Electrochemical Catalysis of a 5-Endo-Trig Cyclization in Bicontinuous Microemulsions

Full text of DOI:10.1021/jo971897u

2
18
J . Org. Chem. 1998, 63, 218-219
Communications
Electr och em ica l Ca ta lysis of a 5-En d o-Tr ig
Sch em e 1
Cycliza tion in Bicon tin u ou s Micr oem u lsion s
J ianxin Gao and J ames F. Rusling*
Chemistry Department, U-60, University of Connecticut,
Storrs, Connecticut 06269-4060
Received October 15, 1997
Microemulsions of oil, water, and surfactant are thermo-
dynamically stable, macroscopically homogeneous, low toxic-
ity alternatives to organic solvents.1 Bicontinuous micro-
emulsions have continuous, dynamic, intertwined oil and
water microphases. They easily dissolve ionic catalysts and
nonpolar reactants and are particularly useful for electro-
2
,3
chemical catalytic synthesis and reaction control.
4
Construction of carbocycles is important in many organic
syntheses. We recently used electrochemical catalysis with
cobalt complexes in microemulsions to make trans-1-deca-
5
to a disfavored process. For example, a designed antibody
catalyzed an otherwise disfavored 6-endo-tet ring closure.
In this paper, we report dramatic improvement in the yield
of disfavored 5-endo-trig cyclization product 4-hydrindanone
lone in high yields from 2-(4-bromobutyl)-2-cyclohexen-1-
7
3
a
one.
Generally, cyclizations follow Baldwin’s rules.6 A 5-endo-
trig cyclization is disfavored, requiring severe distortions of
bond angles and lengths to achieve the necessary reaction
geometry. However, cyclizations can sometimes be directed
2
(eq 1) by using electrochemical catalysis in microemulsions
8
a
made with cetyltrimethylammonium bromide (CTAB) or
sodium dodecyl sulfate (SDS).8b
(
1) (a) Rusling, J . F. In Modern Aspects of Electrochemistry; Conway, B.
E., Bockris, J . O’M., Eds.; Plenum Press: New York, 1994; No. 26, pp 49-
04. (b) Rusling, J . F. In Electroanalytical Chemistry; Bard, A. J ., Ed.;
1
Marcel Dekker: New York, 1994; Vol. 18, pp 1-88. (c) Bourrel, M.;
Schechter, R. S. Microemulsions and Related Systems; Marcel Dekker: New
York, 1988. (d) Evans, D. F.; Mitchell, D. J .; Ninham, B. W. J . Phys. Chem.
1
986, 90, 2817-2825. (d) Rusling, J . F.; Zhou, D.-L.; Gao, J . In Fundamen-
tals and Potential Applications of Electrochemical Synthesis; Weaver, R.
D.; Fisher, F.; Kalhammer, F. R.; Mazur, D., Eds.; Electrochemical
Society: Pennington, NJ , 1997; Proc. Vol., 97-6, pp 137-149.
(2) (a) Zhou, D.-L.; Gao, J .; Rusling, J . F. J . Am. Chem. Soc. 1995, 117,
1
2
1
127-1134. (b) Kamau, G. N.; Rusling, J . F. Langmuir 1996, 12, 2645-
649. (c) Kamau, G. N.; Hu, N.; Rusling, J . F. Langmuir 1992, 8, 1042-
044.
(
3) (a) Gao, J .; Rusling, J . F.; Zhou, D.-L. J . Org. Chem. 1996, 61, 5972-
5
3
977. (b) Zhou, D.-L.; Carrero, H.; Rusling, J . F. Langmuir 1996, 12, 3067-
Transformations of 2-(3-bromopropyl)-2-cyclohexen-1-one9
(1) were catalyzed by reducing 0.2 equiv of vitamin B12a (cob-
III)alamine, Co(III)L) to Co(I)L in an electrochemical cell
with a carbon cloth cathode at 25 °C. Key intermediate 5
074.
(
4) (a) Cooke, M. P., J r.; Gopal, D. Tetrahedron Lett. 1994, 35, 2837-
2
(
2
840. (b) Boger, D. L.; Mathvink, R. L. J . Org. Chem. 1992, 57, 1429-1443.
(
c) Macdonald, T. L.; Mahalingam, S. J . Am. Chem. Soc. 1980, 102, 2113-
115.
5) (a) Scheffold, R.; Rytz, G.; Walder, L. In Modern Synthetic Methods;
(
(Scheme 1) was obtained by oxidative addition of 1 to Co(I)L,
Scheffold, R., Ed.; Wiley: New York, 1983; Vol. 3, pp 355-439. (b) Scheffold,
R.; Abrecht, S.; Orlinski, R.; Ruf, H.-R.; Stamouli, P.; Tinembart, O.; Walder,
L.; Weymuth, C. Pure Appl. Chem. 1987, 59, 363-372. (c) Pattenden, G.
Chem. Soc. Rev. 1988, 17, 361-382 and references therein. (d) Tinembart,
O.; Walder, L.; Scheffold, R. Ber. Bunsen-Ges. Phys. Chem. 1988, 92, 1225-
231. (e) Inokochi, T.; Tsuji, M.; Kawafuchi, H.; Torri, S. J . Org. Chem.
991, 56, 5945-5948. (f) Torri, S.; Inokochi, T.; Yukama, T. J . Org. Chem.
985, 50, 5875-5877. (g) Fry, A. J .; Singh, A. H. J . Org. Chem. 1994, 59,
172-8177. (h) Ozaki, S.; Nakanishi, T.; Sugiyama, M.; Miyamoto, C.;
10,11
formed electrolytically at -0.9 V versus SCE.
Upon
photocleavage of 5 at this potential, the major product was
2-allyl-2-cyclohexen-1-one (3) in both the CTAB microemul-
sion and DMF (Table 1, entries 1 and 2). The yield of 2 was
20%, in agreement with Baldwin’s rules.
1
1
1
8
The yield of 2 was increased to 62-70% by using electro-
chemical cleavage at -1.5 V versus SCE in microemulsions
(entries 3 and 4) in the dark. Yields of 2 at -1.5 V were
again low in DMF, MeOH, and MeOH/water (4:1) (entries
Ohmori, H. Chem. Pharm. Bull. 1991, 39, 31-35.
6) (a) Baldwin, J . E. J . Chem. Soc., Chem. Commun. 1976, 734-736.
b) Baldwin, J . E.; Cutting, J .; Dupont, W.; Kruse, L.; Silberman, L.; Thomas,
R. C. J . Chem. Soc., Chem. Commun. 1976, 736-738.
7) J anda, K. D.; Shevlin, C. G.; Lerner, R. A. Science 1993, 259, 490-
93.
8) For microemulsion preparation and characterization, see: (a) Ceglie,
(
(
5
-7). Catalytic electrolysis of 1 in DMF using vitamin B12a
(
12
4
and a Hg cathode at -1.54 V versus SCE gave 2% of 2
(
and 90% of 4.
A.; Das, K. P.; Lindman, B. Colloids Surf. 1987, 28, 29-40. (b) Georges, J .;
Photocleavage of the cobalt-carbon bond of 5 produces
Chen, J . W. Colloid Polym. Sci. 1986, 264, 896-902.
radical 75
a-c
(Scheme 1), which can undergo hydrogen atom
(
9) For preparation of 1, see: Taber, D. F. J . Org. Chem. 1976, 41, 2649-
2
650.
13
abstraction to form 4, the disfavored ring closure to form
2, and coupling with Co(II)L and loss of [Co-H]
(
(
10) Details of electrolysis are the same as in ref 3a.
5c
11) For NMR data on 2 and 3, see the following. (a) 1H NMR of 2:
to form 3.
1
3
Miyano, M.; Stealey, M. A. J . Org. Chem. 1982, 47, 3186-3188. C NMR
of 2: Cicero, B. L.; Weisbuch, F.; Dana, G. J . Org. Chem. 1981, 46, 914-
19. (b) H and C NMR of 3: Barillier, D.; Benhida, R.; Vazeux, M.
In electrochemical cleavage at -1.5 V, the reaction
proceeds by a different pathway (Scheme 2). Carbanion 8
1
13
9
Phosphorus, Sulfur Silicon 1993, 78, 83-95.
12) Scheffold, R.; Dike, M.; Dike, S.; Herold, T.; Walder, L. J . Am. Chem.
Soc. 1980, 102, 3642-3643.
(
(13) An authentic sample of 4 was prepared according to ref 9, by using
1-propyl bromide.
S0022-3263(97)01897-5 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/06/1998

Communications
J . Org. Chem., Vol. 63, No. 2, 1998 219
Ta ble 1. P r od u cts fr om Ca ta lytic Electr olyses of 1 Usin g
Vita m in B12a
Electrolysis at -1.5 V gave low yields of 2 in DMF and
MeOH (entries 5 and 6), consistent with Baldwin’s rules.
Mass recoveries in these electrolyses were also low, sug-
gesting routes to undetectable products.14 In 4:1 MeOH/
water, the yield of 2 remained low, but the yield of 4
increased to 85% (entry 7).
yield, %a
-
E, V,
time,
2
hour cis + trans 3b
4b
entry reaction medium
vs SCE
1
2
CTAB µEc
0.9 +
vis light
DMF/0.1 M TBABd 0.9 +
4
24
21
70f
62
19
7
65
3
4.5
51
9
Electrolysis at -1.5 V in a CTAB/pentanol/water solution
gave significantly less 2 (46%, entry 8), but nearly twice the
amount of 4 compared to the CTAB microemulsion (entry
vis light
1.5
3
4
5
6
7
CTAB µEe
5
4
1.5
1
2
0
0
0
0
0
29
21
9
50
85
SDS µEg
1.5
1.5
h
3
). This result suggests that tetradecane is necessary for
DMF/0.1 M TBAB
MeOH/0.1 M TBAB 1.6
the best yields of 2.
MeOH/water
1.5
10
These results suggest that the pathway to 2 is faster than
formation of 4 in the microemulsions. These fluids have
(
4/1,v/v)/0.1 M
TBAB
8
CTAB/1-pentanol/
water (6%/7%/87%)
1.5
4
46
0
49
surfactant layers at both oil-water and electrode-micro-
emulsion interfaces.1 The results also imply that the
a
cyclization of 8 occurs at a site with a low concentration of
proton donor, such as one of the interfacial surfactant layers,
or in the oil phase. There is considerable precedent for a
strong influence of surfactant films on electrodes in electro-
chemical catalysis. For example, bimolecular rate-determin-
ing steps can be enhanced by reactant preconcentration in
Average from GC analysis of three electrolyses, no starting
material found in any electrolyses. 3:4 ratio estimated by 1
NMR. Microemulsion composition: CTAB/1-pentanol/tetrade-
b
H
c
d
cane/water ) 17.5/35/12.5/35 (wt %). TBAB ) tetrabutylammo-
e
nium bromide. Electrolysis at -1.5 V without vitamin B12
f
recovered 82% of 1 in CTAB microemulsion. Cis/trans ) 4/1.
g
SDS/1-pentanol/tetradecane/water ) 13.3/26.6/8/52 (wt %). hCis/
1
a,b,d,2b,c
a surfactant layer on an electrode in a microemulsion.
trans ) 6.3/1.
In summary, a 5-endo-trig cyclization was remarkably
facilitated in microemulsions, providing a new example of
electrochemical reaction control by these microheteroge-
neous fluids. The method provides an attractive alternative
for the formation of fused five-membered rings under mild
conditions.
Sch em e 2
Ack n ow led gm en t. This work was supported by Grant
No. CTS-9632391 from the National Science Foundation.
The authors thank J ames M. Bobbitt and De-Ling Zhou
for helpful discussions.
Su p p or tin g In for m a tion Ava ila ble: Details of experiments
and characterization data (3 pages).
formed by reduction of 5 is a likely intermediate.5a,b This
is strongly supported by the disappearance of 3, which
cannot form from 8, in the product mixtures (entries 3-8).
Cyclization of 8 is facilitated in the microemulsion to
improve the yield of 2.
J O971897U
(
14) Preliminary spectroscopic analysis of catalyst recovered from DMF
after electrolysis suggested the possibility of coupling of intermediates (e.g.,
7 or 8) with vitamin B12
.