S. Rele et al. / Tetrahedron Letters 42 (2001) 9093–9095
9095
Table 3. Synthesis of phenanthrenes with salted LVT
reagents
reagents carry out all the reactions attributed to LVT
species more efficiently and at ambient temperature.
Entry
Reagent
Substrate
Product (% yields)a
References
1
2
3
4
5
6
7
Reagent B
11a
11a
11a
11a
11a
11a
11b
12a (87)
Reagent B–LiCl
Reagent B–LiCl
Reagent A
Reagent A–KCl
Reagent A–CsCl
Reagent A–CsCl
12a (65)+13a (17)
12a (60)+13a (20)
13a (36)
13a (81)
13a (84)
b
1. For excellent reviews on the synthetic applications of
low-valent titanium reagents, see: (a) McMurry, J. E.
Chem. Rev. 1989, 89, 1513–1524; (b) Lenoir, D. Synthesis
1989, 883–897; (c) Cintas, P. In Activated Metals in
Organic Synthesis; CRC Press; Boca Raton, 1993; pp.
13b (82)
1
36–152; (d) Lectka, T. In Active Metals—Preparation,
a
Isolated yields.
Characterization, Applications; Furstner, A., Ed.; VCH:
Weinheim, 1996; pp. 85–129; (e) Dushin, R. G. In Com-
prehensive Organometallic Chemistry II; Hegedus, L. S.,
Ed.; Pergamon: Oxford, 1995; Vol. 12, pp. 1071–1095.
. (a) Handa, Y.; Inanaga, J. Tetrahedron Lett. 1987, 28,
b
The reaction was carried out with 8 equiv. salt, in other cases 2
equiv. salt were used.
2
Phenanthrenes synthesis: Previously, a one-pot synthesis
of phenanthrenes from ortho-alkoxy aromatic alde-
5
717–5718; (b) Furstner, A.; Csuk, R.; Rohrer, C.; Weid-
mann, H. J. Chem. Soc., Perkin Trans. 1 1988, 1729–
734.
13
hydes/ketones was developed in this laboratory. The
synthesis involved multiple steps in tandem of which the
dealkoxylation step was found to be unique for the
reagent A. To see the influence of the salted LVT
reagent on the above reaction, a model substrate, 2%-
methoxypropiophenone (11a) was subjected to coupling
1
3. (a) Furstner, A. Pure Appl. Chem. 1998, 70, 1071–1076;
(b) Furstner, A.; Weintritt, H.; Hupperts, A. J. Org.
Chem. 1995, 60, 6637–6641.
4. Dams, R.; Malinowski, M.; Westdrop, I.; Geise, H. Y. J.
Org. Chem. 1982, 47, 248–259.
5
. (a) Balu, N.; Nayak, S. K.; Banerji, A. J. Am. Chem. Soc.
1996, 118, 5932–5937; (b) Talukdar, S.; Nayak, S. K.;
Banerji, A. J. Org. Chem. 1998, 63, 4925–4929 and
references cited therein.
. (a) Furstner, A.; Bogdanovic, B. Angew. Chem. 1996,
1
Chem., Int. Ed. Engl. 1996, 35, 2442–2469.
. Andersson, P. G. Tetrahedron Lett. 1994, 35, 2609–2610.
. Rieke, R. D.; Bales, S. F. J. Am. Chem. Soc. 1974, 96,
with a salted Tyrlik’s reagent [TiCl –Mg–THF (reagent
3
1
4
B) /LiCl (2 equiv.)], when the phenanthrene 13a was
obtained (Scheme 2) in 17% yield along with the stil-
bene 12a (65%) (Table 3, entry 2). Further increase in
the amount of LiCl (8 equiv.) improved the yield of 13a
marginally (Table 3, entry 3). Under similar conditions,
the reagent B alone furnished the stilbene 12a only
6
08, 2582–2609; (b) Furstner, A.; Bogdanovic, B. Angew.
7
8
(
Table 3, entry 1) from which the salt-mediated activa-
tion of LVT reagents was evident.
1
775–1781.
9
. (a) Wessjohann, L.; Gunter, S. Synthesis 1999, 1–36; (b)
Wessjohann, L.; Gabriel, T. J. J. Org. Chem. 1997, 62,
3772–3774.
As expected, the salted reagent A showed more pro-
nounced effect in phenanthrene synthesis. Thus, while
the ketone 11a yielded 13a in 36% yield (Table 3, entry
10. Talukdar, S.; Banerji, A. J. Org. Chem. 1998, 63, 3468–
4
) with reagent A alone, in combination with either
KCl or CsCl, it furnished 13a in vastly improved yields
81 and 84%, respectively) (Table 3, entries 5 and 6).
3470 and references cited therein.
1
1. (a) Jurisson, S.; Berning, D.; Jia, W.; Ma, D. Chem. Rev.
1
1
993, 93, 1137–1156; (b) Whitesell, J. K. Chem. Rev.
989, 89, 1581–1590; (c) Alexakis, A.; Mangeney, P. In
(
Likewise, reaction of 2%-methoxyacetophenone (11b)
Advanced Asymmetric Synthesis; Stephenson, G. R., Ed.;
Chapman and Hall: London, 1996; pp. 93–110.
with CsCl–reagent A furnished the phenanthrene 13b in
82% yield (Table 3, entry 7).
1
2. (a) Kadam, S. M.; Nayak, S. K.; Banerji, A. Tetrahedron
Lett. 1992, 33, 5129–5132; (b) Nayak, S. K.; Kadam, S.
M.; Banerji, A. Synlett 1993, 581–582.
In conclusion, a novel and simple protocol for activa-
tion of the LVT species by exogenous addition of
inorganic salts is reported. Besides being economic, the
method ensures easier product isolation as it does not
involve introduction of any organic additive. The new
1
3. Banerji, A.; Nayak, S. K. J. Chem. Soc., Chem. Commun.
1991, 1432–1434.
1
4. Tyrlik, S.; Wolochowicz, I. Bull. Soc. Chim. Fr. 1973,
2147–2148.