A one-pot synthesis of 1,2-dihydroisoquinoline derivatives from isoquinoline via a four-component reaction

Article abstract of DOI:10.1002/hlca.200890087

A four-component reaction for the synthesis of 1,2-dihydroisoquinoline derivatives is described. The Huisgen 1,4-dipolar intermediate, which is produced from isoquinoline and an electron-deficient acetylene compound 1, reacts with H₂O in the presence of diketene to produce 1,2-dihydroisoquinoline derivatives 2 (Scheme 1). In addition, reaction of isoquinoline, dibenzoylacetylene (= 1,4-diphenylbut-2-yne-1,4-dione), and diketene in the presence of H₂O leads to pyrroloisoquinoline derivative 7. The structures of the compounds 2a-f and 7 were corroborated spectroscopically (IR, ¹H- and ¹³C-NMR, EI-MS) and by elemental analyses. A plausible mechanism for the reaction is proposed (Schemes 2 and 3).

Full text of DOI:10.1002/hlca.200890087

844
Helvetica Chimica Acta – Vol. 91 (2008)
A One-Pot Synthesis of 1,2-Dihydroisoquinoline Derivatives from
Isoquinoline via a Four-Component Reaction
by Abdolali Alizadeh* and Nasrin Zohreh
Department of Chemistry, Tarbiat Modares University, P. O. Box 14115-175, Tehran, Iran
(phone: þ 98-21-88006631; fax: þ 98-21-88006544; e-mail: abdol_alizad@yahoo.com and
aalizadeh@Modares.ac.ir)
A four-component reaction for the synthesis of 1,2-dihydroisoquinoline derivatives is described. The
Huisgen 1,4-dipolar intermediate, which is produced from isoquinoline and an electron-deficient
acetylene compound 1, reacts with H2O in the presence of diketene to produce 1,2-dihydroisoquinoline
derivatives 2 (Scheme 1). In addition, reaction of isoquinoline, dibenzoylacetylene (¼1,4-diphenylbut-2-
yne-1,4-dione), and diketene in the presence of H2O leads to pyrroloisoquinoline derivative 7. The
structures of the compounds 2a – f and 7 were corroborated spectroscopically (IR, 1H- and 13C-NMR, EI-
MS) and by elemental analyses. A plausible mechanism for the reaction is proposed (Schemes 2 and 3).
Introduction. – Isoquinoline derivatives refer to isoquinoline itself, substituted
congeners (e.g., 6-methoxyisoquinoline), and the various reduced species (1,2- or 3,4-
dihydroisoquinolines and 1,2,3,4-tetrahydroisoquinolines), all of which may occur in
their neutral or charged quaternary (isoquinolinium ion) form [1]. Not only frequently
found in naturally occurring alkaloids, the di- and tetrahydroisoquinoline moieties are
also important pharmacophores. Typical examples include indenoisoquinoline (top-
oisomerase I inhibitor) [2], papaverine (smooth-muscle relaxant) [3], saframycin-B
(antitumor agent) [4], and narciclasine (antitumor agent) [5]. They are synthesized in
vivo by a Pictet-Spengler nonenzymatic condensation of biogenic amines (e.g.,
catecholamines and phenylethylamines) with aldehydes or with a-keto acids followed
by decarboxylation [6][7]. Recent studies suggest that some isoquinoline derivatives
may also be formed enzymatically in mammalian brain [8].
Huisgen demonstrated that the reaction of isoquinoline and electron-deficient
acetylene compounds generates a 1,4-dipolar intermediate [9][10], and he trapped the
latter with various dipolarophiles for the formation of five- and six-membered
heterocycles [11]. In recent years, these interesting zwitterions have been used in
multicomponent reactions to produce a considerable number of heterocyclic com-
pounds [12 – 19].
In this paper, we report a simple one-pot reaction between isoquinoline, electron-
deficient acetylene compounds 1a – f, and H2O in the presence of diketene, leading to
1,2-dihydroisoquinoline derivatives 2a – f (Scheme 1).
Results and Discussion. – The one-pot reaction of isoquinoline, 1, H2O, and
diketene proceeded in CH2Cl2 at room temperature to produce 1,2-dihydroisoquinoline
derivatives 2a – f in 85 – 95% yields (Scheme 1). The structures of compounds 2a – f
ꢀ 2008 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 91 (2008)
845
Scheme 1
were deduced from their elemental analysis, IR, and 1H- and 13C-NMR spectra. The MS
of 2a displayed the molecular ion peak at m/z 329, which is consistent with a 1:1:1:1
adduct of isoquinoline, dimethyl but-2-ynedioate, diketene, and H2O having lost CO2.
1
The H-NMR spectrum of 2a exhibited seven signals readily recognized as arising from three Me
groups (d 1.99, 3.68, and 3.95), a CH2 group of (2.63 (J ¼ 2.5, 16.9 Hz) and 3.11 (J ¼ 9.7, 16.9 Hz)), an
olefinic CH moiety (d 5.21), and a CH group (d 5.37,J ¼ 9.9 Hz). The isoquinoline moieties gave rise to
characteristic signals in the aromatic region of the spectrum. No exchange was observed in the 1H-NMR
spectrum of 2a in D2O solution. The 1H-decoupled 13C-NMR spectrum of 2a showed 18 distinct
resonances in agreement with the structure of dimethyl 2-[1-(2-oxopropyl)isoquinolin-2(1H)-yl]but-2-
enedioate. The 1H- and 13C-NMR spectra of compounds 2b – f were similar to those of 2a, except for the
ester moieties, which exhibited characteristic signals with appropriate chemical shifts for the specific
substitution patterns.
When dibenzoylacetylene (¼1,4-diphenylbut-2-yne-1,4-dione) and isoquinoline in
dry CH2Cl2 were allowed to react with H2O in the presence of diketene at room
temperature, a yellow crystalline compound 7 was formed in nearly quantitative yield.
This product was identified as (2E)-2-{1-acetyl-1,10b-dihydro-2-hydroxy-2-phenyl-
pyrrolo[2,1-a]isoquinolin-3(2H)-ylidene}-1-phenylethanone (7).
Although the mechanism of the reaction between isoquinoline, electron-deficient
acetylene compounds 1, and diketene in the presence of H2O has not yet been
established in an experimental manner, a putative mechanism is proposed in Scheme 2.

846
Helvetica Chimica Acta – Vol. 91 (2008)
Based on the well-established chemistry of N-containing heterocycles [12 – 21], it is
reasonable to assume that products 2a – f result from initial addition of isoquinoline to
the electron-deficient acetylene compound and subsequent protonation of the 1:1
adduct 3 by H2O. On the other hand (in a concerted process), an OHꢀ ion attacks the
diketene, and after a proton exchange [22 – 28], 5 is produced. Next, the positively
charged ion of 4 is attacked by the conjugated base 5 of acetoacetic acid to form
intermediate 6 that looses a molecule of CO2 and, therefore, leads to compounds 2a – f.
Scheme 2
Compound 7 apparently results from the enolization and cyclization of intermedi-
ate A, when dibenzoylacetylene was used as an electron-deficient acetylene compound
(Scheme 3) [29].
Scheme 3
In conclusion, we have developed a convenient one-pot method for preparing
isoquinoline derivatives. The present method has the following advantage: not only the
reaction is performed under neutral and aqueous conditions, but also the substrates can
be used in the reaction without any prior activation or modification. The simplicity of
the present procedure makes it an interesting alternative to complex multistep
approaches.

Helvetica Chimica Acta – Vol. 91 (2008)
847
Experimental Part
General. Isoquinoline, diketene, and electron-deficient acetylene compounds were obtained from
Merck (Germany) and Fluka (Switzerland) and were used without further purification. Dibenzoylace-
tylene (¼1,4-diphenylbut-2-yne-1,4-dione) was prepared according to a published procedure [30][31].
Melting points: Electrothermal-9100 apparatus. IR Spectra: Shimadzu-IR-460 spectrometer. 1H- and
13C-NMR Spectra: CDCl3 solns.; Bruker-DRX-500-Avance spectrometer at 500.1 and 125.7MHz, resp.
MS: Finnigan-MAT-8430 mass spectrometer operating at an ionization potential of 20 eV. Elemental
analyses: Heraeus-CHN-O-Rapid analyzer.
Compounds 2a – f: General Procedure (exemplified for 2a). To a magnetically stirred soln. of
isoquinoline (0.13 g, 1 mmol) and H2O (0.02 g, 1 mmol) in CH2Cl2 (2 ml) was added dropwise a soln. of
diketene (0.08 g, 1 mmol) and dimethyl but-2-ynedioate (DMAD; 0.14 g, 1 mmol) at 08. The mixture was
stirred for 10 h at r.t. The solvent was evaporated, and the residue was separated by column
chromatography (silica gel (230 – 240 mesh; Merck) hexane/AcOEt).
Dimethyl (2Z)-2-[1-(2-Oxopropyl)isoquinolin-2(1H)-yl]but-2-enedioate (2a): Yield 310 mg (95%).
Pale yellow powder. M.p. 123 – 1258. IR (KBr): 1728 (COMe), 1696 (CO2Me), 1581 (C¼C), 1556 and
1508 (arom.), 1215 and 1150 (CꢀO, ester). 1H-NMR (CDCl3): 1.99 (s, 3 H); 2.63 (dd, J ¼ 16.9, 2.5, 1 H);
3.11 (dd, J ¼ 16.9, 9.7, 1 H); 3.68 (s, 3 H); 3.95 (s, 3 H); 5.21 (s, 1 H); 5.37( d, J ¼ 9.9, 1 H); 5.95 (d, J ¼ 7.6,
1 H); 6.27( d, J ¼ 7.6, 1 H); 7.07 (d, J ¼ 7.4, 1 H); 7.14 – 7.16 (m, 2 H); 7.21 – 7.23 (m, 1 H). 13C-NMR
(CDCl3): 31.1; 47.3; 51.3; 53.3; 53.9; 90.7; 110.2; 125.0; 125.3; 126.4; 127.5; 128.3; 129.1; 131.3; 149.2; 165.1;
166.7, 205.3. EI-MS: 329 (25, Mþ), 273 (63), 272 (100), 270 (30), 240 (19), 167 (19), 154 (24), 128 (38),
127(38), 115 (19), 102 (11), 77(13), 69 (9), 59 (12), 43 (38). Anal. calc. for C 18H19NO5 (329.35): C 65.64,
H 5.81, N 4.25; found: C 65.51, H 5.91, N 4.46.
Diethyl (2Z)-2-[1-(2-Oxopropyl)isoquinolin-2(1H)-yl]but-2-enedioate (2b): Yield 330 mg (93%).
Pale yellow powder. M.p. 105 – 1078. IR (KBr): 1718 (COMe), 1699 (CO2Et), 1578 (C¼C), 1556 and
1499 (arom.), 1200 and 1150 (CꢀO, ester). 1H-NMR (CDCl3): 1.26 (t, J ¼ 7.1, 3 H); 1.39 (t, J ¼ 7.1, 3 H);
1.99 (s, 3 H); 2.74 (dd, J ¼ 16.9, 2.4, 1 H); 3.13 (dd, J ¼ 16.9, 9.9, 1 H); 4.10 – 4.17( m, 2 H); 4.37– 4.47( m,
2 H); 5.19 (s, 1 H); 5.37( d, J ¼ 9.5, 1 H); 5.95 (d, J ¼ 7.6, 1 H); 6.30 (d, J ¼ 7.6, 1 H); 7.07 (d, J ¼ 7.4, 1 H);
7.13 – 7.15 (m, 2 H); 7.19 – 7.23 (m, 1 H). 13C-NMR (CDCl3): 13.9; 14.4; 31.1; 47.2; 53.8; 59.9; 62.6; 91.1;
110.0; 124.9; 125.4; 126.5; 127.4; 128.2; 129.2; 131.3; 149.1; 164.6; 166.7; 205.3. EI-MS: 357 (9,Mþ), 312
(5), 300 (100), 284 (16), 272 (16), 200 (30), 154 (16), 128 (14), 43 (14). Anal. calc. for C20H23NO5
(357.40): C 67.21, H 6.49, N 3.92; found: C 67.44, H 6.31, N 3.87.
Di(tert-butyl) (2Z)-2-[1-(2-Oxopropyl)isoquinolin-2(1H)-yl]but-2-enedioate (2c): Yield 370 mg
t
(90%). Pale yellow powder. M.p. 120 – 1228. IR (KBr): 1719 (COMe), 1690 (CO2 Bu), 1577 (C¼C),
1556 and 1509 (arom.), 1223 and 1151 (CꢀO, ester). 1H-NMR (CDCl3): 1.46 (s, 9 H); 1.60 (s, 9 H); 1.97
(s, 3 H); 2.7 3 (dd, J ¼ 16.8, 2.7, 1 H); 3.15 (dd, J ¼ 16.8, 10.2, 1 H); 5.08 (s, 1 H); 5.32 (d, J ¼ 9.7, 1 H); 5.92
(d, J ¼ 7.6, 1 H); 6.35 (d, J ¼ 7.6, 1 H); 7.05 (d, J ¼ 7.5, 1 H); 7.12 – 7.20 (m, 3 H). 13C-NMR (CDCl3): 27.9;
28.3; 31.1; 46.9; 53.9; 79.5; 83.9; 93.2; 109.2; 124.7; 125.8; 126.7; 127.0; 128.1; 129.6; 131.3; 149.0; 163.5;
165.9; 205.6. EI-MS: 413 (4, Mþ), 356 (12), 300 (19), 244 (51), 200 (25), 154 (13), 57(100), 43 (32). Anal.
calc. for C24H31NO5 (413.51): C 69.71, H 7.56, N 3.39; found: C 69.53, H 7.32, N 3.46.
Methyl (2Z)-3-[1-(2-Oxopropyl)isoquinolin-2(1H)-yl]prop-2-enoate (2d): Yield 240 mg (88%). Pale
yellow powder. M.p. 105 – 1078. IR (KBr): 1720 (COMe), 1690 (CO2Me), 1602 (C¼C), 1555 and 1520
1
(arom.), 1205 and 1157(C ꢀO, ester). H-NMR (CDCl3): 2.04 (s, 3 H); 2.74 – 2.76 (m, 1 H); 2.98 – 3.07
(m, 1 H); 3.7 1 (s, 3 H); 5.16 (d, J ¼ 13.5, 1 H); 5.41 (br., 1 H); 5.84 (d, J ¼ 7.3, 1 H); 6.33 (d, J ¼ 7.3, 1 H);
7.05 (d, J ¼ 7.5, 1 H); 7.13 – 7.15 (m, 2 H); 7.21 – 7.23 (m, 1 H); 7 .46 d( , J ¼ 13.5, 1 H). 13C-NMR (CDCl3):
31.1; 47.3; 51.0; 52.1; 90.8; 108.5; 124.84; 125.8; 126.2; 127.2; 128.2; 129.8; 130.8; 146.8; 168.9; 205.4. EI-
MS: 271 (12, Mþ), 265 (9), 254 (6), 238 (24), 214 (100), 154 (11), 129 (21), 115 (7), 102 (9), 84 (15), 43
(18). Anal. calc. for C16H17NO3 (271.31): C 70.83, H 6.32, N 5.16; found: C 70.73, H 6.55, N 5.34.
Ethyl (2Z)-3-[1-(2-Oxopropyl)isoquinolin-2(1H)-yl]prop-1-enoate (2e): Yield 240 mg (85%). Pale
yellow powder. M.p. 90 – 928. IR (KBr): 1716 (COMe), 1695 (CO2Et), 1620 (C¼C), 1541 and 1510
1
(arom.), 1284 and 1201 (CꢀO, ester). H-NMR (CDCl3): 1.27( t, J ¼ 7.1, 3 H); 2.00 (s, 3 H); 2.72 – 2.75
(m, 1 H); 2.98 – 3.00 (m, 1 H); 4.12 – 4.20 (m, 2 H); 5.16 (d, J ¼ 13.6, 1 H); 5.39 (br., 1 H); 5.85 (d, J ¼ 7.3,
1 H); 6.33 (d, J ¼ 7.3, 1 H); 7.04 (d, J ¼ 7.5, 1 H); 7.10 – 7.14 (m, 2 H); 7.20 – 7.22 (m, 1 H); 7.44 (d, J ¼ 13.6,

848
Helvetica Chimica Acta – Vol. 91 (2008)
1 H). 13C-NMR (CDCl3): 14.5; 31.1; 47.2; 53.8; 59.6; 91.2; 108.7; 124.8; 125.8; 126.3; 127.2; 128.2; 129.8;
130.7; 146.6; 168.5; 205.5. EI-MS: 285 (20, Mþ), 240 (11), 228 (100), 200 (85), 154 (13), 129 (19), 115 (9),
43 (12). Anal. calc. for C17H19NO3 (285.34): C 71.56, H 6.71, N 4.91; found: C 71.61, H 6.62, N 4.76.
(3Z)-4-[1-(2-Oxopropyl)isoquinolin-2(1H)-yl]but-3-en-2-one (2f): Yield 220 mg (85%). Pale yellow
powder. M.p. 100 – 1028. IR (KBr): 1718 (COMe), 1697 (CO2Me), 1593 (C¼C), 1561 and 1540 (arom.).
1H-NMR (CDCl3): 2.06 (s, 3 H); 2.16 (s, 3 H); 2.78 (br., 1 H); 2.96 (br., 1 H); 5.43 (br., 1 H); 5.60 (d, J ¼
12.4, 1 H); 5.90 (d, J ¼ 7.1, 1 H); 6.35 (d, J ¼ 7.1, 1 H); 7.04 (d, J ¼ 7.6, 1 H); 7.09 – 7.16 (m, 2 H); 7.21 (t, J ¼
7.3, 1 H); 7.41 (d, J ¼ 12.4, 1 H). 13C-NMR (CDCl3): 29.7; 31.1; 47.6; 51.3; 92.8; 109.8; 125.0; 126.1; 127.4;
128.3; 129.7; 131.0; 146.4; 196.2; 205.5. EI-MS: 255 (9, Mþ), 238 (27), 223 (29), 208 (35), 198 (100), 180
(9), 145 (21), 129 (54), 115 (18), 77 (32), 43 (90). Anal. calc. for C16H17NO2 (255.31): C 75.27, H 6.71, N
5.49; found: C 75.33, H 6.54, N 5.28.
(2E)-2-{1-Acetyl-1,10b-dihydro-2-hydroxy-2-phenylpyrrolo[2,1-a]isoquinolin-3(2H)-ylidene}-1-phe-
nylethanone (7): Yield 320 mg (75%). Pale yellow crystals. M.p. 1908 (dec.). IR (KBr): 3490 (OH), 1726
(COMe), 1702 (COPh), 1580 (C¼C), 1555 and 1498 (arom.), 1165 (CꢀOH). 1H-NMR (CDCl3): 2.35 (s,
3 H); 4.14 (d, J ¼ 9.4, 1 H); 5.73 (d, J ¼ 9.4, 1 H); 6.05 (s, 1 H); 6.37( d, J ¼ 7.5, 1 H); 6.69 (d, J ¼ 7.5, 1 H);
6.89 (d, J ¼ 7.5, 1 H); 7.17 (d, J ¼ 7.2, 1 H); 7.21 – 7.28 (m, 3 H); 7 .32 t(, J ¼ 7.7, 2 H); 7.36 (t, J ¼ 7.6, 2 H);
7.47 (t, J ¼ 7.6, 1 H); 7.52 (d, J ¼ 6.6, 2 H); 7.79 (d, J ¼ 7.6, 2 H); 9.01 (s, 1 H). 13C-NMR (CDCl3): 31.2;
59.9; 61.3; 67.8; 84.6; 89.1; 116.5; 122.1; 123.8; 124.8; 125.7; 127.7; 128.1; 128.2; 128.3; 128.7; 130.6; 131.6;
131.9; 138.9; 140.2; 166.8; 188.9; 204.9. EI-MS: 421 (2, Mþ), 360 (16), 277(23), 236 (10), 167(17), 149
(33), 129 (51), 105 (100), 94 (24), 77 (72), 57 (32), 43 (44). Anal. calc. for C28H23NO3 (421.49): C 79.79, H
5.50, N 3.32; found: C 79.61, H 5.68, N 3.41.
REFERENCES
[1] K. S. P. McNaught, P. A. Carrupt, C. Altomare, S. Cellamare, A. Carotti, B. Testa, P. Jenner, C. D.
Marsden, Biochem. Pharmacol. 1998, 56, 921.
[2] C. Marchand, S. Antony, K. W. Kohn, M. Cushman, A. Ioanoviciu, B. L. Staker, A. B. Burgin, L.
Stewart, Y. Pommier, Mol. Cancer Ther. 2006, 5, 287; E. Haslam, ꢁShikimic Acid Metabolism and
Metabolitesꢂ, John Wiley & Sons, New York, 1993.
[3] T. Kaneda, Y. Takeuchi, H. Matsui, K. Shimizu, N. Urakawa, S. Nakajyo, J. Pharmacol. Sci. 2005, 98,
275.
[4] Y. Mikami, K. Yokoyama, H. Tabeta, K. Nakagaki, T. Arai, J. Pharmacobio-dynam. 1981, 4, 282.
[5] G. R. Pettit, V. Gaddamidi, D. L. Herald, S. B. Singh, G. M. Cragg, J. M. Schmidt, F. E. Boettner, M.
Williams, Y. Sagawa, J. Nat. Prod. 1986, 49, 995.
[6] R. Deitrich, V. Erwin, Annu. Rev. Pharmacol. Toxicol. 1980, 20, 55.
[7] H. Rommelspacher, T. May, R. Susilo, Planta Med. 1991, 57, 85.
[8] T. Nagatsu, Neurosci. Res. 1997, 29, 99.
[9] R. Huisgen, in ꢁTopics in Heterocyclic Chemistryꢂ, Ed. R. Castle, John Wiley & Sons, New York,
1969, Chapt. 8, p. 223; R. Huisgen, Z. Chem. 1968, 8, 290.
[10] R. Huisgen, Proc. Chem. Soc. (London) 1961, 357; R. Huisgen, Angew. Chem., Int. Ed. 1963, 2, 633;
P. Garner, W. B. Ho, S. K. Grandhee, W. J. Youngs, V. O. Kennedy, J. Org. Chem. 1991, 56, 5893; P.
Garner, W. B. Ho, C. Shin, J. Am. Chem. Soc. 1993, 115, 10742; J. A. Monn, M. Valli, J. Org. Chem.
1994, 59, 2773; C. W. G. Fiswick, R. J. Foster, R. E. Carr, Tetrahedron Lett. 1996, 37, 3915.
[11] R. Huisgen, M. Morikawa, K. Herbig, E. Brunn, Chem. Ber. 1967, 100, 1094.
[12] I. Yavari, D. M. Ghazanfarpour-Darjani, M. Sabbaghan, Z. Hossaini, Tetrahedron Lett. 2007, 48,
3749.
[13] I. Yavari, M. Sabbaghan, Z. Hossaini, Synlett 2006, 15, 2501.
[14] V. Nair, B. Rema Devi, L. R. Varma, Tetrahedron Lett. 2005, 46, 5333.
[15] V. Nair, S. Devipriya, S. Eringathodi, Tetrahedron Lett. 2007, 48, 3667.
[16] I. Yavari, Z. Hossaini, M. Sabbaghan, Tetrahedron Lett. 2006, 48, 6037.
[17] I. Yavari, Z. Hossaini, M. Sabbaghan, M. Ghazanfarpour-Darjani, Monatsh. Chem. 2007, 138, 67 7 .
[18] V. Nair, A. R. Sreekanth, A. T. Biju, N. P. Rath, Tetrahedron Lett. 2003, 44, 729.

Helvetica Chimica Acta – Vol. 91 (2008)
849
[19] V. Nair, A. R. Sreekanth, N. Abhilash, M. M. Bhadbhade, R. C. Gonnade, Org. Lett. 2002, 4, 3575.
[20] V. Nair, A. N. Pillai, P. B. Beneesh, E. Suresh, Org. Lett. 2005, 7, 4625.
[21] V. Nair, A. N. Pillai, R. S. Menon, E. Suresh, Org. Lett. 2005, 7, 1189.
[22] A. Alizadeh, N. Zohreh, S. Rostamnia, Tetrahedron 2007, 63, 8083.
[23] M. Mansson, Y. Nakase, S. Sunner, Acta Chem. Scand. 1968, 22, 17 1.
[24] J. M. Briody, D. P. N. Satchell, J. Chem. Soc. 1965, 87, 3778.
[25] J. M. Briody, D. P. N. Satchell, Chem. Ind. (London, U.K.) 1964, 893.
[26] H. Eck, to Wacker Chemie GmbH, Br. Patent GB1346701, 1974; Ger. Offen. DE2154875, 1973
(Chem. Abstr. 1973, 79, 18109).
[27] E. Marcus, J. K. Chan, C. B. Strow, J. Org. Chem. 1966, 31, 1369.
[28] M. Pochan, to Lonza Ltd., Swiss Patent CH523223, 1972 (Chem. Abstr. 1972, 77, 100857); A.
Stocker, to Lonza, US. Patent US3778474, 1973 (Chem. Abstr. 1974, 80, 59503); G. Künstle, H. Spes,
H. Siegl, to Wacker-Chemie GmbH, US. Patent US4129596, 1978; Ger. Offen. DE2647499, 1978
(Chem Abstr. 1978, 442479).
[29] I. Yavari, A. Mokhtarporyani-Sanandaj, L. Moradi, Tetrahedron Lett. 2007, 18, 6709.
[30] L. Skattebol, E. R. H. Jones, M. C. Whiting, Org. Synth., Coll. Vol. 4 1963, 792.
[31] K. Bowden, I. M. Heilbron, E. R. H. Jones, B. C. Weedon, J. Chem. Soc. 1946, 39.
Received December 4, 2007