion 3, which itself is the product of SET oxidation
of 1 to the radical cation 2 followed by fragmentation.
In this instance, the oxonium ion 3 collapses to 4 by pro-
ton loss rather than suffering an interception with the
2
MeO2C
5
6
86
54
OH
O
O
SnBu3
O
H
1
3
14
O
O
MeO C
2
MeO C
1
2
2
solvent (Ritter reaction). We concluded that incorpo-
ration of a nucleophilic centre at C3 into these sub-
strates would enhance the likelihood of oxonium ion
OH
Ph
O
O
O
SnBu3
O
H
H
7
13
capture. Gratifyingly, exposure of the stannane 5 to
CAN in acetonitrile, as above, resulted in the disappear-
ance of starting material (TLC; 45 min) and ultimately
afforded the bicyclic acetal 6 in 54% isolated yield
15
16
Ph
Ph
MeO2C
O
MeO C
2
7
8
30
27
(
Scheme 3).
OH
Ph
Ph
O
SnBu3
18
We have subsequently shown that this SET-intramole-
cular capture sequence is relatively general (Table 1) lead-
1
7
1
4
Ph
ing to the synthesis of functionalized furo[2.3-b]pyrans
Ph
MeO2C
in moderate to good overall yields. Whilst CAN per-
forms admirably in such reactions, the use of other
single electron oxidants (e.g., [Fe(Cp) ]PF ) failed to
MeO C
2
OH
OH
O
O
2
6
O
H
H
O
SnBu3
20
Ph
1
9
Ph
CAN (2 eq),
Ph
MeO C
CH CN, 20 o
MeO C
MeO2C
MeO C
2
2
2
C
3
OH
OH
b
54%
9
0
0
O
SnBu3
O
22
O
5
SnBu3
O
2
1
TBSO
TBSO
Ph
MeO C
2
OH
1
53
O
O
SnBu3
O
O
H
O
H
24
2
3
6
a
All compounds are racemic.
Complex mixture of products.
b
Scheme 3. Intramolecular oxonium capture.

M. R. Attwood et al. / Tetrahedron Letters 47 (2006) 3607–3611
3609
O
CAN (2 eq), CH CN,
3
HO
HO
20 o
C
O
Ph
H C
OH
3
Ph
X
O
O
= nOe
O
H
O
H
SnBu3
Ph
H
H
25
2
8
O
10
CAN (2 eq), AcOH,
0 oC, 5 hr
Ph
O
Ph
MeO C
H
O
2
MeO C
7
2
O
Ph
H C
H
OH
3
O
40%
H
Ph
O
O
O
26
SiMe3
O
H
O
H
O
H
Ph
CH3
6
O
O
O
CAN (2 eq), MeOH (10 eq),
NHTs CH3CN, 20 oC, 4hr
12
NHTs
OMe
Figure 2. Stereochemical assignments.
63%
O
GeMe3
O
28
27
(
d.r. = 3:1)
promote the initial SET, presumably due to a mismatch-
Scheme 4. Oxidation of related organometallics.
1
5
ing of redox potentials. The stereochemical outcome
of these cyclization reactions has been probed using
NOE difference techniques, as in the case of 10 and 12
(
Fig. 2), the results of which indicate that cis-fused prod-
Ph
Ph
MeO C
2
ucts are produced in each case (Fig. 2).
BF .OEt2
3
MeO2C
O
O
o
CH Cl , 20 C
2
2
O
The oxidation of a-alkoxystannanes obviously proceeds
under very mild conditions and is tolerant of a number
of common functional groups including ester (entries 1–
O
SnBu3
32 %
SnBu3
30
29
1
6
8
), electron-rich aromatics (entries 5 and 6) and TBS-
protected alcohol functionality (entry 10). Notably, the
cyclization of allylic alcohols does not proceed well (en-
tries 7–9). Curiously diol 25 also appears to be wholly
O
O
Ph
H C
3
9
b
Ph
uncreative towards CAN.
O
H
MeO2C
O
Bu Sn
LA
3
H
The ease in which stannanes such as 5 undergo this SET-
fragmentation reaction should be compared to our ear-
O
O
SnBu3
7
via
lier study concerning the oxidation of the silane 26.
3
2
31
Here we found that oxidation of silane 26 with CAN
proceeded slowly in acetonitrile and was best conducted
in acetic acid at 70 ꢁC. Under these conditions, the ace-
tal 6 could be isolated in somewhat diminished isolated
yields (40%). Furthermore whilst the carbenium 3, de-
rived from 1, could not be captured by the solvent ace-
Scheme 5. Generation of oxonium ions via a 1,5-H shift.
In conclusion, we have demonstrated that a-alkoxyst-
annanes undergo SET oxidation–fragmentation reac-
tions or 1,5-hydride shifts generating oxonium ions
which can be trapped by a pendant alcohol moiety
resulting in the isolation of a variety of furo[2,3-b]pyr-
ans. Synthetic applications of this methodology will be
the focus of future investigations.
1
3
tonitrile, dissolution of the germane 27 in acetonitrile
containing methanol (10 equiv) followed by the addition
of CAN (2 equiv) at 20 ꢁC for 4 h resulted in the isola-
tion of 28, as a 3:1 mixture of diastereoisomers, in
1
7
6
3% yield.
On a purely qualitative basis, the results depicted in
Schemes 3 and 4 infer that the reactivity of the germane
Acknowledgements
2
7 towards oxidation lies somewhere between that of the
silane 26 and the stannane 5 and is a trend which corre-
lates with the available oxidation potential data listed in
Figure 1, (i.e., ease of oxidation C–Sn bond > C–Ge
bond > C–Si bond).
We thank GSK (P.S.G.), Roche (M.L.L.), Xenova
(S.P.T.) the DTI and the EPSRC for support of this
work.
Finally, we have also observed that exposure of alde-
References and notes
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3
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9
in this case proceeds via a 1,5-hydride shift, as depicted
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3610
M. R. Attwood et al. / Tetrahedron Letters 47 (2006) 3607–3611
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R
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1
1
6; ceric ammonium nitrate (530 mg, 0.97 mmol) was
1995, 36, 283–286; Zhao, Y. K.; Quayle, P.; Kuo, E. A.
dissolved in acetonitrile (10 mL). To this mixture was
added stannane 5 (255 mg, 0.46 mmol) and the reaction
mixture stirred for 45 min. The reaction mixture was
added to 1 M sodium carbonate soln. (10 mL). The
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the combined organic extracts were dried (MgSO ). The
solvent was removed in vacuo and the crude product
was purified by flash column chromatography (8:2 pet.
ether 40–60, EtOAc) to give 89 mg (74%) of the title
compound 6 as an amorphous white solid. R
f
(8:2 pet. ether
4
1
7
0–60, EtOAc) = 0.15; mp 94–95 ꢁC; mmax (film), 2886 (w),
ꢀ1
31, 6077–6080.
728 (s) cm ; d (300 MHz, CDCl ), 7.30 (3H, m, Ar),
H
3
7
. Beddoes, R. L.; Lewis, M. L.; Gilbert, P.; Quayle, P.;
Thompson, S. P.; Wang, S.; Mills, K. Tetrahedron Lett.
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O), 3.55 (3H, s,
CO CH ), 3.10 (1H, dd J = 4.0, 11.5 Hz, CHPh), 2.50
CHHO), 4.00 (3H, m, CHHO, CH
2
1
996, 37, 9119–9122.
. Yoshida, J.; Murata, T.; Isoe, S. J. Organomet. Chem.
988, 345, C23–C27.
2
3
8
9
(
2H, m, CHH–CHPh, CHH–CH O), 2.25 (1H, m, CHH–
2
1
CH
72.1 (CO
Ar), 101.8 (C-1), 64.5 (C-3), 61.3 (C-8), 54.4 (C-5), 51.7
OCH ), 43.8 (C-6), 31.9 (C-4), 26.2 (C-7); m/z (CI, NH ),
requires
requires C,
8.69%; H, 6.92%; found C, 68.89%; H, 7.16%. Represen-
2 C 3
O), 1.75 (1H, m, CHH–CHPh); d (75 MHz, CDCl ),
. For ET reactions of stannanes see: (a) Lochynski, S.;
Boduszek, B.; Shine, H. J. J. Org. Chem. 1991, 56, 914–
1
(
(
2
Me), 140.6 (Ar), 128.4 (Ar), 128.3 (Ar), 127.4
920; The oxidative cleavage of C–Sn bonds using CAN has
3
3
+
precedent: Hanessian, S.; Ninkovic, S. J. Org. Chem. 1996,
2
2
6
80 ([M+NH
80.1549; found: 280.1550; Anal. C15
4 4
] , 100%); HRMS C15H22NO
6
1, 5418–5424; Hannesian, S.; L e´ ger, R. Synlett 1992, 402–
4
04; Hanessian, S.; L e´ ger, R. J. Am. Chem. Soc. 1992, 114,
3115–3117; Narasaka, K.; Okauchi, T.; Arai, N. Chem.
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H O
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mada, S. Chem. Lett. 1993, 125–128; Narasaka, K.;
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(
film) 2957 (w), 2886 (w), 1729 (s), 1455 (w), 1434 (w), 1252
(
m), 1208 (m), 1147 (w), 1118 (w), 1100 (w), 1050 (m)
ꢀ
1
cm ; dH (300 MHz, CDCl ) 1.02 (3H, d, J = 7.0 Hz,
3
CH
(
3
–CH), 1.65–1.75 (1H, m, OCH
1H, m, OCH –CHH), 2.14 (2H, ddd, J = 5.0, 8.0,
3.0 Hz, OCH –CHH), 2.49 (1H, ddd, J = 7.5, 8.5,
2
–CHH), 1.95–2.05
2063–2070; Chen, C.; Mariano, P. S. J. Org. Chem. 2000,
2
65, 3252–3254; Yoon, U. C.; Kim, K. T.; Oh, S. W.; Cho,
1
1
3
4
2
D. W.; Mariano, P. S. Bull. Korean Chem. Soc. 2001, 22,
267–1269; Other reagents have been utilized in C–Sn
oxidations: Cr(VI) Still, W. C. J. Am. Chem. Soc. 1997, 99,
836–4838; Pb(IV) Yamamoto, M.; Irie, S.; Miyashita,
3.0 Hz, OCH
.76 (3H, s, CO
.05 (1H, apparent q, J = 8.0 Hz, OCHH–CH
2
–CHH), 3.70–3.80 (1H, m, OCHH–CH
2
),
),
1
2
Me), 3.85–3.98 (2H, m, 2 · OCHH–CH
2
2
), 5.18 (1H,
4
s, OCHO); dC (75 MHz, CDCl ) 17.2, 28.1, 31.6, 31.9,
3
M.; Kohmoto, S.; Yamada, K. Chem. Lett. 1989, 221–222;
Yamamoto, M.; Munakata, H.; Kishikawa, K.; Kohmoto,
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5
1.9, 53.9, 56.48, 64.7, 100.8, 173.1; m/z (CI) 218
+ + +
(
[M+NH
4
] , 75%), 201 (MH , 100%), 185 ([MꢀMe] ,
+
2
0%), 169 ([MꢀOMe] , 25%); HRMS
C
10 17 4
H O
max
+
(
[M+H] ) requires 201.1127; found 201.1123; 10 m
5940; Cu(II) Takeda, T.; Inoue, T.; Fujiwara, T. Chem.
(
film) 2950 (w), 2893 (w), 1727 (s), 1454 (w), 1210 (m),
ꢀ1
Lett. 1988, 985–988; V(V) Hirao, T.; Morimoto, C.;
Takada, T.; Sakurai, H. Tetrahedron Lett. 2001, 42, 1961–
1
H 3
056 (m) cm ; d (300 MHz, CDCl ) 1.95 (1H, dt,
J = 3.0, 14.0 Hz, CHH–CHPh), 2.27–2.37 (1H, m, OCH2–
CHH), 2.45–2.57 (1H, m, OCH –CHH), 2.57 (1H, appar-
ent q, J = 13.0 Hz, CHH–CHPh), 3.25 (1H, dd, J = 3.5,
1963; O
3
Linderman, R. J.; Jaber, M. Tetrahedron Lett.
2
1
994, 35, 5993–5996; H O Falck, J. R.; Lai, J.; Venkata
2
2
Rama, D.; Lee, S. Tetrahedron Lett. 1999, 40, 2715–2718.
b) It is also possible that decomposition of radical cations
such as 2 (Scheme 2) could proceed via the generation of
1
3.5 Hz, OCHPh–CH
2 2
–CHPh), 3.60 (3H, s, CO Me), 4.10
(
(
1H, dt, J = 3.5, 11.5 Hz, OCHH–CH ), 4.32 (1H, appar-
2
2
ent q, J = 10.0 Hz, OCHH–CH ), 5.15 (1H, dd, J = 3.0,

M. R. Attwood et al. / Tetrahedron Letters 47 (2006) 3607–3611
2.0 Hz, OCHPh), 5.57 (1H, s, OCHO), 7.20–7.55 (10H, 2.60–2.70 (1H, m, OCH
3611
1
2
–CHH), 3.40 (3H, s, CO
2
Me),
m, Ar); d
C
(50 MHz, CDCl
3
) 31.6, 34.5, 44.5, 52.3, 53.1,
3.41–3.47 (1H, m, PhCH), 3.93 (1H, q, J = 6.0 Hz,
6
1
2
3
4.2, 73.7, 103.1, 126.8, 128.2, 128.2, 128.9, 140.5, 142.2,
OCHH–CH ), 4.28 (1H, dt, J = 2.5, 9.0 Hz, OCHH–
CH ), 4.75 (1H, q, J = 4.0 Hz, OCH–CH@CH), 5.70 (1H,
2
2
+
+
72.1; m/z (CI) 356 ([M+NH
9%), 193 (80%), 188 (100%); HRMS C21
38.1518; found 338.1525; 12 mmax (film) 2948 (w), 2893
4
] , 19%), 339 ([M+H] ,
H
22
O
4
requires
s, OCHO), 6.25 (1H, dd, J = 6.0, 16.0 Hz, OCH–
CH@CH), 6.68 (1H, d, J = 16.0 Hz, OCH–CH@CH),
ꢀ
1
(
w), 1733 (s), 1452 (m), 1046 (s) cm ; dH (300 MHz,
CDCl ) 2.10–2.21 (1H, m, CHPh–CHH), 2.39–2.51 (2H,
m, CHPh–CHH, OCH –CHH), 2.65–2.75 (1H, m, OCH
CHH), 3.40 (3H, s, CO Me), 3.50 (1H, dd, J = 5.0, 7.0 Hz,
7.10–7.40 (10H, m, Ar); dC (50 MHz, CDCl ) 32.3, 33.7,
3
3
44.7, 52.3, 59.2, 67.6, 71.3, 102.8, 126.9, 127.6, 128.1,
2
2
–
128.7, 128.1, 129.0, 129.8, 130.9, 137.1, 141.5, 173.3, m/z
+
+
(CI) 383 ([M+NH ] , 40%), 365 ([M+H] , 10%), 347
2
4
CHPh–CH
1H, dt, J = 4.0, 8.5 Hz, OCHH–CH
J = 6.0, 8.0 Hz, OCHPh), 5.75 (1H, s, OCHO), 7.25–7.43
10H, m, Ar); dC (75 MHz, CDCl ) 33.3, 34.0, 44.4, 51.8,
2
), 3.97 (1H, q, J = 6.0 Hz, OCHH–CH
2
), 4.32
24 4
(30%), 219 (100%); HRMS C23H O requires 364.1475;
found 364.1670; 24 mmax (film) 2952 (s), 2930 (s), 2895 (m),
(
2
), 5.12 (1H, dd,
2857 (m), 1471 (w), 1463 (w), 1254 (m), 1147 (w), 1093 (s),
ꢀ
1
(
1076 (s), 1034 (m) cm ; dH (300 MHz, CDCl ) 0.00 (6H,
3
3
5
1
3
8.6, 67.1, 72.1, 102.6, 125.7, 127.1, 127.5, 128.3, 128.4,
2
s, SiMe ), 0.85 (9H, s, Si-t-Bu), 1.40–1.70 (4H, m, H-4a, H-
+
28.5, 141.1, 142.2, 173.0; m/z (CI) 356 ([M+NH
39 ([M+H] , 29%), 210 (40%), 193 (100%); HRMS
4
] , 28%),
6a,b, H-7a), 1.80–2.00 (2H, m, H-4b, H-7b), 3.26 (1H, d,
J = 9.5 Hz, SiOCHH), 3.30–3.40 (1H, m, H-8a), 3.42 (1H,
d, J = 9.5 Hz, SiOCHH), 3.76–3.84 (1H, m, H-8b), 4.05
(1H, dt, J = 4.5, 8.5 Hz, H-3a), 3.90 (1H, q, J = 8.5 Hz, H-
+
C H O requires 338.1518; found 338.1525; 14 mmax
2
1
22
4
(
film) 2954 (w), 2887 (w), 1729 (s), 1256 (m), 1208 (m),
ꢀ
1
1
048 (m), 1027 (m) cm ; d
H
(300 MHz, CDCl
3
) 1.8–1.9
3b), 4.80 (1H, s, OCHO); d
C
(75 MHz, CDCl
3
) ꢀ5.7,
(
2
1H, m, OCH –CHH) 2.15–2.37 (2H, m, 2 · OCH –CHH)
ꢀ5.6, 18.2, 21.1, 25.8, 26.2, 28.9, 46.5, 63.7, 66.5, 66.7,
2
2
+
+
.58 (1H, dt, J = 8.0, 12.5 Hz, OCH –CHH), 3.05 (1H, dd,
102.3; m/z (CI) 290 ([M+NH ] , 50%), 273 ([M+H] ,
4
29
2
J = 5.0, 11.0 Hz, CH-(3-furyl)), 3.55 (3H, s, CO
2
Me), 3.93
100%), 215 (18%); HRMS
273.1886; found 273.1887.
14 29 3
C H O Si requires
(
1H, dt J = 4.5, 12.0 Hz, OCHH–CH ), 3.95–4.08 (2H, m,
2
2
· OCHH–CH ), 4.15 (1H, apparent q, J = 8.0 Hz,
14. This ring system is present in a number of natural
products. For leading references see: Messer, R.; Schmitz,
A.; Moesch, L.; H a¨ ner, R. J. Org. Chem. 2004, 69, 8558–
8560; Willis, M. C.; Flower, S. Synlett 2003, 1491–1493;
Br u¨ ggemann, M.; McDonald, A. I.; Overman, L. E.;
Rosen, M. D.; Schwink, L.; Scott, J. P. J. Am. Chem. Soc.
2003, 125, 15284–15285.
2
OCHH–CH
2
), 5.37 (1H, s, OCHO), 6.31 (1H, s, br,
OCH@CH), 7.32 (1H, s, br, OCH), 7.39 (1H, s, br, OCH);
d
1
C
(50 MHz, CDCl
3
) 27.1, 32.8, 34.9, 52.4, 54.1, 61.3, 65.0,
01.9, 110.7, 125.2, 140.1, 143.4, 172.9; m/z (CI) 270
+
+
(
[M+NH
4
] , 100%), 253 ([M+H] , 18%); HRMS
+
C
1
13
H
17
O
5
([M+H] ) requires 253.1076; found 253.1077;
6 mmax (film) 2952 (w), 2891 (w), 1730 (m), 1208 (m) cm
ꢀ1
;
15. cf. The following redox potentials:
dH (300 MHz, CDCl ) 1.89–1.97 (1H, m, OCH –CHH),
3
2
2
.17–2.30 (1H, m, OCH
2
–CHH), 2.40–2.50 (1H, m,
CeðIVÞ þ eꢀ $ CeðIIIÞ E0 þ 1:72 V
OCH
1H, dd, J = 5.0, 10.0 Hz, CH-(2-furyl)), 3.57 (3H, s,
CO Me), 3.97–4.05 (3H, m, 3 · OCHH–CH ), 4.17 (1H,
apparent q, J = 8.0 Hz, OCHH–CH ), 5.40 (1H, s,
OCHO), 6.10 (1H, d, J = 3.0 Hz, OCH@CH–CH), 6.31
1H, dd, J = 1.5, 3.0 Hz, OCH@CH), 7.37 (1H, dd,
2 2
–CHH), 2.51–2.61 (1H, m, OCH –CHH), 3.30
þ
ꢀ
0
½
ðCpÞ Feꢁ þ e $ ½ðCpÞ Feꢁ E þ 0:40 V
(
2
2
2
2
2
(Housecroft, C. E.; Sharpe, A. G. In Inorganic Chemistry;
Pearson: Harlow, 2001; pp 613, 629).
(
16. Competing intramolecuar Friedel–Crafts alkylation (see
Fillion, E.; Beingessner, R. L. J. Org. Chem. 2003, 68,
9485–9488; Nagata, T.; Nakagawa, M.; Nishida, A. J.
Am. Chem. Soc. 2003, 125, 7484–7485) was not observed.
17. The electrochemical oxidation of a-alkoxygermanes has
been reported: Yoshida, J.; Morita, Y.; Itoh, M.; Ishichi,
Y.; Isoe, S. Synlett 1992, 843–844.
18. For the chemistry of a-stannylacetals see: Cintrat, J.-C.;
L e´ at-Crest, V.; Parrain, J.-L.; Le Grognec, E.; Beaudet, I.;
Quintard, J.-P. Eur. J. Org. Chem. 2004, 4251–4267, and
references cited therein.
+
J = 1.5 Hz, OCH); m/z (CI) 270 ([M+H] , 100%), 253
(
+
+
[M+H] , 52%); HRMS C13
H
17
O
5
([M+H] ) requires
2
53.1076; found 253.1080; 18 mmax (film) 2950 (w), 2890
(
(
w), 1728 (w), 1495 (w), 1452 (w), 1263 (w), 1211 (m), 1164
ꢀ1
w), 1079 (m), 1058 (w), 1027 (w) cm ; d
) 1.87 (1H, dt, J = 3.0, 13.5 Hz, PhCH), 2.25–2.35
1H, m, OCH –CHH), 2.45–2.55 (1H, m, OCH –CHH),
H
(300 MHz,
CDCl
(
3
2
2
2
1
8
.55–2.65 (1H, m, CHPh–CHCH), 3.18 (1H, dd, J = 3.5,
3.5 Hz, PhCH–CHHPhCH), 4.09 (1H, dt, J = 3.0,
.0 Hz, OCHH–CH ), 4.28 (1H, q, J = 8.0 Hz, OCHH–
2
CH ), 4.75–4.82 (1H, m, OCH–CH@CH), 5.05 (1H, s,
19. Hydride transfer from stannylcarbinols has been
employed in the synthesis of acylstannanes: Marshall, J.
A.; Gung, W. Y. Tetrahedron Lett. 1989, 30, 2183–2186;
Quintard, J.-P.; Elissondo, B.; Mouko-Mpegna J. Orga-
nomet. Chem. 1983, 251, 175–187; For examples of 1,5-
hydride shifts see: W o¨ fling, J.; Frank, E.; Schneider, G.;
Tietze, L. F. Eur. J. Org. Chem. 2004, 90–100; Krohn, K.;
Fl o¨ rke, U.; H o¨ fker, U.; Tr a¨ ubel, M. Eur. J. Org. Chem.
1999, 3495–3499; An excellent review on this general area
can be found in: Watt, C. I. F. Adv. Phys. Org. Chem.
1988, 24, 57–112.
2
OCHO), 6.40 (1H, dd, J = 6.0, 16.0 Hz, OCH–CH@CH),
6
.75 (1H, d, J = 16.0 Hz, OCH–CH@CH), 7.20–7.50
(
10H, m, Ar); d
C
(50 MHz, CDCl
3
) 31.9, 32.5, 44.5, 52.3,
5
1
6
3.7, 64.6, 72.3, 102.8, 127.0, 128.0, 128.2, 128.8, 129.0,
+
29.5, 131.6, 137.2, 140.5, 172.2; m/z (CI) 382 ([M+NH
4
] ,
+
3%), 365 ([M+H] , 15%), 347 (30%), 219 (100%), HRMS
C H O requires 364.1675; found 364.1673; 20 mmax
2
3
24
4
(
(
film) 2949 (w), 1732 (s), 1495 (w), 1451 (w), 1202 (w), 1042
ꢀ
1
s) cm ; d
H
(300 MHz, CDCl
3
) 2.00–2.12 (1H, m, PhCH–
–CHH),
CHH), 2.30–2.40 (2H, m, PhCH–CHH, OCH
2