Solvent effect on the reactivity of 1,10-phenanthroline-5,6-dione towards diazomethane

Article abstract of DOI:10.1016/S0040-4020(01)00122-3

In an aprotic medium, such as THF, Et₂O or CH₂Cl₂, the reaction of 1,10-phenanthroline-5,6-dione with diazomethane gave 5,6-methylenedioxy-1,10-phenanthroline as the only product. In contrast, in a protic solvent, such as 2-propanol or ethanol, the nucleophilic attack of CH₂N₂ occurred on carbonyl carbons, resulting in the formation of dispiro[5,6-dihydro-1,10-phenanthroline-5,6-dioxirane] as the main product. When the reaction with CH₂N₂ was carried out in methanol, the only product which could be isolated from the reaction mixture, dimethyl 2,2′-bipyridine-3,3′-dicarboxylate, resulted from a break of the C(5)-C(6) bridge.

Full text of DOI:10.1016/S0040-4020(01)00122-3

TETRAHEDRON
Pergamon
Tetrahedron 57 (2001) 2799±2805
Solvent effect on the reactivity of 1,10-phenanthroline-5,6-dione
towards diazomethane
Wiesøaw Z. Antkowiakp and Adam Sobczak
Â
Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
Received 10 November 2000; revised 21 December 2000; accepted 18 January 2001
AbstractÐIn an aprotic medium, such as THF, Et2O or CH2Cl2, the reaction of 1,10-phenanthroline-5,6-dione with diazomethane gave
5,6-methylenedioxy-1,10-phenanthroline as the only product. In contrast, in a protic solvent, such as 2-propanol or ethanol, the nucleophilic
attack of CH2N2 occurred on carbonyl carbons, resulting in the formation of dispiro[5,6-dihydro-1,10-phenanthroline-5,6-dioxirane] as the
main product. When the reaction with CH2N2 was carried out in methanol, the only product which could be isolated from the reaction
mixture, dimethyl 2,20-bipyridine-3,30-dicarboxylate, resulted from a break of the C(5)±C(6) bridge. q 2001 Elsevier Science Ltd. All rights
reserved.
1. Introduction
1, as we found later on, the homocyclic quinone gave a
spiro-oxirane derivative in an aprotic solvent, while in
methanol it is transformed into a product of the enlarged
middle ring to a seven-membered one.6,7
1,10-Phenanthroline and a number of its derivatives, sub-
stituted mainly at the 2,9, the 4,7 or the 5,6 positions, play an
important role in complex chemistry because of their unique
properties as chelating agents.1,2,3 1,10-Phenanthroline-5,6-
dione (1) is of particular interest, since two nucleophilic
centers (nitrogen and oxygen lone pairs) are composed in
a molecule of such a quinone, with all the atoms, except
hydrogens, being of sp2 hybridization.4 The presence of two
electronegative heteroatoms creates not only the basic prop-
erties in the Lewis sense but also, because of the resonance
conjugation, make it possible to alter the electron density in
different parts of the molecule, especially by the interaction
of an external electrophile with the unshared pairs of elec-
trons of the heteroatom. As a consequence, a dramatic
change in reactivity can occur, which is not observed
in the case of the corresponding aromatic homocyclic
analogue, phenanthrenequinone.5 This is also seen in the
reaction with CH2N2, in which, contrary to the heterocyclic
2. Results and discussion
We have found8 that 1,10-phenanthroline-5,6-dione (1),
when dissolved in THF and treated with diazomethane,
gave 5,6-methylenedioxy-1,10-phenanthroline (2) as the
only product (Scheme 1). Neither the formation of a product
of an enlarged dione ring6,9 by a methylene insertion via a
rearrangement of the preliminary diazomethane addition
intermediate, nor the formation of oxirane or dioxirane
derivatives was observed.
The formation of the 1,3-dioxolene ring in this reaction
resembled the result of a phenanthrolinequinone treat-
ment with an anion generated from 2-nitropropane10 or
Scheme 1.
Keywords: 1,10-phenanthroline; quinones; diazo compounds; solvents and solvent effects.
Corresponding author. Tel.: 148-61-829-13-18; fax: 148-61-865-80-08; e-mail: wzantk@amu.edu.pl
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(01)00122-3

2800
W. Z. Antkowiak, A. Sobczak / Tetrahedron 57 (2001) 2799±2805
nitroethane,11 in which either 5,6-isopropylidenedioxy-
1,10-phenanthroline or an ethylidene derivative, respect-
ively, was obtained. Our attempts to adopt this method in
the synthesis of 5,6-methylenedioxy-1,10-phenanthroline
by using nitromethane anion instead of nitropropane failed
and we were not able to ®nd the desired compound in the
product mixture. The formation of the 1,3-dioxolene system
by the treatment of quinones with diazomethane derivatives
had already been reported but with reference to 9,10-
phenanthrenedione and 4,7-phenanthroline-5,6-dione, and
in the reaction with diazoethane6 or phenyl- and diphenyl-
diazomethane,12 respectively. However, both the reaction
conditions leading to the dioxolene formation as well as
the stability of the resulting products towards hydrolytic
agents differed from those relating to 1,10-phenanthroline-
5,6-dione.
Scheme 2.
dimethyl 2,20-bipyridine-3,30-dicarboxylate (4). A similar
result, thought with a better yield of 4 (about 30%), was
obtained when 1 was treated with N-methyl-N-nitrosourea
in the presence of potassium carbonate in methanol follow-
ing the procedure described for 4,7-phenanthroline-5,6-
dione, which, however, led to the formation of
dispiro[5,6-dihydro-4,7-phenanthroline-5,6-dioxirane].14
In an aprotic solvent, the unsolvated carbonyl oxygens are
exposed to the diazomethane attack, but, because of the
conjugated system of both carbonyls, the nucleophilic attack
is preferred with a consequent shift of p electrons towards
the second oxygen and enolate anion formation; the
intermediate product of addition then underwent an
intramolecular cyclization with a simultaneous loss of a
nitrogen molecule.
Unexpectedly, the use of methanol instead of a higher
alcoholic homologue caused a change in the course of the
reaction, leading mainly to the formation of dimethyl 2,20-
bipyridine-3,30-dicarboxylate (4). It seems most probable
that, in this case, the small methanol molecules not only
solvate the oxygen, but also act effectively as nucleophiles
attacking carbon faster than those of diazomethane. As a
result, a hemiacetal or even a double full acetal is formed.
When the bridge carbons gained the sp3 hybridization, it is
most probable that, partly at least because of the crowded-
ness, a rearrangement occurs with a simultaneous reduction
of diazomethane at the expense of the C(5)±C(6) bridge elec-
trons (Scheme 3). Actually, the exact mechanism of this trans-
formation is not yet proved and the observations are dif®cult
to interpret without further experimental evidence.
When 1,10-phenanthrolinequinone was dissolved in 2-
propanol (or ethanol, but the results in such a case were
less satisfying) and treated with an ethereal solution of
diazomethane, the reaction occurred differently, yielding
dispiro[5,6-dihydro-1,10-phenanthroline-5,6-dioxirane] (3)
as the main product. In the case of both dioxolene 2 as
well as dispirodioxirane 3, the structure suggestions which
were based on the spectral data were con®rmed by an X-ray
analysis.13
Protic solvents change the environmental situation of the
quinone molecule, because of the solvation ability of
heteroatoms by hydrogen bonding. While the carbonyl
oxygen is shielded by the rather bulky isopropyl alcohol
molecules, the carbonyl carbon is the atom most sensitive
to a nucleophilic attack and, in the competition between the
alcohol and diazomethane molecules, it appeared that the
latter was more effective. As a result, dispirodioxirane 3 is
formed by the mechanism generally accepted for similar
reactions (Scheme 2).
Contrary to the reactivity, which is characteristic for acetals,
of 1,3-dioxolene derived from 9,10-phenanthrenedione12 or
other quinone systems reported in the literature, 5,6-methyl-
enedioxy-1,10-phenanthroline was found to be extremely
resistant to hydrolysis by aqueous acids, even when kept
in 40% HBr´aq at 908C for 1 h. The removal of the protect-
ing methylene group was only possible by an oxidative
treatment with bromine, which yielded 1,10-phenanthro-
line-5,6-dione. The enhanced stability revealed by the acetal
in an acidic medium is probably the result of the intra-
molecular electron density shift towards the electron-with-
drawing protonated nitrogen, which makes the oxygen less
nucleophilic and, thus, less sensitive to protonation (Scheme
4, in which the participation of only one nitrogen is shown
for simplicity).
However, when, as a solvent for 1, methanol was used
instead of a higher homologue, the post-reaction mixture
composition differed dramatically and the only product,
which could be isolated in a fair yield, had the structure of
Scheme 3.

W. Z. Antkowiak, A. Sobczak / Tetrahedron 57 (2001) 2799±2805
2801
Scheme 4.
Scheme 5.
The non-reactivity of the dioxolene system changed dramati-
cally when 5,6-methylenedioxy-1,10-phenanthroline was
subjected to a catalytic hydrogenation in the presence of
Adams' catalyst, as a result of which 1,2,3,4-tetrahydro-
The acetylation of 1,2,3,4-tetrahydro-5,6-methylenedioxy-
1,10-phenanthroline (5) to 6 causes the nitrogen electrons
to be more tightly bound to the amide system and, thus, less
available for the intramolecular long distance assistance by
resonance in hydrolysis, accompanied by oxidation
(Scheme 5). The planarity of both the acetamide group
itself, because of the partly C±N double bond character of
the resonance amide structure (1639 cm21), as well as of its
arrangement with the aromatic fragment of the molecule
[though unfavourable due to the steric (CH3, N-10) or
dipole±dipole (CvO, N-10) repulsion], can be concluded
from the molecular model analysis and the NMR data. The
chemical shift of pseudo-axial and pseudo-equatorial
protons located in the C-2 position, close to the amide nitro-
gen, revealed a distinct difference (up to 1.81 ppm), which
shows the different magnetic environment of both hydro-
gens as a result of a different anisotropic interaction caused
mainly by the acetyl group [for H(3p-e)-H(3p-a), being in a
similar relationship to the aromatic system Dˆ0.35 ppm].
Such a conformation makes it possible to withdraw the
electrons effectively by the resonance from the acetal
region. It seems very likely that, because of similar reasons,
this time caused by an additional protonation of nitrogens,
no accelerating effect of the reaction rate was observed
when 5 was attempted to be hydrolysed in aqueous acid.
²
5,6-methylenedioxy-1,10-phenanthroline (5) was obtained.
The resulting tetrahydro derivative, by immediate treatment
with acetic anhydride and storing the reaction mixture over-
night at room temperature, was easily transformed into a
stable 1-acetyl-1,2,3,4-tetrahydro-5,6-methylenedioxy-
1,10-phenanthroline (6).
However, when the parent free amine 5 was stored for a few
hours, either in a neat state or in a polar solvent, such as
chloroform (most likely by the contribution of a trace of
moisture), it changed spontaneously into 1,2,3,4-tetra-
hydro-1,10-phenanthrolino-5,6-dione (7). The regeneration
of the quinone system resembles the deprotection of 2 by
bromine, but this time it occurred at the expense of the
internal fragment, which had been derived from CH2N2,
instead of the external reagent. This transformation was
not stimulated by acids or bases.
These observations, as shown in Scheme 5, can be inter-
preted as being the result of a change in the intramolecular
availability of electrons in different parts of the molecule, by
long-distance nucleophilic assistance exerted by the nitro-
gen's unshared pair of electrons via the p electron system.
To prove the structure of dispirodioxirane 3 obtained by the
diazomethane treatment of phenanthrolinequinone in
2-propanol, the dioxirane derivative, as shown in Scheme
6, was subjected to a reduction by LiAlH4, which yielded
5,6-dihydro-5,6-dihydroxy-5,6-dimethyl-1,10-phenanthro-
line (8). The product was then oxidized, ®rst by Pb(OAc)4 to
3,30-diacetyl-2,20-bipyridine (9) and, next, by MCPBA to
²
In similar conditions, the hydrogenation of 1,10-phenanthroline, in the
presence of PtO2, gave, in good yield, the corresponding 1,2,3,4-tetrahy-
dro derivative as the only product, the physical properties of which were
identical with those reported for that compound synthesized by different
methods.15,16

2802
W. Z. Antkowiak, A. Sobczak / Tetrahedron 57 (2001) 2799±2805
Scheme 6.
3,30-diacetyl-2,20-bipyridine 1,10-dioxide (10). The struc-
tures of all these products were proved by spectroscopic
data.
H-10), 8.38 (2H, dd, Jˆ8.2, 1.9 Hz, H-4 and H-7), 7.82
(2H, dd, Jˆ8.2, 4.4 Hz, H-3 and H-8), 6.47 (2H, s, CH2);
1H NMR (CD2Cl2) d: 9.04 (2H, dd, Jˆ4.3, 1.8 Hz, H-2 and
H-9), 8.27 (2H, dd, Jˆ8.3, 1.8 Hz, H-4 and H-7), 7.64 (2H,
dd, Jˆ8.3, 4.3 Hz, H-3 and H-8), 6.34 (2H, s, CH2); 13C NMR
(CD2Cl2) d: 148.32 (C-2 and C-9), 142.97 (C-5 and C-6),
137.35 (C-10a and C-10b), 127.93 (C-4 and C-7), 123.09
(C-3 and C-8), 118.24 (C-4a and C-6a), 103.27 (CH2); MS:
224 (100%, M1), 196 (7%), 168 (10%), 166 (29%), 139
(15%), 112 (13%); HRMS for M1, C13H8N2O2, calcd:
224.0586, found: 224.0571; for (M228), C12H8N2O, calcd:
196.0637, found: 196.0647.
3. Experimental
3.1. General
Melting points were determined by a hot plate method (only
occasionally a BuÈchi 535 capillary apparatus was used) and
are uncorrected. 1H and 13C NMR spectra were recorded on
a VARIAN GEMINI 300 spectrometer. The chemical shift
values are in ppm measured from TMS as a standard.
Proton and carbon assignments were based on COSY and
HETCOR experiments. IR spectra were measured on an FT-
IR BRUKER IFS 113v instrument for KBr discs. MS spec-
tral data were obtained on an AMD 402 mass spectrometer.
3.1.2. Dispiro[5,6-dihydro-1,10-phenanthroline-5,6-
dioxirane] (3). To a suspension of 1,10-phenanthroline-
5,6-dione (1, 100 mg, 0.48 mmol) in 50 mL of anhydrous
isopropyl alcohol was added a solution of diazomethane in
diethyl ether (25 mL) obtained from 550 mg (5.34 mmol) of
N-methyl-N-nitrosourea. Stirring at room temperature was
continued overnight and then the resulting clear solution
was concentrated under diminished pressure yielding
133 mg of crude residue, which, according to the TLC
pattern, was composed of a main product, Rf 0.7, accom-
panied by two others, Rf 0.5 and 0.6, respectively. The main
product 3 was obtained in a pure state (65 mg, 57%) by
chromatography on SiO2, when the column was washed
with an AcOEt±benzene (4:1) mixture; the colourless
solid product did not melt when heated up to 3608C. IR
(cm21): 3071, 2992, 1578, 1561, 1421, 949, 895, 853,
TLC analyses were carried out using MERCK DC-Alu-
folien, Kieselgel 60 WF254s and AcOEt±iPrOH±conc.
NH3´aq. (8:4:1) or AcOEt±MeOH (7:3) as a developing
system. Column chromatography was carried out using
MERCK Kieselgel 60 (230±400 mesh) as the stationary
phase, while hexane, benzene, AcOEt, CH2Cl2, CHCl3 and
5% MeOH in CHCl3 were the eluting solvents.
3.1.1. 5,6-Methylenedioxy-1,10-phenanthroline (2). A stir-
red solution of 1,10-phenanthroline-5,6-dione3 (1, 226 mg,
1.08 mmol) in 60 mL of anhydrous tetrahydrofuran was
treated with an ethereal solution of diazomethane prepared
from N-methyl-N-nitrosourea (2.315 g, 22.48 mmol) in
80 mL of diethyl ether. The yellow solution was stirred at
room temperature overnight and, next, the resulting non-
homogeneous reaction mixture was concentrated under
diminished pressure yielding 234 mg (97%) of a solid residue,
which contained almost pure 2 of Rf 0.7. The crude product,
when recrystallized from methanol, gave as a ®rst crop
108 mg (45%) of bright yellow needles melting at 274±
2768C, while the recrystallization of an analytical sample
from anhydrous ethanol furnished thin plates of mp 280±
2818C. IR (cm21): 3022, 1661, 1590, 1550, 1515, 1460,
1398, 1365, 1302, 1136, 1065, 1027, 965, 795, 733, 622; 1H
NMR (DMSO) d: 9.05 (2H, dd, Jˆ4.4, 1.9 Hz, H-2 and
1
805, 744, 607; H NMR (CDCl3) d: 8.82 (2H, dd, Jˆ4.7,
1.6 Hz, H-2 and H-9), 7.65 (2H, dd, Jˆ8.0, 1.6 Hz, H-4 and
H-7), 7.37 (2H, dd, Jˆ8.0, 4.7 Hz, H-3 and H-8), 3.42 (2H,
d, Jˆ6.3 Hz, CH2), 2.73 (2H, d, Jˆ6.3 Hz, CH2); 13C NMR
(CDCl3) d: 151.09 (C-10a and C-10b), 150.38 (C-2 and C-
9), 131.22 (C-4 and C-7), 130.83 (C-4a and C-6a), 124.38
(C-3 and C-8), 56.77 (CH2), 55.1 (C-5 and C-6); MS: 238
(M1, 41%), 220 (70%), 208 (68%), 193 (69%), 180 (100%),
164 (18%), 154 (20%), 44 (23%); HRMS for M1,
C14H10N2O2, calcd: 238.0742, found: 238.0754.
3.1.3. Dimethyl 2,20-bipyridine-3,30-dicarboxylate (4)
from 1. A suspension of 1,10-phenanthroline-5,6-dione (1,
500 mg, 2.38 mmol) in 60 mL of anhydrous methanol, when
stirred in a 2-propanol/solid CO2 bath, was supplied with a

W. Z. Antkowiak, A. Sobczak / Tetrahedron 57 (2001) 2799±2805
2803
precooled down to 2758C diethyl ether solution
of diazomethane prepared from 2.6 g (25.24 mmol) of N-
methyl-N-nitrosourea. Stirring at that temperature was
continued for a further 15 min, then the cooling bath was
removed, and the reaction mixture was ®rst allowed to
reach room temperature overnight and, next, concentrated
under diminished pressure. The resulting brown oil
(656 mg) was composed, according to the TLC pattern, of
three compounds from which one revealed Rf 0.6, that
resembled the value of the starting quinone. From a silica
gel column, using an AcOEt±benzene (4:1) mixture, was
eluted a homogeneous product 4 as colourless crystals
(64 mg, 10%) of Rf 0.7 and mp 153±1568C, which is
consistent with the lit.17,18 IR (cm21): 3004, 2954, 1718,
1582, 1561, 1454, 1434, 1415, 1309, 1300, 1216, 1135,
(11%); HRMS for M1, C13H12N2O2, calcd: 228.0899,
found: 228.0916, for (M215), C12H9N2O2, calcd:
213.0664, found: 213.0646; MIKES for M1: 213, 211,
200 for (M2CH3): 185.
The ®nal elution of the column by ethyl acetate gave a red
solid (25 mg, 13%), which was identi®ed as quinone 7.
3.1.6. 1-Acetyl-1,2,3,4-tetrahydro-5,6-methylenedioxy-
1,10-phenanthroline (6). A yellow solution of 1,2,3,4-
tetrahydro-5,6-methylenedioxy-1,10-phenanthroline (5,
33 mg, 0.14 mmol) in 1 mL of acetic anhydride was left
overnight at ambient temperature which caused a change
of the colour to red. After an addition of 20 mL of water,
the reaction mixture was ®rst neutralized by solid NaHCO3
and then extracted with CH2Cl2 (3£10 mL). The organic
layer was dried over Na2SO4 and concentrated. From the
red oily residue, the pure amide 6 was obtained in the
form of a solidifying oil (27 mg, 69%) by puri®cation
over a silica gel (0.5 g) column when 30% AcOEt in PhH
was used as eluant. Mp 180±1818C. IR (cm21): 3080, 3006,
2956, 2933, 2901, 1639, 1461, 1420, 1382, 1374, 1329,
1
1053, 961, 766; H NMR (CDCl3) d: 8.78 (2H, dd, Jˆ4.7,
1.6 Hz, H-6 and H-60), 8.37 (2H, dd, Jˆ8.0, 1.6 Hz, H-4 and
H-40), 7.45 (2H, dd, Jˆ8.0, 4.7 Hz, H-5 and H-50), 3.69 (6H,
s, 2£CH3); 13C NMR (CDCl3) d: 165.86 (CO), 159.29 (C-2
and C-20), 151.52 (C-6 and C-60), 138.08 (C-4 and C-40),
125.25 (C-3 and C-30), 122.62 (C-5 and C-50), 52.27
(2£CH3); MS: 272 (9%, M1), 257 (9%), 241 (100%), 213
(17%), 199 (11%), 182 (7%), 170 (8%); HRMS for M1,
C14H12N2O4, calcd: 272.0797, found: 272.0782.
1
1282, 1211, 1068, 1032, 999, 809, 786; H NMR (CDCl3)
d: 8.78 (1H, dd, Jˆ4.1, 1.9 Hz, H-9), 8.13 (1H, dd, Jˆ8.5,
1.9 Hz, H-7), 7.32 (1H, dd, Jˆ8.5, 4.1 Hz, H-8), 6.22 (2H, d,
Jˆ3.3 Hz, CH2), 4.86 (1H, m, H-2), 3.05 (1H, m, H-2), 3.00
(1H, m H-4), 2.74 (1H, m, H-4), 2.28 (1H, m, H-3), 1.93
(1H, m, H-3), 1.92 (3H, s, CH3); 13C NMR (CDCl3) d:
172.29 (CO), 148.01 (C-9), 141.42, 138.14, 137.77,
131.85, 128.26 (C-7), 120.63, 120.46 (C-8), 113.48,
102.39 (CH2), 42.86 (C-2), 23.46 (CH3), 23.39 (C-3),
20.76 (C-4); MS: 270 (30%, M1), 228 (100%), 213
(12%), 211 (9%), 199 (16%), 185 (4%), 170 (10%), 142
(20%), 115 (6%); HRMS for M1, C15H14N2O3, calcd:
270.1004, found: 270.0989, for (M242), C13H12N2O2,
calcd: 228.0899, found: 228.0896.
3.1.4. Oxidative hydrolysis of 2 by bromine. A stirred
solution of 5,6-methylenedioxy-1,10-phenanthroline (2,
29 mg, 0.12 mmol) in 1 mL of glacial acetic acid was
supplied with 0.02 mL of bromine which caused an immedi-
ate separation of an orange precipitate. The subsequent
addition of water (10 mL) gave a homogeneous solution
from which the product was isolated by extraction with
CH2Cl2 (3£10 mL). The organic layer, when dried over
anhydrous Na2SO4 and concentrated, yielded 25 mg (92%)
of pure 1,10-phenanthroline-5,6-dione (1). A trace of a
further amount of the quinone was additionally recovered
when the remaining aqueous layer was neutralized by means
of solid NaHCO3 and, next, re-extracted with CH2Cl2.
3.1.7. 1,2,3,4-Tetrahydro-1,10-phenanthroline-5,6-dione
(7). A solution of 1,2,3,4-tetrahydro-5,6-methylenedioxy-
1,10-phenanthroline (5, 37 mg) in 20 mL of CHCl3 was
supplied with 1 g of silica gel (Kieselgel 60) and the suspen-
sion was stirred for 6 days, which caused a change of its
colour to brown, but, according to TLC, no signi®cant
progress of the reaction occurred. Next, 5 drops of water
were added and stirring was continued for a further 3 days,
after which a completion of the reaction was checked by
TLC (developed by AcOEt±MeOH, 7:3), according to
which the product of Rf 0.6 was only contaminated by a
trace of the starting material. The reaction mixture, when
supplied with 20 mL of 5% methanol in CH2Cl2, was
®ltered through a thin layer of SiO2 and concentrated
under diminished pressure yielding a red solid of 7
(31 mg, 89%), not melting up to 2808C. IR (cm21): 3294,
3.1.5. 1,2,3,4-Tetrahydro-5,6-methylenedioxy-1,10-
phenanthroline (5). A solution of 5,6-methylenedioxy-
1,10-phenanthroline (2, 200 mg, 0.89 mmol) in 50 mL of
anhydrous methanol was supplied with 10 mg of PtO2
(Adams' catalyst) and the resulting suspension was shaken
at room temperature in a hydrogen atmosphere under
pressure of 0.055 MPa for 3 h. After removing the catalyst
by ®ltration, the resulting bright yellow solution (the colour
of which changed quickly to brown when kept in open air)
was concentrated yielding 185 mg of a brown oil. The crude
product was then subjected to column chromatography on
silica gel (4 g). The use of benzene as an eluting solvent
furnished a yellow solidifying oil of 5 (124 mg, 61%, Rf
0.9). IR (cm21): 3402 (br.), 2929, 2859, 1722, 1703, 1655,
1
1493, 1445, 1387, 1341, 1276, 1104, 1067, 970; H NMR
1
(CDCl3) d: 8.51 (1H, dd, Jˆ4.1, 1.6 Hz, H-9), 7.98 (1H, dd,
Jˆ8.5, 1.6 Hz, H-7), 7.25 (1H, dd, Jˆ8.5, 4.1 Hz, H-8), 6.04
(2H, s, CH2), 5.75 (1H, br., NH), 3.49 (2H, t, Jˆ5.5 Hz, H-
2), 2.85 (2H, t, Jˆ6.5 Hz, H-4), 2.07 (2H, m, H-3); 13C
NMR (CDCl3) d: 145.27 (C-9), 143.96, 138.67, 132.72,
129.47, 128.01 (C-7), 121.72 (C-8), 114.74, 103.97,
102.11 (CH2), 41.57 (C-2). 21.85 (C-3), 21.47 (C-4); MS:
228 (100%, M1), 213 (15%), 211 (12%), 199 (23%), 185
(8%), 170 (15%), 167 (8%), 149 (14%), 142 (37%), 115
2919, 2850, 1687, 1586, 1551, 1518, 1432, 1333, 1199; H
NMR (CDCl3) d: 8.70 (1H, dd, Jˆ4.9, 1.9 Hz, H-9), 8.33
(1H, dd, Jˆ8.0, 1.9 Hz, H-7), 7.60 (4.81 after D2O was
added, 1H, s, NH), 7.50 (1H, dd, Jˆ8.0, 4.9 Hz, H-8),
3.61 (2H, m, H-2), 2.72 (2H, t, Jˆ6.3 Hz, H-4), 2.00 (2H,
m, H-3); 13C NMR (CDCl3) d: 181.04 (C-5 or C-6), 173.14
(C-5 or C-6), 152.24 (C-9), 149.67, 147.83, 134.95 (C-7),
127.07, 125.47 (C-8), 109.77, 41.35 (C-2), 20.30 (C-3),
19.14 (C-4); MS: 214 (37%, M1), 186 (62%), 157,

2804
W. Z. Antkowiak, A. Sobczak / Tetrahedron 57 (2001) 2799±2805
(100%), 130 (34%); HRMS for M1, C12H10N2O2, calcd:
214.0742, found: 214.0749.
M11), 240 (0.1%, M1), 239 (0.5%), 226 (15%), 225
(100%), 197 (22%), 183 (46%), 168 (5%), 155 (6%), 141
(2%), 128 (5%), 101 (3%), 78 (5%), 51 (4%), 43 (30%);
HRMS for (M11), C14H13N2O2, calcd: 241.0977, found:
241.0963.
3.1.8. 5,6-Dihydro-5,6-dihydroxy-5,6-dimethyl-1,10-
phenanthroline (8). To a stirred solution of dispiro[5,6-
dihydro-1,10-phenanthroline-5,6-dioxirane] (3, 335 mg,
1.41 mmol) in 10 mL of CH2Cl2 was added 175 mg of
LiAlH4 and then the resulting suspension was diluted with
10 mL of anhydrous THF, which caused a vigorous reaction
and a change of the colour to brown. After storing the
suspension overnight, while kept in an ice-bath, it was trea-
ted with 5 mL of water and, next, the organic solvents were
removed under diminished pressure. The residue was
extracted with a CH2Cl2/CHCl3 mixture (3£75 mL) and
the obtained solution was ®rst dried over Na2SO4 and then
concentrated, yielding 126 mg of a light brown residue. The
crude product was puri®ed by column chromatography on
silica gel using 3±6% of MeOH in CHCl3 as the eluant,
which yielded 94 mg (28%) of a slightly coloured solid of
8. An analytically pure sample, in the form of a colourless
material not melting up to 2808C, was prepared by treating
the chromatographically puri®ed product with a small
amount of methanol followed by decantation. IR (cm21):
3250 (br.), 2986, 2931, 1582, 1564, 1419, 1210, 1069,
3.1.10. 3,30-Diacetyl-2-20-bipyridine 1,10-dioxide (10). To
a solution of 3,30-diacetyl-2,20-bipyridine (9, 38 mg,
0.16 mmol) in 3 mL of CH2Cl2, while stirred and kept in
a cooling bath (iPrOH/solid CO2), a commercial 85%
3-chloroperoxybenzoic acid (250 mg, 1.23 mmol) dissolved
in 5 mL of CH2Cl2 was added. Stirring at 2758C was
continued for 1 h and then the reaction mixture was
allowed to reach the room temperature overnight. The
resulting solution was introduced on 1 g of silica gel and
the column was washed, ®rst, with CH2Cl2 by which almost
all of the m-chlorobenzoic acid was removed. By using 3%
MeOH in CHCl3, almost pure 10 was obtained, the
rechromatography of which gave 41 mg (95%) of a colour-
less solid not melting up to 3708C (Rf 0.2 when AcOEt±
MeOH 7:3 was used as a developing phase). IR (cm21):
3088, 2927, 1693, 1420, 1368, 1295, 1248, 1189, 1015,
1
917, 903, 801, 721; H NMR (CDCl31CD3OD) d: 8.38
(2H, dd, Jˆ6.6, 1.1 Hz, H-6 and H-60), 7.89 (2H, dd,
Jˆ8.0, 1.1 Hz, H-4 and H-40), 7.58 (2H, dd, Jˆ8.0,
6.6 Hz, H-5 and H-50), 2.60 (6H, s, 2£CH3); 13C NMR
(CDCl31CD3OD) d: 195.47 (2£CO), 141.35 (C-6 and C-
60), 141.19 (C-2 and C-20), 136.81 (C-3 and C-30), 126.86
(C-4 and C-40), 125.92 (C-5 and C-50), 26.72 (2£CH3); MS:
273 (1%, M11), 272 (5%, M1), 257 (3%), 241 (10%), 230
(12%), 229 (86%), 226 (15%), 225 (100%), 214 (11%), 213
(72%), 197 (36%), 194 (19%), 183 (69%), 171 (74%), 168
(20%), 155 (16%), 143 (26%), 131 (13%), 128 (15%), 120
(9%), 116 (18%), 78 (25%), 51 (21%); HRMS for M1,
C14H12N2O4, calcd: 272.0797, found: 272.0783.
1
1043, 955, 812, 752; H NMR (DMSO) d: 8.58 (2H, dd,
Jˆ4.7, 1.6 Hz, H-2 and H-9), 8.03 (2H, dd, Jˆ7.8, 1.6 Hz,
H-4 and H-7), 7.43 (2H, dd, Jˆ7.8, 4.7 Hz, H-3 and H-8),
5.46 (2H, s, OH, exchangeable with D2O), 1.18 (6H, s,
2£CH3); 1H NMR (CDCl31CD3OD) d: 8.63 (2H, dd,
Jˆ4.5, 1.8 Hz, H-2 and H-9), 8.13 (2H, dd Jˆ7.7, 1.8 Hz,
H-4 and H-7), 7.42 (2H, dd, Jˆ7.7, 4.5 Hz, H-3 and H-8),
4.72 (s, OH), 1.35 (6H, s, 2£CH3): 13C NMR
(CDCl31CD3OD) d: 147.94 (C-10a and C-10b), 147.85
(C-2 and C-9), 140.34 (C-4a and C-6a), 132.51 (C-4 and
C-7), 124.10 (C-3 and C-8), 75.88 (C-5 and C-6), 23.88
(2£CH3); MS: 242 (M1, 30%), 225 (100%), 209 (7%),
207 (7%), 199 (54%), 181 (26%), 157 (16%), 122 (26%);
HRMS for M1, C14H14N2O2, calcd: 242.1055, found:
242.1039.0.
3.1.11. 5,6-Isopropylenedioxy-1,10-phenanthroline.
When the reaction of quinone 1 with 2-nitropropane anion
was carried out by us following the literature procedure,10 it
appeared that the reaction was already complete at room
temperature and after 15 min (instead of 608C and 24 h);
the product obtained in almost quantitative yield (instead
of 67%), when recrystallized from ethyl ether, gave yellow
needles of mp 160±1658C (hot plate method), 158±1608C
(capillary method) (lit.10 140±1438C), revealing identical
spectral properties with those already reported.10
3.1.9. 3,30-Diacetyl-2,20-bipyridine (9). A solution of 5,6-
dihydro-5,6-dihydroxy-5,6-dimethyl-1,10-phenanthroline
(8, 139 mg, 0.57 mmol) in 4 mL of glacial AcOH when
stirred was supplied with Pb(OAc)4 (279 mg, 0.63 mmol).
When stirred for 3 h, the resulting turbid solution, according
to TLC, contained none of the starting material, but, instead,
only one product of Rf 0.7. After storing overnight, the
reaction mixture was diluted with 10 mL of H2O, then
neutralized by solid NaHCO3 and, ®nally, extracted with
CH2Cl2 (3£30 mL). The organic layer, when dried over
Na2SO4 and concentrated, gave 158 mg of a pale brown
residue, which was puri®ed by a silica gel (3 g) column,
from which, using 30±60% AcOEt in PhH as an eluant,
118 mg (86%) of colourless crystals of 9 were obtained.
Mp 174±1768C. IR (cm21): 3363, 3061, 2967, 1693,
1579, 1553, 1409, 1354, 1277, 1253, 1208, 1106, 1046,
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1
974, 817, 749, 637; H NMR (CDCl3) d: 8.66 (2H, dd,
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1.6 Hz, H-4 and H-40), 7.41 (2H, dd, Jˆ8.0, 4.7 Hz, H-5
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C-60), 136.26 (C-3 and C-30), 135.84 (C-4 and C-40),
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be diminished to such an extent that the compound was not

W. Z. Antkowiak, A. Sobczak / Tetrahedron 57 (2001) 2799±2805
2805
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