Lewis acid promoted annulation of p-quinoneimines by allylsilanes: A facile entry into benzofused heterocycles

Article abstract of DOI:10.1021/ol025503j

(equation presented) Lewis acid promoted addition of allyltriisopropylsilane to p-quinoneimines afforded different benzofused heterocycles in moderate to good yields depending on the conditions employed.

Full text of DOI:10.1021/ol025503j

ORGANIC
LETTERS
2
002
Vol. 4, No. 6
53-955
Lewis Acid Promoted Annulation of
p-Quinoneimines by Allylsilanes: A
Facile Entry into Benzofused
Heterocycles†
9
,‡
‡
‡
§
Vijay Nair,* C. Rajesh, R. Dhanya, and Nigam P. Rath
Organic Chemistry DiVision, Regional Research Laboratory (CSIR),
TriVandrum, India, and Department of Chemistry, UniVersity of Missouri,
St. Louis, Missouri 63121
gVn@csrrltrd.ren.nic.in
Received January 2, 2002
ABSTRACT
Lewis acid promoted addition of allyltriisopropylsilane to p-quinoneimines afforded different benzofused heterocycles in moderate to good
yields depending on the conditions employed.
6
Benzoquinones are versatile intermediates in organic syn-
thesis; they can participate as dienes, dienophiles, hetero-
natural product skeletons such as those of CC-1065 and
1
7
neolignans of the type licarin-B. Recently, we have reported
dienes, and heterodienophiles as well as dipolarophiles in
the dipolar cycloaddition of carbonyl ylides to p-quinone-
cycloaddition reactions.2 In contrast to the enormous interest
,3
(2) (a) Eaton, P. E.; Or, Y. S.; Branca, S. J. J Am. Chem. Soc. 1981,
4
in the chemistry of benzoquinones, the quinoneimines, their
103, 2134. (b) Engler, T. A.; Sampath, U.; Naganathan, S.; Vander Velde,
D.; Takusagawa, F.; Yohannes, D. J. Org. Chem. 1989, 54, 5712. (c) Ansell,
M. F.; Gosden, A. F.; Leslie, V. J.; Murray, R. A. J. Chem. Soc. C 1971,
5
aza analogues, have received only limited attention. Boger
and Engler have elegantly employed the Lewis acid promoted
addition of weak nucleophiles such as styrene, enamines,
and allylmetals to quinoneimines to create some interesting
1
401. (d) Horspool, W. M.; Tedder, J. M.; Din, Z. U. J. Chem. Soc. C
1969, 1692. (e) Al-Hamdany, R.; Ali, B. J. Chem. Soc., Chem. Commun.
978, 397. (f) Ansell, M. F.; Leslie, V. J. J. Chem. Soc. C 1971, 1423. (g)
Nair, V.; Kumar, S. Synlett 1996, 1035.
3) (a) Nair, V.; Kumar, S. J. Chem. Soc., Chem. Commun. 1994, 1341.
1
(
*
Fax: +91-471-491712.
(b) Nair, V.; Radhakrishnan, K. V.; Sheela, K. C.; Rath, N. P. Tetrahedron
1999, 55, 14199. (c) Nair, V.; Mathew, B. Tetrahedron Lett. 2000, 41, 6919.
(4) Adams, R.; Reifschneider, W. Bull. Chim. Soc. Fr. 1958, 23 and
references therein.
(5) (a) Friedrichsen, W.; Bottcher, A. Heterocycles 1981, 425. (b) Heine,
H. W.; Barchiesi, B. J.; Williams, E. A. J. Org. Chem. 1984, 49, 2560. (c)
Fujita, S. J. Chem. Soc., Chem. Commun. 1981, 425. (d) Holmes, T. J., Jr.;
Lawton, R. G. J. Org. Chem. 1983, 48, 3146.
†
This paper is dedicated with best regards and affection to Professor
Gilbert Stork, whose seminal contributions have profoundly influenced
organic synthesis, on the occasion of his 80th birthday.
‡
Regional Research Laboratory (CSIR).
University of Missouri.
§
(1) (a) The Chemistry of Quinonoid Compounds; Patai, S., Rappoport,
Z., Eds.; John Wiley and Sons: New York, 1988; Vol. 2, Parts 1 and 2. (b)
Naturally Occurring Quinones, Recent AdVances; Thomson, R. H.; Chapman
and Hall: New York, 1987.
(6) Boger, D. L.; Coleman, R. S. J. Am. Chem. Soc. 1988, 110, 4796.
Also see: Boger, D. L.; Zarrinmayeh, H. J. Org. Chem. 1990, 55, 1379.
1
0.1021/ol025503j CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/01/2002

8
imines. In this context and in view of our general interest
in this area, we have undertaken an investigation of the Lewis
acid promoted addition of allylsilane to quinoneimines. It is
worthy of note that although a good deal of the chemistry
of this silicon-stabilized nucleophile is known,9-14 its addition
to quinoneimines has remained practically unexplored. A
preliminary account of some unprecedented results we have
obtained are presented here.
Scheme 2
Our studies commenced by exposing a solution of p-
quinone diimine 1a and allylsilane 2a in dichloromethane
to ZnCl . In the event, a slow but unprecedented bisannu-
2
lation of the quinoneimine by allylsilane leading to the
pyrroloindole derivative 3a, in which the two silyl groups
are trans, occurred. The results of our optimization studies
revealed a striking influence of the amount and nature of
the Lewis acid used and temperature employed on the course
of the reaction. For instance, when the reaction was carried
4
out at -41 °C in the presence of 2.4 equiv of SnCl , a
dihydroindole derivative arising from monoannulation re-
sulted. Other Lewis acids also afforded the same product,
albeit in lower yields (see Supporting Information). Interest-
ingly, at room temperature, when the reaction was promoted
by BF
3
‚OEt
2
(1.1 equiv), yet another reactivity profile
manifested and the product was an indane derivative (Scheme
1
5
1).
Scheme 1
The soft Lewis acid ZnCl
2
coordinates the hard tosylimine
nitrogen loosely (weak hard-soft interaction). The â-silyl-
cation formed initially by the addition of allylsilane to the
(11) For heterocyclic construction using allylsilane, see: (a) Angle, S.
R.; El-Said, N. A. J. Am. Chem. Soc. 1999, 121, 10211. (b) Kiyooka, S.;
Shiomi, Y.; Kira, H.; Kaneko, Y.; Tanimori, S. J. Org. Chem. 1994, 59,
In the absence of any systematic study on the nature of
1
(
958. (c) Panek, J. S.; Beresis, R. T. J. Am. Chem. Soc. 1993, 115, 7898.
d) Akiyama, T.; Yamanaka, M. Synlett 1996, 1095.
12) For addition of allylsilane to CdN compounds, see: (a) Uyehara,
16
the Lewis acid-imine complexes, a plausible explanation
for the formation of the above products can be furnished by
invoking the chemical variants of the initially formed
â-silylcation as shown in Scheme 2.
(
T.; Yuuki, M.; Masai, H.; Matsumoto, M.; Ueno, M.; Sato, T. Chem. Lett.
1995, 789. (b) Panek, J. S.; Jain, N. F. J. Org. Chem. 1994, 59, 2674. (c)
Roberson, C. W.; Woerpel, K. A. J. Org. Chem. 1999, 64, 1434. (d)
Brocherieux-Lanoy, S.; Dhimane, H.; Poupon, J.-C.; Vanucci, C.; Lhommet,
G. J. Chem. Soc., Perkin Trans. 1 1997, 2163. (e) Akiyama, T.; Sugano,
M.; Kagoshima, H.; Tetrahedron Lett. 2001, 42, 3889. (f) Isaka, M.;
Williard, P. G.; Nakamura, E. Bull. Chem. Soc. Jpn. 1999, 72, 2115.
(13) For allylsilane addition to quinonoid compounds, see: (a) Hosomi,
A.; Sakurai, H. Tetrahedron Lett. 1977, 18, 4041. (b) Naruta, Y.; Uno, H.;
Maruyama, K.; Tetrahedron Lett. 1981, 22, 5221. (c) Ipaktschi, J.; Heydari,
A. Angew. Chem., Int. Ed. Engl. 1992, 31, 313. (d) Angle, S. R.; Boyce, J.
P. Tetrahedron Lett. 1994, 35, 6461. (e) Murphy, W. S.; Neville, D.
Tetrahedron Lett. 1997, 38, 7933. (f) Takuwa, A.; Sasaki, T.; Iwamoto,
H.; Nishigaichi, Y. Synthesis 2001, 63.
(14) For reviews, see: (a) Sakurai, H. Pure Appl. Chem. 1982, 54, 1.
(b) Hosomi, A. Acc. Chem. Res. 1988, 21, 200. (c) Fleming, I.; Dunogues,
J.; Smithers, R. Org. React. 1989, 37, 57. (d) Kn o¨ lker, H.-J. J. Prakt. Chem.
1997, 339, 304. (e) Masse, C. E.; Panek, J. S. Chem. ReV. 1995, 95, 1293.
(f) Fleming, I.; Barbero, A.; Walter, D. Chem. ReV. 1997, 97, 2063. (g)
Yamamoto, Y.; Asao, N. Chem. ReV. 1993, 93, 2207.
(
7) (a) Engler, T. A.; Lynch, K. O., Jr.; Chai, W.; Meduna, S. P.
Tetrahedron Lett. 1995, 36, 2713. (b) Engler, T. A.; Chai, W.; Latessa, K.
J. Org. Chem. 1996, 61, 9297.
(
8) Nair, V.; Rajesh, C.; Dhanya, R.; Vinod, A. U. Tetrahedron Lett.
001, 42, 2045
9) Allylsilane as allyl anion equivalent: Hosomi, A.; Sakurai, H. J. Am.
Chem. Soc. 1977, 99, 1673.
10) For carbocyclic construction using allylsilane, see: (a) Danheiser,.
2
(
(
R. L.; Dixon, B. R.; Gleason, R. W. J. Org. Chem. 1992, 57, 6094. (b)
Panek, J. S.; Jain, N. F. J. Org. Chem. 1993, 58, 2345 (c) Monti, H.; Audran,
G.; Monti, J.-P.; L e´ andri, G. Synlett 1994, 403. (d) Kn o¨ lker, H.-J.; Foitzik,
N.; Goesmann, H.; Graf, R. Angew. Chem., Int. Ed. Engl. 1993, 32, 1081.
e) Kn o¨ lker, H.-J.; Jones, P. G.; Pannek, J.-B. Synlett 1990, 429. (f) Brengel,
G. P.; Rithner, C.; Meyers, A. I. J. Org. Chem. 1994, 59, 5144. (g) Hojo,
M.; Murakami, C.; Nakamura, S.; Hosomi, A. Chem. Lett. 1998, 331.
(
954
Org. Lett., Vol. 4, No. 6, 2002

20
Lewis acid complexed quinoneimine is quenched by the
imine nitrogen to afford an iminium species D as depicted
in Scheme 2. This electrophilic species undergoes attack by
a second molecule of allylsilane, and the quenching of the
â-silylcation so formed by the enamide nitrogen affords 3a
after aromatization. An alternate explanation is that since
electrophilic sites, and their reaction seemed to be interest-
ing both from the mechanistic and synthetic standpoints. In
practice, the reaction afforded dihydrobenzofuran derivative
(Scheme 4) irrespective of the Lewis acid and temperature
2
the ZnCl -catalyzed reaction is so slow, the initially formed
Scheme 4
monoadduct is further oxidized by the unreacted imino-
quinone affording an iminium intermediate that undergoes
17
the second addition of allylsilane. In the case of hard Lewis
acids, SnCl and BF ‚OEt , the initial coordination to the
4
3
2
imine nitrogen is strong (hard-hard interaction) and hence
the monocoordinated species is highly reactive. Here the
stability of the â-silylcation formed holds the key. At -41
°
4
C in the presence of SnCl , the silylcation formed is stable
so that an imide-enamide-type equilibrium is established
prior to the quenching of the cation. This results in the
formation of 4a. When the reaction is carried out at room
employed (see Supporting Information). In this case, con-
ceivably, the initial addition of allylsilane occurs in a
conjugate fashion to the imine moiety. The subsequent
quenching of the silylcation by the keto oxygen furnishes
the dihydrobenzofuran derivative.
Thus, from the present study it is apparent that allylsilanes
temperature in the presence of BF
3 2
‚OEt , the initially formed
â-silylcation is highly reactive so that the quenching of the
cationic species, with a concomitant 1,2-silyl shift, through
the C-terminus of the enaminoborane occurs prior to tau-
tomerization, culminating in the formation of 5a, which is
the thermodynamically favored product. In this scheme of
events, the low nucleophilicity of sulfonimide nitrogen also
is important; otherwise it is likely to quench the â-silylcation
as soon as it is formed (Scheme 2).
2
1
undergo facile addition to p-quinoneimines affording formal
[3 + 2] and [2 + 3] adducts. The products are substituted
dihydroindole, dihydrobenzofuran, and indane derivatives.
Efforts to extend the scope of the reaction and to examine
further transformation of the adducts are currently underway.
A general observation that can be made from the above
study is that although lower temperature and presence of
excess Lewis acid favor the formation of dihydroindole
derivative, elevated temperature and stoichiometric amount
of Lewis acid promote the indane derivative formation. It
may be discerned that both higher temperature and excess
Lewis acid would allow tautomerization to preponderate over
â-silylcation quenching.18
Acknowledgment. C.R. and R.D. thank Council of
Scientific and Industrial Research, New Delhi for research
fellowships. Financial assistance from American Cyanamid
Company, U.S.A. is gratefully acknowledged.
Supporting Information Available: Schemes showing
effect on the reaction of the nature and amount of Lewis
acid used and the temperature employed. General experi-
In the case of ring-substituted p-quinoneimine 1b, the
reaction proceeded only when promoted by SnCl , in which
4
case the expected dihydroindole derivative resulted. When
1
13
mental procedure; IR, H NMR and C NMR spectral data
of compounds 3a, 4a-c, 5a, and 6a,b; and single-crystal
X-ray structure for 3a. This material is available free of
charge via the Internet at http://pubs.acs.org.
allyltriphenylsilane 2b was employed, it required a combina-
4 2
/Me
AlCl19 for the reaction to occur (Scheme
tion of SnCl
).
p-Benzoquinone monoimines appeared to be impressive
3
OL025503J
(
15) For characterization data, see Supporting Information.
substrates for the present study as they offer four different
(16) Denmark has spectroscopically studied the metal enolate formed
by Lewis acid addition of allyltrimethylsilane to enones: Denmark, S. E.;
Almstead, N. G. Tetrahedron 1992, 48, 5565.
(
(
17) The authors are thankful to a reviewer for suggesting this pathway.
18) The ability of allylsilanes to act as either two- or three-atom
Scheme 3
components in formal dipolar cycloaddition is well precedented. It is,
however, noteworthy that the versatility of the quinoneimine and the multiple
reaction profiles they elicit are predicated by the availability of different
nucleophilic sites and the possibility of tautomerization.
(19) It is believed that Me2AlCl acts as a proton sponge thereby
preventing the protodesilylation of the starting material, allyltriphenysi-
lane: Snider, B. B.; Rodini, D. J.; Conn, R. S. E.; Sealfon, S. J. J. Am.
Chem. Soc. 1979, 101, 5285. For an excellent study employing Me2AlCl
in allylsilane addition, see: Organ, M. G.; Winkle, D. D.; Huffman, J. J.
Org. Chem. 1997, 62, 5254.
(
20) Engler, T. A.; Wanner, J. Tetrahedron Lett. 1997, 38, 6135.
(21) This contrasts with the low nucleophilicity of the imine nitrogen,
which plays a crucial role in the scheme of events as mentioned earlier.
Org. Lett., Vol. 4, No. 6, 2002
955