Stereoselective epoxide generation with cyclic rhodium carbenoids: A new access to spiro-indolooxiranes

Article abstract of DOI:10.1055/s-2004-817750

The reaction of cyclic diazoamides with aryl aldehydes catalyzed by rhodium(II) acetate leads to intermolecular stereoselective epoxide ring formation. A series of spiro-indolooxiranes has been synthesized following the described method in a facile manner. The use of aryl dialdehydes in the course of reaction of cyclic diazoamide resulted the formation of bis-spiro- indolooxiranes.

Full text of DOI:10.1055/s-2004-817750

LETTER
639
Stereoselective Epoxide Generation with Cyclic Rhodium Carbenoids:
A New Access to Spiro-indolooxiranes
a
a
b
A
S
N
ewAccess
e
to
S
piro-in
n
dolooxirane
g
s
odagounder Muthusamy,* Chidambaram Gunanathan, Munirathinam Nethaji
a
Central Salt & Marine Chemicals Research Institute, Bhavnagar - 364 002, India
Fax +91(278)2567562; E-mail: salt@csir.res.in
b
Department of Inorganic & Physical Chemistry, Indian Institute of Science, Bangalore - 560 012, India
Received 26 October 2003
th
This paper is dedicated with best wishes to Professor Goverdhan Mehta on the occasion of his 60 birthday.
8
lineated a useful method for the formation of oxirane by
intercepting the metal carbene with alkyl sulfide. Recent-
Abstract: The reaction of cyclic diazoamides with aryl aldehydes
catalyzed by rhodium(II) acetate leads to intermolecular stereose-
lective epoxide ring formation. A series of spiro-indolooxiranes has
ly, we have been extensively involved in developing new
9
been synthesized following the described method in a facile man- synthetic strategies using diazo carbonyl compounds.
ner. The use of aryl dialdehydes in the course of reaction of cyclic The reactivity of cyclic diazo ketones and amides was
diazoamide resulted the formation of bis-spiro-indolooxiranes
studied with olefins and heteroaromatic dipolarophiles to
1
0
11
Key words: carbenoids, diazo ketones, oxiranes, rhodium(II) ace- furnish cyclopropanation, C-H insertion or cyclo-
adducts12 via 1,3-dipolar cycloaddition reactions. To the
best of our knowledge, only simple acyclic diazo carbonyl
compounds have been used in the epoxide generation,
which mainly led to the benzylidene or methylidene trans-
fer. Continuing our interest in the reactions of cyclic
tate, spiro compounds
Diazo moiety has become a key component in a number
of synthetic transformations since from the first recorded
diazoamides1 and motivated by the recent reports, we
0,11
6,7
1
synthesis of a-diazo carbonyl compound by Curtius in
herein delineate the rhodium(II) acetate catalyzed reaction
useful precursors in organic synthesis can be traced to of cyclic diazoamides with aryl aldehydes that leads to the
their ready participation in cyclopropanation, insertion re- stereoselective construction of spirocyclic oxiranes.
1
883. The emergence of diazo carbonyl compounds as
actions and ylide formation upon exposure to transition
2
metal catalysts. The metal-carbenoid generated transient
ylides can undergo 1,3-dipolar cycloaddition reaction
with a range of dipolarophiles, rearrangement reactions or
cyclization to three-membered ring (aziridine or epoxide
formation). The cyclization of transition metal generated
carbonyl ylides, in principle, can deliver the oxirane ring
N2
a R1 = CH3
1
e R1 = propargyl
1f R = H
1
1
1
1b R = CH Ph
2
O
1
1
c R = p-xylenyl
1
N
R1
1d R = allyl
Figure 1
2
,3
systems. However, the literature reports on carbonyl
ylides are dominated by 1,3-dipolar cycloaddition reac-
tions rather than the formation of the oxirane ring system.
Initially, we planned to study the reactions of cyclic diazo-
amides 1 (Figure 1) with aldehydes in the presence of
rhodium(II) acetate catalyst. The required N-substituted
4
Originally, Huisgen reported that the formation of 7%
oxirane in the reaction between dimethyl diazomalonate
3
-diazooxindoles (1a–e) were assembled by N-alkylation
13
and benzaldehyde catalyzed by Cu(acac) . But the forma-
2
of 3-diazooxindole (1f) using methyl iodide, benzyl bro-
mide, p-xylenyl bromide, allyl bromide or propargyl bro-
mide in the presence of sodium hydride/DMF in 80% to
tion of oxirane was not observed when the reaction was
catalyzed by Rh (OAc) . The rhodium(II)-catalyzed de-
2
4
composition of ethyl diazoacetate in the presence of
aldehydes furnished dioxolanes (by means of 1,3-dipolar
cycloaddition of the carbonyl ylide intermediate with a
second equivalent of aldehyde) and did not produce ox-
9
5% yield. Subsequently, we studied the rhodium(II) ace-
tate catalyzed reactions of cyclic diazoamide 1a with ben-
zaldehyde in the presence of a catalytic amount of
rhodium(II) acetate under reflux conditions to afford the
5
1
iranes.
spiro-indolooxirane 3a in 57% yield (Scheme 1). The H
NMR spectrum of 3a revealed the presence of two sin-
glets at d = 3.08 and 4.64 ppm for N-methyl and OCH
Despite the commonality and selectivity (vide infra) of
rhodium(II) acetate catalyzed reactions of diazo carbonyl
compounds, they were not found to produce the oxirane
1
3
protons, respectively. Furthermore, C and DEPT exper-
iments disclosed the presence of characteristic quaternary
carbon at d = 62.5 ppm and a CH signal at 68.1 ppm,
which unequivocally confirms the formation of the spiro-
oxirane ring system. All other data were in good agree-
ment with the assigned structure. The reaction of other
diazoamides 1b–e with benzaldehyde also produced the
spiro-oxiranes in moderate to good yields. We further car-
6
ring systems until the recent report by Doyle and
7
followed by Davies. In an alternative route, Aggarwal de-
SYNLETT 2004, No. 4, pp 0639–0642
0
9.
0
3.
2
0
0
4
Advanced online publication: 10.02.2004
DOI: 10.1055/s-2004-817750; Art ID: D26203ST
©
Georg Thieme Verlag Stuttgart · New York

6
40
S. Muthusamy et al.
LETTER
ried out the similar reactions with 4-methoxy benzalde- To generalize the intermolecular spiro-oxirane formation,
hyde to furnish the spiro-indolooxiranes in good yield and we have carried out the reactions with more substituted
the results are described in Table 1. Interestingly, spiro- aromatic aldehydes to furnish the respective spiro-in-
indolooxirane derivatives have use as anticonvulsants, di- dolooxiranes (Figure 2) as single diastereomer in very
uretics, sedatives, sleep potentiators and also show trans- good yields and the results are given in Table 2. The reac-
1
4,15
aminase inhibiting activity.
tion did not work in the presence of electron withdrawing
substituents such as nitro-group.
N2
R2
+
OHC
N
O
R1
1
2
Rh2(OAc)4
1,2-dichloroethane
O
R2
O
N
R1
3
Scheme 1
Table 1 Synthesis of Spiro-indolooxiranes
Figure 3
Entry
R1
R2
Yield (%) of 3a
a
b
c
d
e
f
CH3
H
57
64
65
61
55
64
84
81
77
73
Table 2 Synthesis of Spiro-indolooxiranes
Entry R1
R2
H
H
H
H
H
R3
R4
Yield (%)a
CH Ph
H
2
4-CH C H CH
2
H
4
5
6
7
8
9
CH3
OCH3 OCH3 65
OCH3 OCH3 82
OCH3 OCH3 81
OCH3 OCH3 73
OCH3 OCH3 63
3
6
4
Allyl
H
CH Ph
2
Propargyl
CH3
H
4-CH C H CH
2
3
6
4
OCH3
OCH3
OCH3
OCH3
OCH3
Allyl
g
h
i
CH Ph
Propargyl
2
4-CH C H CH
CH Ph
OCH3 OCH3 OCH3 82
OCH3 OCH3 OCH3 80
3
6
4
2
2
Allyl
Propargyl
10
Propargyl
a
j
Yields are unoptimized and refer to isolated and chromato-
graphically pure compounds 4–10.
a
Yields are unoptimized and refer to isolated and chromato-
graphically pure compounds 3.
Mechanistically, we propose the formation of carbonyl
ylide 11 (Figure 4) as a reactive intermediate. The subse-
quent selective cyclization of this intermediate 11 leads to
the formation of single isomer with Z-stereochemistry. In-
terestingly, the reaction was repeated in the presence of
two equivalents of aldehyde to provide the spiro-oxirane
system without forming the dioxolane system. Important-
ly, the conformation of ylides 11 may be favorable over
the 1,3-dipolar cycloaddition due to the faster ring
closure, with a second equivalent of aldehyde to produce
the dioxolane system.
The stereochemistry of spiro-indolooxiranes was deter-
mined as Z based on the single crystal X-ray analysis1
of the representative product 3g (Figure 3).
6,17
R2
O
R3
R4
O
N
To advance this process further, we considered the forma-
tion of the bis-spiro-indolooxirane ring system using dial-
dehydes. To this end, phthalic dicarboxaldehyde was
chosen as the prototypical substrate and the rhodium(II)
acetate catalyzed reaction carried out using 2.5 equiva-
R1
4-10
Figure 2
Synlett 2004, No. 4, 639–642 © Thieme Stuttgart · New York

LETTER
A New Access to Spiro-indolooxiranes
641
lents of cyclic diazoamide 1b. Column chromatographic The bis-oxirane formations were further generalized us-
purification of the reaction mixture afforded two products ing aromatic dialdehydes (12a,b) to deliver the corre-
1
3a and 14a in 27% and 6% yields, respectively. Spectro- sponding bis- as well as mono-epoxides (13b–d and
scopic analysis clearly revealed the formation of com- 14b–d, Scheme 2, Table 3).
pound 13a, a bis-oxirane system, with minor amounts of
In conclusion, we have demonstrated the novel stereo-
mono-oxirane compound 14a. The stereochemistry of the
bis-oxiranes is tentatively assigned based on the above
studies. This process forms an interesting example in
which the bis-oxirane ring system is synthesized from the
diazo carbonyl compound. The free aldehyde group
present in the mono-epoxide 14a can also be further func-
tionalized to obtain dissymmetric bis-oxirane ring sys-
tems.
selective synthesis of mono- and bis-spiro-indolooxiranes
using cyclic rhodium carbenoids generated from the cy-
clic diazoamides with various aromatic aldehydes and di-
aldehydes. The scope and further applications of this
theoretically interesting transformation towards the
strained ring system are currently under active investiga-
tion in our laboratory and will be disclosed in due course.
Typical Procedure for the Synthesis of Spiro-oxiranes: An oven-
dried 50 mL flask was charged with aldehyde (1.2 mmol) and rhod-
ium(II) acetate in a freshly distilled dry 1,2-dichloroethane (5 mL)
under nitrogen atmosphere. A dry 1,2-dichloroethane (15 mL) solu-
tion of cyclic diazoamide (1.0 mmol) was added dropwise to the
above reaction mixture at 60 °C for the period of 1 h and followed
by TLC. After completion of the reaction, the solvent was concen-
trated under reduced pressure and the reaction mixture purified by
chromatography using the flash silica-gel column (hexane/EtOAc
R2
O
H
N
R1
O
1
1
Figure 4
7
5:25) to afford the pure spiro-indolooxiranes. All new compounds
exhibited spectral data consistent with their structures. Selected
spectral data:
CHO
OHC
3
¢-Phenyl-1-methylspiro[indole-3,2¢-oxiran]-2(1H)-one
(3a):
Yellow solid; mp 112–114 °C (hexane/EtOAc). IR (KBr): 3067,
2929, 1720, 1617, 1494, 1470, 1453, 1373, 1345, 1246, 1217, 1111,
1
1
2a Phthalic dicarboxaldehyde
2b Terephthaldicarboxaldehyde
–1
1
1
027, 893, 742 cm . H NMR (200 MHz, CDCl ): d = 3.08 (s, 3 H,
3
N-CH ), 4.64 (s, 1 H, OCH), 6.83 (d, 1 H, J = 7.7 Hz, ArH), 7.04–
1
, Rh2(OAc)4
3
1
3
1,2-dichloroethane
7.18 (m, 3 H, ArH), 7.27–7.46 (m, 4 H, ArH), 7.56–7.68 (1 H).
C
NMR (50.3 MHz, CDCl ): d = 27.0 (N-CH ), 62.5 (quat-C), 68.1
3
3
(
OCH), 109.2 (CH), 122.2 (CH), 123.2 (CH), 128.0 (CH), 128.3
O
(CH), 129.3 (CH), 130.8 (CH), 131.4 (quat-C), 132.4 (quat-C),
O
+
1
2
45.2 (quat-C), 174.3 (quat-C). MS (EI): m/z (%) = 251 (100) [M ],
23 (53), 194 (38), 165 (9), 117 (24), 105 (36), 90 (37), 77 (32).
O
O
N
R1
Anal. Calcd for C H NO : C, 76.48; H, 5.21; N, 5.57. Found: C,
16 13 2
N
R1
76.26; H, 5.17; N, 5.62.
1
3a-d
3
¢-(4-Methoxyphenyl)-1-benzylspiro[indole-3,2¢-oxiran]-2(1H)-
+
one (3g): Colorless solid; mp 148–150 °C (hexane/EtOAc). IR
O
(KBr): 3027, 2935, 1732, 1614, 1515, 1465, 1360, 1246, 1173,
–
1
1
1
035, 754 cm . H NMR (200 MHz, CDCl ): d = 3.78 (s, 3 H,
3
CHO
OCH ), 4.64 (s, 1 H, OCH), 4.73 (d, B part of AB-system, 1 H,
3
O
N
J = 15.8 Hz, NCH ), 4.89 (d, A part of AB-system, 1 H, J = 15.8 Hz,
2
R1
NCH ), 6.75 (d, 1 H, J = 7.7 Hz, ArH), 6.91 (d, 2 H, J = 8.0 Hz,
2
14a-d
ArH), 7.04 (t, 1 H, J = 7.7 Hz, ArH), 7.07–7.24 (m, 5 H, ArH), 7.57
1
3
(
(
d, 2 H, J = 8.0 Hz, ArH). C NMR (50.3 MHz, CDCl ): d = 44.6
3
Scheme 2
N-CH ), 55.8 (OCH ), 62.6 (quat-C), 68.5 (OCH), 110.2 (CH),
2
3
1
13.8 (CH), 114.5 (quat-C), 122.2 (CH), 123.2 (CH), 124.3 (quat-
Table 3 Synthesis of Bis-spiro-indolooxiranes
C), 128.0 (CH), 128.3 (CH), 129.3 (CH), 129.4 (CH), 130.5 (CH),
36.2 (quat-C), 144.2 (quat-C), 160.2 (quat-C), 170.8 (quat-C). MS
1
Entry
Dialdehyde R1
Yield of 13 Yield of 14
(
(EI): m/z (%) = 357 (2) [M ], 307 (15), 238 (10), 167 (7), 130 (20),
120 (24), 102 (20), 91 (100), 65 (15), 51 (20); Anal. Calcd for
C H NO : C, 77.29; H, 5.36; N, 3.92. Found: C, 77.02; H, 5.41; N,
+
%)a
(%)a
2
3
19
3
a
b
c
12a
12a
12b
12b
CH Ph
27
37
31
35
6
2
3
.95.
Allyl
11
5
3¢-(3,4,5-Trimethoxyphenyl)-1-(prop-2-ynyl)spiro[ind ole-3,2¢-
oxiran]-2(1H)-one (10): Orange solid; mp 144–146 °C (hexane/
EtOAc). IR (KBr): 3281, 1732, 1692, 1591, 1466, 1422, 1266,
CH3
–
1 1
1
129, 1007, 739 cm . H NMR (200 MHz, CDCl ): d = 2.25 (s, 1
3
d
CH Ph
7
2
H, CCH), 3.86 (s, 3 H, OCH ), 3.88 (s, 6 H, OCH ), 4.46 (s, 2 H, N-
3
3
a
CH ), 4.60 (s, 1 H, OCH), 6.88 (s, 2 H, ArH), 7.11–7.22 (m, 3 H,
Yields are unoptimized and refer to isolated and chromato-
2
1
3
ArH), 7.42 (t, 1 H, J = 7.4 Hz, ArH). C NMR (50.3 MHz, CDCl3):
d = 30.1 (N-CH ), 56.7 (OCH ), 56.9 (OCH ), 62.9 (quat-C), 68.8
graphically pure compounds 13 and 14.
2
3
3
(
(
OCH), 73.3 (quat-C), 77.1 (CH), 105.5 (CH), 107.4 (CH), 110.3
CH), 122.3 (CH), 123.7 (CH), 124.1 (quat-C), 127.4 (quat-C),
Synlett 2004, No. 4, 639–642 © Thieme Stuttgart · New York

6
42
S. Muthusamy et al.
LETTER
(4) de March, A.; Huisgen, R. J. Am. Chem. Soc. 1991, 104,
1
30.8 (CH), 143.2 (quat-C), 153.4 (quat-C), 169.7 (quat-C). MS
+
(
(
EI): m/z (%) = 366 (26) [M + 1], 365 (100) [M ], 337 (26), 322
91), 298 (21), 165 (38), 150 (26), 102 (26); Anal. Calcd for
4952.
(5) Doyle, M. P.; Forbes, D. C.; Protopopova, M. N.; Stanley, S.
A.; Vasbinder, M. M.; Xavier, K. R. J. Org. Chem. 1997, 62,
7210.
C H NO : C, 69.03; H, 5.24; N, 3.83. Found: C, 69.28; H, 5.30; N,
2
1
19
5
3
.41.
(
6) Doyle, M. P.; Hu, W.; Timmons, D. J. Org. Lett. 2001, 3,
33.
(7) Davies, H. M. L.; DeMeese, J. Tetrahedron Lett. 2001, 42,
803.
1
,4-Di(1-benzylspiro[indole-3,2¢-oxiran]-2(1H)-one-3¢-yl)ben-
9
zene (13d): Colorless solid; mp 168–170 °C (hexane/EtOAc). IR
–
1 1
(KBr): 3056, 2928, 1730, 1615, 1468, 1359, 1265, 1180 cm . H
6
NMR (200 MHz, CDCl ): d = 4.76 (s, 2 H, OCH), 4.77 (d, B part of
AB-system, 2 H, J = 15.7 Hz, NCH ), 5.00 (d, A part of AB-system,
2
3
(
8) Aggarwal, V. K.; Alonso, E.; Hynd, G.; Lydon, K. M.;
Palmer, M. J.; Porcelloni, M.; Studley, J. R. Angew. Chem.
Int. Ed. 2001, 40, 1430.
2
H, J = 15.7 Hz, NCH ), 6.78 (d, 2 H, J = 7.7 Hz, ArH), 7.07 (t, 2
2
H, J = 7.7 Hz, ArH), 7.22–7.27 (m, 14 H, ArH), 7.68 (s, 4 H, ArH).
1
3
(9) (a) Muthusamy, S.; Gunanathan, C. Chem. Commun. 2003,
40. (b) Muthusamy, S.; Babu, S. A.; Nethaji, M.
C NMR (50.3 MHz, CDCl ): d = 44.9 (N-CH ), 62.7 (quat-C),
3
2
4
6
1
1
8.4 (OCH), 110.4 (CH), 122.4 (CH), 123.4 (CH), 124.2 (quat-C),
Tetrahedron 2003, 59, 8117. (c) Muthusamy, S.; Babu, S.
A.; Gunanathan, C.; Ganguly, B.; Suresh, E.; Dastidar, P. J.
Org. Chem. 2002, 67, 8019. (d) Muthusamy, S.; Babu, S.
A.; Gunanathan, C. Tetrahedron Lett. 2002, 43, 3931.
27.7 (CH), 128.2 (CH), 128.4 (CH), 129.5 (CH), 130.8 (CH),
33.1 (quat-C), 136.2 (quat-C), 144.4 (quat-C), 170.7 (quat-C). MS
+
(
EI): m/z (%) = 576 (4) [M ], 444 (6), 355 (9), 237 (9), 223 (13), 146
(
16), 91 (100); Anal. Calcd for C H N O : C, 79.15; H, 4.89; N,
3
8
28
2
4
(
e) Muthusamy, S.; Babu, S. A.; Gunanathan, C.
4
.86. Found: C, 79.39; H, 4.95; N, 4.81.
Tetrahedron Lett. 2002, 43, 5981.
3
¢-(4-Formylphenyl)-1-benzylspiro[indole-3,2¢-oxiran]-2(1H)-
(
(
10) Muthusamy, S.; Gunanathan, C. Synlett 2003, 1559.
11) (a) Muthusamy, S.; Gunanathan, C.; Babu, S. A.; Suresh, E.;
Dastidar, P. Chem. Commun. 2002, 824. (b) Muthusamy,
S.; Gunanathan, C. Synlett 2002, 1783.
(12) (a) Pirrung, M. C.; Blume, F. J. Org. Chem. 1999, 64, 3642.
(b) Pirrung, M. C.; Lee, Y. R. J. Am. Chem. Soc. 1995, 117,
one (14d): Colorless solid; mp 108–110 °C (hexane/EtOAc). IR
(KBr): 2924, 1727, 1694, 1611, 1491, 1468, 1361, 1303, 1178,
–
1
1
1
001, 746 cm . H NMR (200 MHz, CDCl ): d = 4.76 (s, 1 H,
3
OCH), 4.80 (d, B part of AB-system, 1 H, J = 12.7 Hz, NCH ), 4.95
2
(d, A part of AB-system, 1 H, J = 12.7 Hz, NCH ), 6.81 (d, 1 H,
2
J = 7.6 Hz, ArH), 7.09 (t, 1 H, J = 7.3 Hz, ArH), 7.17–7.32 (m, 6 H,
ArH), 7.66–7.69 (m, 1 H, ArH), 7.79 (d, 2 H, J = 8.1 Hz, ArH), 7.91
4814. (c) Pirrung, M. C.; Lee, Y. R. J. Chem. Soc., Chem.
Commun. 1995, 673. (d) Pirrung, M. C.; Lackey, K.; Zhang,
J.; Sternbach, D. D.; Brown, F. J. Org. Chem. 1995, 60,
2112.
1
3
(
d, 2 H, J = 8.0 Hz, ArH), 10.01 (s, 1 H, CHO). C NMR (50.3
MHz, CDCl ): d = 44.6 (N-CH ), 65.3 (quat-C), 67.3 (OCH), 110.5
3
2
(
(
(
CH), 122.5 (CH), 123.5 (CH), 128.0 (CH), 128.4 (CH), 128.7
CH), 129.4 (CH), 129.7 (CH), 130.4 (quat-C), 130.7 (CH), 131.1
CH), 135.9 (quat-C), 138.9 (quat-C), 140.6 (quat-C), 144.4 (quat-
(
(
(
(
13) Cava, M. P.; Little, R. L.; Naipier, D. R. J. Am. Chem. Soc.
1958, 80, 2257.
14) Anthony, W. C. (Upjohn Co.); US 3,413,299, 1968; Chem.
Abstr. 1969, 70, 47294j.
15) Upjohn, Co. Neth. Appl. 6,505,845, 1966;Chem. Abstr.
1967, 67, 21850a.
+
C), 192.4 (CHO). MS (EI): m/z (%) = 356 (9) [M + 1], 355 (30 [M ],
2
Anal. Calcd for C H NO : C, 77.73; H, 4.82; N, 3.94. Found: C,
7
36 (23), 220 (11), 208 (24), 165 (8), 134 (16), 102 (15), 91 (100);
23
17
3
7.95; H, 4.89; N, 3.91.
16) Crystal data for compound 3g: Colorless rectangular crystal.
3
C H NO , M = 357.39, 0.50 × 0.08 × 0.05 mm , triclinic,
2
3
19
3
space group p-1 with a = 5.9327(13) Å, b = 10.800(2) Å,
c = 14.812(3) Å, a = 90.925(4)°, b = 94.846(4)°,
g = 101.966(4)°, V = 924.6(4) Å , T = 293(2) K,
R = 0.0496, wR = 0.1204 on observed data, z = 2,
Acknowledgment
3
This research was supported by Department of Science and Techno-
logy, New Delhi. We are grateful to Prof. W. Sander, Rühr Univer-
sity, Germany for providing mass spectral analyses. C. G. thanks
CSIR, New Delhi for the award of a Senior Research Fellowship.
1 2
–
3
Dcalcd = 1.284 g cm , F(000) = 376, Absorption
–
1
coefficient = 0.085 mm , l = 0.71073 Å, 3567 reflections
were collected on a smart apex ccd single crystal CCD
diffractometer, 2632 observed reflections [I 2s (I)]. The
–
3
References
largest difference peak and hole = 0.234 and –0.246e Å ,
respectively. The structure was solved by direct methods and
(
1) (a) Curtius, T. Bercht. 1883, 16, 2230. (b) Curtius, T. J.
Prakt. Chem. 1888, 38, 396.
2
refined by full-matrix least squares on F using SHELXL-97
software.
(
2) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds.
From Cyclopropanes to Ylides; Wiley-Interscience: New
York, 1998.
(
17) Crystallographic data for 3g have been deposited with the
Cambridge Crystallographic Data Center as supplementary
publication no CCDC-222010. Copies of the data can be
obtained free of charge on application to 12, Union Road,
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(
3) For recent reviews see: (a) Mehta, G.; Muthusamy, S.
Tetrahedron 2002, 58, 9477. (b) Padwa, A.; Weingarten, M.
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