7.19 (s, 10 H) and 2-phenylacetophenone 2 (0.165 g,. 14%), m.p. 58-59 OC (lit. l3 m.p. 60 OC). IR (KBr):. 3080, 3060, 1690, 1610 cm-l. NMR (CDC13): 6 4.1 (s,.
This article was downloaded by: On: 17 January 2011 Access details: Access Details: Free Access Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 3741 Mortimer Street, London W1T 3JH, UK
Synthetic Communications
Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713597304
A Facile Reductive Cleavage of Allylic and Benzylic Esters with Low Valent Titanium Reagents K. Satyanarayanaa; N. Chidambarama; S. Chandrasekarana a Department of Chemistry, Indian Institute of Technology, Kanpur, India
To cite this Article Satyanarayana, K. , Chidambaram, N. and Chandrasekaran, S.(1989) 'A Facile Reductive Cleavage of
Allylic and Benzylic Esters with Low Valent Titanium Reagents', Synthetic Communications, 19: 11, 2159 — 2166 To link to this Article: DOI: 10.1080/00397918908052611 URL: http://dx.doi.org/10.1080/00397918908052611
PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
SYNTHETIC COMMUNICATIONS, 19(11&12), 2159-2166 (1989)
A FACILE REDUCTIVE CLEAVAGE OF ALLYLIC AND BENZYLIC
ESTERS WITH LOW VALENT TITANIUM REAGENTS
K. Satyanarayana,
*
N. Chidambaram and S. Chandrasekaran
Downloaded At: 08:50 17 January 2011
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
-
The reductive cleavage of allylic and benzylic esters titanium(I1) reagent derived from Mg/Hg-TiC14 yielded the corresponding acids a and dimeric hydrounder mild reaction conditions. carbons
a with
Allylic and benzylic esters are often used as protective groups for carboxylic acids. methods
There are a
few
available for the non-saponicative hydrolysis
of these esters. Reported methods include the specific deblocking
of cinnamyl esters by Corey and Tius
using
successive methoxymercuration and demercuriocarboxylation procedure,' and cleavage of allylic lithium have
dimethylcuprate.
esters with
Cleavage of benzylic
esters
been achieved with nitrosonium hexafluorophosph-
ate,3 palladium on carbonI4 sodium in liquid
-
* To whom
-
-
correspondence should be addressed. 2159
Copyright 0 1989 by Marcel Dekker, Inc.
ammonia5
2160
SATYANARAYANA, CHIDAMBARAM, AND CHANDRASEKARAN
and
chromium
Barton’
has
trioxide
chlorotrimethylsilane.6
and
reported the deoxygenation of
sterically
hindered esters with lithium/ethylamine. Earlier work from our laboratories has shown
that
the low valent titanium reagent generated by the reduction
of titanium tetrachloride with amalgamated magne-
sium is very useful in the reductive coupling of carbonyl
compounds’
Downloaded At: 08:50 17 January 2011
nitro compounds. benzylic
in
the
selective reduction of
We anticipated that the allylic
and
esters of carboxylic acids on treatment with
low valent anionic
and
titanium reagents would form
intermediate
A
which would
the
radical
readily
undergo
cleavage of the C-0 bond with the formation of carboxylate anion and a stable allylfienzyl radical (Scheme 1):
B R’ = -CH2Ph or -CH2-CH=CH2
Hence the
it appeared reasonable to study this method
deblockine of allylic and benzylic
esters
for
under
mild reaction conditions. Herein cleavage of
we
report
our results on
the
allylic and benzylic esters
reductive
with
Ti(I1)
CLEAVAGE OF ALLYLIC AND BENZYLIC ESTERS
2161
reagents generated by the reduction of TiC14 with amalgamated magnesium and they are summarised in the Table. Esters at lic
bd (Table) on treatment with Ti(I1)
for 2 h yielded the corresponding carboxy-
0-20 OC acids
and the dimeric hydrocarbons
acetophenone
5 (14%) was also formed.
Formation
earlier
is possible that the dimeric hydrocarbons 2a-f
formed
of
like 5 from benzylbenxoates have been reported 10 in the reaction with lithium naphthalenide.
ketones
Downloaded At: 08:50 17 January 2011
U . In
apart from the above .products, 2-phenyl-
the case of
It
reagents
from
reaction
diols 4~
conditions
alicyclic ester
by
hydrogenolysis
under
whereas the diol 4g derived
are the from
undergoes deoxygenation to yield the
olefin 2g. l 1 (Scheme 2) :
R-CH2-CH2-R
R-CHzCH-R
2le.f
2g
Another pathway for the formation of the dimeric hydrocarbons lic acids is
based
2ra;f could be by further reduction of carboxy-
with low valent titanium reagents. on the observation that benzoic acid
This
on
2162
SATYANARAYANA, CHIDAMBARAM, AND CHANDRASEKARAN
TABLE
Reductive Cleavage of Allylic and Beneylic Esters with TiC14/Mg-Hg
:
Entry
Substrate
Dimeric hydrocarbona
Acida
(Yield %)b
(Yield
%Ib
0
II
Downloaded At: 08:50 17 January 2011
1
Ph-C-0-CH$h lA
PhCH 2- CH $h 2.a (18%)
Ph-COOH 3 2 (64%)
+ PhCH2-C-Ph 8
2
d
s
Ph-C-OCH2CH=CH2
(14%)
Za ( 2 3 % )
& I (57%)
Ih 3
4
0 II 4-tBu-C6H4 -COCH2CH=CH,
8
4-Me-C 6H4-COCH 2CH=CH2
hi 5
0 I1 4-C1-C6H4-COCH2CH=CH2
La
4-tBu-C6H4-COOH
4-Me-C # 4-CH 2-
)
29 (18%)
4-C1-CgHq-CH2-)
2a ( 2 0 % )
4-tBu-C6H4COOH
4-Me-C 6H4-COOH
& (67%) i
4-C1-C6H4-C00H 2 3 2 (43%)
CLEAVAGE OF A L L Y L I C AND BENZYLIC ESTERS
2163
Table (contd.)
-
0
6
II
3-C1-C 6H4-COCH 2CH=CH2
be 7
3-C1-CgH4-CH2-)
3-C1-C 6H4-COOH
3€ ( 4 2 % )
2 s (17%)
C gH lCH=CHC@
CgHll-COOCH2CH=CH2
CSHll-COOH
Eis
u
Downloaded At: 08:50 17 January 2011
8
2 a (38%)
-
4-Me-CI;H4-COOMe
Lh 9
Ph-COOH
&L
(70%)
2.Q a) All the products gave satisfactory spectral data and were compared with authentic samples. b) Yield refers to pure isolated products.
treatment with
TiCll/Mg-Hg under
conditions yielded
the
same
the dimeric hydrocarbon
reaction
(15%)
along with recovered starting material (70%). In
order
to show that only allylic and
benzylic
esters undergo this reductive cleavage with facility to yield
the
toluate
corresponding carboxrlic
acids,
methyl
fi waB subjected to the same reaction condi-
tions with TiC14/Mg-Hg. The only products that could be isolated
in the reaction were the dimeric
hydrocarbon
2164
a
SATYANARAYANA, CHIDAMBARAM, AND CHANDRASEKARAN
(30%) and benail (12%) along with recovered starting
material
(41%).
Titanium tetrachloride was Habn,
Germany
determined apparatus
Downloaded At: 08:50 17 January 2011
recorded
with
and
was
obtained
used
a hi-melt
such.
Riedel-de
M.ps.
were
capillary melting
and are uncorrected. on
as
from
point
Infrared spectra were
Perkin-Elmer model 1320 and 580
spectro-
meters. Proton magnetic resonance spectra were recorded at
90 MHz on a Varian EM-390 instrument and at 80 MHz
on a Brucker WP-80 instrument.
To a solution of mercuric chloride (0.243 g, mmol)
in anhydrous tetrahydrofuran (10 ml),
0.9
magnesium
powder (0.72 g, 30 mg atom) was added and the resulting mixture was stirred at room temp. under nitrogen atmosphere,
for 0.25 h.
withdrawn portions
The turbid supernatent liquid
and the amalgam was washed with of THF.
three-5 ml
20 ml THF was added to the amalgam,
cooled to 0 OC and titanium tetrachloride (2.267 g, mmol, tion
was
12
1.31 ml) was added slowly, followed by the addiof beneylbeneoate
(1.272 g,
6 mmol) in
5
ml
THF. The reaction mixture was stirred for 2 h by which time the temperature was allowed to raise to 20 O C . 10%
CLEAVAGE OF A L L Y L I C AND BENZYLIC E S T E R S
2165
aq. K2C03 solution (10 ml) was added and stirred for 10 min.
(25 ml) was added and
Chloroform
mixture The
was
filtered over a pad of Celite
filtrate
aqueous
was
thoroughly
and
with
sand.
saturated
The bicarbonate layer was neutralised
10% HC1 solution at 0 The
with
0
C and was extracted with chloro-
chloroform layer was washed with brine
dried over anhyd. Downloaded At: 08:50 17 January 2011
washed
reaction
bicarbonate solution and the organic layer was
separated.
form.
the
sodium sulphate.
and
Evaporation of the
solvent afforded benzoic acid 23 (0.472 g,
64%).
M.p.
by
flash
120-122 OC (lit. l2 M.p. 120-122 OC). The
neutral
chromatography g,
18%),
on
purification
on silica gel yielded dibenzyl
m.p. 50-52 OC (lit. l2 m.p. 52
3060, 2920, 1600 (s, 10 H)
7.19
portion
14%),
m.p.
3080,
3060,
ern-'. and
IR (KBr):
H' NMR (CDC13): 6 2.83 ( s , 4 H), 2-phenylacetophenone
58-59 OC (lit.l 3 m.p. 1690,
OC).
(0.2
1610 cm-l.
60 OC).
2
(0.165 g,
IR
(KBr):
NMR (CDC13): 6 4.1 (s,
2 H), 7.2 (s, 5 H), 7.4 ( m , 3 H), 7.9 (m, 2 H). Acknoulednemm.
The
authors thank the Department of
Science and Technology, New Delhi for financial support.
Ref e rences
2.
Corey, E. J. and Tius, M. A., Tetrahedron Lett., 1977, 2081. Ho, T. L., SYnth. C o m m u ., ~ 1978, &, 15.
3.
Ho, T. L. and Olah, G. A., &nthe&,
1.
1977, 418.
2166
4.
5. 6. 7.
8. 9.
Downloaded At: 08:50 17 January 2011
10.
11.
12. 13.
SATYANARAYANA, CHIDAMBARAM, AND CHANDRASEKARAN
Anantharamaiah, G. M. and Sivanandaiah, K.M., J . Chem. S Q E . , .I, 1977, 490. Roberts, C. W., J . Am. Chem . S Q S . , 1954, 76, 6203. Aizpurua, J. M., Juaristi, M., Lecea, B. and Palomo, C., Tetrahechn, 1985, U , 2903. Boar, R. G., Joukhader, L., McGhie, J. F., Misra, S. C., Barrett, A. G. M., Barton, D. H. R. and Prokopiar, P. A., J . Chem . S s . , Chem . co- 8 1978, 68. Bhushan, V. and Chandrasekaran, S., LZhaglistrv let