Ring modifications in camphorimines purely organic or promoted by Pt(II)

Article abstract of DOI:10.1080/00397911.2012.702290

The reactivity of 3-oxo-camphorsulfonylimine (1) was explored toward the formation of new organic species in processes strictly organic or catalyzed by platinum. Synthesis and characterization of (1S)-1-[7,7-dimethyl-2-(4- ethinylphenylimino)-3-oxo-bicyclo [2.2.1]heptanyl]-methanesulfonamide (2), (3aS,7R)-7-hydroxy-8,8-dimethyl-7-(Nmethylamino-1-propynyl)-4,5,6, 7-tetrahydro-3H-3a,6-methano-2,1-benzisothiazole 2,2-dioxide (4a), (3aS,6aR,9aR)-8-benzyl-10,10-dimethyl-6a-hydroxy-9-(E-2-phenylethylidene)-3,3-a, 4,5,6,7-hexahydro-1H,9H-3a,6-methano-indeno[3a,4c]isothiazole 2,2-dioxide (6), and (2S, 3aS,6S)-9-benzyl-5,6-dihydro-11,11-dimethyl-10-phenylacetyl-3H-3a,6- methano-1H-yclonon [c]isothiazol-7(4H)-one 2-oxide (7) are reported as well as the activation of (1aS,3aS,7R)-7-hydroxy-1a,7-bis(3-phenyl-1-propynyl)-8,8- dimethyl-1,1a,4,5,6,7-hexahydro-3H-3a,6-methano-2,1-benzisothiazole 2,2-dioxide (3a) toward ring annulation or ring expansion by reaction with Pt(II) depending on the reaction conditions. Copyright

Full text of DOI:10.1080/00397911.2012.702290

Synthetic Communications1, 43: 2305–2313, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2012.702290
RING MODIFICATIONS IN CAMPHORIMINES PURELY
ORGANIC OR PROMOTED BY Pt(II)
M. Fernanda N. N. Carvalho,1 Ana S. D. Ferreira,1 and
Rudolf Herrmann2
1
´
Centro de Quımica Estrutural, Instituto Superior Tecnico, Universidade
Tecnica de Lisboa, Lisboa, Portugal
´
´
2Institut fu¨r Physik, Universita¨t Augsburg, Augsburg, Germany
GRAPHICAL ABSTRACT
Abstract The reactivity of 3-oxo-camphorsulfonylimine (1) was explored toward the forma-
tion of new organic species in processes strictly organic or catalyzed by platinum. Synthesis
and characterization of (1S)-1-[7,7-dimethyl-2-(4-ethinylphenylimino)-3-oxo-bicyclo
[2.2.1]heptanyl]-methanesulfonamide (2), (3aS,7R)-7-hydroxy-8,8-dimethyl-7-(N-
methylamino-1-propynyl)-4,5,6,7-tetrahydro-3H-3a,6-methano-2,1-benzisothiazole 2,2-dioxide
(4a),
(3aS,6aR,9aR)-8-benzyl-10,10-dimethyl-6a-hydroxy-9-(E-2-phenylethylidene)-3,3-
a,4,5,6,7-hexahydro-1H,9H-3a,6-methano-indeno[3a,4c]isothiazole 2,2-dioxide (6), and (2S,
3aS,6S)-9-benzyl-5,6-dihydro-11,11-dimethyl-10-phenylacetyl-3H-3a,6-methano-1H-yclonon
[c]isothiazol-7(4H)-one 2-oxide (7) are reported as well as the activation of (1aS,3aS,7R)-7-
hydroxy-1a,7-bis(3-phenyl-1-propynyl)-8,8-dimethyl-1,1a,4,5,6,7-hexahydro-3H-3a,6-methano-
2,1-benzisothiazole 2,2-dioxide (3a) toward ring annulation or ring expansion by reaction with
Pt(II) depending on the reaction conditions.
Supplemental materials are available for this article. Go to the publisher’s online edition
of Synthetic Communications1 to view the free supplemental file.
Keywords Cascade processes; catalysis; platinum; ring annulations; ring expansion
Received April 9, 2012.
Address correspondence to M. Fernanda N. N. Carvalho, Centro de Quımica Estrutural, Instituto
´
Superior Tecnico, Universidade Tecnica de Lisboa, Av. Rovisco Pais 1049-001, Lisboa, Portugal. E-mail:
´
fcarvalho@ist.utl.pt
´
2305

2306
M. F. N. N. CARVALHO, A. S. D. FERREIRA, AND R. HERRMAN
Scheme 1. Ring opening promoted by reaction of 4-aminophenylethyne with 1.
INTRODUCTION
The stoichiometric addition of halogens or Brønsted acids (e.g., HCl) to
dialkynes of type 3 (Scheme 1) starts a cascade reaction leading to annulation of a
five-membered ring that forms from three of the triple-bond carbon atoms via
cationic intermediates, combined with the reduction of sulfur(VI) to sulfur(IV)
(oxygen transfer from sulfur to carbon).[1] This reactivity is possible because the
two alkyne groups are kept in close vicinity by the rigid camphor skeleton.
The catalytic isomerization with Pt(II) does not normally stop at the stage of
ring annulation but continues the cascade with bond cleavage between the carbon
atoms (C2, C3), which initially carried the alkynes, resulting in ring expansion to
a tricyclic ring system with nine members.[2–5] We now report the isolation of the first
product (6) of annulation of a five-membered ring to the camphor skeleton promoted
by reaction of PtCl2 with 3a (R ¼ benzyl).When [PtCl2(EtCN)2] (a form of Pt(II) that
is readily soluble in organic solvents) is used as catalystinstead of PtCl2 for activation
of 3a, the product of ring expansion (7) is obtained, which resembles taxol with
respect to the larger ring, the dimethylmethano bridge, and the points of attachment
of the heterocyclic ring.
In contrast to ring annulation or ring expansion, the rupture of the sulfonyli-
mine ring in 1 leads to 2 in a purely organic process.
RESULTS AND DISCUSSION
The rupture of the sulfonylimine ring in 3-oxo-camphorsulphonylimine (1)
=
promoted by reaction with the lithium salt of 4-aminophenylethyne (R C6H4NH2)
forming (1S)-1-[7,7-dimethyl-2-(4-ethinylphenylimino)-3-oxo-bicyclo[2.2.1]heptanyl]-
methanesulfonamide (2) (Scheme 1) contrasts with the addition to the carbonyl
=
group of the deprotonated N-methylpropargylamine (R CH2NHMe), forming
(3aS,7R)-7-hydroxy-8,8-dimethyl-7-(N-methylamino-1-propynyl)-4,5,6,7-tetrahydro-
3H-3a,6-methano-2,1-benzisothiazole 2,2-dioxide (CH2NHMe, 4a, Scheme 2).
Ring rupture was unexpected because previous reactions involving 3-oxo-
camphorsulfonylimine and lithiated alkynes underwent addition by nucleophilic
attack to the carbonyl group (4), to the imine group (5), or to both groups (3)
(Scheme 2), keeping intact the tricyclic structure of the camphorsulfonylimine.[6,7]
Ring rupture leading to 2 indicates that the NH2 group instead of the terminal
alkyne carbon atom is involved in attack to the imine group. The process is followed

RING MODIFICATIONS IN CAMPHORIMINES
2307
Scheme 2. Reactivity trends in reaction of camphorsulfonylimine with lithiated alkynes.
by cleavage of the sulfonamide bond, leaving to a purely carbocyclic compound. It
is not the presence of the NH groups as such that triggers this reactivity because
=
N-methyl-propargylamine (N-methyl-prop-2-yn-1-amine, R CH2NHMe) reacts, as
expected, with its terminal carbon atom.[2] To clarify the situation we studied by
density functional theory (DFT) the influence of aliphatic vs. aromatic amino groups
on the stability of the carbanions (both with and without Liþ counterions) obtained
by deprotonation of the respective alkynes at either the terminal carbon atom or the
amino group (for details, see Supplemental Material). According to these calcula-
tions, carbanions (without counterions) are greatly stabilized by solvent effects
(calculated for tetrahydrofuran, THF, as used in the experimental procedures).
The effect is lower for the ion pairs with Liþ, but still exceeds that of the neutral
amines. Thus we found that for 4-aminophenylethyne deprotonation at nitrogen is
slightly preferred over deprotonation at the terminal carbon atom (e.g., 0.3 kcal=
mol in THF solution with the Liþ counterion), while for N-methylpropargylamine
there is a considerable preference for deprotonation at the carbon atom (12.4 kcal=
mol under the same conditions). Calculation and experiment are thus in good agree-
ment with respect to formation of 2.
In 2 (LH), there are several groups that can bind to transition metals. However,
in CH2Cl2 no reaction occurs with Pt or Pd chlorides in the absence of base. Et3N
is essential to deprotonate the amine group and promote coordinationto PdCl2,
affording [PdCl(L)Et3N] ꢀ Et2O (8) (reaction 1).
PdCl2 þ LH þ 2Et3N ! ½PdClðLÞEt3Nꢁ þ Et3NHCl
ð1Þ
The structural characterization of 8 by x-rays was not possible (no suitable
crystals were obtained) and its low solubility precluded NMR data. Nevertheless
the infrared (IR) spectrum displays bands in the region of the uncoordinated CC

2308
M. F. N. N. CARVALHO, A. S. D. FERREIRA, AND R. HERRMAN
triple bonds (2203 cmꢂ1), SO2 (1339, 1152 cmꢂ1), and a band in the NH region
(3243 cmꢂ1), pointing tocoordination by the nitrogen atom of the amine group. Con-
comitant coordination by the imine group is supported by the considerable shift to
greater values of the C N stretch (1674 cmꢂ1) compared to that in 2 (1599 cmꢂ1).
=
In contrast to the formation of complex 8 by reaction of PdCl2 with 2, a cascade
process is promoted in reaction of PtCl2 with 3a affording the organic compound 6
[(3aS,6aR,9aR)-8-benzyl-10,10-dimethyl-6a-hydroxy-9-(E-2-phenylethylidene)-3,3a,4,
5,6,7-hexahydro-1H,9H-3a,6-methano-indeno[3a,4c]isothiazole2,2-dioxide](Scheme3).
Ring annulation in 6 contrasts with ring expansion promoted by [PtCl2(EtCN)2] in 3a,
affording compound 7 [(2S,3aS,6S)-9-benzyl-5,6-dihydro-11,11-dimethyl-10-pheny-
lacetyl-3H-3a,6-methano-1H-cyclonon[c]isothiazol-7(4H)-one 2-oxide] (Scheme 3).
Discrimination in formation of 6 or 7 is attributedto the solubility of the Pt(II)
species; that is, [PtCl2(EtCN)2] is readily soluble in organic solvents whereas PtCl2 is only
sparingly soluble, which rends the reaction very slow and no ring expansion occurs.
Compound 6 is an unprecedented reduction product, formed in the ring annu-
lation cascade promoted by Pt(II), which has basically the same structure as the
addition products of dialkynes 3 with halogens[2] but with hydrogen atoms instead
of the additional halogen atoms. The reduction is promoted by Pt(II), which is in
turn oxidized to paramagnetic Pt(III) ill-defined complexes that could not be fully
characterized. The hydrogen source may either be a trace of water or protons that
result from oxidation reactions of 3a. Because the yield of compound 6 is only
25% and no further products could be identified from the reaction mixture, we can-
not decide this question. The action of PtCl2 may even be stoichiometric rather than
catalytic.
Scheme 3. Ring annulation and ring expansion promoted by reaction of 3a with Pt(II).

RING MODIFICATIONS IN CAMPHORIMINES
2309
Figure 1. Correlation of experimental and calculated 13C NMR data for E (a) and Z (b) isomer of
compound 6. (Figure is provided in color online.)
The basic structure of product 6 can readily be determined by NMR methods
(see Supplemental Material). However, the decision between E or Z configuration at
=
the exocyclic C C double bond remains difficult on the basis of the NMR data
because only one isomer was isolated and no camparison can be made. We therefore
decided to calculate NMR data of both E and Z isomers and make the decision
according to the best fit to the experimental data (for details, see Supplemental
Material). As observed in similar cases[2] 13C NMR data proved to be more reliable
1
than H. Figure 1 shows the comparison of experimental and calculated 13C NMR
chemical shifts. One can clearly see that the overall fit of the chemical shifts fits better
to the E isomer. A detailed comparison of the chemical shifts of the double-bond
carbon atoms confirms the attribution of the E configuration to compound 6 (see
Supplemental Material for chemical shift data).
CONCLUSIONS
Two new types of compounds were obtained from 3-oxo-camphorsulphonyli-
mine (1) in a purely organic process (2) or by catalysis with Pt(II) (6).
Compound 2 evidences the relevance of the substituent R-group of the aromatic
moiety of the alkyne (HCꢃCC6H4NH2) in directing the deprotonation of the
amine rather the alkyne group of 4-aminophenylethyne. Nucleophilic attack by the

2310
M. F. N. N. CARVALHO, A. S. D. FERREIRA, AND R. HERRMAN
deprotonate amine group is responsible for the rupture of the sulfonylimine ringin 1,
which contrasts with reactivitypromoted by nucleophilic attack by the deprotonated
alkyne.
Compound 6 provides the experimental evidence for the annulation of a
five-membered ring to the camphor skeleton during the process of ring expansion-
from six to nine members catalyzed by Pt(II). This type of compound was proposed
to form[2] in the ring enlargement process but had never been isolatedin Pt(II)-
catalyzed processes. The isolation of compound 6 further reinforces the relevance
of the experimental conditions in the cascade process that leads from the camphor
dialkyne (3a) to compound 7.
No modifications are observed in 2 by reaction with Pt(II) whereas
[PdCl(L)Et3N] forms by reaction with Pd(II).
EXPERIMENTAL
3-Oxo-camphorsulfonylimine (1),[8] the camphor dialkyne 3a[7,6], and trans-
[PtCl2(EtCN)2][9,10] were obtained by published methods. PtCl2 was purchased from
Sigma-Aldrich and the solvents from Panreac. All reactions were made under nitro-
gen atmosphere using the Schlenk technique. Infrared (IR) spectra were obtained in
KBr pellets with a Jasco Fourier transform (FT)=IR 4100 spectrometer. NMR spec-
tra [1H, 13C, distortionless enhancement by polarization transfer (DEPT), heteronuc-
lear single quantum correlation (HSQC), heteronuclear multiple bond correlation
(HMBC)] were obtained in CDCl3 or dimethylsulfoxide (DMSO-d6) using Bruker
Avance IIþ Spectrometers (300 or 400 MHz). Tetramethylsilane (TMS) (d ¼ 0 ppm)
was used as internal reference.
(1S)-1-[7,7-Dimethyl-2-(4-ethinylphenylimino)-3-oxo-bicyclo[2.2.1]
heptan-1-yl]-methane Sulfonamide (2)
Butyllithium (3.45 cm3,1.6 M in n-hexane) was slowly added under nitrogen to
a mixture of 3-oxo-camphorsulfonylimine (1, 0.50 g, 2.2 mmol) and 4-aminopheny-
lethyne (A, 0.64 g, 5.5 mmol) in Et2O (30 cm3). The mixture was stirred at rt until
complete consumption of 1. The solid was filtered off and dissolved in H2O
(30 cm3), and the solution extracted with CH2Cl2 (3 ꢄ 50 cm3) and dried over CaCl2
for a couple of hours. After filtration to separate the drying agent, the solution was
evaporated to dryness, affording an orange compound (2, 0.45 g, 1.1 mmol, yield
50%). Elemental analysis (%) for C18H20N2O3S ꢀ Et2O: Found: C, 63.6; N, 6.9; H,
7.1; S, 7.6. Calculated: C, 63.2; N, 6.7; H, 7.2; S, 7.7. IR (cmꢂ1): 3365 (nNH2),
1
2109 (nCꢃC), 1752 (nCO), 1599, (nCN), 1339 (nSO2asym), 1156 (nSO2sym). H NMR
(CDCl3, d ppm): 7.41 (d, JHH ¼ 8.2, 2H), 6.74 (d, JHH ¼ 8.2, 2H), 5.5 (s, 2H), 3.76,
3.38 (d, JHH ¼ 15.1, 2H), 3.04 (s, 1H), 2.55–1.50 (m, 4H), 2.48 (d, JHH ¼ 5.0, 1H),
1.09 (s, 3H), 1.08 (s, 3H). 13C NMR (CDCl3, d ppm): 196.5 (C-2), 168.5 (C-3),
148.1, 132.7, 118.7 (C-Ph), 83.4, 79.0 (value obtained in DMSO-d6) (CꢃC), 58.6
(C-4), 55.9 (C-1), 54.7 (C-8), 46.1 (C-7), 29.1 (C-6), 22.2 (C-5); 20.7, 17.8 (C-9,10).
For numbering of the carbon atoms, see Fig. 2.

RING MODIFICATIONS IN CAMPHORIMINES
2311
Figure 2. Numbering of carbon atoms for compounds 2 and 4a.
(3aS,7R)-7-Hydroxy-8,8-dimethyl-7-(N-methylamino-1-propynyl)-4,5,
6,7-tetrahydro-3H-3a,6-methano-2,1-benzisothiazole 2,2-Dioxide (4a)
Butyllithium (3.1 cm3, 1.6 M in n-hexane) was added dropwise to a solution of
N-methylprop-2-yn-1-amine (B, 0.38 cm3, 4.5 mmol) in 10 ml of diethyl ether. The mix-
ture was stirred for 1 day at rt. Then 3-oxo-camphorsulfonylimine (1, 0.50 g, 2.2 mmol)
was added and after one more day the reaction was quenched with H2O (2 cm3). The
aqueous layer was extracted with CH2Cl2 (3 ꢄ 40 cm3), dried over MgSO4, filtered to
separate the drying agent, and taken to dryness, affording an orange powder (0.20 g,
0.68 mmol, yield, 15%). Elemental analysis (%) for C14H20N2O3S ꢀ CH2Cl2: Found: C,
47.5; H, 5.9; N, 7.4; S, 8.4. Calculated: C, 47.1; H, 5.8; N, 7.3; S, 8.4. IR (cmꢂ1): 3399
(nOH), 2252 (nCꢃC), 1653 (nCN), 1337 (nSO2asym), 1161 (nSO2sym). 1H NMR (CDCl3, d
ppm): 5.02 (br, 2H), 3.61–3.44 (m, 2H), 3.20, 3.08 (2d, JHH ¼ 13.5, 2H), 2.47 (d,
JHH ¼ 2.4, 3H), 2.24–1.74 (m, 4H), 2.28 (d, JHH ¼ 2.7, 1H), 1.08 (s, 3H), 1.06 (s,
3H). 13C NMR (CDCl3, d ppm): 195.1 (C-2), 85.6, 72.4 (CꢃC), 64.2 (C-1), 56.0
(C-4), 50.0 (C-8), 47.4 (C-7), 39.1 (CH2N-), 34.8 (-NHCH3), 29.6 (C-3), 28.0 (C-6),
23.6 (C-5); 21.2, 21.0 (C-9,10). For numbering of the carbon atoms, see Fig. 2.
(3aS,6aR,9aR)-8-Benzyl-10,10-dimethyl-6a-hydroxy-9-(E-2-
phenylethylidene)-3,3a,4,5,6,7-hexahydro-1H,9H-3a,6-methano-
indeno[3a,4c]isothiazole 2,2-Dioxide (6)
Compound 3a (0.38 g, 0.84 mmol) and 3a (0.38 g, 0.84 mmol) and 3a (0.38 g,
0.84 mmol) and PtCl2(0.10 g, 0.38 mmol) were stirred in CH2Cl2 (55 cm3) at rt for 7
days. The solvent was then evaporated, and the brownish oil was extracted with
Et2O (2 ꢄ 5 cm3). Compound 6 precipitated upon partial evaporation of Et2O as a
pale yellow compound (0.10 g, 0.021 mmol), yield 25%. Elemental analysis (%) for
(C28H31NO3S) 1=8CH2Cl2: Found: C, 71.3; N, 3.2; H, 7.1; S, 5.7. Calculated: C,
71.6; N, 3.0; H, 6.6; S, 6.8. IR (cmꢂ1): 3339 (nOH), 1660; 1601 (nCC), 1323 (nSO2asym),
1097; 1061 (nSO2sym). 1H NMR (CDCl3, d ppm): 7.3–7.1 (m, 8H), 7.04 (s, 1H), 7.02 (s,
1H), 6.97 (s, 1H), 5.54 (s, 1H), 3.5–3.4 (m, 4H), 3.31, 2.98 (2d, JHH ¼ 13.2, 2H),2.50 (s,
1H),2.00 (d, JHH ¼ 4.2, 1H), 1.75, 1.5 (m, 2H), 1.70, 1.38 (m, 2H), 1.36 (s, 3H), 0.91 (s,
3H). 13C NMR (CDCl3, d ppm): 147.2 (C-11), 139.9 (C-13), 137.8 (C-23), 137.7
(C-17), 136.5 (C-14), 129.0 (C-12), 128.0–128.7 (C-18 to C-22), 126.6 (C-20), 126.5
(C-26), 89.7 (C-3), 84.8 (C-2) 60.2 (C-1), 52.5 (C-4), 51.8 (C-8), 51.1 (C-7), 38.5

2312
M. F. N. N. CARVALHO, A. S. D. FERREIRA, AND R. HERRMAN
Figure 3. NMR labeling for compound 7.
(C-16), 35.9 (C-15), 27.1 (C-6), 24.7 (C-5), 22.7 (C-9), 22.2 (C-10). For numbering of
the carbon atoms, see Fig. 3.
(2S,3aS,6S)-9-Benzyl-5,6-dihydro-11,11-dimethyl-10-phenylacetyl-
3H-3a,6-methano-1H-cyclonon[c]isothiazol-7(4H)-one 2-Oxide (7)
A solution of 3a (0.19 g, 0.42 mmol) and [PtCl2(EtCN)2] (0.070 g, 0.19 mmol) in
toluene (15 cm3) were stirred overnight. The solvent was then completely evaporated,
and the dark red oily solid was extracted with Et2O (15 cm3). The solution was con-
centrated (ca. 5 cm3), and n-pentane was added (15 cm3). Compound 7 precipitated as
a white solid (0.035 g; 0.073 mmol), yield 17%. Elemental analysis (%) for
(C28H29NO3S) ꢀ 5=4H2O: found: C, 68.9; N, 2.9; H, 6.4; S, 6.8. Calculated: C, 68.9;
N, 2.9; H, 6.5; S, 6.6 (m=z, 460). IR (cmꢂ1): 1688 (nCO), 1624 (nC¼C), 1495 (nring),
1
1057 (nSO). H NMR (C6D6, d ppm): 12.17 (s, 1H), 7.6–6.8 (m, 10 H), 5.77 (s, 1H),
4.02, 3.64 (d, 13.8, 2H), 3.28, 3.02 (d, 15.5, 2H), 2.53, 1.85 (d, 14.1, 2H), 2.19 (d,
6.5, 1H), 1.9-0.9 (m, 4H), 1.28 (s, 3H), 0.78 (s, 3H). 13C NMR (C6D6, d ppm):
207.4 (C-3), 200.8 (C-12), 162.9 (C-2), 137.5 (C-14), 132.5 (C-13), 137.9, 135.9 (C7
and C23), 130.1–127.2 (CH, Ph), 108.1 (C-11), 66.8 (C-4), 61.3 (C-1), 59.2 (C-8),
47.7 (C-7), 47.1, 47.0 (C-15 and C-16), 34.2, 24.8 (C-5 and C-6), 28.5, 21.6 (C-9
and C-10). The numbering of the carbon atoms is shown in Fig. 3.
[PdCl(L)Et3N] (8)
PdCl2 (0.079 g; 0.44 mmol) plus compound 2 (0.32 g; 0.92 mmol) and Et3N
(0.26 cm3, 1.8 mmol) were mixed in CH2Cl2 (40 cm3) stirred for 9 days at rt. The dark
precipitate formed was filtered off, washed with Et2O, and dried under vacuum
(0.20 g; 0.31 mmol, yield 70%). Elemental analysis (%) for [PdCl(C18H18NO3-
S)Et3N] ꢀ Et2O: Found: C, 51.3; N, 6.4; H, 5.5; S, 5.0. Calculated: C, 51.0; N, 6.4;
H, 5.9; S, 4.9. IR (cmꢂ1): 3243 (nNH), 2203 (nCC), 1748 (nCO), 1674, (nCN), 1596
(nCCring), 1339 (nSO2asym), 1152 (nSO2sym). NMR: not sufficiently soluble.
ACKNOWLEDGMENTS
ˆ
FCT-Fundac¸a˜o para a Ciencia e Tecnologia (PEst-OE=QUI=UI0100=2011)
and the NMR Network are greatfully acknowledged for financial support and
facilities access, respectively.

RING MODIFICATIONS IN CAMPHORIMINES
2313
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