A simple method for the conversion of propargyl alcohols to symmetrical 1,5-diynes using low valent titanium reagents

Article abstract of DOI:10.1016/j.tetlet.2006.03.097

Reaction of propargyl alcohols with low valent titanium species, prepared using the TiCl₄/Et₃N and TiCl₄/Zn reagent systems, gives the corresponding symmetrical 1,5-diynes in 56-74% yields.

Full text of DOI:10.1016/j.tetlet.2006.03.097

Tetrahedron Letters 47 (2006) 3549–3552
A simple method for the conversion of propargyl alcohols
to symmetrical 1,5-diynes using low valent titanium reagents
Galla V. Karunakar and Mariappan Periasamy*
School of Chemistry, University of Hyderabad, Central University P.O., Hyderabad 500 046, India
Received 1 January 2006; revised 3 March 2006; accepted 15 March 2006
Available online 5 April 2006
Abstract—Reaction of propargyl alcohols with low valent titanium species, prepared using the TiCl4/Et3N and TiCl4/Zn reagent
systems, gives the corresponding symmetrical 1,5-diynes in 56–74% yields.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1,5-Diynes are an important class of compounds useful
for the synthesis of enediynes,1 1,5-enynes,2 1,5-dienes,3
alkylidenecyclopentenones, butenolides,4 pyrroles,5
unsaturated macrocyclic compounds6 and several phar-
maceutically important compounds.7 Hence, the devel-
opment of methods for the synthesis of 1,5-diynes is
important. During the course of our research efforts
towards the development of organotitanium reagents,8,9
we have developed a one-pot method for the synthesis of
1,5-diynes from the corresponding propargyl alcohols
using low valent titanium species. The results are
reported herein.
OH
R2
R1
R1
R1
R2
R2
TiCl4/Et3N
or
TiCl4/Zn
0 oC, 1 h
CH2Cl2
H
"TiCl3"
0-25 oC, 6 h
Scheme 1.
obtained in the case of the 1,5-diyne 2h was found to
be dl as revealed by single crystal X-ray analysis.11
The ORTEP diagram of the crystal structure of the
1,5-diyne 2h is shown in Figure 1.
We observed that the reaction of undec-5-yn-4-ol 1a
(R1 = C5H11, R2 = C3H7) with the low valent titanium
species, produced in situ using the TiCl4/Et3N or
TiCl4/Zn reagent system, gave the corresponding 1,5-
diyne 2a in a 71% yield (Scheme 1).10 We also examined
the reaction of propargyl alcohol 1a using the titanium
reagent prepared with various amines including Bu3N,
iPr2NEt and Et3N (Table 1, entries 1–3).
The reaction in the case of the propargyl alcohol 1k gave
the corresponding allenyne 3a in 51–61% yields using
different amines (Scheme 2).12
The structure of the allenyne 3a was confirmed by single
crystal X-ray analysis.13 The ORTEP diagram of 3a is
shown in Figure 2.
Optimum results were obtained using the readily acces-
sible triethylamine (Table 1, entry 1). Several other
propargyl alcohol derivatives were converted to the
corresponding symmetrical 1,5-diynes under these
conditions (Table 1). The yields were in the range of
58–74%. The 1,5-diynes were obtained as diastereomeric
mixtures in some cases (Table 1). The major isomer
A tentative mechanism involving reaction of the Ti(III)
species,8h produced in situ with the propargyl alcohol
followed by homolysis of the carbon oxygen bond, to
give a Ti(IV) and propargyl radical species may be con-
sidered. The propargyl radicals could then couple to give
the 1,5-diyne and allenyne depending upon the steric
requirements (Scheme 3).
We also examined this transformation using the tita-
nium reagent prepared by reducing TiCl4 with Zn, since
this system also gives TiCl3 as the major species (Scheme
1).14 The results are summarized in Table 2.
Keywords: Symmetrical 1,5-diynes; Low valent titanium species; Prop-
argyl alcohols.
*
Corresponding author. Tel.: +91 40 23134814; fax: +91 40
23012460; e-mail: mpsc@uohyd.ernet.in
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.03.097

3550
G. V. Karunakar, M. Periasamy / Tetrahedron Letters 47 (2006) 3549–3552
Table 1. Conversion of propargyl alcohols into 1,5-diynes using the TiCl4/R3N reagent systema
Entry
Substrate
Reducing agent
Productb
Diastereomeric ratioc
Yieldd (%)
R1
R1
R2
R2
OH
R2
H
R1
1
Et3N
100:0
71
1a
R1 = C5H11 R2 = C3H7
R1 = C5H11 R2 = C3H7
2a
2
3
4
5
6
7
8
9
10
1a
Bu3N
iPr2NEt
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
2a
100:0
100:0
86:14
100:0
100:0
100:0
100:0
100:0
87:13
66
61
68
69
74
68
58
63
61
1a
2a
R1 = C5H11, R2 = iBu 1b
R1 = C5H11, R2 = C7H15 1c
R1 = C5H11, R2 = C9H19 1d
R1 = Ph, R2 = C4H9 1e
R1 = Ph, R2 = C7H15 1f
R1 = Ph, R2 = C9H19 1g
R1 = Ph, R2 = 1-Naphth 1h
R1 = C5H11, R2 = iBu 2b
R1 = C5H11, R2 = C7H15 2c
R1 = C5H11, R2 = C9H19 2d
R1 = Ph, R2 = C4H9 2e
R1 = Ph, R2 = C7H15 2f
R1 = Ph, R2 = C9H19 2g
R1 = Ph, R2 = 1-Naphth 2h
a The reactions were carried out using TiCl4 (2 mmol), R3N (4 mmol) and propargyl alcohol (2 mmol).
b All the products (2a–h) were identified by IR, 1H NMR, 13C NMR and mass spectral data and the products 2a–f and 2h were also characterized by
elemental analysis.
c Diastereomeric ratios were estimated from 1H NMR (400 MHz) spectral signals.
d Yields of isolated products.
Figure 2. An ORTEP representation of the crystal structure of
allenyne 3a. (Thermal ellipsoids are drawn at 20% probability.)
Figure 1. An ORTEP representation of the crystal structure of 1,5-
diyne 2h. (Thermal ellipsoids are drawn at 15% probability.)
_
3 Cl
+
H
C
2Et3N
+
Et2N
CH
TiCl4
+
"TiCl3"
_
Et3NHCl
OH
R2
R3
R1
C
C
Et3N
TiCl2
C
C
C
Intractable
organic product
O
R1
C C
R2
TiCl4/R3N
OH
R3
25 oC, 6 h,
C
C
CH2Cl2
TiCl4/Et3N
C
O
TiCl2
R1
58%
R2
R3
R1
C
R2
1k
C
C
C C
TiCl4/Bu3N 61%
TiCl4/PhNEt2 51%
3a
R3
R2
Scheme 2.
R1
R1
C
R3
R3
R2
R2
C
C C
C
R2
R3
R3
C
C
Previously, 1,5-diynes had been prepared via the reac-
tion of 1,3-dilithiopropyne and propargyl chloride,15a
or 3-silylpropargyl carbonates using a palladium cata-
lyst,15b and via the reaction of propargyl carbonates
C
C
R1
R1
Scheme 3.

G. V. Karunakar, M. Periasamy / Tetrahedron Letters 47 (2006) 3549–3552
3551
Table 2. Conversion of propargyl alcohols into 1,5-diynes using the TiCl4/Zn reagent systema
Entry
Substrate
Productb
Diastereomeric ratioc
Yieldd (%)
R1
R2
R2
OH
R2
R1
1
100:0
63
R1
1a
R1 = C5H11 R2 = C3H7
2a
2
3
4
5
6
R1 = C5H11, R2 = C9H19 1d
R1 = Ph, R2 = C4H9 1e
R1 = Ph, R2 = 1-Naphth 1h
R1 = C5H11, R2 = 1-Naphth 1i
R1 = C5H11, R2 = Ph 1j
R1 = C5H11, R2 = C9H19 2d
R1 = Ph, R2 = C4H9 2e
100:0
100:0
84:16
83:17
87:13
58
68
71
66
56
R1 = Ph, R2 = 1-Naphth 2h
R1 = C5H11, R2 = 1-Naphth 2i
R1 = C5H11, R2 = Ph 2j
a The reactions were carried out using TiCl4 (2 mmol), Zn (4 mmol) and propargyl alcohol (2 mmol).
b All the products (2a–j) were identified by IR, 1H NMR, 13C NMR and mass spectral data and the products 2a–h were also characterized by
elemental analysis.
c Diastereomeric ratios were estimated from 1H NMR (400 MHz) spectral signals.
d Yields are of isolated products.
mediated by Ti(OiPr)2Cl2/Mg.15c Since 1,5-diynes can
now be readily accessed via simple one-pot procedures,
the methods described here have considerable potential
for further synthetic exploitation.
6. (a) Sondheimer, F.; Ben-Efraim, D. A.; Gaoni, Y. J. Am.
Chem. Soc. 1961, 83, 1682–1685; (b) Sondheimer, F.; Ben-
Efraim, D. A.; Wolousky, R. J. Am. Chem. Soc. 1961, 83,
1675–1681.
7. (a) Gilchrist, T. L. J. Chem. Soc., Perkin Trans. 1 1999,
2849–2866; (b) Pyrroles, Chemistry of Heterocyclic Com-
pounds; Jones, R. A., Ed.; Wiley: New York, 1990; Vol. 48,
Acknowledgements
(c) Faills, A. G.; Forgione, P. Tetrahedron 2001, 57, 5899–
5913.
We thank the ILS-UOH, for a senior research fellowship
to G.V.K. and a research Grant to M.P. Support of the
DST, for the 400 MHz NMR facility under the FIST
program and also for the National Single Crystal
XRD facility is gratefully acknowledged. We are also
grateful to the UGC, for support under the ‘University
of Potential for Excellence (UPE)’ and the Centre for
Advance Study (CAS) programs.
8. (a) Periasamy, M.; Jayakumar, K. N.; Bharathi, P. J. Org.
Chem. 2005, 70, 5420–5425; (b) Periasamy, M.; Suresh, S.;
Ganesan, S. S. Tetrahedron Lett. 2005, 46, 5521–5524; (c)
Suresh, S.; Periasamy, M. Tetrahedron Lett. 2004, 45,
6291–6294; (d) Periasamy, M.; Kishorebabu, N.; Jaya-
kumar, K. N. Tetrahedron Lett. 2003, 44, 8939–8941; (e)
Periasamy, M. ARKIVOC 2002, VII, 151–166; (f) Perias-
amy, M.; Jayakumar, K. N.; Bharathi, P. Chem. Commun.
2001, 1728–1729; (g) Bharathi, P.; Periasamy, M. Org.
Lett. 1999, 1, 857–859; (h) Periasamy, M.; Srinivas, G.;
Karunakar, G. V.; Bharathi, P. Tetrahedron Lett. 1999,
40, 7577–7580.
References and notes
9. Bharathi, P.; Periasamy, M. Organometallics 2000, 19,
5511–5513.
1. (a) Dai, W. M.; Fong, K. C. Tetrahedron Lett. 1996, 37,
8413–8416; (b) Dai, W.; Fong, K. C.; Danjo, H.; Nishi-
moto, S. Angew. Chem., Int. Ed. Engl. 1961, 35, 779–781;
(c) Jones, G. B.; Wright, J. M.; Plourde, G. W., II; Hynd,
G.; Huber, R. S.; Mathews, J. E. J. Am. Chem. Soc. 2000,
122, 1937–1944; (d) Nuss, J. M.; Murphy, M. M.
Tetrahedron Lett. 1994, 35, 37–40; (e) Negishi, E.; Rand,
C. L.; Jadhav, K. P. J. Org. Chem. 1981, 46, 5041–5044; (f)
Myers, A. G.; Dragovich, P. S. J. Am. Chem. Soc. 1992,
114, 5859–5860; (g) Zein, N.; Schroeder, D. R. In
Advances in DNA Sequence Specific Agents; Jones, G. B.,
Ed.; Jai Press: Greenwich, CT, 1998; Vol. 3.
2. (a) Keinan, E.; Bosch, E. J. Org. Chem. 1986, 51, 4006–
4016; (b) Henrick, C. A. Tetrahedron 1977, 33, 1845–1889;
(c) Taber, D. F.; He, Y.; Xu, M. J. Am. Chem. Soc. 2004,
126, 13900–13901; (d) Uenishi, J.; Matsui, K. Tetrahedron
Lett. 2001, 42, 4353–4355.
10. Typical procedure for the preparation of 1,5-diynes using
the TiCl4/Et3N reagent system: In dichloromethane
(35 mL), TiCl4 (0.38 g, 0.2 mL, 2 mmol) and Et3N (0.4 g,
0.56 mL, 4 mmol) were taken at 0 ꢁC under N2. The
reaction mixture was stirred for 1 h at 0 ꢁC. To this,
undec-5-yn-4-ol 1a (0.34 g, 2 mmol) was added and the
reaction mixture stirred for another 6 h at 25 ꢁC. Satu-
rated NH4Cl solution (10 mL) was added and the reaction
mixture stirred for 10 min. The organic layer was sepa-
rated and the aqueous layer was extracted with CH2Cl2
(2 · 15 mL). The combined organic extract was washed
with brine solution (5 mL) and dried over anhydrous
Na2SO4. The solvent was removed and the residue was
chromatographed on a silica gel column using hexane as
eluent to afford the 1,5-diyne 2a (0.214 g, 71%). A similar
procedure was followed for experiments using propargyl
alcohol (2 mmol), TiCl4 (2 mmol), Zn (4 mmol) in DCM
(35 mL) and THF (2 mL). Spectral data for products 2a–j.
Compound 2a: IR (neat) 2961, 2235, 1460 cmÀ1; (diaste-
3. Dumond, Y.; Negishi, E. J. Am. Chem. Soc. 1999, 121,
11223–11224.
4. Sugamwara, S.; Uemura, K.; Tsukada, N.; Inoue, Y.
J. Mol. Cat. A: Chem. 2003, 195, 55–61.
1
reomeric ratio) dr 100:0; H NMR (400 MHz, CDCl3, d
5. Balasubramanian, R.; Keith, A. J.; Armstrong, D.; Odom,
A. L. Org. Lett. 2004, 6, 2957–2960.
ppm) 0.89–0.97 (m, 12H), 1.21–1.36 (8H), 1.50–1.57 (8H),
1.88–1.92 (4H), 2.21–2.24 (4H), 4.54–4.58 (m, 2H); 13C

3552
G. V. Karunakar, M. Periasamy / Tetrahedron Letters 47 (2006) 3549–3552
NMR (100 MHz, CDCl3, d ppm): 13.2, 13.9, 18.7, 19.5,
H = 5.38%. Compound 2i: IR (KBr) 2928, 2231,
1456 cmÀ1; dr 83:17; 1H NMR (400 MHz, CDCl3, d
ppm) 0.85–0.96 (t, 6H, J = 8.4 Hz), 1.19–1.57 (m, 12H),
1.57–2.26 (4H), 4.87 (s, 1H), 5.05 (s, 1H), 7.31–8.19 (m,
14H); 13C NMR (100 MHz, CDCl3, d ppm): 14.0, 18.2,
22.2, 28.3, 28.7, 31.0, 40.9, 80.5, 85.0, 123.3, 125.3, 125.4,
125.8, 127.1, 127.6, 129.1, 133.7, 136.0; MS (EI) m/z =
470. Compound 2j: IR (KBr) 2930, 2232, 1462 cmÀ1; dr
87:13; 1H NMR (400 MHz, CDCl3, d ppm) 0.91 (t, 6H,
J = 7 Hz), 1.22–1.46 (m, 8H), 1.60–1.74 (m, 4H), 2.30–
2.34 (m, 4H), 5.23 (s, 1H), 5.64 (s, 1H), 7.26–7.37 (m, 6H),
7.37–7.58 (m, 4H); 13C NMR (100 MHz, CDCl3, d ppm):
13.9, 18.9, 22.1, 28.3, 31.1, 69.5, 78.1, 88.7, 127.6, 127.8,
128.2, 139.3.; MS (EI) m/z = 370.
22.1, 28.1, 30.9, 41.6, 49.3, 78.6, 87.2; MS (EI) m/z = 302.
Elemental analysis for C22H38, calculated C = 87.34%,
H = 12.66%, observed C = 87.37%, H = 12.63%. Com-
1
pound 2b: IR (neat) 2959, 2237, 1467 cmÀ1; dr 86:14; H
NMR (400 MHz, CDCl3, d ppm) 0.82–1.00 (m, 18H),
1.29–1.42 (m, 10H), 1.48–1.61 (4H), 1.78–1.85 (4H), 2.17–
2.24 (4H), 4.54–4.57 (2H). Additional signals for the
minor isomer 1.86–1.91 (4H), 1.94–2.01 (4H), 2.37–2.45
(2H, m); 13C NMR (100 MHz, CDCl3, d ppm): 13.4, 18.7,
21.9, 22.3, 25.7, 28.1, 30.8, 48.2, 48.6, 87.2, 98.5; MS (EI)
m/z = 330. Elemental analysis for C24H42, calculated
C = 87.19%, H = 12.81%, observed C = 87.17%, H =
12.83%. Compound 2c: IR (neat) 2928, 2233, 1458 cmÀ1
;
1
dr 100:0; H NMR (400 MHz, CDCl3, d ppm) 1.88–1.67
(m, 12H), 1.23–1.32 (m, 24H), 1.43–1.49 (8H), 1.81–1.86
(4H), 2.14–1.18 (4H), 4.45–4.49 (2H); 13C NMR
(100 MHz, CDCl3, d ppm): 14.1, 18.7, 22.6, 26.2, 28.1,
28.8, 29.1, 29.4, 31.0, 31.6, 31.9, 39.7, 49.7, 78.7,87.3; MS
(EI) m/z = 414. Elemental analysis for C30H54, calculated
C = 86.88%, H = 13.12%, observed C = 86.81%, H =
11. Crystal data: For the 1,5-diyne 2h: molecular formula:
C76H52, MW = 965.18, triclinic, space group: P1,
˚
˚
˚
a = 10.1221(8) A, b = 14.9303(12) A, c = 18.7341(15) A,
a = 90.8400(10)ꢁ, b = 103.840(2)ꢁ, c = 90.520(2)ꢁ, V =
2748.5(4) A , Z = 2, qc = 1.166 mg mÀ3
,
l = 0.066
3
˚
mmÀ1, T = 298 K, of the 21,406 reflections collected,
7174 were unique [Rint = 0.0563]. Refinement on all data
converged at R1 = 0.0734, wR2 = 0.2016. (Deposition
number CCDC 293657.)
13.19%. Compound 2d: IR (neat) 2959, 2231, 1462 cmÀ1
;
1
dr 100:0; H NMR (400 MHz, CDCl3, d ppm) 1.67–1.88
(m, 12H), 1.23–1.32 (m, 24H), 1.43–1.49 (m, 8H), 1.81–
1.86 (8H, m), 2.14–2.18 (m, 8H), 4.45–4.49 (2H); 13C
NMR (100 MHz, CDCl3, d ppm): 14.1, 18.7, 22.2, 22.6,
24.5, 25.7, 26.2, 28.1, 28.8, 29.1, 31.0, 31.6, 31.9, 39.7, 49.7,
78.7, 87.3; MS (EI) m/z = 470. Elemental analysis calcu-
lated for C34H62, calculated C = 86.73%, H = 13.27%,
observed C = 86.71%, H = 13.29%. Compound 2e: IR
12. Procedure for the preparation of allenyne 3a using the
TiCl4/Et3N reagent system: In dichloromethane (35 mL),
TiCl4 (0.38 g, 0.2 mL, 2 mmol) and Et3N (0.3 g, 0.42 mL,
3 mmol) were taken at 0 ꢁC under N2. The reaction
mixture was stirred for 1 h at 0 ꢁC. To this, 1,1,3-
triphenyl-2-propyne-1-ol 1k, (0.568 g, 2 mmol), was added
and the reaction allowed to stir for another 12 h at 25 ꢁC.
Saturated NH4Cl solution (10 mL) was added and stirring
was continued for 10 min. The organic layer was separated
and the aqueous layer was extracted with CH2Cl2
(2 · 15 mL). The combined organic extract was washed
with brine solution (5 mL) and dried over anhydrous
Na2SO4. The solvent was removed and the residue was
chromatographed on a silica gel column with hexane to
give allenyne 3a (0.34 g, 64%). Spectral data: 3a: IR (KBr)
2926, 2230, 1948, 1489 cmÀ1; 1H NMR (400 MHz, CDCl3,
d ppm) 7.11–7.63 (m, 30H); 13C NMR (100 MHz, CDCl3,
d ppm): 54.8, 87.2, 93.5, 115.8, 123.5, 126.9, 127.0, 127.4,
127.8, 128.0, 128.1, 128.2, 128.3, 128.7, 128.8, 131.6, 135.0,
136.2, 143.8, 209.3; MS (EI) m/z = 534. Elemental analysis
for C42H30, calculated C = 94.34%, H = 5.66%; observed
C = 94.43%, H = 5.55%.
;
(neat) 2992, 2234, 1486 cmÀ1 dr 100:0; 1H NMR
(400 MHz, CDCl3, d ppm) 1.02 (t, 6H, J = 7 Hz), 1.40–
1.47 (m, 4H), 1.59–1.66 (m, 4H), 2.06–2.12 (m, 4H), 4.82
(t, 2H, J = 6.4 Hz), 7.34–7.50 (m, 10H); 13C NMR
(100 MHz, CDCl3, d ppm): 13.9, 22.0, 28.4, 39.1, 49.3,
86.0, 87.5, 122.2, 128.3, 128,7, 131.8; MS (EI) m/z = 342.
Elemental analysis for C26H30, calculated C = 91.17%,
H = 8.83%, observed C = 91.21%, H = 8.79%. Com-
1
pound 2f: IR (neat) 2932, 2231, 1478 cmÀ1; dr 100:0; H
NMR (400 MHz, CDCl3, d ppm): 0.85 (t, J = 7.1 Hz, 6H),
1.22–1.51 (m, 10H), 1.62–1.73 (m, 4H), 1.18–1.46 (m, 6H),
2.06–2.15 (m, 4H), 4.84 (s, 2H), 7.10–7.21 (m, 10H); 13C
NMR (100 MHz, CDCl3, d ppm): 14.1, 22.7, 26.3, 28.8,
29.1, 31.4, 39.4, 49.4, 86.1, 87.6, 122.3, 128.4, 128.7, 131.8;
MS (EI) m/z = 426. Elemental analysis for C32H42,
calculated C = 90.08%, H = 9.92%, observed C =
90.11%, H = 9.89%. Compound 2g: IR (neat) 2926,
13. Crystal data: For the allenyne 3a: C42H30, MW = 534.66,
˚
triclinic, space group: P1, a = 9.3743(6) A, b = 10.2376(7)
1
2231, 1491 cmÀ1; dr 100:0; H NMR (400 MHz, CDCl3,
A, c = 16.0252(10) A, a = 86.6500(10)ꢁ, b = 89.4930(10)ꢁ;
˚
˚
3
˚
d ppm) 0.92 (t, 6H, J = 6.8 Hz), 1.25–1.42 (m, 24 H), 1.59–
1.68 (m, 4H), 2.04–2.10 (m, 4H), 4.80 (s, 2H), 7.33–7.48
(m, 10H); 13C NMR (100 MHz, CDCl3, d ppm): 14.1,
22.7, 26.3, 29.3, 29.5, 29.6, 29.7, 31.9, 39.4, 49.4, 86.0, 87.5,
122.3, 127.8, 127.9, 131.8; MS (EI) m/z = 482. Compound
c = 78.4450(10)ꢁ, V = 1504.19(17) A , Z = 2, qc =
1.180 mg mÀ3, l = 0.067 mmÀ1, T = 298 K, of the 17,711
reflections collected, 7064 were unique [Rint = 0.0485].
Refinement on all data converged at R1 = 0.0564,
wR2 = 0.1612. (Deposition number CCDC 293656.)
14. Periasamy, M.; Srinivas, G.; Suresh, S. Tetrahedron Lett.
2001, 42, 7123–7125.
1
2h: IR (KBr) 2930, 2223, 1461 cmÀ1; dr 87:13; H NMR
(400 MHz, CDCl3, d ppm) 5.21 (1H, dl), 5.92 (1H, meso),
7.18–7.90 (m, 24H); 13C NMR (100 MHz, CDCl3, d ppm):
63.6, 68.4, 69.7, 87.0, 88.7, 124.2, 125.1, 125.2, 125.5,
126.2, 126.7, 127.9, 128.3, 128.9, 129.4, 130.5, 131.8, 132.9,
133.8; MS (EI) m/z = 482. Elemental analysis for C38H26,
calculated C = 94.57%, H = 5.43%, observed C = 94.62%,
15. (a) Pereira, A. R.; Cabezas, J. A. J. Org. Chem. 2005, 70,
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