Maleic acid derivatives in the synthesis of 3-substituted 3,4-dihydroquinoxalin-2(1H)-ones

Article abstract of DOI:10.1007/s11172-014-0407-z

A process for preparing 3-substituted 3,4-dihydroquinoxalin-2(1H)-ones is proposed. It is based on the reaction of o-phenylenediamine with amides, di- and mono-esters of maleic acid as well as (E)-3-(5-phenyl-1,3,4-oxadiazol-2-yl) acrylic acid in the pres

Full text of DOI:10.1007/s11172-014-0407-z

Russian Chemical Bulletin, International Edition, Vol. 63, No. 1, pp. 137—140, January, 2014
137
Maleic acid derivatives in the synthesis of 3ꢀsubstituted
3,4ꢀdihydroquinoxalinꢀ2(1H)ꢀones*
S. S. Rozhkov, K. L. Ovchinnikov, and A. V. Kolobov
Yaroslavl State Technical University,
88 Moskovsky prosp., 150023 Yaroslavl, Russian Federation.
Fax: (4852) 44 1360. E ꢀmail: serg_rozhkov@mail.ru
A process for preparing 3ꢀsubstituted 3,4ꢀdihydroquinoxalinꢀ2(1H)ꢀones is proposed. It is
based on the reaction of oꢀphenylenediamine with amides, diꢀ and monoꢀesters of maleic acid
as well as (E)ꢀ3ꢀ(5ꢀphenylꢀ1,3,4ꢀoxadiazolꢀ2ꢀyl)acrylic acid in the presence of N,N´ꢀcarbonylꢀ
diimidazole.
Key words: Michael reaction, 3,4ꢀdihydroquinoxalinꢀ2(1H)ꢀone, maleimide, maleic acid
monoamide, oꢀphenylenediamine.
Scheme 1
Compounds containing dihydroquinoxalinꢀ2(1H)ꢀone
fragment are widely used in a number of scientific and
technical areas. They have antibacterial,1 antimycotic,2
and antidepressant3 activities, antiphlogistic and analgeꢀ
sic action,4 they are used as dyes, electroluminescent maꢀ
terials, and organic semiconductors.5
Little attention is given to the synthesis of 3,4ꢀdihydroꢀ
quinoxalinꢀ2(1H)ꢀones with the use of maleic acid derivaꢀ
tives in the literature; however, their sulfurꢀ and oxygenꢀ
containing analogs are known to be obtained in high yields.
For instance, reaction of оꢀaminothiophenol or оꢀamiꢀ
nophenol with maleic anhydride leads to (3,4ꢀdihydroꢀ3ꢀ
oxoꢀ2Hꢀ1,4ꢀbenzothiazinꢀ2ꢀyl)acetic or (3,4ꢀdihydroꢀ3ꢀ
oxоꢀ2Hꢀ1,4ꢀbenzoxalinꢀ2ꢀyl)acetic acids (2a and 2b reꢀ
spectively)6 via the formation of corresponding intermeꢀ
diate 1a or 1b (Scheme 1).
Since оꢀphenylenediamine readily reacts with maleic
anhydride to give products of monoꢀ and diacylation,
Nꢀarylmaleimides 3 are used as substrates (Scheme 2). Apꢀ
parently, the reaction proceeds via the formation of subꢀ
stituted succinimide 4, which is then subjected to intramoꢀ
lecular acylation to afford arylamides of (1,2,3,4ꢀtetrahyꢀ
droꢀ2ꢀoxoquinoxalinꢀ3ꢀyl)acetic acid 5 in 72—80% yields
(see Refs 7 and 8).
It can be seen from the data mentioned above that the
ring formation in both cases includes different sequences
of acylation reaction and Michaelꢀtype Nꢀalkylation.
Maleic acid esters and amides are wellꢀknown as
Michael acceptors; however, there are no published exꢀ
amples of their use in 3,4ꢀdihydroquinoxalinꢀ2(1H)ꢀone
synthesis.
X = S (a), O (b)
Initially we tried to synthesize substituted 3,4ꢀdihydꢀ
roquinoxalinꢀ2(1H)ꢀones by the reaction between оꢀpheꢀ
nylenediamine and aromatic maleic acid monoamides,
namely, (Z)ꢀ4ꢀoxoꢀ4ꢀarylaminoꢀ2ꢀbutenoic acids 6,
which happen to be starting materials in the synthesis of
maleimides9 (Scheme 3). The reaction proceeds smoothly
at reflux in isopropyl alcohol with DMF additive for better
solubility. The yield of target 3,4ꢀdihydroquinoxalinꢀ
2(1H)ꢀones 7 was 55—72%.
This approach seems to be more convenient than the
one depicted in Scheme 2, because synthesis becomes one
stage shorter: formation of Nꢀarylmaleimides 3 from corꢀ
responding amides 6 is eliminated.
* According to data of cluster of conferences in organic chemistry
"OrgChemꢀ2013" (June 17—21, 2013, St. Petersburg, Repino).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 0137—0140, January, 2014.
1066ꢀ5285/14/6301ꢀ0137 © 2014 Springer Science+Business Media, Inc.

138
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 1, January, 2014
Rozhkov et al.
Scheme 2
R = H, 4ꢀMe, 4ꢀOMe, 4ꢀEt, 2ꢀCl, 2ꢀNO2
Scheme 3
R = H (a), Me (b), OMe (c), Cl (d), NO2 (e)
Since compounds structurally similar to maleic acid
monoamides have to behave in a similar way, monoethyl
and diethyl maleates and (E)ꢀ3ꢀ(5ꢀphenylꢀ1,3,4ꢀoxadiꢀ
azolꢀ2ꢀyl)acrylic acid were chosen as the starting materiꢀ
als for the synthesis of 3,4ꢀdihydroquinoxalinꢀ2(1H)ꢀone
derivatives. Common structural fragment for all mentioned
compounds is double bond conjugated with two electronꢀ
withdrawing substituents.
Ethyl (1,2,3,4ꢀtetrahydroꢀ2ꢀoxoquinoxalinꢀ3ꢀyl)acetꢀ
ate (9) was synthesized via the reaction of оꢀphenylenediꢀ
amine and monoethyl maleate 8. The reaction was carried
out at reflux in isopropyl alcohol for 1 h, the yield of
product was ~30% (Scheme 4). Replacement of PriOH by
water, which was offered for reactions with maleimides7
(see Scheme 2), or the use of diethyl maleate 10 in
Nꢀmethylpyrrolidone (NꢀMP) as the substrate did not lead
to any increase in product 9 yield. There are reported exꢀ
amples of ethyl (1,2,3,4ꢀtetrahydroꢀ2ꢀoxoquinoxalinꢀ3ꢀ
yl)acetate synthesis according to more complex twoꢀstage
routes.10,11
(E)ꢀ3ꢀ(5ꢀPhenylꢀ1,3,4ꢀoxadiazolꢀ2ꢀyl)acrylic acid 12
has been synthesized12 in two successive stages with the
isolation of intermediate (Z)ꢀ4ꢀ(N´ꢀbenzhydrazido)ꢀ4ꢀ
oxoꢀ2ꢀbutenoic acid 11. The first stage was acylation of
benzoic acid hydrazide by maleic anhydride in glacial aceꢀ
tic acid. Then intramolecular dehydration of resulting acid
11 in DMF induced by phosphoryl chloride took place
(Scheme 5). Formation of highly acidic medium during
Scheme 4
Scheme 5

Substituted 3,4ꢀdihydroquinoxalinꢀ2(1H)ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 1, January, 2014
139
(JSC Vekton), N,N´ꢀcarbonyldiimidazole (SigmaꢀAldrich Co.)
were used as starting materials. (Z)ꢀ4ꢀOxoꢀ4ꢀarylaminoꢀ2ꢀ
butenoic acids,14 diethyl15 and monoethyl16 esters of maleic acid
were synthesized according to literature procedures.
Synthesis of arylamides of (1,2,3,4ꢀtetrahydroꢀ2ꢀoxoquinoxꢀ
alinꢀ3ꢀyl) acetic acid (7a—e). (Z)ꢀ4ꢀOxoꢀ4ꢀarylaminoꢀ2ꢀbutenoic
acid 6 (0.024 mol) was dissolved at slight heating in a mixture of
isopropyl alcohol (30 mL) and DMF (2 mL). Then оꢀphenylenediꢀ
amine (2.83 g, 0.024 mol) was added and the solution was reꢀ
fluxed for 1 h. The reaction mixture was cooled and mixed with
200 mL of cold water. The resulting crystalline precipitate was
filtered off and washed with isopropyl alcohol.
NꢀPhenylꢀ(1,2,3,4ꢀtetrahydroꢀ2ꢀoxoquinoxalinꢀ3ꢀ yl)acetꢀ
amide (7a). The yield was 55%, m.p.. 218—221 C (see Ref. 7:
220—223 C). IR, /cm–1: 3386, 3349, 3275, 3144 (NH); 1669
(C=O); 1645 (C=O (IA)); 1604 (Ar); 1551 (C=O (IIA));
749, 690 (1,2ꢀ and monosubstituted Ar). 1H NMR : 2.59 (dd, 1 H,
СН2, J = 15.5 Hz, J = 8.0 Hz); 2.90 (dd, 1 H, СН2, J = 15.5 Hz,
J = 4.2 Hz); 4.24 (m, 1 H, СН); 5.93 (s, 1 H, NH); 6.61 (m, 1 H,
Ar); 6.76 (m, 3 H, Ar); 7.08 (t, 1 Н, Ar, J = 7.9); 7.30 (t, 2 H, Ar,
J = 7.6 Hz); 7.62 (d, 2 H, Ar, J = 7.7 Hz); 10.20 (s, 1 H, NHCO);
10.45 (s, 1 H, NHCO).
the last reaction, apparently, promotes configuration
change, and as a result only the more thermodynamically
stable Eꢀisomer is isolated. Moreover, similar (E)ꢀ3ꢀ(5ꢀarylꢀ
1,3,4ꢀoxadiazolꢀ2ꢀyl)acrylic acids can be obtained by the
reaction between 5ꢀaryltetrazoles and fumaryl chloride.13
Refluxing the mixture of (E)ꢀ3ꢀ(5ꢀphenylꢀ1,3,4ꢀoxaꢀ
diazolꢀ2ꢀyl)acrylic acid 12 and оꢀphenylenediamine in isoꢀ
propyl alcohol for 1 h led to resinification or reaction
mixture. The use of N,N´ꢀcarbonyldiimidazole (CDI) alꢀ
lowed us to successfully synthesize 3ꢀ[(5ꢀphenylꢀ1,3,4ꢀ
oxadiazolꢀ2ꢀyl)ꢀmethyl]ꢀ3,4ꢀdihidroquinoxalinꢀ2(1H)ꢀ
one (13), presumably, due to the replacement of the first
alkylation stage by acylation. The yield of the target prodꢀ
uct was 62% (Scheme 6).
Scheme 6
Nꢀ(pꢀTolyl)ꢀ(1,2,3,4ꢀtetrahydroꢀ2ꢀoxoquinoxalinꢀ3ꢀ yl)ꢀ
acetamide (7b). The yield was 62%, m.p.. 240—242 C (see Ref. 7:
251—253 C). IR, /cm–1: 3385, 3280, 3203, 3066 (NH); 1678
(C=O); 1649 (C=O (IA)); 1540 (C=O (IIA)); 1517 (Ar); 816
1
(1,4ꢀsubstituted Ar); 737 (1,2ꢀsubstituted Ar). H NMR : 2.30
(s, 3 H, СН3); 2.60 (dd, 1 H, СН2, J = 15.6 Hz, J = 8.5 Hz); 2.89
(dd, 1 H, СН2, J = 15.6 Hz, J = 4.8 Hz); 4.20 (m, 1 H, СН); 5.85
(s, 1 H, NH); 6.60 (m, 1 H, Ar); 6.74 (m, 3 H, Ar); 7.06, 7.46
(both d, each 2 H, Ar, J = 8.1 Hz); 9.85 (s, 1 H, NHCO); 10.20
(s, 1 H, NHCO).
Nꢀ(4ꢀMethoxyphenyl)ꢀ(1,2,3,4ꢀtetrahydroꢀ2ꢀoxoquinꢀ
oxalinꢀ3ꢀyl)acetamide (7c). The yield was 67%, m.p.. 209—211 C
(see Ref. 7: 212—215 °C). IR, /cm–1: 3380, 3328, 3260, 3069
(NH); 1682 (C=O); 1640 (C=O (IA)); 1547 (C=O (IIA)); 1513
(Ar); 1252, 1034 (C—O—C); 830 (1,4ꢀsubstituted Ar); 737
(1,2ꢀsubstituted Ar). 1H NMR : 2.59 (dd, 1 H, СН2, J = 15.2 Hz,
J = 7.9 Hz); 2.89 (dd, 1 H, СН2, J = 15.3 Hz, J = 4.1 Hz); 3.75
(s, 3 H, OMe); 4.19 (m, 1 H, СН); 5.9 (s, 1 H, NH); 6.58 (m, 1 H,
Ar); 6.71 (m, 3 H, Ar); 6.88, 7,54 (both d, each 2 H, Ar, J = 8.6 Hz);
9.78 (s, 1 H, NHCO); 10.22 (s, 1 H, NHCO).
Nꢀ(4ꢀChlorophenyl)ꢀ(1,2,3,4ꢀtetrahydroꢀ2ꢀoxoquinoxalinꢀ
3ꢀyl)acetamide (7d). The yield was 73%, m.p.. 225—227 C.
IR, /cm–1: 3386, 3350, 3272, 3069 (NH); 1680 (C=O); 1648
(C=O (IA)); 1545 (C=O (IIA)); 1511 (Ar); 836 (1,4ꢀsubstitutꢀ
ed Ar); 735 (1,2ꢀsubstituted Ar). 1H NMR : 2.62 (dd, 1 H, СН2,
J = 15.1 Hz, J = 7.8 Hz); 2.91 (dd, 1 H, СН2, J = 15.1 Hz,
J = 4.2 Hz); 4.23 (m, 1 H, СН); 6.01 (s, 1 H, NH); 6.62 (m, 1 H,
Ar); 6.75 (m, 3 H, Ar); 7.35, 7.65 (both d, each 2 H, Ar, J = 8.2 Hz);
10.17 (s, 1 H, NHCO); 10.33 (s, 1 H, NHCO). 13C NMR ():
38.5 (CH2); 52.4 (CH); 113.6, 114.6, 117.8, 120.5, 122.6, 125.7,
126.4, 128.3, 133.6, 137.83 (Ar); 166.2, 168.4 (C=O).
i. CDI, 1,4ꢀdioxane; ii.
, 101 C.
To sum up, we have investigated synthetic approaches
to 3ꢀsubstituted 3,4ꢀdihidroquinoxalinꢀ2(1H)ꢀones startꢀ
ing from maleic anhydride and aromatic оꢀdiamines. The
way to obtain 3ꢀsubstituted 3,4ꢀdihidroquinoxalinꢀ2(1H)ꢀ
ones is proposed, it is based on reaction of оꢀphenylenediꢀ
amine with amides, diꢀ and monoꢀesters of maleic acid as
well as with (E)ꢀ3ꢀ(5ꢀphenylꢀ1,3,4ꢀoxadiazolꢀ2ꢀyl)acrylic
acid in the presence of N,N´ꢀcarbonyldiimidazole.
Experimental
1
H и 13C NMR spectra were recorded on Bruker MSLꢀ300
and Bruker AMꢀ300 spectrometers, respectively, in solutions in
DMSOꢀd6. IR spectra were recorded on a Spectrum RX1 FTꢀIR
spectrometer in KBr plates as mineral oil mulls. Melting points
were determined on a NAGEMA PHMKꢀ05 instrument. Eleꢀ
mental analysis was performed on a Perkin Elmer Instruments
Series II CHNS/O Analyzer 2400. High resolution mass spectra
were obtained on a MicrOTOF II (Bruker Daltonics) instruꢀ
ment, using electrospray ionization (ESI). Commercially availꢀ
able оꢀphenylenediamine, maleic anhydride, benzhydrazide
Nꢀ(4ꢀ Nitrophenyl)ꢀ(1,2,3,4ꢀ tetrahydroꢀ 2ꢀ oxoquinꢀ
oxalinꢀ3ꢀ yl)acetamide (7e). The yield was 72%, m.p.. 227—230 C.
IR, /cm–1: 3389, 3355, 3278, 3070 (NH); 1687 (C=O); 1651
(C=O (IA)); 1599 (Ar); 1549 (C=O (IIA)); 1503, 1346 (NO2);
854, 735 (1,4ꢀ and 1,2ꢀsubstituted Ar). 1H NMR : 2.66 (dd, 1 H,
СН2, J = 15.6 Hz, J = 8.2 Hz); 2.98 (dd, 1 H, СН2, J = 15.6 Hz,
J = 4.3 Hz); 4.3 (m, 1 H, СН); 6.07 (s, 1 H, NH); 6.67 (m, 1 H,
Ar); 6.82 (m, 3 H, Ar); 7.87, 8.20 (both d, each 2 H, Ar, J = 8.5 Hz);
10.20 (s, 1 H, NHCO); 10.45 (s, 1 H, NHCO). 13C NMR ():

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Rozhkov et al.
39.0 (CH2); 52.5 (CH); 113.8, 114.8, 118.1, 118.8, 122.8, 124.9,
125.9, 133.9, 142.1, 145.2 (Ar); 166.7, 169.4 (C=O).
suspension. The gas started to evolve at approximately 50 C
heating, and it was followed with suspension dissolution. The
solution was heated for 30 min. Then оꢀphenylenediamine was
added and the mixture was refluxed for 2 h. After that, the reacꢀ
tion mixture was cooled and poured into water. The precipitate
formed was filtered off, washed with water and ethyl alcohol.
Recrystallization from ethyl alcohol was carried out for purificaꢀ
tion. The yield was 62%, m.p. 189—191 C. IR, /cm–1: 3338,
3203 (NH); 1667 (C=O (IA)); 1601 (Ar); 1548 (N—С=О (IIA));
1532 (C=N); 1277, 1127, 1032 (C—O—C); 749, 707, 688 (1,2ꢀ and
monosubstituted Ar). 1H NMR, : 2.84 (m, 2 Н, СН2); 5.30
(m, 1 Н, СН); 6.01 (s, 1 H, NH); 6.89 (m, 1 Н, Ar); 6.97
(m, 3 H, Ar); 7.62 (m, 3 Н, Ar); 7.95 (d, 2 H, Ar, J = 7.8 Hz);
9.69 (s, 1 H, NHCO). 13C NMR (): 37.6 (CH2); 53.7 (CH);
121.5, 121.8, 121.9, 123.3, 124.8, 126.5, 129.5, 129.6, 132.1,
137.6 (Ar), 164.1, 166.8, 169.8 (C—O—C, C=O). Found (%):
С, 66.18; Н, 4.34; N, 18.14. С17H14N4O2. Calculated (%): С,
66.66; Н, 4.61; N, 18.29. Found: m/z 306.1111 [M]+;
С17H14N4O2; calculated: M = 306.1117.
Synthesis of ethyl (1,2,3,4ꢀtetrahydroꢀ2ꢀoxoquinoxalinꢀ3ꢀyl)
acetate (9). A. Procedure with the use of monoethyl maleate.
оꢀPhenylenediamine (2 g, 0.0185 mol) was dissolved in isopropꢀ
yl alcohol (5 mL) (water can also be used as a solvent, 5 mL).
Monoethyl maleate 8 (2.93 g, 0.0203 mol) was added to the
resulting mixture and it was refluxed for 1 h. Cooled reaction
mixture was mixed with 100 mL of cold water. The product
precipitated as a resin, which crystallized when washed with
water. The product was purified by recrystallization from ethyl
or isopropyl alcohol. The yield was 34%.
B. Procedure with the use of diethyl maleate. оꢀPhenylenediꢀ
amine (2 g, 0.0185 mol) and Nꢀmethylpyrrolidone (1 mL) were
mixed. Diethyl maleate 10 (3.49 g, 0.0203 mol) was added to the
resulting mixture and the solution was heated for 5 h at 80 C. On
heating the mixture was wholly dissolved. Cooled reaction mixꢀ
ture was mixed with 100 mL of cold water. The product precipiꢀ
tated as a resin, which crystallized when washed with water. The
product was purified by recrystallization from ethyl or isopropyl
alcohol. The yield was 29%, m.p. 115—117 C (106—108 C (see
Ref. 10), 103—105 C (see Ref. 11). IR, /cm–1: 3365, 3200,
3059 (NH); 1712, 1673 (C=O); 1506 (Ar); 1200, 1034 (С—O—С);
742 (1,2ꢀsubstituted Ar). 1H NMR, : 1.21 (t, 3 H, Me, J = 7.5 Hz);
2.60 (dd, 1 H, СН2, J = 15.6 Hz, J = 6.9 Hz); 2.75 (dd, 1 H,
СН2, J = 15.6 Hz, J = 5.3 Hz); 4.05—4.15 (m, 3 H, ОСН2, СН);
5.91 (s, 1 H, NH); 6.58 (t, 1 H, Ar, J = 7.2 Hz); 6.7 (m, 3 H, Ar);
10.25 (s, 1 H, NHCO). 13C NMR (): 14.0 (CH3); 36.7 (CH2);
52.5 (CH); 60.1 (OCH2); 113.5, 114.8, 118.0, 122.8, 125.8, 133.8
(Ar); 166.4, 170.3 (C=O).
References
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(Z)ꢀ4ꢀ(N´ꢀBenzhydrazido)ꢀ4ꢀoxoꢀ2ꢀbutenoic acid (11). A soꢀ
lution of benzoic acid hydrazide (13.6 g, 0.1 mol) in glacial
acetic acid (35 mL) was added to a solution of maleic anhydride
(10.8 g, 0.11 mol) in glacial acetic acid (30 mL) at intensive
stirring. After the end of addition, precipitate was formed immeꢀ
diately from the reaction mixture. 20 min later the precipitate
was filtered off and washed with glacial acetic acid. The yield
was 91%, m.p. 177—179 C. IR, /cm–1: 3210 (NH); 2720 (OH);
1707 (C=O); 1651 (C=O (IA)); 1628 (C=C); 1588 (Ar); 1538
(N—С=О (IIA)); 920 (OH); 714 (monosubstituted Ar). 1H NMR,
: 6.35 (d, 1 Н, СН=СН, J = 12.2 Hz); 6.41 (d, 1 Н, СН=СН,
J = 12.3 Hz); 7.48 (t, 2 Н, Ar, J = 7.5 Hz); 7.56 (t, 1 Н, Ar,
J = 7.4 Hz); 7.90 (d, 2 Н, Ar, J = 7.5 Hz); 10.65 (s, 1 H,
NHCO); 10.90 (s, 1 H, NHCO); 13.20 (s, 1 H, OH).
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(Е)ꢀ3ꢀ(5ꢀPhenylꢀ1,3,4ꢀoxadiazolꢀ2ꢀyl) acrylic acid (12). Acid
11 (2.34 g, 0.01 mol) was dissolved in DMF (10 mL), and phosꢀ
phoryl chloride (1.1 mL, 0.012 mol) was gradually added at inꢀ
tensive stirring, the temperature being maintained below 40 C,
and the reaction mixture was left for 1 h at room temperature.
Then the reaction mixture was poured into a mixture of water
and ice. The white precipitate that formed was filtered off and
washed with water. Recrystallization from ethyl alcohol was carꢀ
ried out for purification. The yield was 64%, m.p. 191—193 C.
IR, /cm–1: 2627, 2541 (OH); 1714 (C=O); 1650 (C=C); 1604 (Ar);
1520 (C=N); 1262, 1175, 1022 (C—O—C); 964 (transꢀCH=CH);
927 (OH); 688 (monosubstituted Ar). 1H NMR, : 6.94 (d, 1 Н,
СН=СН, J = 15.9 Hz); 7.47 (d, 1 Н, СН=СН, J = 16.2 Hz);
7.61 (m, 3 H, Ar); 8.09 (d, 2 Н, Ar, J = 8.4 Hz); 13.19 (s, 1 H, ОН).
3ꢀ[(5ꢀPhenylꢀ1,3,4ꢀoxadiazolꢀ2ꢀyl)ꢀmethyl]ꢀ3,4ꢀdihydroquinꢀ
oxalinꢀ2(1Н)ꢀone (13). Anhydrous 1,4ꢀdioxane (10 mL) was addꢀ
ed to (Е)ꢀ3ꢀ(5ꢀphenylꢀ1,3,4ꢀoxadiazolꢀ2ꢀyl)acrylic acid 12 (2 g,
0.009 mol). CDI (2.26 g, 0.014 mol) was added to the resulting
16. M. Dymicky, R. L. Buchanan, Org. Prep. Proced. Int., 1985,
17, 2, 121.
Received October 31, 2013;
in revised form December 12, 2013