InCl3 and In(OTf)3 catalyzed reactions: Synthesis of 3-acetyl indoles, bis-indolylmethane and indolylquinoline derivatives

Article abstract of DOI:10.1016/S0040-4020(01)01227-3

Indium trichloride and indium triflate were found to be effective catalysts for the acetylation of indoles to 3-acetyl indoles and is reported for the first time in good yield. Indium triflate is also found to be an efficient catalyst for the synthesis of bis-indolylmethane and indolylquinoline derivatives.

Full text of DOI:10.1016/S0040-4020(01)01227-3

TETRAHEDRON
Pergamon
Tetrahedron 58 32002) 1229±1232
InCl3 and InꢀOTf)3 catalyzed reactions: synthesis of 3-acetyl
indoles, bis-indolylmethane and indolylquinoline derivatives
Rajagopal Nagarajan and Paramasivan T. Perumalp
Organic Chemistry Division, Central Leather Research Institute, Adyar, Chennai 600 020, India
Received 9 July 2001; revised 12 November 2001; accepted 6 December 2001
AbstractÐIndium trichloride and indium tri¯ate were found to be effective catalysts for the acetylation of indoles to 3-acetyl indoles and is
reported for the ®rst time in good yield. Indium tri¯ate is also found to be an ef®cient catalyst for the synthesis of bis-indolylmethane and
indolylquinoline derivatives. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
Friedel±Crafts alkylation,17 Diels±Alder reaction,18 acetyl-
ation of alcohols and amines19 and also in the synthesis of
tetrahydrofurans.20
Indoles and its myriad derivatives continue to capture the
attention of synthetic organic chemists, and a large number
of original indole ring syntheses and application of known
methods to problems in indole chemistry have been
reported.1 Acetyl indoles are used as starting material for
the synthesis of carbazoles,2 pyridocarbazoles3 and
carbolines.4 Several catalysts like Si3O2CCH2CH2-
2. General procedure
To a stirred solution of indole 31a) in excess acetic
anhydride, 20 mol% InCl3 or 5 mol% In3OTf)3 is added
and stirred for appropriate time. After usual workup,
3-acetyl indoles obtained are given in Table 1 3Scheme 1).
COOCH3)4/SnCl2,5 HClO4,6 SiCl4 and ZnCl2 have been
used for the acetylation of indoles, but the yields are very
low.
7
8
Table 1. Synthesis of 3-acetyl indoles catalyzed by 20 mol% InCl3 and
5 mol% of In3OTf)3
Okauchi et al.9 reported that the indoles were converted into
metal derivatives with Et2AlCl or Me2AlCl followed by
treatment with acid chloride to give acetyl indoles. We
wish to report our observation on acetylation of indoles
catalyzed by InCl3 under mild conditions.
Substrates
R1 R2
Time 3min)
Yield 3%)a,b
InCl3
In3OTf)3
InCl3
In3OTf)3
1
2
3
4
H
H
SO2Ph
Tosyl
H
CH3
H
25
30
35
30
30
35
20
25
65
54
81
78
52
68
92
86
In the literature, InCl3 has been used as a catalyst for the
aldol condensation,10 imino Diels±Alder reactions,11
rearrangement of epoxides,12 Prins-type cyclization,13
Bignelli reaction,14 a-phenyl thioketones.15 Recently, the
synthetic potential of InCl3 in organic synthesis has been
reviewed.16 Similarly, indium tri¯ate is also used for the
H
a
Yield obtained with 20 mol% InCl3 and 5 mol% In3OTf)3.
The yield is based on isolation by column chromatography and the
products were characterized by IR, NMR and mass spectrum.
b
Scheme 1.
Keywords: indium trichloride; indium tri¯ate; acetylation; 3-acetyl indoles; bis-indolylmethane.
Corresponding author. Tel.: 191-44-4913289; fax: 191-44-4911589; e-mail: ptperumal@hotmail.com
p
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020301)01227-3

1230
R. Nagarajan, P. T. Perumal / Tetrahedron 58 '2002) 1229±1232
The acid catalyzed reaction of electron-rich heterocyclic
compounds with p-dimethylaminobenzaldehyde is known
as Ehrlich Test21 for p-electron excessive heterocycles
such as pyrrole and indoles. The analogous reaction of
indoles with other aromatic or aliphatic aldehydes and
ketone produces azafulvenium salts. The azafulvenium
salts undergo further addition with another indole molecule
to afford bis-indolylmethanes. Protic acids22 and Lewis
acids23 were found to catalyze this reaction; however,
more than stoichiometric amounts of the Lewis acids are
required because the acids are trapped by nitrogen.24
Recently, Yadav et al. reported that the use of 10 mol% of
LiClO4 is found to effect the substitution of indoles with
carbonyl compounds.25 Here, we report the indium tri¯ate
catalyzed reaction of indoles with substituted benzalde-
hydes. The catalyst offers several advantages including
mild reaction conditions, cleaner reactions, shorter reaction
times, high yield of the products, lower catalytic loading as
well as simple experimental and isolation procedures which
make it useful for the synthesis of bis-indolylmethanes.
3Scheme 2). The results obtained with substituted benzalde-
hydes are given in Table 2.
Electron withdrawing group, NO2 decreases the yield of the
reaction and electron donating methoxy group increases the
rate of the reaction.
Compounds containing either the indole or the quinoline
moiety possess a wide range of biological activity. A few
reports are available regarding compounds bearing both the
indole and quinoline moiety26±29 which possess a wide
range of biological activity. Imino Diels±Alder reaction of
imines with electron-rich dienophiles to give simple quino-
line derivatives and this reaction is found to be catalyzed by
TFA,30 BF3±Et2O31 and GdCl3.32 The indolylquinolines
have been synthesized by the reaction of indolylimine
with cyclopentadiene catalyzed by In3OTf)3.
To a stirred solution of indolylimine 35a) with cyclopenta-
diene in acetonitrile, 5 mol% of In3OTf)3 was added and
stirred for 25 min. After workup, the product 6a was
obtained in 82% yield 3Scheme 3).
To a stirred solution of indole 31a) with benzaldehyde 33a),
5 mol% In3OTf)3 is added and stirred for 25 min. After
workup, bis-indolylmethane 4a is obtained in 71% yield
In conclusion, we have shown that InCl3 and In3OTf)3 are
Scheme 2.
found to be ef®cient catalysts for acetylation of indoles
giving better yields in shorter reaction times. Indium tri¯ate,
effectively catalyses the reaction of indole with benzalde-
hydes to give bis-indolylmethane and also in the synthesis
of indolyl quinoline derivatives. The catalyst offers several
advantages including mild reaction conditions, cleaner reac-
tions, shorter reaction times, high yield of the products,
lower catalytic loading as well as simple experimental and
isolation procedures, which make it useful for the synthesis
of bis-indolylmethanes.
Table 2. Reaction of indoles with substituted benzaldehydes employing
5 mol% of In3OTf)3
No.
Substituents
R1 R2
Product
Time 3min)
Yield 3%)
1
2
3
H
NO2
OMe
H
H
OH
4a
4b
4c
253300)25
303600)25
35
71
76
86
Scheme 3. 3a) RˆH, 82%; 3b) RˆCl, 79%.

R. Nagarajan, P. T. Perumal / Tetrahedron 58 '2002) 1229±1232
1231
3. Experimental
Jˆ7.2 Hz), 8.22 3s, 1H), 7.94 3d, 2H, Jˆ7.2 Hz), 7.84 3d,
1H, Jˆ6.9 Hz), 7.34 3s, 2H), 7.28 3d, 2H, Jˆ7.2 Hz), 2.57
3s, 3H), 2.35 3s, 3H); 13C NMR 375 MHz, CDCl3) d 193.5,
145.9,134.5, 132.2, 130.2, 127.5, 127.1, 125.7, 124.8, 123.1,
121.6, 113.0, 27.8, 21.6; MS m/z 313 3M1); Anal. Calcd for
C17H15NO3S: C, 65.14; H, 4.83; N, 4.47; Found: C, 65.32;
H, 4.76; N, 4.37.
Mass spectra were recorded on Varian VG70-70H mass
spectrometer. Melting points were measured in capillary
tubes and are uncorrected. Analytical TLC was performed
on precoated sheets of silica gel G of 0.25 mm thickness
containing PF 254 indicator 3Merck, Darmstadt). Column
chromatography was performed with silica gel 360±120
mesh, S.d Fine, Boisar). IR spectra were recorded as solids
in KBr pellets on a Perkin±Elmer FTIR spectrometer. NMR
spectra were obtained on a Bruker spectrometer. H NMR
spectra were recorded at 300 MHz in CDCl3 and the
chemical shifts are given in d relative to the solvent
Ê
377.0). MeCN was distilled from CaH2 and dried over 4 A
molecular sieves.
3.2. Typical procedure for the synthesis of bis-
indolylmethanes
1
To a mixture of indole 4a 32.5 mmol) substituted benzalde-
hydes 3a±3c 31.25 mmol) in acetonitrile 37 mL), indium
tri¯ate 30.035 g, 5 mol%) was added and stirred at room
temperature for the appropriate time. When the reaction
was complete, water 310 mL) was added to quench the reac-
tion and extracted with CH2Cl2 33£10 mL). The combined
organic layers were dried using anhydrous Na2SO4, ®ltered
and the solvent evaporated. The crude products were
puri®ed by column chromatography and eluted with ethyl
acetate±petroleum ether mixture to afford the products
3.1. General procedure for acetylation of indoles to
3-acetyl indoles
To a stirred mixture of the indole 32.5 mmol) in acetic
anhydride 35 mL) protected by guard tube, indium tri¯ate
30.07 g, 5 mol%) was added and stirred for appropriate time.
After the reaction was complete, water 350 mL) was added
and stirred for 15±20 min. To this solid NaHCO3 was added
in portions to aid faster precipitation of acetyl indole and
extracted with CH2Cl2 33£20 mL) The organic layer was
washed with saturated NaHCO3 310 mL), brine 310 mL)
and dried over anhydrous Na2SO4, then concentrated
under reduced pressure. The residue was puri®ed by column
chromatography, eluted with ethylacetate±petroleum ether
3:7 to yield the corresponding 3-acetyl indoles.
3.2.1. 3,30-Bis-indolyl phenylmethane ꢀ4a). 0.572 g 371%)
of pink colored solid; mp 125±1268C 3lit.35 124±1258C); IR
1
3KBr) 3416, 1634, 1378, 737 cm21; H NMR 3300 MHz,
CDCl3) d 7.58 3brs, 2H), 7.45±7.18 3m, 13H), 6.51 3s,
2H), 5.91 3s, 1H); 13C NMR 375 MHz, CDCl3) d 137.1,
134.3, 133.7, 130.2, 130.1, 130.0, 127.1, 125.1, 123.0,
119.4, 118.9, 114.3, 21.5; MS m/z 322 3M1); Anal. Calcd
for C23H18N2: C, 85.68; H, 5.63; N, 8.69; Found: C, 85.59;
H, 5.68; N, 8.54.
3.2.2. 3,30-Bis-indolyl-ꢀ3-nitrophenyl)methane ꢀ4b).
0.697 g 376%) of pink colored solid; mp 261±2628C3d)
3lit.35 2608C) IR 3KBr) 3468, 3060, 1649, 1569, 1240,
3.1.1. 3-Acetyl indole ꢀ2a). 0.207 g 352%) of colorless
solid; mp 191±1928C 3lit.34 190±1918C); IR 3KBr) 3310,
1675, 1368, 851 cm21 1H NMR 3300 MHz, CDCl3) d
;
1
769 cm21; H NMR 3300 MHz, CDCl3) d 8.18 3brs, 2H),
9.27 3brs, 1H), 8.45 3s, 1H), 7.76±6.79 3m, 4H), 2.51 3s,
3H); 13C NMR 375 MHz, CDCl3) d 197.0, 132.4, 131.6,
122.5, 121.3, 118.9, 111.6, 110.9, 27.8; MS m/z 159 3M1);
Anal. Calcd for C10H9NO: C, 75.44; H, 5.70; N, 8.81;
Found: C, 76.10; H, 5.79; N, 8.75.
8.06 3d, 1H, Jˆ7.2 Hz), 7.94 3s, 2H), 7.67 3d, 1H,
Jˆ7.5 Hz), 7.41 3m, 4H), 7.17 3t, 2H), 7.03 3d, 2H,
Jˆ7.2 Hz), 6.59 3s, 2H), 5.96 3s, 1H), 13C NMR 375 MHz,
CDCl3) d 136.6, 134.8, 129.1, 126.5, 123.7, 123.5, 122.2,
121.4, 119.5, 118.1, 111.3, 39.9; MS m/z 368 3M1); Anal.
Calcd for C23H17N3O2; C, 75.19; H, 4.66; N, 11.44; Found:
C, 75.41; H, 4.69; N, 11.54.
3.1.2. 2-Methyl-3-acetyl indole ꢀ2b). 0.294 g 368%) of
colorless solid; mp 195±1968C 3lit.33 195±1968C); IR
1
3KBr) 3302, 1658, 1362, 840 cm21; H NMR 3300 MHz,
3.2.3.
3,30-Bis-indolylꢀ4-hydroxy-5-methoxyphenyl)-
methane ꢀ4c). 0.791 g 386%) of pink colored solid; mp
CDCl3) d 9.18 3brs, 1H), 7.80±6.94 3m, 4H), 2.87 3s, 3H),
2.48 3s, 3H); 13C NMR 375 MHz, CDCl3) d 191.5, 135.1,
132.3, 128.2, 121.4, 115.3, 110.3, 26.9, 12.6; MS m/z 173
3M1); Anal. Calcd for C11H11NO: C, 76.26; H, 6.41; N,
8.09; Found: C, 75.78; H, 6.32; N, 7.99.
1
99±1018C; IR 3KBr) 3500, 3412, 1634, 1383, 741 cm1; H
NMR 3300 MHz, CDCL3) d 9.81 3brs, 2H), 7.91 3s, 1H),
7.39±6.80 3m, 11H), 6.63 3s, 2H), 5.80 3s, 1H), 3.74 3s, 3H);
13C NMR 375 MHz, CDCl3) d 143.8, 136.7, 136.1, 127.0,
123.5, 121.9, 121.3, 119.9, 119.2, 114.0, 111.4, 55.8, 39.8;
MS m/z 368 3M1); Anal. Calcd for C24H20N2O2; C, 78.23;
H,5.47; N, 7.61; Found: C, 78.54; H, 5.39; N, 7.70.
3.1.3. N-Benzenesulfonyl-3-acetyl indole ꢀ2c). 0.688 g
392%) of colorless solid; mp 160±1618C 3lit.34 159±
;
1608C); IR 3KBr) 1667, 1383, 842 cm21 1H NMR
3300 MHz, CDCl3) d 8.32 3s, 1H), 7.94±7.24 3m, 9H),
2.55 3s, 3H); 13C NMR 375 MHz, CDCl3) d 193.3, 137.6,
134.9, 132.7, 131.5, 130.3, 129.2, 127.8, 126.6, 125.4,
123.7, 121.8, 113.5, 27.9; MS m/z 299 3M1); Anal. Calcd
for C16H13NO3S: C, 64.18; H, 4.38; N, 4.68; Found: C,
64.56; H, 4.31; N, 4.55.
3.3. General procedure for cycloaddition
A mixture of imine 5a or 5b 32.5 mmol), In3OTf)3 30.035 g,
5 mol%) cyclopentadiene 35 mmol) in acetonitrile 37 mL)
was stirred at room temperature for the appropriate time.
To the reaction mixture was added aqueous saturated
NaHCO3 solution 35 mL) and the solution was extracted
with CHCl3 33£10 mL). The combined organic layer was
washed with water, brine, dried over Na2SO4, ®ltered and
3.1.4. N-p-Toluenesulfonyl-3-acetyl indole ꢀ2d). 0.673 g
386%) of colorless solid; mp 137±1388C; IR 3KBr) 1657,
1378, 857 cm21; 1H NMR 3300 MHz, CDCl3) d 8.34 3d, 1H,

1232
R. Nagarajan, P. T. Perumal / Tetrahedron 58 '2002) 1229±1232
8. Douglas, B.; Krikpatrick, J. L.; Moore, B. P.; Weisbach, J. A.
Aust. J. Chem. 1964, 17, 246.
the solvent evaporated. The residue was puri®ed by column
chromatography eluting with 90:10 ethyl acetate±petroleum
ether to afford the cycloadducts.
9. Okauchi, T.; Honaga, M.; Minami, T.; Owa, T.; Kiloh, K.;
Yoshino, H. Org. Lett. 2000, 1485.
3.3.1. 4-[ꢀ1-Phenylsulfonyl)-indole-3-yl]-3a,4,5,9b-tetra-
hydro-3H-cyclopenta[c] quinoline ꢀ6a). 0.873 g 382%) of
colorless solid; mp 165±1668C; IR 3KBr) 3409, 2949, 1480,
10. 3a) Mukaiyama, T.; Ohno, T.; Han, J. S.; Kobayashi, S. Chem.
Lett. 1991, 949. 3b) Mukaiyama, T. Org. React. 1982, 28, 203.
3c) Loh, T. P.; Pei, J.; Lin, M. Chem. Commun. 1996, 2315.
3d) Kobayashi, S.; Busujima, T.; Nagayama, S. Tetrahedron
Lett. 1998, 39, 1579.
1401, 1385, 720 cm21 1H NMR 3300 MHz, CDCl3) d
;
8.07±6.80 3m, 12H), 6.72 3m, 1H), 6.68 3d, 1H,
Jˆ7.8 Hz), 5.83 3m, 1H), 5.61 3m, 1H), 4.86 3d, 1H,
Jˆ2.6 Hz), 4.14 3d, 1H, Jˆ8.1 Hz), 3.77 3brs, 1H, NH),
3.22 3m, 1H), 2.60 3m, 1H), 1.69 3m, 1H); 13C NMR
375 MHz, CDCl3) d 147.3, 137.9, 135.3, 135.2,134.1,
133.7, 132.6, 129.6, 127.2, 126.6, 126.5, 126.3, 125.1,
125.0, 123.2, 119.4, 119.1, 116.0, 113.9, 113.7, 50.7, 45.7,
43.2, 32.4; MS m/z 426 3M1); Anal. Calcd for C26H22N2O2S;
C, 73.21; H, 5.20; N, 6.57; Found: C, 72.99; H, 5.21; N,
6.59.
11. Mukaiyama, T.; Ohno, T.; Nishimura, T.; Suda, S.;
Kobayashi, S. Chem. Lett. 1991, 1059. 3b) Miyai, T.; Onishu,
Y.; Baba, A. Tetrahedron Lett. 1998, 39, 6291. 3c) Miyai, T.;
Onishu, Y.; Baba, A. Tetrahedron 1999, 55, 1017.
12. 3a) Babu, G.; Perumal, P. T. Tetrahedron Lett. 1997, 38, 5025.
3b) Babu, G.; Perumal, P. T. Tetrahedron 1998, 54, 1627.
3c) Babu, G.; Nagarajan, R.; Natarajan, R.; Perumal, P. T.
Synthesis 2000, 661. 3d) Hadden, M.; Stevenson, P. J.
Tetrahedron Lett. 1999, 40, 1215.
13. Ranu, B. C.; Jana, U. J. Org. Chem. 1998, 63, 8212.
14. Yang, J.; Viswanathan, G. S.; Li, C. J. Tetrahedron Lett. 1999,
40, 1627.
3.3.2. 8-Chloro-4-[ꢀ1-phenylsulfonyl)-indole-3-yl]-3a,4,
5,9b-tetrahydro-3H-cyclopenta[c]
0.910 g 379%) of colorless solid; mp 182±1838C; IR
quinoline
ꢀ6b).
15. Babu, G.; Sridhar, N.; Perumal, P. T. Synth. Commun. 2000,
30, 1609.
1
3KBr) 3425, 3100, 2900, 1450, 1380, 750 cm21; H NMR
3300 MHz, CDCl3) d 8.03±7.85 3m, 5H), 7.60±7.21 3m,
5H), 7.02 3s, 1H), 6.92 3d, 1H, Jˆ6.3 Hz), 6.56 3d, 1H,
Jˆ8.5 Hz), 5.75 3s, 1H), 5.61 3m, 1H), 4.80 3d, 1H,
Jˆ2.6 Hz), 4.06 3d, 1H, Jˆ8.5 Hz), 3.77 3s, 1H), 3.09 3m,
1H), 2.48 3m, 1H), 1.61 3m, 1H); 13C NMR 375 MHz,
CDCl3) d 143.8, 137.9, 135.5, 134.5, 133.9, 132.6, 130.4,
129.8, 127.9, 127.6, 126.4, 125.6, 124.8, 123.9, 123.7,
122.1, 120.6, 120.1, 117.9, 114.9, 112.9, 51.4, 49.9, 43.6,
32.2; MS m/z 460 3M1), 462 3M12); Anal. Calcd for
C26H21ClN2O2S; C, 67.74; H, 4.59; N, 6.09; Found: C,
67.94; H, 4.57; N, 6.11.
16. Ranu, B. C.; Hajra, A.; Jana, U. J. Org. Chem. 2000, 65, 6270.
17. Sengupta, S.; Mandal, S. Tetrahedron Lett. 1999, 40, 8685.
18. Babu, G.; Perumal, P. T. Aldrichimica Acta 2000, 33, 16.
19. Chauhan, K.; K, .; Frost, C. G.; Love, I.; Waite, D. Synlett
1999, 1743.
20. Loh, T-P.; Hu, Q-Y.; Ma, L-T. J. Am. Chem. Soc. 2001, 123,
2450.
21. 3a) Ehrlish, P. Med. Woche 1901, 151. 3b) Urk, H. Pharm.
Weekbl. 1929, 66, 473. 3c) Morgan, L.; Schunior, R. J.
J. Org. Chem. 1962, 27, 3696. 3d) Dolpin, D. J. J. Heterocycl.
Chem. 1979, 7, 275.
22. 3a) Gregorovich, B.; Liang, K.; Clugston, D.; MacDonald, S.
Can. J. Chem. 1968, 46, 3291. 3b) Roomi, M.; MacDonald, S.
Can. J. Chem. 1970, 48, 139.
Acknowledgements
23. 3a) Chatterji, A.; Manna, S.; Banerji, J.; pascard, C.; Prange,
T.; Shoolery, J. J. Chem. Soc., Perkin Trans. 1 1980, 533.
3b) Noland, W.; Venkiteswaran, M.; Richards, C. J. Org.
Chem. 1961, 26, 4241.
We thank the Council of Scienti®c and Industrial Research,
New Delhi, India for ®nancial support.
24. Kobayashi, S.; Araki, M.; Yasuda, M. Tetrahedron Lett. 1995,
36, 4467.
References
25. Yadav, J. S.; Subba Reddy, B. V.; Murthy, V. S. R.; Mahesh
Kumar, G.; Madan, Ch. Synthesis 2001, 783.
1. 3a) Gribble, G. W. Contemp. Org. Synth. 1994, 1, 145.
3b) Gribble, G. W. J. Chem. Soc., Perkin Trans. 1 2000, 1045.
2. Jeevanandam, A.; Srinivasan, P. C. J. Chem. Soc., Perkin
Trans. 1 1995, 2663.
26. Rykowski, A.; Lipinska, T. Synth. Commun. 1996, 26, 4409.
27. Bahner, C. T.; Kinder, H.; Gutman, L. J. Med. Chem. 1965, 8,
397.
3. 3a) Gribble, G. W.; Keavy, D. J.; Davis, D. A.; Saulnier, M. G.;
Pelcman, B.; Barden, T. C.; Sibi, M. P.; Olson, E. R.;
Belbruno, J. J. Org. Chem. 1992, 57, 5878. 3b) Gribble,
G. W.; Saulnier, M. G.; Sibi, M. P.; Obaza-Nutiatits, J. A.
J. Org. Chem. 1984, 49, 4518.
28. Sugasaw, S.; Deguchi, Y. Chem. Pharm. Bull. 1960, 8, 87.
29. Deguchi, Y. Jgaku. Shigen Kenkyusho Nempo. 1956, 11
Chem. Abstr. 1960, 54, 2336.
30. Grieco, P. A.; Bahsas, A. Tetrahedron Lett. 1988, 29, 5855.
31. Povarov, L. S. Russ. Chem. Rev. 1967, 36, 656.
32. Ma, Y.; Qian, C.; Xie, M.; Sun, J. J. Org. Chem. 1999, 64,
6462.
4. Markgraf, J. H.; Synder, S. A.; Vosburg, D. A. Tetrahedron
2000, 56, 5329.
5. Kost, A. N.; Mitropal'skaya, V. N.; Pornova, S. L.; Krasnova,
V. A. J. Gen. Chem. USSR 'Engl. Transl.) 1964, 34, 3025.
6. Dorofeenko, G. N. Zh. Veses. Khim. Obshehestvaim. D. I.
Mendeleev 1960, 5, 354 Chem. Abstr. 1960, 54, 22563.
7. Yur'ev, Y. K.; Elyakov, G. B. Zh. Obshch. Kim. 1956, 26,
2350 Chem. Abstr. 1957, 51, 5042.
33. Anthony, W. C. J. Org. Chem. 1960, 25, 2049.
34. Ketcha, D. M.; Gribble, G. W. J. Org. Chem. 1985, 50, 5451.
35. Rees, C. W.; Sabet, C. R. J. Chem. Soc. 1965, 680.