Synthesis of β-lactones by the regioselective, cobalt and Lewis acid catalyzed carbonylation of simple and functionalized epoxides

Article abstract of DOI:10.1021/jo010295e

The PPNCo(CO)₄ and BF₃·Et₂O catalyzed carbonylation of simple and functionalized epoxides in DME gives the corresponding β-lactones regioselectively in good to high yields. The carbonylation occurred selectively at the uns

Full text of DOI:10.1021/jo010295e

5
424
J . Org. Chem. 2001, 66, 5424-5426
Syn th esis of â-La cton es by th e Regioselective, Coba lt a n d Lew is
Acid Ca ta lyzed Ca r bon yla tion of Sim p le a n d F u n ction a lized
Ep oxid es
†
‡
,†
J ong Tae Lee, P. J . Thomas, and Howard Alper*
Centre for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa,
0 Marie Curie, Ottawa, Ontario, Canada K1N 6N5, and Corporate R&D, The Dow Chemical Company,
Midland, Michigan 48674
1
halper@uottawa.ca
Received March 19, 2001
The PPNCo(CO)
4
and BF
3
2
‚Et O catalyzed carbonylation of simple and functionalized epoxides in
DME gives the corresponding â-lactones regioselectively in good to high yields. The carbonylation
occurred selectively at the unsubstituted C-O bond of the epoxide ring, and this reaction tolerates
various functional groups such as alkenyl, halide, hydroxy, and alkyl ether.
In recent years, metal-catalyzed carbonylative ring
2 8
Co (CO) as catalyst and 3-hydroxypyridine as cocata-
7
expansion reactions of heterocyclic compounds have been
shown to be useful and efficient one-step procedures for
lyst. In connection with our continued efforts for the
development of carbonylative ring expansion reactions
of various heterocyclic compounds, we became interested
in the noted claims. However, when we repeated this
reaction at both Dow Chemical and at the University of
Ottawa, we obtained polyester as a dominant product
with only a small amount of the desired â-lactone. For
example, repetition of the reported reaction of propylene
oxide under the described reaction conditions afforded
1
2
3
the syntheses of lactams, lactones and thiolactones.
The insertion of carbon monoxide into a heterocycle is a
simple, atom economical method for organic synthesis.
The use of this strategy for the direct synthesis of
â-lactones from epoxides and carbon monoxide has
industrial potential, not only because of the nature of the
reaction but also because the reactant epoxides and
carbon monoxide are readily available at low cost (eq 1).
75% of polyester 1(M
w
) 3,350, M
w n
/M ) 1.21) and only
7
1
5% of â-butyrolactone(2) (eq 2). Drent and Kragtwijk
reported the formation of 2 in 93% conversion and 90%
selectivity. One might consider that polyester 1 was
While the cobalt-catalyzed carbonylation reaction of
4
5
aliphatic epoxides to â-lactones or â-hydroxy esters has
been known for a long time, the yields and selectivities
are very low. In the case of styrene oxide, an epoxide
having an aromatic substituent, R-phenyl-â-propiolac-
tone, was obtained in 67% yield by using RhCl(CO)-
formed from lactone 2 generated under the reaction
conditions. To confirm this possibility we reacted 2, or a
mixture of 2 and propylene oxide, under exactly the same
reaction conditions, but 2 was recovered in almost
as the catalyst.6
(PPh )
3 2
In 1993, an improved method was claimed for the
carbonylation of aliphatic epoxides to â-lactones using
2 8
quantitative yield. Note, however, that the Co (CO) /3-
hydroxypyridine catalyst system was applied successfully
for the carbomethoxylation of epoxides with carbon
†
University of Ottawa.
Corporate R&D, The Dow Chemical Company.
‡
8
monoxide/methanol. Given these findings, we endeav-
(
1) (a) Alper, H.; Urso, F.; Smith, D. J . J . Am. Chem. Soc. 1983,
ored to develop a new catalyst system for the realization
of the synthesis of â-lactones from epoxides and carbon
monoxide in a reproducible manner.
Following numerous unsuccessful attempts with com-
plexes of different metals (Pd, Rh, Ru, Ni, and Co) as
1
1
2
05, 6737. (b) Calet, S.; Urso, F.; Alper, H. J . Am. Chem. Soc. 1989,
11, 931. (c) Tanner, D.; Somfai, P. Bioorg. Med. Chem. Lett. 1993, 3,
415. (d) Roberto, D.; Alper, H. J . Am. Chem. Soc. 1989, 111, 7539. (e)
Piotti, M.; Alper, H. J . Am. Chem. Soc. 1996, 118, 111.
2) (a) Aumann, R.; Ring, H. Angew. Chem., Int. Ed. Engl. 1977,
6, 50. (b) Nienburg, H. J .; Elschnigg, G. Ger. Pat. 1,066,572; Chem.
(
1
Abstr. 1961, 55, 10323h. (c) Alper, H.; Arzoumanian, H.; Petrignani,
J . F.; Maldonado, M. S. J . Chem. Soc., Chem. Commun. 1985, 340. (d)
Shimizu, I.; Maruyama, T.; Makuta, T.; Yamamoto, A. Tetrahedron
Lett. 1993, 34, 2135. (e) Alper, H.; Eisenstat, A.; Satyanarayana, N.
J . Am. Chem. Soc. 1990, 112, 7060. (f) J enner, G.; Kheradmand, H.;
Kiennemann, A. J . Organomet. Chem. 1984, 277, 427.
catalysts (e.g., Pd(OAc)
PCy or dppp, Ru (CO)12/(BINAP, Ni(acac)
(CO) /PBu or 2,2′-bipyridine, etc.), we found that PPN-
Co(CO) [3, PPN ) bis(triphenylphosphine)iminium, [(C
Pd] NCo(CO) ], used in conjunction with a Lewis
acid such as BF ‚Et O or SnCl in DME or THF, can
2
/PPh
3
or dppp, [Rh(COD)Cl]
2
/
3
3
2
/dppp, Co -
2
8
3
4
6
-
H
5
)
3
2
4
(
3) (a) Wang, M. D.; Calet, S.; Alper, H. J . Org. Chem. 1989, 54, 20.
b) Khumtaveeporn, K.; Alper, H. J . Am. Chem. Soc. 1994, 116, 5662.
4) Pollock, J . M.; Shipman, A. J . GB-A-1,020, 575; Chem. Abstr.
966, 64, P16015g.
5) (a) McClure, J . D.; Fischer, R. F. US-A-3,260, 738; Chem. Abstr.
(
3
2
4
(
catalyze the carbonylation of epoxides, affording â-lac-
1
(
1
6
966, 65, P8767a. (b) Kawabata, Y. Nippon Kagaku Kaishi 1979, 5,
35.
(7) Drent, E.; Kragtwijk, E. Eur. Pat. Appl. EP 577, 206; Chem.
Abstr. 1994, 120, 191517c.
(6) Kamiya, Y.; Kawato, K.; Ohta, H. Chem. Lett. 1980, 1549.
(8) Hinterding, K.; J acobsen, E. N. J . Org. Chem. 1999, 64, 2164.
1
0.1021/jo010295e CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/19/2001

Synthesis of â-Lactones
J . Org. Chem., Vol. 66, No. 16, 2001 5425
Ta ble 1. Ca r bon yla tion of P r op ylen e Oxid e to
Ta ble 2. Ca r bon yla tion of Ep oxid es to â-La cton es
a
â-Bu tyr ola cton e
GC yield
entry
catalyst (mol %)
solvent
THF
DME
DME
DME
DME
(%)
1
2
3
3 (1) + BF3‚Et2O (1)
3 (1) + BF3‚Et2O (1)
3 (1) + B(C6F5)3 (1)
3 (1)
64
77
85
-
7
13
b
4
5
6
Co2(CO)8 (5)
Co2(CO)8 (0.5) + PPNCl (1) + DME
BF3‚Et2O (1)
7
8
9
Co2(CO)8 (0.5) + PPNCl (1) + DME
BF3‚Et2O (2)
11
35
Co2(CO)8 (0.5) + PPNCl (1) + THF
BF3‚Et2O (1)
Co2(CO)8 (0.5) + PPNCl (1) + 1,4-dioxane
BF3‚Et2O (1)
11
1
1
1
1
0
1
2
3
Co2(CO)8 (0.5) + PPNCl (1) + CH2Cl2
BF3‚Et2O (1)
-
Co2(CO)8 (0.5) + PPNCl (1) + benzene
BF3‚Et2O (1)
trace
76
Co2(CO)8 (1) + PPNCl (2) +
BF3‚Et2O (2)
THF
c
23d
Co2(CO)8 (1) + CTAB (2) +
THF
BF3‚Et2O (2)
a
All reactions were run on a 10 mmol scale of propylene oxide
in 10 mL of solvent (5 mL in the case of THF) at 80 °C under 900
psi of CO for 24 h. b Reaction time: 7 h. Mixture of regioisomers
1
c
was obtained (2/regioisomer ) 4/1, by H NMR). Cetyltrimethyl-
d
ammonium bromide. 15% polyester was also formed.
tones in good to excellent yields. When propylene oxide
a
Condition A: 5 mmol of epoxide, 0.1 mmol (2 mol %) of 3 and
was reacted with 1 mol % each of 3 and BF
3
2
‚Et O, in
0
9
.1 mmol (2 mol %) of BF3.Et2O in 10 mL of DME at 80 °C under
00 psi of CO. Condition B: 2.5 mmol of epoxide was used instead
DME at 80 °C under 900 psi of carbon monoxide for 24
h, the corresponding â-lactone 2 was obtained selectively
of 5 mmol. Condition C: B(C6F5)3 was used instead of BF3‚Et2O,
.5 mmol of epoxide, reaction was run at 110 °C. Condition D: 20
mmol of epoxide was used instead of 5 mmol.
2
in 77% yield, with a trace amount of the regioisomer of
1
2
(determined by GC and H NMR) (entry 2, Table 1).
The reaction using B(C
Lewis acid was completed within 7 h in 85% yield but
produced mixture of regioisomers. By H NMR spectros-
copy, the ratio of 2/regioisomer was found to be 4/1 (entry
6
F
5
)
3
instead of BF
3
‚Et
2
O as a
1
a trace amount of the regioisomer detected by H NMR
in several cases. Furthermore, this reaction tolerates
various functional groups such as alkenyl (4c, 4d ), halide
1
(
4e), hydroxy (4g), and alkyl ether (4h ), affording the
3
, Table 1). Using THF as the solvent for the reaction
gave 2 in 64% yield with 9% of polymeric material (entry
, Table 1). Reaction without a Lewis acid, or using Co
CO) as the catalyst but no Lewis acid, resulted in the
corresponding â-lactones 5 in 57-87% yields. An aryl-
substituted epoxide, styrene oxide (4f), was recovered
unchanged on attempted carbonylation even under higher
reaction temperatures (130 °C) (entry 6, Table 2). In the
case of alkyl-substituted epoxides, the reactions of longer
alkyl chain substituted epoxides (4a , 4b) were slower
than that of propylene oxide and needed 2 mol % of
catalyst to complete the reactions (compare entry 2 of
Table 1 with entries 1 and 2 of Table 2). Reactions of
functionally substituted epoxides required 4 mol % of
catalyst and longer reaction times (48 h) (entries 3, 4, 5
and 8, Table 2). In the case of disubstituted epoxide,
trans-2,3-epoxybutane (4i), the reaction did not proceed
1
(
2
-
8
recovery of propylene oxide, or the isolation of 2 in 7%
yield, respectively (entries 4 and 5, Table 1). In situ
formation of 3, by adding Co
as well as BF ‚Et O, in different solvents gave 0-35%
yields of 2 (entries 6-11, Table 1). When propylene oxide
was reacted in the presence of 1 mol % of Co (CO) , 2
mol % of PPNCl, and 2 mol % of BF ‚Et O in THF, 76%
2 8
(CO) and 2 equiv of PPNCl
3
2
2
8
3
2
of 2 was obtained (entry 12, Table 1) and thus this result
was comparable to that in entry 2 of Table 1. Use of
cetyltrimethylammonium bromide(CTAB) instead of PP-
NCl in the latter reaction gave only 23% of 2 with 15%
of polyester(entry 13, Table 1). Consequently the very
bulky [PPN] cation, by being weakly bound or close to
the cobalt center, may enhance the catalytic activity.9
The scope of the epoxide carbonylation reaction was
investigated with a variety of monosubstituted epoxides
under the optimum reaction conditions (entry 2, Table
under the optimum conditions. However, when B(C
was used instead of BF ‚Et O at 110 °C, the correspond-
ing â-lactone, 5i, was formed in 20% yield (the unreacted
i was recovered) with retention of stereochemistry
6 5 3
F )
3
2
4
(
10
entry 9, Table 2). To confirm the stereochemistry of
this reaction, we also reacted cis-2,3-epoxybutane (4j)
under the same reaction conditions, and also obtained
the corresponding cis-disubstituted â-lactone, 5j, in 24%
yield with retention of stereochemistry (entry 10, Table
1
). The carbonylation reaction occurred selectively at the
unsubstituted C-O bond of the epoxide ring, with only
(
10) The stereochemistry of 5i was determined by 1H NMR and is
(
9) Kondo, T.; Okada, T.; Mitsudo, T. Organometallics 1999, 18,
in accordance with literature data. Dervan, P. B.; J ones, C. R. J . Org.
Chem. 1979, 44, 2116.
4
123.

5
426 J . Org. Chem., Vol. 66, No. 16, 2001
Lee et al.
2
). The results of the stereochemistry for these reactions
2 8
are opposite to those for the Co (CO) -catalyzed synthesis
of â-lactams from aziridines and carbon monoxide which
resulted in inversion of stereochemistry1 (eq 3). To make
e
of catalyst only. Although, no major side products or
polymer were formed, the isolated yield was only 44%
due to the instability and low boiling point of 5k (entry
1
1, Table 2).
In conclusion, PPNCo(CO)
4
and BF
3
2
‚Et O is a useful
certain that the stereochemical results were directly
comparable, trans-2,3-dimethyl-1-(2-phenylethyl)aziri-
catalytic system for the regioselective carbonylation of
aliphatic epoxides to â-lactones. Yields are often appre-
ciably higher when compared with other known catalyst
dine was subjected to carbonylation using the 3/B(C
catalyst system instead of Co (CO) . Indeed, as in the case
of the aziridine Co (CO) carbonylation reaction, the
6 5 3
F )
systems (e.g., Co
2
(CO)
8
, Co
2
(CO)
8
2 8
/pyridine, Co (CO) /3-
2
8
hydroxypyridine, and RhCl(CO)(PPh )
3 2
).
2
8
corresponding cis-3,4-dimethyl-1-(2-phenylethyl)-2-aze-
tidinone was obtained in 81% yield with inversion of
stereochemistry (eq 4). These results raise intriguing
questions regarding the difference in the stereochemistry
of carbonylation reactions using epoxides and aziridines
with the same catalytic system.
Finally, the parent epoxide, ethylene oxide (4k ), was
carbonylated to â-propiolactone (5k ), and the reaction
was completed within 24 h in the presence of 0.5 mol %
Ack n ow led gm en t. We are grateful to the Dow
Chemical Co. for support of this research.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails for the synthesis of â-lactones and spectral and analytical
data of new compounds (5b, 5c, 5d , and 5h ). This material is
available free of charge via the Internet at http://pubs.acs.org.
J O010295E