Electronic effects in migratory groups. [1,4]- versus [1,2]-rearrangement in rhodium carbenoid generated bicyclic oxonium ylides

Article abstract of DOI:10.1021/jo010431f

The variety of α-diazo β-keto esters (3a-f, 8a-f) with varying substituents (ED/EW) on the phenyl ring of the O-benzyl group were prepared. The rhodium(II) acetate catalyzed decomposition of diazo compounds in benzene reflux conditions. The ratio of 1,4 versus 1,2 migration product was determined. It was found that an increase in electron density on the benzylic carbon of the migrating group prefers 1,4 migration products (4, 9) while a decrease in electron density leads to a preponderance of 1,2 migration products (5, 10). The results obtained were correlated to the mechanistic aspect of the product selectivity. The intermediacy of the intramolecular oxonium ylide formation was demonstrated by crossover experiments. The preference for the formation of 2,3 sigmatropic rearrangement product over 1,2 and 1,4 was demonstrated by performing the reaction with α-diazo β-keto esters (13a, 13b) with O-allyl and O-propargyl at C3. The effect of solvent, temperature, and mole percentage of rhodium(II) acetate was also studied.

Full text of DOI:10.1021/jo010431f

J . Org. Chem. 2001, 66, 6323-6332
6323
Electr on ic Effects in Migr a tor y Gr ou p s. [1,4]- ver su s
[1,2]-Rea r r a n gem en t in Rh od iu m Ca r ben oid Gen er a ted Bicyclic
Oxon iu m Ylid es
Navnath P. Karche, Santosh M. J achak, and Dilip D. Dhavale*
Department of Chemistry, Garware Research Centre, University of Pune, Pune-411 007, India
ddd@chem.unipune.ernet.in
Received April 25, 2001
The variety of R-diazo â-keto esters (3a -f, 8a -f) with varying substituents (ED/EW) on the phenyl
ring of the O-benzyl group were prepared. The rhodium(II) acetate catalyzed decomposition of diazo
compounds in benzene reflux conditions. The ratio of 1,4 versus 1,2 migration product was
determined. It was found that an increase in electron density on the benzylic carbon of the migrating
group prefers 1,4 migration products (4, 9) while a decrease in electron density leads to a
preponderance of 1,2 migration products (5, 10). The results obtained were correlated to the
mechanistic aspect of the product selectivity. The intermediacy of the intramolecular oxonium ylide
formation was demonstrated by crossover experiments. The preference for the formation of 2,3
sigmatropic rearrangement product over 1,2 and 1,4 was demonstrated by performing the reaction
with R-diazo â-keto esters (13a , 13b) with O-allyl and O-propargyl at C3. The effect of solvent,
temperature, and mole percentage of rhodium(II) acetate was also studied.
The intramolecular generation of oxonium ylides by
rhodium(II)-catalyzed decomposition of R-diazo carbonyl
compounds and subsequent transformation to diverse
products has received great attention in the past decade.1
In general, the oxonium ylides undergo three major
reaction pathways, which include (a) the â-hydride
elimination,2 (b) the [1,2]-migration (Steven’s rearrange-
ment),3 and (c) the [2,3]-sigmatropic rearrangement.4
Thijs and Zwanenburg had first proposed an intramo-
lecular formation of four-membered oxonium ylide, in the
reaction of R,â-epoxy diazomethyl ketones with activated
copper powder in hydroxylic solvents, to produce alkene
oxoacetals (eq 1).5 In 1984, Doyle and co-workers reported
ment product in the intramolecularly generated oxonium
ylide from R-diazo ketone bearing a cyclic acetal (eq 2).3c
Subsequently, the intramolecular generation of allylic
oxonium ylides and their [2,3]-sigmatropic rearrange-
ments in the synthesis of useful oxygen heterocycles
gained a lot of interest (eq 3).4 Besides these usual
the formation of product in the reaction of acrolein
dimethyl acetal and ethyl diazoacetate via the interme-
diacy of the oxonium ylide.6 Soon after, Roskamp and
J ohnson had noticed the formation of [1,2]-rearrange-
(1) For general reviews of rhodium-carbenoids, see: (a) Adams, J .;
Spero, D. M. Tetrahedron 1991, 47, 1765. (b) Padwa, A.; Krumpe, K.
E. Tetrahedron 1992, 48, 5385. (c) Ye, T.; McKervey, M. A. Chem. Rev.
1994, 94, 1091. (d) Padwa, A.; Weingarten, M. D. Chem. Rev. 1996,
96, 223. (e) Doyle, M. P.; Forbes, D. C. Chem. Rev. 1998, 98, 911. (f)
Sulikowski, G. A.; Cha, K. L.; Sulikowski, M. M. Tetrahedron: Asym-
metry 1998, 9, 3145.
pathways, Pirrung and co-workers in 1991 first observed
an example of [1,4]-migration in the rhodium(II)-cata-
lyzed decomposition of an R-diazo-â-keto ester (eq 4).7 The
(2) Bien, S.; Gillon, A.; Kohen, S. J . Chem. Soc., Perkin Trans. 1
1976, 489.
(3) (a) Brogan, J . B.; Bauer, C. B.; Rogers, R. D.; Zercher, C. K.
Tetrahedron Lett. 1996, 37, 5053. (b) Doyle, M. P.; Ene, D. G.; Forbes,
D. C.; Tedro, J . S. Tetrahedron Lett. 1997, 38, 4367. (c) Roskamp, E.
J .; J ohnson, C. R. J . Am. Chem. Soc. 1986, 108, 6062.
(4) (a) Pirrung, M. C.; Werner, J . A. J . Am. Chem. Soc. 1986, 108,
6060. (b) Clark, J . S. Tetrahedron Lett. 1992, 33, 6193. (c) Doyle, M.
P.; Bagheri, V.; Harn, N. K. Tetrahedron Lett. 1988, 29, 5119.
(5) Thijs, L.; Zwanenburg, B. Tetrahedron. 1980, 36, 2145.
(6) Doyle, M. P.; Griffin, J . H.; Chinn, M. S.; Van Leusen, D. J . Org.
Chem. 1984, 49, 1917.
second report by West and co-workers described the
isolation of the [1,4]-migration product, albeit in very low
(7) Pirrung, M. C.; Brown, W. L.; Rege, S.; Laughton, P. J . Am.
Chem. Soc. 1991, 113, 8561.
10.1021/jo010431f CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/29/2001

6324 J . Org. Chem., Vol. 66, No. 19, 2001
Karche et al.
Ta ble 1. Electr on ic Effect of Su bstitu en t on th e
Sch em e 1a
F or m a tion of 1,4 a n d 1,2 Migr a tion P r od u cts
products
diazo
compd
time
(min)
ratio
1,4:1,2
combined
yielda(%)
entry
1,4
1,2
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
3f
8a
8b
8c
8d
8e
8f
10
30
30
30
10
10
30
30
30
10
10
30
4a
4b
4c
4d
4e
4f
9a
9b
9c
9d
9e
9f
5a
5b
5c
5d
5e
62:38
100:0
100:0
100:0
38:62
32:68
100:0
100:0
100:0
58:42
60:40
100:0
77
75
75
76
81
82
76
73
76
78
76
65
5f
10a
10b
10c
10d
10e
10f
10
11
12
a
Isolated yields after column chromatography.
tion is the reaction conditions (i.e., solvent, temperature,
and molar ratio of catalyst to substrate).13 Our present
study is related to the specificity due to substrate. In this
aspect, we changed the migratory aptitude of the migrat-
ing group (by incorporating electron-donating and electron-
withdrawing groups in the phenyl ring of the benzyl
group) that is bonded to the oxygen of an oxonium ylide
generated from Rh(II)-catalyzed decomposition of R-diazo
â-keto ester. We report here the general trend that an
increase in the electron density on the benzylic carbon
of the migratory group results in the preferential [1,4]-
migration pathway while a decrease in the electron
density leads to the preponderance of the [1,2]-migration
product. The results thus obtained are correlated to the
mechanistic aspects in the formation of the [1,4]- and
[1,2]-migrated product.
a
Key: (a) BF3‚OEt2, EDA, CH2Cl2, 0 °C, 3 h; (b) MsN3, CH3CN,
30 °C, 3 h; (c) Rh2O(Ac)4, benzene, reflux, 10-30 min.
yield, in the Cu(II) carbenoid-derived oxonium ylides.8
The same reaction, however, failed to give the [1,4]-
migration product in the presence of rhodium(II) acetate.
Recently, we have substantiated this uncommon behavior
and demonstrated that the formation of the [1,4]-migra-
tion product, via the intermediacy of oxonium ylide, is
also a prominent process.9 Our results showed that the
decomposition of the sugar derived R-diazo-â-keto ester
3a , catalyzed with rhodium(II) acetate, gave the [1,4]-
migrated product 4a in major amount (62%) in competi-
tion with the [1,2]-rearrangement product 5a (38%). In
the case of 3b, in which the migratory -OBn group is
replaced with -OPMB, the formation of [1,4]-migration
product 4b was the only isolated product in 80% yield
(Scheme 1). This precedent provided us a useful system
to study the intramolecular competition between the
formation of [1,4]- and [1,2]-migration products, as a
function of migratory aptitudes of the migrating group,
in the rhodium carbenoid generated bicyclic oxonium
ylides.
Many competitive studies related to the product selec-
tivity in rhodium carbenoid reactions, leading to either
C-H insertion or rearrangements, are reported. These
are mainly classified in two types. The first and the most
commonly used methodology is catalyst specific in which
product selectivity is dependent on the electrophilic
nature of the rhodium(II) catalyst (by variation of ligands
on rhodium).10 The chiral rhodium catalysts are known
to give chemo- and stereoselectivity in product forma-
tion.11 The second type of studies are substrate specific.
A few examples of this type are known wherein six-
membered versus five-membered oxonium ylide forma-
tion (which is dependent on which diastereotopic oxygen
out of the two possible oxygen atoms is involved in the
oxonium ylide formation) decides the product distribu-
tion.12 The third factor that controls the product forma-
Resu lts a n d Discu ssion
The required D-glucose-derived â-keto esters, with
varying substituents on the phenyl ring of the benzyl
group at C3 oxygen, were prepared as per the procedure
reported earlier by us.14 Thus, the individual reactions
of 1,2-O-isopropylidene-R-D-xylo-pentodialdoses 1a-f with
ethyl diazoacetate (EDA) in the presence of BF3‚OEt2 in
dichloromethane at 0 °C (for electron-donating substit-
uents the reactions were performed at -50 °C) afforded
the corresponding sugar â-keto esters 2a -f. The diazo
transfer with mesyl azide completed the transformation
of â-keto esters 2a -f to the corresponding R-diazo â-keto
esters 3a -f in good yields. The reactions of 3a -f with
Rh2(OAc)4 (2 mol %) were conducted under benzene reflux
conditions until the starting material was consumed as
indicated by TLC (Scheme 1). The reaction mixture was
directly chromatographed, and the corresponding 1,4-
migrated products 4a -f and 1,2-migrated products 5a ,e,f
were isolated in good yields (70-82%).15 The results are
summarized in Table 1. We have also tested the general-
ity of this reaction with aromatic substrates. In this case,
reaction of the aromatic aldehyde derivatives 6a -f using
EDA and BF3‚OEt2 afforded poor yields of â-keto esters.
(8) West, F. G.; Naidu, B. N.; Tester, R. W. J . Org. Chem. 1994, 59,
6892.
(9) Dhavale, D. D.; Desai, V. N.; Saha, N. N. J . Chem. Soc., Perkin
Trans. 1 2000, 147.
(12) Zercher, C. K.; Brogan, J . B.; Bauer, C. B.; Rogers, R. D.
Tetrahedron Lett. 1996, 37, 5053.
(13) Wee, A. G. H.; Liu, B.; McLeod, D. D. J . Org. Chem. 1998, 63,
4218.
(10) (a) Doyle, M. P. Acc. Chem. Res. 1986, 19, 348. (b) Pirrung, M.
C.; Morehead, A. T. J . Am. Chem. Soc. 1994, 116, 8991. (c) Taber, D.
F.; Green, J . H.; Zhang, W.; Song, R. J . Org. Chem. 2000, 65, 5436.
(11) Ye, T.; Garcia, F. C.; McKervey, A. M. J . Chem. Soc., Perkin
Trans. 1, 1995, 1373.
(14) Dhavale, D. D.; Bhujbal, N. N.; J oshi, P.; Desai, S. G. Carbo-
hydr. Res. 1994, 263, 303.
(15) No product corresponding to an alternative pathway such as
C-H insertion or Buchner reaction (possible with the in situ generated
rhodium carbenoid) was isolated.

Electronic Effects in Migratory Groups
J . Org. Chem., Vol. 66, No. 19, 2001 6325
Sch em e 2a
Ta ble 2. Effect of Rea ction Con d ition s on th e Rea ction
of 3a w ith Rh od iu m Aceta te
Rh2(OAc)4
(mol %)
T
(°C)
ratio
1,4:1,2
yielda
(%)
entry
solvent
time
1
2
3
4
5
6
2
2
2
2
5
2
CH2Cl2
CH2Cl2
C6H6
C6H6
C6H6
25 1 h
40 1 h
25 36 h
80 10 min
80 10 min
90b
77
78
78
62:38
64:36
60:40
C6H5CH3 110 10 min
a
b
Isolated yields after column chromatography. Yield of recov-
ered compound.
only isolable compounds in greater than 70% yields
(Table 1, entries 2-4, 7-9).19 Conversely, the reverse
trend was noticed in the case of substrates 3e,f (with
electron-withdrawing substituents) wherein the 1,4-
migrated products 4e,f were obtained in minor amounts
while the 1,2-migrated products 5e,f were the major ones
(Table 1, entries 5 and 6). However, in the case of 3a and
8e (unsubstituted benzyl group), the predominant forma-
tion of 1,4-migrated product (∼60%) over 1,2-migrated
product (∼40%) was noticed (Table 1, entries 1 and 11).
A similar trend was noticed for 8d (3′-methoxybenzyl-
substituted), although there is an overall increase in the
electron density in the phenyl group (Table 1, entry 10).
To understand the effect of the reaction conditions13
(solvent, temperature, and molar ratio) on the product
selectivity, we have performed the reactions with the
model substrate 3a (Table 2). The reaction of 3a with
rhodium acetate (2 mol %) in dichloromethane at room
temperature or under reflux conditions afforded a com-
plex mixture of products (Table 2, entries 1 and 2) while
in benzene at room temperature it was noticed to be very
sluggish and even after 36 h nearly quantitative amounts
of starting materials were recovered (Table 2, entry 3).
The optimum conditions (benzene reflux, 10 min, Table
2, entry 4) afforded the 1,4-migrated and 1,2-migrated
products 4a and 5a , respectively, in a ratio of 62:38 in
77% yields. An increase in the amount of Rh2(OAc)4 (5
mol %) had no significant effect (Table 2, entry 5). To
test whether even higher temperature would be advanta-
geous, the reaction was performed in refluxing toluene.
However, this did not alter the course of the reaction
(Table 2, entry 6).
Next, the competitive reaction pathway between [2,3]-
sigmatropic rearrangement and [1,4]- or [1,2]-rearrange-
ment was studied. To explore such a possibility, D-glucose-
derived 3-O-allyl-â-keto ester 12a and 3-O-propargyl-â-
keto ester 12b (obtained from 1,2-O-isopropylidene-R-D-
xylo-pentodialdoses 11a and 11b) were converted to the
corresponding R-diazo-â-keto esters 13a and 13b in good
yields (Scheme 3). The individual reactions of 13a and
13b with rhodium(II) acetate (2 mol %) under benzene
reflux conditions (10 min) furnished [2,3]-sigmatropic
rearrangement products 14a and 14b, respectively, in
good yields (∼75%). This indicated that the in situ
generated oxonium ylides have a preference for the
symmetry-allowed [2,3]-sigmatropic rearrangement over
the [1,2]- and [1,4]-migration products.20 In view of the
fact that in metal carbenoid reactions [2,3]-sigmatropic
a
Key: (a) Activated Al2O3, EDA, 25 °C, 3 h; (b) MsN3, CH3CN,
30 °C, 3 h; (c) Rh2O(Ac)4, benzene, reflux, 10-30 min.
However, the use of EDA and activated alumina under
solvent free conditions as reported earlier by us16 gave
the corresponding â-keto esters 7a -f in good yields.17 The
reaction of 7a -f with mesyl azide gave R-diazo â-keto
esters 8a -f, respectively (Scheme 2). Treatment of 8a -e
with Rh2(OAc)4 (2 mol %) under benzene reflux conditions
gave identical results, and corresponding 1,4-migrated
products 9a -e and 1,2 migrated products 10d ,e were
isolated in 70-80% yields (Table 1).18
The 1,4- and 1,2-migrated products (4, 9 and 5, 10)
were well characterized by spectroscopic and analytical
data. The characteristic features for 1,2-migrated prod-
ucts were as follows. The IR spectra showed two carbonyl
frequencies at 1779 and 1744 cm-1 indicating the pres-
ence of a five-membered ring ketone (furan-3-one) and
the ester carbonyl group, respectively. The 1H NMR
spectra showed an AB quartet at δ ∼3.26 (J ) 14.0 Hz)
indicating the presence of a -CCH2Ph group instead of
-OCH2Ph functionality. The 13C NMR spectrum showed
a ketone carbonyl at δC ∼202.3 and ester carbonyl at δC
∼166.9. The assignments of the 1,4-migration products
were also made by spectral studies. The IR spectra
showed a carbonyl stretching frequency at 1714 cm-1
corresponding to R,â-unsaturated ester functionality. In
1
the H NMR spectrum, the -OCH2Ph group displayed a
signal at δ ∼5.16 (AB quartet with J ) 12.1 Hz or singlet)
and 13C NMR showed only one ester carbonyl at δC
∼160.1 and two olefin carbons. The structure of 4a was
further confirmed by 13C DEPT, 2D NMR experiments
such as HETCORR, COSY, and elemental analysis data.9
Examination of the results indicated that the rhodium-
(II)-catalyzed reactions of R-diazo â-keto esters 3b-d and
8a -c,f (with electron-donating substituents) afforded
respective 1,4-migrated products 4b-d and 9a -c,f as the
(16) Dhavale, D. D.; Patil, P. N.; Mali, R. S. J . Chem. Soc., 1994,
152.
(17) The reactions of 2-O-(4′-nitrobenzyl) benzaldehyde and 2-O-(4′-
carbemethoxybenzyl) benzaldehyde with EDA either in the presence
of BF3-OEt2 in dichloromethane or activated alumina under solvent
free conditions failed to give the corresponding â-keto esters under
variety of reaction conditions.
(18) We have repeated the reaction of benzenepropanoic acid, 2-O-
methyl-R-diazo-â-oxoethyl ester (8f), as reported first by Pirrung et
al. (see ref 7). In our hands, the reaction under benzene reflux condition
afforded 1,4-migrated product 9f in 65% yield.
(19) In all these reactions the 1H and 13C NMR spectrum of the crude
mixture showed signals (<5%), which could be assigned to the 1,2-
migrated product. However, our attempts to isolate the product in pure
form were unsuccessful.
(20) Identical results with aromatic substrates have been reported
(see refs 4 and 7).

6326 J . Org. Chem., Vol. 66, No. 19, 2001
Karche et al.
Sch em e 3a
Sch em e 4
a
Key: (a) BF3‚OEt2, EDA, CH2Cl2, 0 °C, 3 h; (b) MsN3, CH3CN,
30 °C, 3 h; (c) Rh2O(Ac)4, benzene, reflux, 10 min.
rearrangements have the lower activation energy as
compared with other possible pathways,4 the reaction was
performed at lower temperature. The same reaction at
35 °C (lower activation energy) in benzene (3 h) or in
dichloromethane (1 h) also afforded 14a and 14b in 86%
and 78% yields, respectively, indicating that the reaction
pathway was indeed a [2,3]-sigmatropic rearrangement.21
The absolute configuration at the newly generated
stereocenter C6 in 1,2-migrated product 5f and 2,3-
sigmatropic rearrangement product 14a , was established
by NOEDIF experiments. Thus, 5f showed NOE between
the benzylic (-CH2) protons and R-H3, R-H4 as well as
two aromatic protons (ortho to the benzylic group) but
no NOE with H1 and H2, while for 14a , an NOE was
observed between allylic (-CH2) protons and R-H3, R-H4
as well as three olefinic protons but no NOE was observed
with H1 and H2. This indicated that in both products 5f
and 14a the migrating group comes from the R-face
resulting in (R) absolute configuration at C6.
Mech a n istic Stu d y of th e Rea ction . Although dif-
ferent mechanisms involved in the rhodium(II) carbenoid-
mediated 1,2-rearrangement, [2,3]-sigmatropic rearrange-
ment, and C-H insertion products are well documented
in the literature, an explanation for the formation of 1,4-
migration product, in the rhodium(II) catalyzed reaction,
is lacking. West and co-workers,8 however, proposed a
mechanism in the Cu(II)-catalyzed decomposition of
R-diazo ketone for the formation of the [1,2]- and [1,4]-
migrated products (Scheme 4). It has been reported that
the difference in Rh(II)- and Cu(II)-catalyzed decomposi-
tion follow different mechanistic pathways.1 Therefore,
an independent mechanism for the formation of 1,4-
migrated product had been proposed by us (Scheme 5).9,22
We assumed that the metal-bound five-membered oxo-
nium ylide A or B, generated from substrate 3, plays an
important role in the product selectivity. Examination
of models revealed that, in the oxonium ylide B, the
distance between the migration origin and the terminus
is large, thus ruling out its intermediacy in the 1,4-
migrated product. On the other hand, we hypothesized
a somewhat different type of four-centered oxabicyclo-
[3.2.0]heptane transition state (TS) C, via the interme-
diacy of the oxonium ylide A, wherein the Rh-C6 bond
(metal carbenoid bond) is aligned with the O-CH2Ar
bond. As the reaction proceeds, the migration of the
-CH2Ar group from oxygen to Rh is completed leading
to TS D. We feel that the TS D is the true intermediate
in the formation of both the products 4 and 5. We would
like to attribute the differences in the selectivity of the
formation of product 4 or 5 to the change in electrophi-
licity of the Rh complex, in the TS D, due to the electronic
effects of the substituent in the migrating group. In the
case of an electron-rich aromatic ring, due to the stronger
back-bonding interaction, the electrophilicity of Rh de-
creases and the metal carbenoid bond (Rh-C6) becomes
weaker as compare to Rh-CH2Ar bond.23 Thus, as shown
in Scheme 5, free rotation about the metal carbenoid bond
(Rh-C6) brings -CH2Ar (migrating group) close to the
CdO group (TS E). The rupture of the weak Rh-C6 bond
followed by the migration of the benzyl group to oxygen,
and exclusion of Rh(II) acetate afforded [1,4]-migrated
product 4 by a concerted pathway. However, in the case
of electron-poor substituents, due to the increase in
electrophilicity of the Rh complex, the bond between Rh-
C6 becomes stronger than the Rh-CH2Ar bond.23 As a
result, the reaction is initiated by cleavage of the weak
Rh-CH2Ar bond followed by formation of a new C-C
bond (between benzylic carbon and C6) and cleavage of
the Rh-C6 bond with loss of Rh(II) acetate in a three-
membered TS F by a concerted process to afford 1,2-
rearranged product 5.24
An examination of Table 1 indicated that the reaction
time required for the formation of 1,4-migrated product
in the electron-rich migratory group is more (30 min)
than that required (10 min) for the completion of the
(23) Pirrung et al. studied the effect of ligands on rhodium in the
product selectivity of 1,2 versus C-H insertion. In this study, it has
been noticed that in the electron-rich rhodium complexes (e.g., rhodium
pivalate) the stronger back-bonding interactions resulted into the
shorter Rh-Rh bond and consequently weaker σ bond between metal
and carbenoid. A reverse trend had been noticed for electron-poor
complexes (e.g., rhodium trifluoro acetate); see ref 10b.
(21) No product corresponding to either [1,4]- or [1,2]-rearrangement
was detected in the 1H NMR spectrum of the crude reaction mixture
(at reflux or lower temperature).
(22) We are thankful to Prof. Pirrung for helpful discussions.

Electronic Effects in Migratory Groups
J . Org. Chem., Vol. 66, No. 19, 2001 6327
Sch em e 5
reactions where the unsubstituted or electron-withdraw-
ing group is present (compare entries 2-4 and 7-9 with
all other entries). We would like to attribute this anomaly
to the change in Lewis acid character of the Rh complex.
The reduction of the Lewis acidity of the complex, for an
electron-donating substituent on the phenyl ring, de-
creases the rate of the formation of products, whereas in
the case of electron-withdrawing substituent the increase
in Lewis acidity of the complex enhances the rate of
formation of the products. This observation was noticed
to be parallel with that reported by McKervey and co-
workers wherein rhodium (II) carboxylates were found
to be more reactive (reaction completed in 10 min) than
the Rh(II) MEPY (reaction completed after 3 days even
though 10-fold equiv of catalyst was used).11
We would like to correlate our observation with the
change in charge density at the benzylic carbon. We
predict that the partially developed positive charge on
the benzylic carbon in the TS D stabilized by electron-
donating groups on the phenyl ring favors 1,4-migration,
whereas the positive charge on the benzylic carbon in the
TS D destabilized by electron-withdrawing groups on the
phenyl ring favors 1,2-rearrangement in the intramo-
lecular pathway. Furthermore, we are correlating the
selectivity in product formation with σR or a resonance
effect based on π-electron bonding and delocalization.
Thus, the plot of σR (resonance contribution)25 for the
substituent on the phenyl ring of the migratory group
against percentage of 1,4- and 1,2-migrated products
gives good correlation (Figures 1 and 2). This indicates
that resonance contribution due to the substituent on
phenyl ring affects the percentage of 1,4- and 1,2-
migrated products; i.e., a substituent with positive σR
favors 1,2-migrated products and a substituent with
negative σR favors 1,4 migrated products.
+
An alternative pathway in which PhCH2 (benzyl
cation) is dissociated either from the oxonium ylide B or
from the rhodium(II) species in TS D and then attacked
by the enolate oxygen of another molecule in an inter-
molecular fashion could be possible. To probe the inter-
or intramolecular pathway of the reaction, we performed
a crossover experiment. Thus, the one-pot reaction of
mixture of 8c and 8e in the presence of Rh(II) acetate (2
mol %) in benzene was performed at reflux temperature
for 30 min (eq 5). The reaction after usual workup
afforded 9c in 78% and 9e and 10e in the ratio 61:39
with overall 80% yield. No crossover product was isolated
in the reaction mixture, indicating that the reaction is
(25) Taft, R. W.; Topsom, R. D. Prog. Phys. Org. Chem. 1987, 16,
1-83, 125-191. This report indicates four parameters: σF or field
effect, based on charge-charge or dipole-dipole interactions; σR or
resonance effect, based on π-electron bonding and delocalisation; σR
or polarizability, based on charge-induced dipoles; σx or electronega-
tivity, based on partial ionic character of the σ bond between the
substituent and a bonded atom. However, we would like to confine
our discussion by correlating σR with 1,2- and 1,4-migration product
selectivity.
(24) Previously, we proposed the mechanism via TS G that re-
sembles an oxabicyclo [3.1.0]hexane ring system as shown below; see
ref 9.

6328 J . Org. Chem., Vol. 66, No. 19, 2001
Karche et al.
F igu r e 1. σR versus percentage of 1,4-migrated products for the Rh-catalyzed reaction of sugar R-diazo â-keto esters.
F igu r e 2. σR versus percentage of 1,2-migrated products for the Rh-catalyzed reaction of sugar R-diazo â-keto esters.
exclusively intramolecular. To trap the initially formed
Rh-carbenoid species and to check the inter- versus
intramolecular formation of oxonium ylide, we have
performed the rhodium-catalyzed decomposition reaction
of 3a in the presence of p-methoxy benzyl alcohol (5
equiv) in benzene at reflux (eq 6). The reaction was com-
sponding to -O-(p-methoxybenzyl) insertion was isolated
or detected in the crude 1H NMR spectrum indicating
that the intramolecular oxonium ylide formation is a
rapid process than the intermolecular C-O insertion.26
In another attempt, the intermediacy of 1,2-migratory
product in the formation of 1,4-migratory product was
checked. Thus, reaction of 5a (1,2-migration product) in
the presence of Rh(II) acetate (2 mol %) in benzene at
reflux for 8 h resulted in the quantitative recovery of the
starting compound. The 1,4-migration product was not
1
detected even in the H NMR of the crude product. This
experiment thus ruled out the intermediacy of 5a in the
formation of 4a . Thus, the intramolecular bicyclic oxo-
(26) The decomposition of R-diazo carbonyl compound in the pres-
ence of alcohol gives C-O insertion product via the formation of
intermolecular oxonium ylide formation; see: Hosten, N. G. C. Bull.
Soc. Chim. Belg. 1985, 94, 183.
pleted in 10 min and afforded a mixture of 4a and 5a in
the ratio 60:40 (combined yield 78%). No product corre-

Electronic Effects in Migratory Groups
J . Org. Chem., Vol. 66, No. 19, 2001 6329
26.3, 14.0. Anal. Calcd for C20H24O9: C, 58.82; H, 5.88.
Found: C, 58.96; H, 5.76.
nium ylide mechanistic pathway, as depicted in Scheme
5, via the participation of the rhodium metal could be
the most probable mechanism for the formation of 1,4-
migrated product. However, the role of rhodium catalyst
to generate a carbene species followed by 1,4-migration
by radical pathway also could not be ruled out.
E t h yl 6-d eoxy-3-O-(3′,4′-d im et h oxyb en zyl)-1,2-O-iso-
p r op ylid en e-r-D-xylo-h ep t-5-u lofu r a n u r on a te (2d ): reac-
tion performed at -50 °C, for 3 h; white solid; mp 62-64 °C;
72% yield; Rf ) 0.38 (PE/ethyl acetate ) 6:4); [R]D ) -56.8 (c
0.25, CHCl3); IR (Nujol), 1744, 1726 cm-1; 1H NMR (300 MHz,
CDCl3) δ 6.81-6.78 (m, 3H), 6.07 (d, J ) 3.6 Hz, 1H), 4.69 (d,
J ) 3.7 Hz, 1H), 4.58 (d, J ) 3.6 Hz, 1H), 4.46 (AB quartet, J
) 11.1 Hz, 2H), 4.26 (d, J ) 3.7 Hz, 1H), 4.18 (q, J ) 7.2 Hz,
2H), 3.91(s, 3H), 3.87 (s, 3H), 3.64 (AB quartet, J ) 16.8 Hz,
2H), 1.46 (s, 3H), 1.32 (s, 3H), 1.27 (t, J ) 7.2 Hz, 3H); 13C
NMR (75 MHz, CDCl3) δ 201.6, 167.0, 149.0, 148.8, 128.9,
120.4, 112.5, 111.0, 110.9, 106.0, 84.9, 82.9, 81.7, 72.3, 68.6,
61.1, 55.8, 47.5, 26.9, 26.3, 14.0. Anal. Calcd for C21H28O9: C,
59.43; H, 6.60. Found: C, 59.23; H, 6.69.
E t h yl 6-d eoxy-3-O-(4′-ca r b m et oxyb en zyl)-1,2-O-iso-
p r p ylid en e-r-D-xylo-h ep t-5-u lofu r a n u r on a te (2e): reac-
tion performed at 0 °C, for 3 h; thick oil; 73% yield; Rf ) 0.40
(PE/ethyl acetate ) 6:4); [R]D ) -62.2 (c 0.25, CHCl3); IR (neat)
1745,1715 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.85 (d, J ) 8.0
Hz, 2H), 7.20 (d, J ) 8.0 Hz, 2H), 6.05 (d, J ) 3.5 Hz, 1H),
4.73 (d, J ) 3.6 Hz, 1H), 4.61 (d, J ) 3.5 Hz, 1H), 4.48 (AB
quartet, J ) 12.0 Hz, 2H), 4.26 (d, J ) 3.6 Hz, 1H), 4.20 (q, J
) 6.2 Hz, 2H), 3.85 (s, 3H), 3.66 (AB quartet, J ) 18.0 Hz,
2H), 1.45 (s, 3H), 1.32 (s, 3H), 1.25 (t, J ) 6.2 Hz, 3H); 13C
NMR (75 MHz, CDCl3) δ 202.3, 166.6, 166.0, 142.5, 130.4,
128.3, 113.2, 106.2, 85.4, 84.3, 82.6, 72.2, 62.8, 53.4, 48.3, 27.1,
26.8, 14.8. Anal. Calcd for C21H26O9: C, 59.71; H, 6.16.
Found: C, 59.82; H, 6.05.
Con clu sion
We have firmly established that the formation of the
1,4-migration product, in the rhodium carbenoid gener-
ated bicyclic oxonium ylides, is a prominent process in
addition to the usual 1,2-migration or [2,3]-sigmatropic
pathways. We have also demonstrated that the migratory
aptitude of the migrating group is one of the deciding
factors in such competitive processes. The study of effect
of different electrophilic rhodium catalysts, by changing
the ligands, on the product selectivity and mechanistic
aspect involving radical approach is in progress.
Exp er im en ta l Section
Gen er a l Meth od s. Melting points were recorded with a
Thomas-Hoover melting point apparatus and are uncorrected.
IR spectra were recorded with FTIR as a thin film or in Nujol
1
mull or with KBr pellets and are expressed in cm-1. H (300
MHz, 500 MHz) and 13C (75 MHz, 125 MHz) NMR spectra
were recorded in CDCl3 as a solvent. Chemical shifts were
reported in δ (ppm) with reference to TMS as an internal
standard. Elemental analyses were carried out with a C,H
analyzer. Optical rotations were measured using a polarimeter
at 25 °C. Thin-layer chromatography was performed on
precoated plates (0.25 mm, silica gel 60 F254). Flash chroma-
tography was performed on silica gel (200-400 mesh), and
column chromatography was carried out with silica gel (100-
200 mesh). Whenever required, the reactions were carried out
in oven-dried glassware under dry N2. Acetonitrile, benzene,
dichloromethane, and THF, were purified and dried before use.
Petroleum ether (PE) that was used is a distillation fraction
between 40 and 60 °C. Rhodium acetate dimer was purchased
from Fluka; prior to use, Rh2(OAc)4 was activated by heating
at 100 °C under reduced pressure (3 mm of Hg) for 3 h. After
workup, the organic layer was washed with brine, dried over
anhydrous sodium sulfate, and evaporated at reduced pres-
sure. The preparation of sugar R-diazo â-keto esters 3a , 3b,
ans 13a and reactions of R-diazo â-keto esters 3a , 3b, and 13a
with Rh2(OAc)4 in benzene were reported previously by us.9,14
Gen er a l P r oced u r e for th e P r ep a r a tion of â-Keto
Ester s (2c-f, 12b). A solution of aldehyde (1 mmol) and ethyl
diazoacetate (1.5 mmol) in dry CH2Cl2 (15 mL) was cooled
under nitrogen atmosphere. A solution of BF3-etherate (0.3
mmol) in dry CH2Cl2 (2 mL) was added dropwise with control
of the evolution of N2 (20 min). The reaction mixture was
stirred at cooled temperature until the starting material was
consumed and then quenched with a saturated solution of
sodium bicarbonate. The organic layer was separated, and the
aqueous layer was extracted with dichloromethane (10 mL ×
3). The combined organic layer was dried (Na2SO4) and
evaporated on a rotary evaporator. The residue thus obtained
on column chromatography yielded â-keto ester.
Eth yl 6-deoxy-1,2-O-isopr pyliden e-3-O-(4′-n itr oben zyl)-
r-D-xylo-h ep t-5-u lofu r a n u r on a te (2f): reaction performed
at 0 °C, for 3 h; thick oil; 75% yield; Rf ) 0.39 (PE/ethyl acetate
) 6:4); [R]D ) -70.6 (c 0.25, CHCl3); IR (neat) 1745, 1729, 1522,
1
1456 cm-1; H NMR (300 MHz, CDCl3) δ 8.20 (d, J ) 8.7 Hz,
2H), 7.42 (d, J ) 8.7 Hz, 2H), 6.05 (d, J ) 3.6 Hz, 1H), 4.71 (d,
J ) 3.3 Hz, 1H), 4.67 (d, J ) 12.2 Hz, 1H), 4.63 (d, J ) 3.6 Hz,
1H), 4.57 (d, J ) 12.2 Hz, 1H), 4.30 (d, J ) 3.3 Hz, 1H), 4.20
(q, J ) 6.2 Hz, 2H), 3.66 (AB quartet, J ) 17.0 Hz, 2H), 1.48
(s, 3H), 1.34 (s, 3H), 1.26 (t, J ) 6.2 Hz, 3H); 13C NMR (75
MHz, CDCl3) δ 201.7, 166.8, 147.5, 143.9, 127.8, 123.6, 112.7,
105.9, 84.8, 84.3, 81.5, 71.2, 61.2, 47.7, 26.8, 26.2, 14.0. Anal.
Calcd for C19H23NO9: C, 55.74; H, 5.62. Found: C, 55.70; H,
5.52.
Eth yl 6-d eoxy-1,2-O-isop r p ylid en e-3-O-(p r op a r gyl)-r-
D-xylo-h ep t-5-u lofu r a n u r on a te (12b): reaction performed
at 0 °C, for 3 h; thick oil; 72% yield; Rf ) 0.43 (PE/ethyl acetate
) 6:4); [R] ) -88.2; IR (neat) 3274, 2936, 1745, 1724 cm-1; 1H
NMR (300 MHz, CDCl3) δ 6.06 (d, J ) 3.6 Hz, 1H), 4.75 (d, J
) 3.6 Hz, 1H), 4.68 (d, J ) 3.6 Hz, 1H), 4.42 (d, J ) 3.6 Hz,
1H), 4.27-4.11 (m, 4H), 3.60 (AB quartet, J ) 16.2 Hz, 2H),
2.50 (t, J ) 2.4 Hz, 1H), 1.48 (s, 3H), 1.34 (s, 3H), 1.24 (t, J )
7.5 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 200.8, 166.8, 112.5,
105.8, 84.9, 83.2, 81.9, 75.6, 61.1, 58.0, 47.2, 26.8, 26.4, 14.0.
Anal. Calcd for C15H20O7: C, 57.69; H, 6.41. Found: C, 57.75;
H, 6.32.
Gen er a l P r oced u r e for th e P r ep a r a tion of Ar om a tic
â-Keto Ester s 7a -f. A mixture of aromatic aldehyde (1 mmol)
and ethyl diazoacetate (1.5 mmol) was stirred for 10 min under
a nitrogen atmosphere at room temperature. Activated alu-
mina (10 times the weight of aldehyde compound, activated
at 200 °C at 3 mm of Hg for 4 h prior to use) was added, and
the stirring was continued in the solid phase until starting
was consumed. The solid mass was then chromatographed on
a column with a short plug of silica gel and eluted with ethyl
acetate. Evaporation of solvent furnished product that was
further purified by chromatography to give aromatic â-keto
ester.
Ben zen ep r op a n oic a cid , 2-O-(4′-m et h oxyb en zyl)-â-
oxoeth yl ester (7a ): thick oil; 73% yield; Rf ) 0.38 (PE/ethyl
acetate ) 7:3); IR (neat) 1730, 1676, 1608, 1513 cm-1; 1H NMR
(300 MHz, CDCl3) δ 7.85 (dd, J ) 7.7, 1.7 Hz, 1H), 7.46 (dt, J
) 7.7, 1.7 Hz, 1H), 7.34 (d, J ) 7.9 Hz, 2H), 7.02 (m, 2H), 6.92
(d, J ) 7.9 Hz, 2H), 5.09 (s, 2H), 4.08 (q, J ) 7.0 Hz, 2H), 3.95
(s, 2H), 3.82 (s, 3H), 1.18 (t, J ) 7.0 Hz, 3H); 13C NMR (75
Eth yl 6-d eoxy-1,2-O-isop r op ylid en e-3-O-(3′,4′-m eth yl-
en edioxyben zyl)-r-D-xylo-h ept-5-u lofu r an u r on ate (2c): re-
action performed at -50 °C, for 3 h; white solid; mp 56-58
°C; 74% yield; Rf ) 0.41 (PE/ethyl acetate ) 6:4); [R]D ) -52.6
(c 0.25, CHCl3); IR (Nujol) 1745, 1724 cm-1; 1H NMR (300 MHz,
CDCl3) δ 6.77-6.70 (m, 3H), 6.06 (d, J ) 3.6 Hz, 1H), 5.96 (s,
2H), 4.70 (d, J ) 3.5 Hz, 1H), 4.56 (d, J ) 3.6 Hz, 1H), 4.42
(AB quartet, J ) 11.5 Hz, 2H), 4.26 (d, J ) 3.5 Hz, 1H), 4.20
(q, J ) 6.3 Hz, 2H), 3.64 (AB quartet, J ) 17.1 Hz, 2H), 1.46
(s, 3H), 1.32 (s, 3H), 1.27 (t, J ) 6.3 Hz, 3H); 13C NMR (75
MHz, CDCl3) δ 201.6, 167.0, 147.8, 147.4, 130.3, 121.5, 112.5,
108.5, 108.0, 106.0, 101.0, 84.9, 83.2, 81.8, 72.5, 61.6, 47.6, 26.9,

6330 J . Org. Chem., Vol. 66, No. 19, 2001
Karche et al.
MHz, CDCl3) δ 193.8,168.4, 159.9, 158.5, 134.7, 131.3, 129.6,
121.0, 114.3, 113.0, 70.6, 61.2, 55.5, 50.7, 14.2. Anal. Calcd
for C19H20O5: C, 69.51; H, 6.09. Found: C, 69.42; H, 5.95.
71.5, 61.5, 27.0, 26.5, 14.0. Anal. Calcd for C20H22N2O9: C,
55.29; H, 5.07. Found: C, 55.16; H, 5.15.
Eth yl 6-d eoxy-6-d ia zo-3-O-(3′,4′-d im eth oxyben zyl)-1,2-
O-isop r op ylid en e-r-D-xylo-h ep t-5-u lofu r a n u r on a te (3d ):
white solid; mp 66-68 °C; 75% yield; Rf ) 0.30 (PE/ethyl
acetate ) 6:4); [R]D ) +16.1 (c 0.25, CHCl3); IR (Nujol) 2143,
1780, 1713 cm-1; 1H NMR (300 MHz, CDCl3) δ 6.81-6.77 (m,
3H), 6.12 (d, J ) 3.6 Hz, 1H), 5.40 (d, J ) 3.6 Hz, 1H), 4.63 (d,
J ) 12.3 Hz, 1H), 4.61(d, J ) 3.6 Hz, 1H), 4.48 (d, J ) 3.6 Hz,
1H), 4.28 (d, J ) 12.3 Hz, 1H), 4.21-4.00 (m, 2H), 3.87 (s,
6H), 1.50 (s, 3H), 1.34 (s, 3H), 1.26 (t, J ) 6.9 Hz, 3H); 13C
NMR (75 MHz, CDCl3) δ 185.2, 160.6, 148.9, 148.8, 129.4,
120.9, 112.5, 111.3, 110.5, 105.4, 83.5, 82.6, 81.5, 71.8, 61.5,
55.8, 55.7, 27.1, 26.5, 14.1. Anal. Calcd for C21H26N2O9: C,
56.01; H, 5.77. Found: C, 56.11; H, 5.85.
Ben zen ep r op a n oic a cid , 2-O-(2′-m et h oxyb en zyl)-â-
oxoeth yl ester (7b): thick oil; 75% yield; Rf ) 0.37 (PE/ethyl
acetate ) 7:3); IR (neat) 1725, 1693, 1601, 1489 cm-1; 1H NMR
(300 MHz, CDCl3) δ 7.86 (d, J ) 7.8 Hz, 1H), 7.46 (t, J ) 7.2
Hz, 1H), 7.33 (t, J ) 7.2 Hz, 1H), 7.05-6.90 (m, 5H), 5.21 (s,
2H), 4.08 (q, J ) 7.2 Hz, 2H), 4.01 (s, 2H), 3.87 (s, 3H), 1.17 (t,
J ) 7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 193.5, 167.0,
158.0, 156.8, 134.4, 131.0, 129.7, 129.3, 128.8, 120.8, 114.0,
113.9, 70.3, 60.8, 55.2, 50.4, 13.9. Anal. Calcd for C19H20O5:
C, 69.51; H, 6.09. Found: C, 69.63; H, 6.13.
Ben zen ep r op a n oic a cid , 2-O-(3′,4′-m et h ylen ed ioxy-
ben zyl)-5-m eth yl-â-oxoeth yl ester (7c): thick oil; 76% yield;
Rf ) 0.36 (PE/ethyl acetate ) 7:3); IR (neat) 1737, 1671, 1609,
Eth yl 3-O-(4′-ca r bm eth oxyben zyl)-6-d eoxy-6-d ia zo-1,2-
O-isop r op ylid en e-r-D-xylo-h ep t-5-u lofu r a n u r on a te (3e):
white solid; mp 103-105 °C; 73% yield; Rf ) 0.32 (PE/ethyl
acetate ) 6:4); [R]D ) +3.2 (c 0.25, CHCl3); IR (Nujol) 2142,
1
1495 cm-1; H NMR (300 MHz, CDCl3) δ 7.65 (d, J ) 2.0 Hz,
1H), 7.24 (dd, J ) 7.8, 2.0 Hz, 1H), 6.90-6.75 (m, 4H), 5.98 (s,
2H), 5.02 (s, 2H), 4.10 (q, J ) 6.9 Hz, 2H), 3.95 (s, 2H), 2.29
(s, 3H), 1.19 (t, J ) 6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ
193.0, 168.0, 158.1, 148.0, 147.1, 135.0, 131.3, 130.3, 129.7,
121.3, 112.7, 108.3, 108.2, 101.1, 70.6, 60.9, 50.4, 20.2, 14.0.
Anal. Calcd for C20H20O6: C, 67.41; H, 5.61. Found: C, 67.52;
H, 5.58.
1
1777, 1713 cm-1; H NMR (500 MHz, CDCl3) δ 8.01 (d, J )
8.0 Hz, 2H), 7.30 (d, J ) 8.0 Hz, 2H), 6.14 (d, J ) 3.6 Hz, 1H),
5.45 (d, J ) 4.0 Hz, 1H), 4.72 (d, J ) 13.0 Hz, 1H), 4.65 (d, J
) 4.0 Hz, 1H), 4.48 (d, J ) 3.6 Hz, 1H), 4.42 (d, J ) 13.0 Hz,
1H), 4.12 (m, 2H), 3.91 (s, 3H), 1.50 (s, 3H), 1.34 (s, 3H), 1.23
(t, J ) 6.8 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 185.0, 166.5,
160.6, 142.0, 129.7, 127.6, 112.5, 105.4, 83.4, 82.5, 82.4, 71.2,
61.6, 52.1, 27.0, 26.5, 14.0. Anal. Calcd for C21H24N2O9: C,
56.25; H, 5.36. Found: C, 56.16; H, 5.42.
Ben zen ep r op a n oic a cid , 2-O-(3′-m et h oxyb en zyl)-â-
oxoeth yl ester (7d ): thick oil; 71% yield; Rf ) 0.39 (PE/ethyl
acetate ) 7:3); IR (neat) 1725, 1693, 1601, 1489 cm-1; 1H NMR
(300 MHz, CDCl3) δ 7.85 (dd, J ) 8.4, 2.4 Hz, 1H), 7.47-7.24
(m, 3H), 7.04-6.87 (m, 4H), 5.15 (d, J ) 7.2 Hz, 2H), 4.09 (m,
2H), 3.95 (s, 2H), 3.82 (s, 3H), 1.18 (t, J ) 6.9 Hz, 3H);13C NMR
(75 MHz, CDCl3) δ 192.8, 168.0, 158.2, 156.2, 137.4, 134.4,
129.7, 129.3, 127.9, 120.8, 114.0, 113.9, 112.7, 70.4, 60.8, 55.0,
50.4, 14.0. Anal. Calcd for C19H20O5: C, 69.51; H, 6.09.
Found: C, 69.46; H, 6.17.
Eth yl 6-d eoxy-6-d ia zo-1,2-O-isop r op ylid en e-3-O-(4′-n i-
tr oben zyl)-r-D-xylo-h ep t-5-u lofu r a n u r on a te (3f): yellowish
solid; mp 107-109 °C; 75% yield; Rf ) 0.31 (PE/ethyl acetate
) 6:4); [R]D ) +9.4 (c 0.25, CHCl3); IR (Nujol) 2140, 1793, 1716
1
cm-1; H NMR (300 MHz, CDCl3) δ 8.20 (d, J ) 8.7 Hz, 2H),
7.41 (d, J ) 8.7 Hz, 2H), 6.16 (d, J ) 3.9 Hz, 1H), 5.49 (d, J )
3.3 Hz, 1H), 4.78 (d, J ) 13.8 Hz, 1H), 4.66 (d, J ) 3.9 Hz,
1H), 4.52 (d, J ) 13.8 Hz, 1H), 4.51 (d, J ) 3.3 Hz, 1H), 4.30-
4.20 (m, 2H), 1.52 (s, 3H), 1.35 (s, 3H), 1.27 (t, J ) 7.2 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 184.9, 160.6, 147.4, 144.3,
127.9, 123.4, 112.6, 105.3, 83.2, 83.0, 82.3, 75.7, 70.5, 61.7, 27.0,
26.5, 14.1. Anal. Calcd for C19H21N3O9: C, 52.41; H, 4.82.
Found: C, 52.53; H, 4.91.
Ben zen ep r op a n oic a cid , 2-O-(ben zyl)-â-oxoeth yl ester
(7e). thick oil; 77% yield; Rf ) 0.40 (PE/ethyl acetate ) 7:3);
IR (neat) 1738, 1673, 1597, 1483 cm-1 1H NMR (300 MHz,
;
CDCl3) δ 7.87 (dd, J ) 7.8, 1.8 Hz, 1H), 7.50-7.30 (m, 6H),
7.09-6.92 (m, 2H), 5.17 (s, 2H), 4.10 (q, J ) 7.2 Hz, 2H), 3.98
(s, 2H), 1.17 (t, J ) 7.2 Hz, 3H);13C NMR (75 MHz, CDCl3) δ
193.4, 168.0, 158.0, 135.7, 134.4, 131.0, 128.7, 128.5, 128.2,
127.4, 120.9, 112.7, 70.5, 60.8, 50.4, 13.9. Anal. Calcd for
Eth yl 6-d eoxy-6-d ia zo-1,2-O-isop r op ylid en e-3-O-(p r o-
p a r gyl)-r-D-xylo-h ep t-5-u lofu r a n u r on a te (13b): thick oil;
74% yield; Rf ) 0.33 (PE/ethyl acetate ) 6:4); [R] ) +39.2; IR
(neat) 2930, 2138, 1744, 1714 cm-1; 1H NMR (300 MHz, CDCl3)
δ 6.11 (d, J ) 3.6 Hz, 1H), 5.55 (d, J ) 3.6 Hz, 1H), 4.71 (d, J
) 3.6 Hz, 1H), 4.65 (d, J ) 3.6 Hz, 1H), 4.32 (q, J ) 6.9 Hz,
2H), 4.22 (dq, J ) 15.9, 2.4 Hz, 2H), 2.41 (t, J ) 2.4 Hz, 1H),
1.54 (s, 3H), 1.36 (m, 6H); 13C NMR (75 MHz, CDCl3) δ 184.8,
161.0, 112.5, 105.3, 83.4, 82.2, 82.02, 78.3, 74.9, 61.6, 57.3, 27.0,
26.5, 14.2. Anal. Calcd for C15H18N2O7: C, 53.25; H, 5.32.
Found: C, 53.18; H, 5.41.
C
18H18O4: C, 72.48; H, 6.04. Found: C, 72.56; H, 5.94.
Ben zen ep r op a n oic a cid , 2-O-(m eth yl)-â-oxoeth yl ester
(7f): thick oil; 74% yield; Rf ) 0.42 (PE/ethyl acetate ) 7:3);
IR (neat) 1739, 1671, 1598, 1483 cm-1 1H NMR (300 MHz,
;
CDCl3) δ 7.87 (dd, J ) 7.5, 1.8 Hz, 1H), 7.51 (dt, J ) 7.5, 1.8
Hz, 1H), 7.03 (t, J ) 7.5 Hz, 1H), 6.96 (d, J ) 7.5 Hz, 1H),
4.17 (q, J ) 7.2 Hz, 2H), 3.97 (s, 2H), 3.89 (s, 3H), 1.23 (t, J )
7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 193.0, 168.0, 159.0,
134.5, 130.9, 120.7, 111.4, 60.8, 55.5, 50.5, 40.0. Anal. Calcd
for C12H14O4: C, 64.86; H, 6.30. Found: C, 64.73; H, 6.24.
Gen er a l P r oced u r e for th e Syn th esis of r-Dia zo â-Keto
Ester s 3c-f, 13b, a n d 8a -f. To a stirred solution of â-keto
ester (1 mmol) in dry acetonitrile (30 mL) were added triethy-
lamine (2 mmol) and methanesulfonyl azide (1.1 mmol). The
reaction mixture was stirred at room temperature for 3 h and
quenched with aqueous sodium hydroxide (2 M; 1 mL). The
organic layer was separated, and the aqueous layer was
extracted with ethyl acetate (20 mL × 3). The combined
organic layer was dried (Na2SO4) and evaporated on a rotary
evaporator to give thick oil, which on column chromatography
(PE/ethyl acetate 19:1) yielded R-diazo â-keto ester.
Ben zen ep r op a n oic a cid , 2-O-(4′-m et h oxyb en zyl)-r-
d ia zo-â-oxoeth yl ester (8a ): thick oil; 77% yield; Rf ) 0.33
(PE/ethyl acetate ) 7:3); IR (neat) 2133, 1737, 1682, 1614, 1512
1
cm-1; H NMR (300 MHz, CDCl3) δ 7.40 (dt, J ) 7.8, 1.5 Hz,
1H), 7.33 (dd, J ) 7.8, 1.5 Hz, 1H), 7.27 (d, J ) 8.4 Hz, 2H),
7.01 (dt, J ) 7.8, 1.5 Hz, 1H), 6.96 (d, J ) 7.8 Hz, 1H), 6.92 (d,
J ) 8.4 Hz, 2H), 5.00 (s, 2H), 4.12 (q, J ) 7.2 Hz, 2H), 3.81 (s,
3H), 1.14 (t, J ) 7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ
186.1, 160.6, 159.2, 156.0, 132.1, 128.6, 128.4, 128.3, 120.6,
113.7, 112.0, 77.0, 70.1, 61.0, 55.0, 13.9. Anal. Calcd for
C
19H18N2O5: C, 64.40; H, 5.08. Found: C, 64.32; H, 5.14.
Ben zen ep r op a n oic a cid , 2-O-(2′-m et h oxyb en zyl)-r-
Eth yl 6-d eoxy-6-d ia zo-1,2-O-isop r op ylid en e-3-O-(3′,4′-
m e t h yle n e d ioxyb e n zyl)-r-D -xylo-h e p t -5-u lofu r a n u r -
on a te (3c): white solid; mp 61-63 °C; 77% yield; Rf ) 0.34
(PE/ethyl acetate ) 6:4); [R]D ) +12.1 (c 0.25, CHCl3); IR
d ia zo-â-oxoeth yl ester (8b): thick oil; 76% yield; Rf ) 0.32
(PE:ethyl acetate ) 7:3); IR (neat) 2136, 1727, 1693, 1600, 1490
cm-1; 1H NMR (300 MHz, CDCl3) δ 7.43-7.26 (m, 4H), 7.03-
6.87 (m, 4H), 5.13 (s, 2H), 4.11 (q, J ) 7.2 Hz, 2H), 3.84 (s,
3H), 1.10 (t, J ) 7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ
186.2, 160.8, 156.4, 156.2, 132.3, 128.7, 128.5, 127.7, 120.7,
120.5, 112.3, 110.0, 77.2, 65.7, 61.2, 55.2, 14.0. Anal. Calcd
for C19H18N2O5: C, 64.40; H, 5.08. Found: C, 64.33; H, 5.02.
Ben zen ep r op a n oic a cid , 2-O-(3′4′-m eth ylen ed ioxyben -
zyl)-r-d ia zo-â-oxoeth yl ester (8c): thick oil; 75% yield; Rf
) 0.31 (PE/ethyl acetate ) 7:3); IR (neat) 2134, 1726, 1692,
1
(Nujol) 2138, 1778,1728 cm-1; H NMR (300 MHz, CDCl3) δ
6.70 (m, 3H), 6.13 (d, J ) 3.6 Hz, 1H), 5.96 (s, 2H), 5.42 (d, J
) 3.6 Hz, 1H), 4.62 (d, J ) 3.6 Hz, 1H), 4.56 (d, J ) 11.7 Hz,
1H), 4.43 (d, J ) 3.6 Hz, 1H), 4.21 (d, J ) 11.7 Hz, 1H), 4.20-
4.10 (m, 2H), 1.50 (s, 3H), 1.35 (s, 3H), 1.28 (t, J ) 7.2 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 185.0, 160.6, 147.7, 147.4,
130.7, 122.0, 112.4, 108.6, 107.7, 105.4, 101.0, 83.4, 82.6, 81.2,

Electronic Effects in Migratory Groups
J . Org. Chem., Vol. 66, No. 19, 2001 6331
1599, 1487 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.26-7.13 (m,
3H), 6.84-6.76 (m, 3H), 5.96 (s, 2H), 4.93 (s, 2H), 4.21 (q, J )
7.2 Hz, 2H), 2.29 (s, 3H), 1.20 (t, J ) 7.2 Hz, 3H); 13C NMR
(75 MHz, CDCl3) δ 186.1, 159.2, 153.9, 147.8, 147.6, 132.7,
130.4, 130.3, 128.9, 128.1, 120.7, 112.3, 108.1, 107.9, 101.0,
70.5, 61.2, 42.7, 20.2, 14.0. Anal. Calcd for C20H18N2O6: C,
62.82; H, 4.71. Found: C, 62.91; H, 4.79.
Ben zen ep r op a n oic a cid , 2-O-(3′-m et h oxyb en zyl)-r-
d ia zo-â-oxo-eth yl ester (8d ): thick oil; 73% yield; Rf ) 0.34
(PE/ethyl acetate ) 7:3); IR (neat) 2138, 1727, 1693, 1610, 1495
cm-1; 1H NMR (300 MHz, CDCl3) δ 7.46-7.28 (m, 4H), 7.07-
6.89 (m, 4H), 5.07 (s, 2H), 4.12 (q, J ) 7.0 Hz, 2H), 3.84 (s,
3H), 1.15 (t, J ) 7.0 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ
186.5, 160.6, 158.4, 156.4, 156.2, 134.3, 128.8, 128.7, 127.7,
124.8, 120.7, 120.5, 112.3, 110.5, 65.8, 61.2, 55.3, 42.8, 14.0.
Anal. Calcd for C19H18N2O5: C, 64.40; H, 5.08. Found: C,
64.51; H, 5.12.
CDCl3) δ 8.04 (d, J ) 8.0 Hz, 2H), 7.49 (d, J ) 8.0 Hz, 2H),
5.92 (d, J ) 3.0 Hz, 1H), 5.49 (d, J ) 6.5 Hz, 1H), 5.22 (AB
quartet, J ) 12.5 Hz, 2H), 4.87 (d, J ) 3.0 Hz, 1H), 4.84 (d, J
) 6.5 Hz, 1H), 4.31 (q, J ) 6.5 Hz, 2H), 3.95 (s, 3H), 1.51 (s,
3H), 1.36 (s, 3H), 1.29 (t, J ) 6.5 Hz, 3H); 13C NMR (125 MHz,
CDCl3) δ 166.7, 159.7, 145.8, 141.4, 130.1, 129.8, 129.4, 128.0,
127.3, 126.7, 113.1, 105.3, 84.9, 84.3, 83.8, 72.1, 61.1, 52.5, 27.6,
26.6, 14.4. Anal. Calcd for C21H24O9: C, 60.00; H, 5.71.
Found: C, 60.12; H, 5.65.
Eth yl 3,6-a n h yd r o-6-(4′-ca r bm eth oxyben zyl)-1,2-O-iso-
pr opyliden e-r-D-glu co-h ept-5-u lofu r an u r on ate (5e): thick
oil; 50% yield; Rf ) 0.50 (PE/ethyl acetate ) 6:4); [R]D ) +32.4
(c 0.25, CHCl3); IR (neat) 1778, 1721 cm-1; 1H NMR (500 MHz,
CDCl3) δ 7.95 (d, J ) 8.0 Hz, 2H), 7.92 (d, J ) 8.0 Hz, 2H),
5.95 (d, J ) 3.5 Hz, 1H), 4.89 (d, J ) 3.0 Hz, 1H), 4.25-4.18
(m, 4H), 3.93 (s, 3H), 3.35 (AB quartet, J ) 14.0 Hz, 2H), 1.48
(s, 3H), 1.36 (s, 3H), 1.27 (t, J ) 6.2 Hz, 3H); 13C NMR (125
MHz, CDCl3) δ 201.6, 166.7, 139.2, 130.8, 130.5, 130.0, 129.6,
129.1, 113.5, 107.7, 86.5, 85.3, 82.7, 62.6, 52.0, 40.4, 27.3, 26.5,
13.9. Anal. Calcd for C21H24O9: C, 60.00; H, 5.71. Found: C,
60.22; H, 5.79.
Ben zen ep r op a n oic a cid , 2-O-(ben zyl)-r-d ia zo-â-oxoet-
h yl ester (8e). thick oil; 76% yield; Rf ) 0.35 (PE/ethyl acetate
1
) 7:3); IR (neat) 2139, 1726, 1692,1599, 1487 cm-1; H NMR
(300 MHz, CDCl3) δ 7.43-7.30 (m, 7H), 7.08-6.92 (m, 2H),
5.08 (s, 2H), 4.12 (q, J ) 7.2 Hz, 2H), 1.12 (t, J ) 7.2 Hz, 3H);
13C NMR (75 MHz, CDCl3) δ 186.3, 160.8, 156.1, 136.5, 132.3,
128.6, 128.5, 127.9, 126.9, 120.9, 112.2, 70.5, 61.2, 50.8, 14.0.
Anal. Calcd for C18H16N2O4: C, 66.66; H, 4.94. Found: C,
66.53; H, 4.78.
E t h yl
3,6-a n h yd r o-1,2-O-isop r op ylid en e-5-O-(4′-n i-
tr oben zyl)-r-D-xylo-h ep t-5-en ofu r a n u r on a te (4f): thick oil;
26% yield; Rf ) 0.42 (PE/ethyl acetate ) 6:4); [R]D ) +32.1 (c
1
0.25, CHCl3); IR (neat) 1717, 1654 cm-1; H NMR (300 MHz,
CDCl3) δ 8.23 (d, J ) 8.4 Hz, 2H), 7.61 (d, J ) 8.4 Hz, 2H),
5.92 (d, J ) 3.5 Hz, 1H), 5.26 (d, J ) 6.4 Hz, 1H), 5.20 (AB
quartet, J ) 16.6 Hz, 2H), 4.91 (d, J ) 6.4 Hz, 1H), 4.86 (d, J
) 3.5 Hz, 1H), 4.36 (q, J ) 7.1 Hz, 2H), 1.51 (s, 3H), 1.37 (s,
3H), 1.33 (t, J ) 7.1 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ
161.0, 145.5, 143.6, 127.4, 123.7, 113.7, 84.9, 84.0, 82.7, 71.6,
61.3C, 27.7, 26.7, 14.2. Anal. Calcd for C19H21NO9: C, 56.01;
H, 5.15. Found: C, 56.18; H, 5.24.
Eth yl 3,6-a n h yd r o-1,2-O-isop r op ylid en e-6-(4′-n itr oben -
zyl)-r-D-glu co-h ep t-5-u lofu r a n u r on a te (5f): thick oil; 56%
yield; Rf ) 0.49 (PE:ethyl acetate ) 6:4); [R]D ) +30.4 (c 0.25,
CHCl3); IR (neat) 1778, 1744 cm-1; 1H NMR (300 MHz, CDCl3)
δ 8.14 (d, J ) 8.7 Hz, 2H), 7.41 (d, J ) 8.7 Hz, 2H), 5.96 (d, J
) 3.3 Hz, 1H), 4.90 (d, J ) 3.3 Hz, 1H), 4.38 (d, J ) 4.0 Hz,
1H), 4.32 (d, J ) 4.0 Hz, 1H), 4.20 (q, J ) 7.1 Hz, 2H), 3.31 (s,
2H), 1.43 (s, 3H), 1.33 (s, 3H), 1.26 (t, J ) 7.1 Hz, 3H); 13C
NMR (75 MHz, CDCl3) δ 200.7, 166.5, 147.3, 141.6, 131.7,
131.3, 123.4, 123.0, 113.6, 107.9, 86.0, 85.4, 83.0, 78.6, 62.8,
40.0, 27.3, 26.6, 13.9. Anal. Calcd for C19H21NO9: C, 56.01; H,
5.15. Found: C, 56.12; H, 5.06.
Ben zen ep r op a n oic a cid , 2-O-(m eth yl)-r-d ia zo-â-oxo-
eth yl ester (8f): thick oil; 75% yield; Rf ) 0.37 (PE/ethyl
acetate ) 7:3); IR (neat) 2137, 1728, 1694,1599, 1488 cm-1
;
1H NMR (300 MHz, CDCl3) δ 7.43 (dt, J ) 7.5, 1.8 Hz, 1H),
7.32 (dd, J ) 7.5, 1.8 Hz, 1H), 7.03 (t, J ) 7.5 Hz, 1H), 6.90 (d,
J ) 7.5 Hz, 1H), 4.20 (q, J ) 7.2 Hz, 2H), 3.82 (s, 3H), 1.20 (t,
J ) 7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 186.0, 160.8,
156.7, 132.2, 128.4, 120.5, 110.6, 77.0, 61.2, 55.4, 14.0. Anal.
Calcd for C12H12N2O4: C, 58.06; H, 4.83. Found: C, 58.19; H,
4.96.
Gen er a l P r oced u r e for th e Decom p osition of Su ga r
r-Dia zo â-Keto Ester . A solution of R-diazo â-keto ester 3c-
f, 13b (0.200 mmol), and Rh2 (OAc)4 (0.002 mmol) in benzene
(5 mL) under N2 atmosphere was refluxed for 10-30 min (for
electron-rich substituents the reaction takes 30 min and for
electron-deficient substituents it takes 10 min only). On
cooling, the reaction mixture was directly loaded onto a silica
gel column and with PS-ethyl acetate to afford, first, bicycle
5; further elution gave the isomeric bicycle 4. In case of 13b
only 14b was obtained.
Eth yl 3,6-a n h yd r o-1,2-O-isop r op ylid en e-6-(a llen yl)-r-
D-glu co-h ep t-5-u lofu r a n u r on a te (14b): thick oil; 77% yield;
Rf ) 0.44 (PE/ethyl acetate ) 6:4); [R] ) +90.4; IR (neat) 1780,
Eth yl 3,6-a n h yd r o-1,2-O-isop r op ylid in e-5-O-(3′,4′-m e-
t h ylen ed ioxyb en zyl)-r-D-xylo-h ep t -5-en ofu r a n u r on a t e
(4c): thick oil; 75% yield; Rf ) 0.44 (PE/ethyl acetate ) 6:4);
1
1746, 1631 cm-1; H NMR (300 MHz, CDCl3) δ 6.02 (d, J )
1
[R]D ) +19.6 (c 0.25, CHCl3); IR (neat) 1717, 1654 cm-1; H
3.4 Hz, 1H), 5.52 (t, J ) 6.5 Hz, 1H), 5.08 (d, J ) 6.5 Hz, 2H),
4.96 (d, J ) 3.4 Hz, 1H), 4.85 (d, J ) 3.3 Hz, 1H), 4.61 (d, J )
3.3 Hz, 1H), 4.26 (q, J ) 7.4 Hz, 2H), 1.51 (s, 3H), 1.40 (s,
3H), 1.30 (t, J ) 7.4 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ
207.7, 199.3, 166.3, 113.5, 107.8, 89.0, 85.2, 83.4, 82.9, 80.1,
78.8, 62.5, 27.3, 26.6, 13.9. Anal. Calcd for C15H18O7: C, 58.06;
H, 5.80. Found: C, 58.15; H, 5.72.
NMR (300 MHz, CDCl3) δ 6.93 (d, J ) 1.5 Hz, 1H), 6.87 (dd,
J ) 6.5, 1.5 Hz, 1H), 6.77 (d, J ) 6.5 Hz, 1H), 5.96 (s, 2H),
5.94 (d, J ) 3.3 Hz, 1H), 5.48 (d, J ) 6.5 Hz, 1H), 5.05 (AB
quartet, J ) 12 Hz, 2H), 4.85-4.81 (m, 2H), 4.30 (q, J ) 7.3
Hz, 2H), 1.51 (s, 3H), 1.37 (s, 3H), 1.31 (t, J ) 7.3 Hz, 3H); 13
C
NMR (75 MHz, CDCl3) δ 159.8, 147.8, 147.5, 146.1, 131.0,
130.1, 121.1, 113.5, 108.1, 106.0, 101.0, 85.0, 83.8, 82.7, 72.9,
61.1, 27.7, 26.7, 14.2. Anal. Calcd for C20H22O9: C, 59.11; H,
5.41. Found: C, 59.29; H, 5.32.
Gen er a l P r oced u r e for th e Decom p osition of Ar o-
m a tic r-Dia zo â-Keto Ester . A solution of R-diazo â-keto
ester 8a -f (0.200 mmol) and Rh2 (OAc)4 (0.002 mmol) in
benzene (5 mL) under N2 atmosphere was refluxed for 10-30
min (for electron-rich substituents the reaction takes 30 min
and for electron-deficient substituents it takes 10 min only).
On cooling, the reaction mixture was directly loaded onto a
silica gel column and with PE/ethyl acetate to afford, first,
bicycle 9; further elution gave the isomeric bicycle 10.
2-Ben zofu r a n ca r boxylic a cid , 3-O-(4′-m eth oxyben zyl)-
eth yl ester (9a ): thick oil; 76% yield; Rf ) 0.43 (PE/ethyl
acetate ) 7:3); IR (neat) 1710, 1613, 1514 cm-1; 1H NMR (300
MHz, CDCl3) δ 7.64 (dd, J ) 7.6, 1.3 Hz, 1H), 7.47 (dt, J )
7.6, 1.3 Hz, 1H), 7.41-7.20 (m, 4H), 6.87 (d, J ) 7.5 Hz, 2H),
5.38 (s, 2H), 4.45 (q, J ) 6.9 Hz, 2H), 3.97 (s, 3H), 1.43 (t, J )
6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 159.7, 159.4, 153.1,
148.3, 132.4, 129.9, 128.3, 124.3, 123.2, 121.0, 113.9, 112.8,
76.2, 61.2, 55.4, 14.7. Anal. Calcd for C19H18O5: C, 69.93; H,
5.52. Found: C, 69.82; H, 5.41.
E t h yl 3,6-a n h yd r o-5-O-(3′,4′-d im et h oxyb en zyl)-1,2-O-
isop r op ylid en e-r-D-xylo-h ep t -5-en ofu r a n u r on a t e (4d ):
thick oil; 76% yield; Rf ) 0.42 (PE/ethyl acetate ) 6:4); [R]D
)
+22.2 (c 9.25, CHCl3); IR (neat) 1717, 1652 cm-1; 1H NMR (300
MHz, CDCl3) δ 6.99-6.93 (m, 2H), 6.84 (d, J ) 8.1 Hz, 1H),
5.93 (d, J ) 3.6 Hz, 1H), 5.48 (d, J ) 6.3 Hz, 1H), 5.10 (AB
quartet, J ) 12.0 Hz, 2H), 4.83 (m, 2H), 4.28 (q, J ) 6.9 Hz,
2H), 3.88 (s, 6H), 1.51 (s, 3H), 1.37 (s, 3H), 1.32 (t, J ) 6.9 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 159.8, 149.0, 148.9, 146.3,
131.0, 128.9, 120.0, 113.5, 110.9, 110.8, 106.0, 85.0, 83.7, 82.6,
73.0, 60.9, 55.8, 55.7, 27.6, 26.7, 14.2. Anal. Calcd for
C
21H26O9: C, 59.71; H, 6.16. Found: C, 59.62; H, 6.22.
Eth yl 3,6-a n h yd r o-5-O-(4′-ca r bm eth oxyben zyl)-1,2-O-
isopr opyliden e-r-D-xylo-h ept-5-en ofu r an u r on ate (4e): thick
oil; 31% yield; Rf ) 0.43 (PE/ethyl acetate ) 6:4); [R]D ) +42.7
(c 0.25, CHCl3); IR (neat) 1721, 1656 cm-1; 1H NMR (500 MHz,

6332 J . Org. Chem., Vol. 66, No. 19, 2001
Karche et al.
2-Ben zofu r a n ca r boxylic a cid , 3-O-(2′-m eth oxyben zyl)-
eth yl ester (9b): thick oil; 73% yield; Rf ) 0.42 (PE/ethyl
acetate ) 7:3); IR (neat) 1714, 1617, 1514 cm-1; 1H NMR (300
MHz, CDCl3) δ 7.67 (bd, J ) 8.1 Hz, 1H), 7.58-7.38 (m, 3H),
7.34-7.19 (m, 2H), 6.96 (dt, J ) 7.5, 1.0 Hz, 1H), 6.86 (bd, J
) 8.1 Hz, 1H), 5.49 (s, 2H), 4.44 (q, J ) 7.2 Hz, 2H), 3.77 (s,
3H), 1.41 (t, J ) 7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ
159.4, 157.0, 153.1, 148.5, 132.1, 129.4, 129.3, 128.1, 122.9,
121.1, 120.3, 112.5, 110.1, 71.3, 60.9, 55.1, 14.2. Anal. Calcd
for C19H18O5: C, 69.93; H, 5.52. Found: C, 69.79; H, 5.39.
2-Ben zofu r a n ca r b oxylic a cid , 3-O-(3′,4′-m et h ylen e-
d ioxyben zyl)-5-m eth yleth yl ester (9c): thick oil; 76% yield;
Rf ) 0.41 (PE/ethyl acetate ) 7:3); IR (neat) 1719, 1618, 1512
2-Ben zofu r a n ca r b oxylic a cid , 3-O-b en zylet h yl est er
(9e): thick oil; 46% yield; Rf ) 0.45 (PE/ethyl acetate ) 7:3);
1
IR (neat) 1715, 1612, 1512 cm-1; H NMR (300 MHz, CDCl3)
δ 7.67 (dd, J ) 7.4, 1.5 Hz, 1H), 7.54-7.21 (m, 8H), 5.46 (s,
2H), 4.44 (q, J ) 6.9 Hz, 2H), 1.42 (t, J ) 6.9 Hz, 3H); 13C
NMR (75 MHz, CDCl3) δ 159.4, 153.1, 148.2, 136.5, 132.2,
128.4, 128.3, 127.9, 123.1, 122.7, 120.9, 112.7, 76.1, 61.0, 14.3.
Anal. Calcd for C18H16O4: C, 72.97; H, 5.40. Found: C, 72.81;
H, 5.28.
2-Ben zofu r a n ca r boxylic a cid , 3-oxo-2-ben zyleth yl es-
ter (10e): thick oil; 30% yield; Rf ) 0.41 (PE/ethyl acetate )
7:3); IR (neat) 1745, 1614, 1512 cm-1 1H NMR (300 MHz,
;
CDCl3) δ 7.62-7.45 (m, 2H), 7.32-7.02 (m, 7H), 4.20 (q, J )
6.9 Hz, 2H), 3.51 (AB quartet, J ) 14.1 Hz, 2H), 1.21 (t, J )
6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 195.5, 172.1, 165.4,
138.4, 133.3, 130.3, 128.1, 127.9, 127.2, 124.7, 122.5, 119.6,
113.3, 91.4, 62.6, 39.8, 13.9. Anal. Calcd for C18H16O4: C, 72.97;
H, 5.40. Found: C, 73.14; H, 5.58.
1
cm-1; H NMR (300 MHz, CDCl3) δ 7.43 (bs, 1H), 7.37 (bd, J
) 8.5 Hz, 1H), 7.23 (bd, J ) 8.5 Hz, 1H), 7.01 (bs, 1H), 6.92
(bd, J ) 8.4 Hz, 1H), 6.78 (bd, J ) 8.4 Hz, 1H), 5.97 (s, 2H,),
5.33 (s, 2H), 4.46 (q, J ) 7.2 Hz, 2H), 2.44 (s, 3H), 1.46 (t, J )
7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 159.4, 151.7, 147.8,-
147.7, 132.8, 132.4 130.8, 130.4, 129.9, 122.8, 121.9, 120.2,
112.3, 108.8, 108.1, 101.1, 76.0, 61.0, 21.2, 14.4. Anal. Calcd
for C20H18O6: C, 67.79; H, 5.08. Found: C, 67.63; H, 5.18.
2-Ben zofu r a n ca r boxylic a cid , 3-O-(3′-m eth oxyben zyl)-
eth yl ester (9d ): thick oil; 45% yield; Rf ) 0.44 (PE/ethyl
acetate ) 7:3); IR (neat) 1718, 1618, 1512 cm-1; 1H NMR (300
MHz, CDCl3) δ 7.66 (bt, J ) 7.8 Hz, 1H), 7.48-7.40 (m, 3H),
7.26, (m, 1H), 7.06 (d, J ) 7.8 Hz, 1H), 6.87 (dd, J ) 7.8, 1.8
Hz, 2H), 5.41 (s, 2H), 4.46 (q, J ) 7.2 Hz, 2H), 3.80 (s, 3H),
1.43 (t, J ) 7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 159.7,
159.4, 153.1, 148.3, 138.1, 129.8, 129.5, 128.7, 128.2, 123.1,
120.9, 113.8, 113.3, 112.7, 75.9, 61.1, 55.2, 14.4. Anal. Calcd
for C19H18O5: C, 69.93; H, 5.52. Found: C, 69.81; H, 5.68.
2-Ben zofu r a n ca r boxylic a cid , 3-oxo-2-(3′-m eth oxyben -
zyl)eth yl ester (10d ): thick oil; 33% yield; Rf ) 0.40 (PE/
2-Ben zofu r a n ca r boxylic a cid , 3-O-m eth yleth yl ester
(9f): tThick oil; 65% yield; Rf ) 0.46 (PE/ethyl acetate ) 7:3);
1
IR (neat) 1719, 1618, 1512 cm-1; H NMR (300 MHz, CDCl3)
δ 7.77 (dd, J ) 7.8, 1.2 Hz, 1H), 7.48 (t, J ) 7.8 Hz, 1H), 7.42
(d, J ) 7.8 Hz, 1H), 7.24 (dt, J ) 7.8, 1.2 Hz, 1H), 4.44 (q, J )
7.2 Hz, 2H), 4.24 (s, 3H), 1.43 (t, J ) 7.2 Hz, 3H); 13C NMR
(75 MHz, CDCl3) δ 159.3, 153.0, 149.4, 128.2, 123.0, 121.0,
112.7, 61.4, 60.9, 14.3. Anal. Calcd for C12H12O4: C, 65.45; H,
5.45. Found: C, 64.63; H, 5.56.
Ack n ow led gm en t. We are grateful to Prof. N. S.
Narasimhan and Prof. M. S. Wadia for the helpful
discussions. N.P.K. is thankful to UGC for the J RF. The
financial support from UGC, New Delhi, to procure a
high field (300 MHz) NMR facility under the CAS
program is also gratefully acknowledged.
ethyl acetate ) 7:3); IR (neat) 1748, 1725, 1610, 1512 cm-1
;
1H NMR (300 MHz, CDCl3) δ 7.62-7.55 (m, 2H), 7.26-7.01
(m, 4H), 6.86-6.70 (m, 1H), 6.73-6.67 (m, 1H), 4.22 (q, J )
6.9 Hz, 2H), 3.73 (s, 3H), 3.48 (AB quartet, J ) 14.7 Hz, 2H),
1.23 (t, J ) 6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 195.4,
172.1, 165.4, 159.2, 138.4, 131.3, 129.1, 124.7, 122.6, 115.7,
113.5, 113.3, 112.9, 91.3, 62.6, 55.1, 39.8, 14.0. Anal. Calcd
for C19H18O5: C, 69.93; H, 5.52. Found: C, 69.78; H, 5.48.
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra for compounds 3c-f, 4c-f, 5c-f, 8a -f, 9a -f, 10a -f,
13b, 14b. This material is available free of charge via the
Internet at http:// pubs.acs.org.
J O010431F