o-(o-Iodophenyl)phenylselenenyl ethers/t-BuLi system as an alkyllithium equivalent with structural variations

Article abstract of DOI:10.1055/s-2001-14622

o-(o-Iodophenyl)phenylselenenyl ethers/t-BuLi system can function as an alkyllithium equivalent possessing requisite structures based on an anchimeric approach. The synthetic utility as well as the limitation were evaluated in the in situ trapping reactio

Full text of DOI:10.1055/s-2001-14622

LETTER
791
o-(o-Iodophenyl)phenylselenenyl Ethers/t-BuLi System as an Alkyllithium
Equivalent with Structural Variations
Takashi Ooi, Daiki Sakai, Mio Takada, Naoki Komatsu, Keiji Maruoka*
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
Fax +81-75-753-4041; E-mail: maruoka@kuchem.kyoto-u.ac.jp
Received 6 April 2001
observation was the simple reduction of iodobenzene
moiety. This result prompted us to employ phenyselene-
nyl ether of type 2 on the assumption that selenium would
Abstract: o-(o-Iodophenyl)phenylselenenyl ethers/t-BuLi system
can function as an alkyllithium equivalent possessing requisite
structures based on an anchimeric approach. The synthetic utility as
well as the limitation were evaluated in the in situ trapping reaction be more susceptible toward the intramolecular attack of
4
with carbonyl compounds.
initially formed aryl anion. Thus, treatment of o-(o-io-
dophenyl)phenylselenenyl ether 2a with t-BuLi (2 equiv)
in THF at -78 °C for 10 min and subsequent reaction with
benzaldehyde (1 equiv) resulted in the formation of de-
sired secondary alcohol 4 in 54% isolated yield along with
dibenzoselenophene (5, X = Se, 96%) and benzyl pentyl
ether (6, 7%). Although the clean formation of 5 (X = Se)
suggested that the originally expected intramolecular an-
ion translocation process for the generation of
PhCH O(CH ) Li was operative, the chemical yield dif-
Key words: aldehydes, alkylation, alkyllithiums, anchimeric ap-
proach, selenium compounds
Recently we reported the rapid generation of carbon-cen-
tered radicals from o-(o-iodophenyl)phenylthio deriva-
tives 1, where an initially generated biphenyl radical
strongly participates in facilitating the subsequent ho-
2
2 5
molytic cleavage of a carbon-sulfur bond (eq. 1 in Scheme
1
ference between 4 and 5 as well as the production of 6 im-
plied the intervention of the selenium ate complex 7 as an5
alternative reactive species in this alkylation sequence.
Here, the use of Te in place of Se increased the chemical
yield of 4 (77%) (Scheme 2).6
1
). This chemistry led us to investigate the possibility of
generating desired alkyl metal species by the utilization of
such anchimeric effect. Taking both the versatility and the
availability with the limitation of structural types into ac-
,7
2
,3
count, we focused on the combined use of o-(o-iodophe-
nyl)phenylselenenyl derivative 2 and commercially
available alkyllithiums, expecting that various alkyllithi-
um reagents could be efficiently prepared through initial
Li-halogen exchange and subsequent translocation of the
resulting anion as illustrated in Scheme 1 (eq. 2). In this
letter, we wish to report the preliminary results of this
study and address its utility and limitation in the nucleo-
philic carbon-carbon bond formation reactions.
X
O
Ph
I
t-BuLi (2 eq) PhCHO (1 eq)
THF
-78 °C, 10 min
Ph
2
3
a (X = Se)
a (X = Te)
O
Ph
OH
X
4
5
7
4 % (from 2a)
7 % (from 3a)
R
S
R
S
cat Et B
Bu3SnH
3
Li
I
S
Se
O
Ph
R
+
5
H3C
+
1
2
O
Ph
(
eq. 1)
7
6
R
R
Se
Se
Scheme 2
I
Se
t-BuLi
Li
R
Li
+
With the information at hand, we subsequently evaluated
the synthetic utility of the present system as an alkyllithi-
um equivalent with a variety of structures in carbonyl
alkylations. Here, we employed the in situ trapping meth-
od and selected results are listed in the Table. The mixture
of 2a and benzaldehyde (2 equiv) in THF was treated with
t-BuLi (3 equiv) at -78 °C for 10 min to furnish the alky-
lation product in 60% yield (entry 1). As expected, siloxy
and alkenyl moieties were found to be preserved with this
procedure, and the corresponding secondary alcohols
(eq. 2)
Scheme 1
We initiated the examination on the feasibility of generat-
ing alkyllithiums by the treatment of o-(o-iodophe-
nyl)phenylthio ether 1 (R = (CH ) OBn) with t-BuLi,
2
5
which turned out to be totally unsuccessful and the main
Synlett 2001 No. 6, 791–792 ISSN 0936-5214 © Thieme Stuttgart · New York

7
92
T. Ooi et al.
LETTER
Table In situ Alkylation of Carbonyls by o-(o-Iodophenyl)phenyl-
selenenyl Ethers/t-BuLi
Acknowledgement
a
This work was partially supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science
and Technology, Japan.
Se
OH
R2
I
Se
I
R
+
Se
I
t-BuLi
1
2
R R C=O
R1
THF
R
-78 °C
References and Notes
(
1) T. Ooi, M. Furuya, D. Sakai, and K. Maruoka, Adv. Synth.
Catal. 2001, 343, 166.
(
2) Review: (a) D. M. Huryn, In Comprehensive Organic
Synthesis; B. M. Trost, I. Fleming, L. A. Paquette, Eds.,
Pergamon Press: New York, 1991, Vol. 1, Chapter 1.2. (b) V.
J. Lee, In Comprehensive Organic Synthesis; B. M. Trost, I.
Fleming, L. A. Paquette, Eds., Pergamon Press: New York,
1991, Vol. 4, Chapter 1.2.
(
3) (a) B. J. Wakefield, The Chemistry of Organolithium
Compounds; Pergamon: Oxford, 1974. (b) M. A. Beswick, D.
S. Wright, Comprehensive Organometallic Chemistry II; E.
W. Abel, F. G. A. Stone, G. Wilkinson, Eds., Pergamon:
Oxford, Vol. 1, 1, 1995. (c) M. Gray, M. Tinkl, V. Snieckus,
Comprehensive Organometallic Chemistry II; E. W. Abel, F.
G. A. Stone, G. Wilkinson, Eds., Pergamon: Oxford, Vol. 11,
1
, 1995. (d) B. J. Wakefield, Organolithium Method,
a
Unless otherwise noted, the reaction was carried out with 2 equiv
Academic Press: London, 1988.
1
2
b
of R R C = O and 3 equiv of t-BuLi in THF at -78 °C for 10 min.
Isolated yield. Use of 3 equiv of benzaldehyde and 4 equiv of t-Bu-
Li.
(
4) C. Paulmier, Selenium Reagents and Intermediates in Organic
Synthesis, Pergamon Press: Oxford, 1986.
c
(
5) We assumed that the ate complex 7 would not be nucleophilic
enough to react with benzaldehyde under the reaction
conditions and could give 5 and 6 by the workup procedure,
lowering the chemical yield of 4. Although this thought led us
to attempt the alkylation at higher temperature, the yield of 4
was not improved. However, involvement of the ate complex
were obtained in good yields (entries 2 and 3). The sele-
nenyl benzyl ether with tertiary amide functionality, on
exposure to the optimized conditions, functioned as the
desired benzyllithium equivalent with high efficiency and
hence the in situ trapping with several aromatic and ali-
phatic aldehydes as well as cyclohexanone worked well
8
of type 7 is still conceivable in this system and the extent
would be highly dependent on the structure of substrate, which
is difficult to precisely estimate at present.
(
6) This result probably stems from more facile lithium-tellurium
exchange. For relative rates of lithium-metalloid exchange
reactions, see: T. Kanda, S. Kato, N. Kanbe, Y. Kohara, N.
Sonoda, J. Phys. Org. Chem. 1996, 9, 29.
(7) We decided to conduct the following alkylation experiments
with selenium derivatives mainly due to the ease of the
synthesis.
(
entries 4-7). Moreover, the reaction with the selenenyl
ether possessing secondary amide moiety also appeared
feasible, though the chemical yield of the alkylation prod-
uct was lowered (entry 8).
A typical experimental procedure is as follows (Table, en-
try 1): To a solution of selenenyl ether 2a (161 mg, 0.3
mmol) and benzaldehyde (61 L, 0.6 mmol) in freshly
distilled THF (3 mL) was added a 1.51 M pentane solution
of t-BuLi (596 L, 0.9 mmol) at -78 °C under argon. After
stirring at -78 °C for 10 min, the reaction was quenched by
(
8) Alkylation with selenium ate complexes, see, for example: W.
Dumont, P. Bayet, A. Krief, Angew. Chem., Int. Ed. Engl.
1974, 13, 804.
Article Identifier:
437-2096,E;2001,0,06,0791,0792,ftx,en;Y07701ST.pdf
1
addition of saturated NH Cl solution. Extractive workup
4
was performed with ethyl acetate and the organic extracts
were dried over Na SO . Evaporation of solvents and pu-
2
4
rification of the residual oil by column chromatography
on silica gel (ethyl acetate/hexane = 1:5 as eluant) gave
6
-benzyloxy-1-phenyl-1-heptanol (4) as a colorless oil
(
51 mg, 0.18 mmol, 60% yield).
Synlett 2001, No. 6, 791–792 ISSN 0936-5214 © Thieme Stuttgart · New York