Stereoselective synthesis of enol acetates by the reaction of alkenylboronates with (diacetoxyiodo)benzene and sodium iodide

Article abstract of DOI:10.1039/a801469h

Stereochemically pure (E)- and (Z)-alk-1-en-1-yl acetates have been easily prepared by acetoxylation of the (Z)-and (E)-alk-1-en-1-ylboronic acids or their esters, respectively, with (diacetoxyiodo)benzene and sodium iodide, in reasonable yields.

Full text of DOI:10.1039/a801469h

View Article Online / Journal Homepage / Table of Contents for this issue
Stereoselective synthesis of enol acetates by the reaction of
alkenylboronates with (diacetoxyiodo)benzene and sodium iodide
Miki Murata, Kaname Satoh, Shinji Watanabe and Yuzuru Masuda*
Department of Materials Science, Kitami Institute of Technology, Kitami 090-8507, Japan
Stereochemically pure (E)- and (Z)-alk-1-en-1-yl acetates
have been easily prepared by acetoxylation of the (Z)-
and (E)-alk-1-en-1-ylboronic acids or their esters, respect-
ively, with (diacetoxyiodo)benzene and sodium iodide, in
reasonable yields.
Table 1 Synthesis of enol acetates (Scheme 1)
1
-Alkenyboronic
2
a
Entry
esters
(OR )
Product
Yield (%)
2
1
2
3
4
5
6
7
8
9
(E)-1a
(E)-1a
(E)-1b
(E)-1c
(E)-1d
(E)-1e
(E)-1f
(Z)-1b
(Z)-1e
(OH)
(OPr )
(Z)-2a
(Z)-2a
(Z)-2b
(Z)-2c
(Z)-2d
(Z)-2e
(Z)-2f
(E)-2b
(E)-2e
93 (85)
97
2
i
2
Although many useful synthetic reactions using organoboron
(OH)
(77)
(82)
(85)
(71)
2
1
i
compounds have been reported, these do not include a pro-
(OPr )
2
2
i
cedure for synthesis of the corresponding alkenyl acetates from
alkenylboron compounds. However there have been several
reports of useful synthetic reactions in which enol esters served
as intermediates for carbon᎐carbon or carbon᎐heteroatom
(OPr )
(OH)2
b
(OH)
62
2
i
(OPr )
(70)
(72)
2
2
i
(OPr )
2,3
bond formations. Enol esters can be prepared from carbonyl
4
5
a
b
compounds or alkynes, but there are many difficulties in the
synthesis of stereodefined enol esters of aldehydes especially of
the (E)-isomers.†
GC and/or isolated (in parentheses) yields are based on 1 used.
17% yield of (E)-β-iodostyrene was also produced.
A
Previously, we reported a synthesis of alkyl acetates by
acetoxylation of trialkylboranes with (diacetoxyiodo)benzene
or lead() acetate. We have now considered the analogous
formation of alkenyl acetates via alkenylboron compounds.‡
Thus, we here describe a stereoselective conversion of alk-1-en-
Although simple treatment of alkenylboronic acids or esters
(instead of alkenylborane) with (diacetoxyiodo)benzene (IBA)
did not give alk-1-enyl acetates as expected, it was found that a
modified procedure with addition of sodium iodide and DMF
as solvent was a remarkably efficient method of acetoxylation
affording alk-1-enyl acetates. For instance, the treatment of
6
6a
1
-ylboronic esters 1 to alk-1-en-1-yl acetate 2 by the treatment
with (diacetoxyiodo)benzene in the presence of sodium iodide
(E)-oct-1-en-1-ylboronic acid 1a with PhI(OAc) (1.1 equiv.) in
2
(
Scheme 1).
the presence of NaI (1.1 equiv.) and DMF at room temperature
produced (Z)-oct-1-en-1-yl acetate 2a in 93% yield (GC)
(isolated, 85%) and in >99% isomeric purity, but such reaction
in the absence of NaI afforded no detectable amount of 2a.
Lead() acetate also acted in the same manner as IBA to pro-
vide (Z)-2a in 77% yield. The results obtained with represent-
ative 1 are summarized in Table 1. The reactions proceeded
stereospecifically under mild conditions, and consequently for
all compounds 1 studied no regio- or stereo-isomers of 2 were
formed.
R1
i
i
R1
OCOCH3
2
B(OR )2
E)-1
(
(Z)-2
R1
R1
2
B(OR )2
OCOCH3
(Z)-1
(E)-2
R1 = C6H13
R1 = Bu
R1 = MeCO(CH2)2
R1 = NC(CH2)2
R1 = But
Following this, as was expected, (E)-alk-1-en-1-yl acetates
(entries 8 and 9) could be also prepared by employing the
corresponding (Z)-alk-1-en-1-ylboronic esters in a similar
reaction to that described above.
The yields and the stereoselectivity of the products seemed
not to depend on steric hindrance in 1 (entries 6 and 9). How-
ever, the reaction employing (E)-β-styrylboronic acid 1f yielded
significant amounts (17%) of (E)-β-iodostyrene as a by-product
whose stereochemistry was consistent with that of 1f (entry 7),
along with the major (Z)-2f (62% yield), suggesting perhaps
electronic effects.§ A mechanistic study was attempted.
Similar treatment of 1a to that above with the known acetyl
1
1
1
1
1
1
a
b
c
d
e
f
R1 = Ph
2
i
R = H or Pr
Scheme 1 Reagents and conditions: i, PhI(OCOCH ) , NaI, DMF,
3
2
room temp.
And then, since respective (E)- and (Z)-1-alk-1-en-1-ylboronic
esters can be readily prepared regio- and stereo-selectively by1
the hydroboration reaction of alk-1-ynes or 1-haloalk-1-ynes,
their acetoxylation would allow for the formation of geo-
metrically pure (E)- or (Z)-enol acetates 2.
hypoiodite (CH COOI) formed in situ from (diacetoxyiodo)-
3
7
benzene (1.1 equiv.) and iodine (0.55 equiv.) gave only 44%
yield of 2a, but this was improved with the addition of sodium
acetate (1.1 equiv) to provide 2a in 89% yield. We suggest that
this reaction proceeds via formation of acetyl hypoiodite and
acetoxy anion from (diacetoxyiodo)benzene and sodium iodide.
†
It has been reported that the anti-Markovnikov addition of carb-
5c
oxylic acids to alkynes afforded (Z)-alk-1-en-1-yl esters, though the
addition of acetic acid to hex-1-yne gave the corresponding enol acetate
in only low yield.
‡
The authors have found the following reactions in the presence of
§ Recently, it has been reported that a reaction of alk-1-en-1-ylboronic
6
b,c
PhI(OAc) or Pb(OAc) .
acids with (diacetoxyiodo)benzene in the presence of BF ؒEt O yielded
2
4
3
2
8
alk-1-en-1-yl(phenyl)iodonium salts. The present formation of (E)-1-
(
E)-RCH᎐CHB(C H ) → (E)-RCH᎐CHC H
6 11 2 6 11
᎐ ᎐
iodoalk-1-ene as by-product may involve such boron–iodine exchange
9
R B ϩ HC᎐CRЈ → RC᎐CRЈ ϩ (Z)-RCH᎐CRЈ (OAc)
followed by a nucleophilic substitution with sodium iodide.
3
᎐
᎐
᎐
J. Chem. Soc., Perkin Trans. 1, 1998
1465

View Article Online
Although our evidence for the reaction mechanism is still
inconclusive,§ bearing in mind the inversion of starting geo-
metry and a probable in situ formation of hypoiodite, this reac-
J 12.5, 7.4), 7.06 (dt, 1H, J 12.5, 1.3); δ (CDCl ) 13.7, 20.6,
C 3
22.0, 26.8, 31.6, 115.0, 135.4, 168.1; m/z (EI) 142.0995 (C H O
8
14
2
requires 142.0994).
7a,c
tion is considered to proceed through anti-addition
of the
hypoiodite to the carbon–carbon double bond of alk-1-en-1-
ylboronate followed by anti-deiodoboration with the aid of
10
Acknowledgements
acetoxy anion, as shown in Scheme 2.
We thank the Ministry of Education of Japan for a Grant-in-
Aid for Scientific Research (No. 08650999), in support of the
work.
H
I
OCOCH3
H
CH3COOI
(E)-1
R
B(OH)2
References
CH3COO –
1 For reviews, see: (a) H. C. Brown, Organic Synthesis via Boranes,
Wiley, New York, 1975; (b) A. Pelter, K. Smith and H. C. Brown,
Borane Reagents, Academic Press, New York, 1988; (c) D. S.
Matteson, Stereodirected Synthesis with Organoboranes, Springer,
Berlin, 1995.
2 For examples of precursors of tin enolates, see; J. Tsuji, I. Minami
and I. Shimizu, Tetrahedron Lett., 1983, 24, 4713; M. Kosugi,
I. Hagiwara, T. Sumiya and T. Migita, Bull. Chem. Soc. Jpn., 1984,
OCOCH3
–
H
B(OH)2
OCOCH3
H
(Z)-2
R
I
Scheme 2
5
7, 242; Y. Masuyama, T. Sakai, T. Kato and Y. Kurusu, Bull.
Chem. Soc. Jpn., 1994, 67, 2265; Y. Masuyama, Y. Kobayashi and
Y. Kurusu, J. Chem. Soc., Chem. Commun., 1994, 1123.
3 For examples of cycloaddition of alkenyl esters, see; A. Wexler, R. J.
Balchunis and J. S. Swenton, J. Chem. Soc., Chem. Commun., 1975,
As discussed above, this reaction is not only interesting as a
new approach to the synthesis of enol acetates but also useful to
obtain geometrically pure (E)- or (Z)-alk-1-en-1-yl acetates
respectively, and further investigations for mechanistic studies
and synthetic applications are currently in progress in our
laboratory.
6
5
01; L. F. Tietze, A. Montenbruck and C. Schneider, Synlett, 1994,
09; M. C. Pirrung and Y. R. Lee, Tetrahedron Lett., 1994, 35, 6231.
4
5
T. J. Cousineau, S. L. Cook and J. A. Secrist, III, Synth. Commun.,
1
3
979, 9, 157; H. O. House and V. Kramar, J. Org. Chem., 1963, 28,
362.
For ruthenium-catalyzed addition of carboxylic acids, see; (a)
M. Rotem and Y. Shvo, Organometallics, 1983, 2, 1689; (b)
T. Mitsudo, Y. Hori, Y. Yamakawa and Y. Watanabe, J. Org. Chem.,
Experimental
Typical procedure: preparation of (Z)-oct-1-en-1-yl acetate 2a
1
987, 52, 2230; (c) H. Doucet, B. Martin-Vaca, C. Bruneau and
The flask was charged with (diacetoxyiodo)benzene (5.5 mmol),
P. H. Dixneuf, J. Org. Chem., 1995, 60, 7247.
3
NaI (5.5 mmol), DMF (30 cm ) and (E)-1a (0.78 g, 5.0 mmol)
6 (a) Y. Masuda and A. Arase, Bull. Chem. Soc. Jpn., 1978, 51, 901;
(b) Y. Masuda, A. Arase and A. Suzuki, Chem. Lett., 1978, 665;
prepared by the method described in the literature [ref. 1(a),
p. 64]. The reaction mixture was stirred at room temperature
for 16 h. The product was extracted with diethyl ether, and the
(
c) Y. Masuda, M. Hoshi and A. Arase, Chem. Lett., 1980, 413.
(a) K. Aoki and Y. Ogata, Bull. Chem. Soc. Jpn., 1968, 41, 1476;
b) A. Varvoglis, Synthesis, 1984, 709; (c) E. B. Merkushev, N. D.
7
(
extract was washed with water and dried over MgSO . After
4
Shimakhina and G. M. Koveshnikova, Synthesis, 1980, 486.
M. Ochiai, M. Toyonari, T. Nagaoka, D.-W. Chen and M. Kida,
Tetrahedron Lett., 1997, 38, 6709.
removal of the solvent, the residue was purified by chrom-
8
atography over silica gel to give (Z)-2a (0.73 g, 85%); νmax(neat)/
Ϫ1
cm 1759, 1672 and 751; δ (CDCl ) 0.8–1.0 (m, 11H), 1.9–2.2
9 D. Hellwinkel, W. Lindner and W. Schmidt, Chem Ber., 1979, 112,
81.
H
3
2
(
m, 2H), 2.10 (s, 3H), 4.79 (q, 1H, J 6.5¶), 6.92 (d, 1H, J 6.5);
1
0 H. C. Brown and O. J. Cope, J. Am. Chem. Soc., 1964, 86, 1801;
H. C. Brown, T. Hamaoka and N. Ravindran, J. Am. Chem. Soc.,
δ (CDCl ) 13.0, 19.6, 21.6, 23.4, 27.9, 28.2, 30.7, 113.2, 133.1,
C
3
1
67.0; m/z (EI) 170.1293 (C H O requires 170.1307).
10 18 2
1
1
973, 95, 6456; H. C. Brown and J. B. Campbell, Jr., J. Org. Chem.,
980, 45, 389.
(
E)-Hex-1-en-1-yl acetate 2b
11 H. C. Brown and T. Imai, Organometallics, 1984, 3, 1392; H. C.
Using (Z)-1b prepared by the method described in the liter-
ature, a similar procedure to above afforded (E)-2b in 70%
isolated yield; νmax(neat)/cm 1755, 1675 and 936; δ (CDCl )
Brown and Y. Somayaji, Synthesis, 1984, 919.
11
Ϫ1
H
3
0
.7–1.4 (m, 7H), 1.9–2.2 (m, 2H), 2.07 (s, 3H), 5.41 (dt, 1H,
Paper 8/01469H
Received 20th February 1998
Accepted 10th March 1998
¶
J Values are given in Hz.
1
466
J. Chem. Soc., Perkin Trans. 1, 1998