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The effect of triphenylphosphine on ring-opening of aliphatic epoxides with potassium fluoride-poly (hydrogen fluoride)
ELSEVIER
Journal of Fluorine Chemistry 85 ( 1997) 147-149
The effect of triphenylphosphine on ring-opening of aliphatic epoxides with potassium fluoride-poly (hydrogen fluoride) Masanori Tamura * , Motonari Shibakami, Akira Sekiya Natiunal
qf Mutrwls
Institute
and
Received
Chemical
Research.
10 January
1997;
I-I
Hi,rquhi.
Tsukubu,
Iburcrki
305.
Japan
accepted 19 May 1997
Abstract The ring-opening reaction of aliphatic epoxides with potassium fluoride-poly( hydrogen fluoride) triphenylphosphine. It is assumed that phosphonium fluoride species formed from triphenylphosphine reaction. 0 1997 Elsevier Science S.A. ~qw~~rr(s:
Pofawum
fluoride-poIy{
hydrogen
fluoride);
Fluorinating
agent; Ring openjn g; Epoxides:
1. Introduction
c-4
Potassiumfluoride-poIy( hydrogen fluoride) ( KF(HF),,) saltsare easy-to-handlesolid reagentswhich are easily prepared from potassiumfluoride and anhydrous hydrogen fluoride [ I]. From the viewpoint that they are poly( hydrogen fluoride) species,they are expected to be solid alternatives to anhydrous hydrogen fluoride or amine-HF. which are effective nucleophilic fluorinating agents [ 21. Recently, we have demonstratedthe utility of KF( HF), as nucleophilic fluorinating agentsfor the first time [ 3,4]. When KF( HF),> is usedfor ring-opening reactions of epoxides and for halofluorination of alkenes,the reactions proceedin a regio- and stereoselective manner to afford the corresponding fluorohydrins and halofluorides respectively. Especially, the stereoselectivity of the ring-opening reaction is quite unique, namely the reaction proceedsvia predominantly cis-addition of hydrogen fluoride to the epoxide. Concerning this ring-opening of epoxides, however, the substrate is limited
only to aromatic
epoxides, such as styrene
oxide. If aliphatic epoxides are reacted with KF(HF),, the yields of corresponding fluorohydrins are very low [ 31. In this study, we investigate the ring-opening of aliphatic epoxides with KF(HF), and find that a catalytic amount of triphenylphosphineenhancesthis reaction. * Corresponding Organic Chemistry. ccmail.nimc.go.jp 0022-I
139/97/$17.00
PUSOO22-1
author. Fluorine Chemistry Laboratory, Department of Tel./Fax: +81 298 54 4570; e-mail: mtamura@ 0 1997 Elsevier
139(97)00069-9
Science S.A. All rights reserved
is enhanced by a catalytic amount of work
as fluorinating
agents
in this
Triphenylphocphine
KF(HF),,
F
additive *
1
2 a : R = C,c,H2j
OH OH
R&
+
F
R A/ 3
-
b:R=PhOCH2-
Scheme I.
2. Results and discussion
The reaction of 1-dodeceneoxide (la) with KH,F, was initially attempted (Scheme 1). Without additives, although the ring-opening reaction proceededat 8O”C, the yields of corresponding fluorohydrins (2a and 3a) were very low becauseof undesirablesidereactions suchaspolymerization (Table I, entry 1) However, the yield was improved when the reaction was carried out in the presenceof a catalytic amount of trialkylphosphine (entry 2). And when triphenylphosphine( Ph3P) was usedasan additive, the fluorohydrins were obtained in 64% yield (entry 3). The effect of Ph,P on the reaction using other KF(HF), or substrateswas examined. When la was reacted with K2HsF7,the ring-opening reaction proceededat room temperature, but the combined yield of 2a and 3a wasonly 12% (entry 5). If a catalytic amount of Ph3P was used as an additive, the yield was improved to 44% (entry 6). And although the reaction of phenyl glycidyl ether (lb) with KH,F, did not proceedat all (entry 7), the reactionproceeded
148
M. Tumura
Table 1 The effect of phosphines Entry
on the ring-opening
Substrate
et al. /Journal
of aliphatic
epoxides
@‘Fluorine
Chenti.vtq
147-149
*
Additive
KF(HF),,
85 (1997)
Time (h)
Products
(2 +3)
Yield h (9%) 1 2 3 4 5 6 7 8
-
KW, KW,
la la la la la la lb lb
32 72 72 45 7 3 32
n-Bu,P Ph,P Ph,P’BrPh,P Ph,P
KHzF, K&F, WW, K&&F, KHzF, KHIF,
Selectivity
9’
72
h (2:3)
84:16
40 64 66 12”
‘73127 69:3 1 68:32 92:8
44 0’ 33 +
80:20 79:2 I
A Epoxide ( 1 mmol), KF( HF), (5 mmol), and an additive (0.1-0.2 mmol) were stirred at 80 “C in 1.2.dichloroethane. h Yield and selectivity were determined by ‘“F-NMR of the crude product (C,H,CF? was used as internal standard). ’ The substrate
(ca. 30%)
’ The reaction
was conducted
was recovered. at room
temperature.
’ The substrate ( 100%) was recovered. ’ The substrate (ca. 45%) was recovered.
in the presence of a catalytic amount of Ph,P and afforded 2b and 3b in 33% yield (entry 8). To consider the mechanism of this reaction, the reaction of la with KH2F3 was attempted in the presence of a catalytic amount of tetraphenylphosphonium bromide (Ph,P+Br) (entry 4). As a result, the corresponding fluorohydrins were obtained in 66% yield and the regioselectivity 2a:3a was 68:32, which was almost the same result as the reaction using Ph,P (entry 3). This result suggests that the mechanism of the reaction using Ph,P is similar to that using Ph,P+Br-. It has been reported that tetraphenylphosphonium fluoride species, such as Ph,P+HF;, form from Ph,P+Brand hydrogen fluoride [ 51, and that these phosphonium fluorides work as nucleophilic fluorinating agents [5,6]. Consequently, it is assumed that the ring-opening of epoxides with KH2F, in the presence of a catalytic amount of Ph,P+Brproceeds via formation of tetraphenylphosphonium fluoride species such as PhlP+F(HF); and that fluorination with the phosphonium fluoride follows, as shown in Scheme 2. Similarly, ring-opening reactions in the presence of Ph,P would also proceed by fluorination with phosphonium fluoride species. It is known that ring-opening of epoxides with Ph,P in the presence of acid readily occurs to form P-hydroxyalkyltriphenylphosphonium salts [ 71. Consequently. in the case of the ring-opening of epoxides with KF( HF), in the presKF(HF), PbP+Br
-
PbP+
F(HF);
Ph3P
+
(1) +Ph3
R’-
2
RCH(OH)CHzScheme
3.
ence of a catalytic amount of Ph,P, it is assumed that phydroxyalkyltriphenylphosphonium fluoride species such as RCH( OH)CH*-Ph3P+F( HF); are formed from epoxide, Ph3P, and KF(HF),. RCH(OH)CH,-Ph,P+F(HF); then fluorinates more epoxide to form RCH( OH)CH*Ph,P+F( HF);- ,, and RCH( OH)CH,-Ph,P+F( HF); is regenerated with KF( HF), (Scheme 3).
(1)
3. Experimental
Scheme
I
VWm-
details
A typical experimental procedure is as follows. To KHpF, (5 mmol) in a Teflon@ (PFA) vessel was added a solution of the epoxide ( 1 mmol) and an additive (0.1-0.2 mmol) in 1,2-dichloroethane (5 ml). The reaction mixture was stirred at 80 “C for a period indicated in Table 1, and quenched with aqueous sat. NaHCO,. After the usual work up, yields and selectivity of the products were determined by ‘“F-NMR of
M. Tnmuru
et al. /Journal
of Fhorinr
the crude product (C,H,CF, was usedasinternal standard). The products were purified and identified by comparisonof their IR, ‘H-NMR, and 19F-NMR spectra with those of authentic samples[S-10].
4. Conclusion We have demonstratedthe effect of triphenylphosphineon ring-opening reactionsof aliphatic epoxides with KF( HF),. A catalytic amountof triphenylphosphineenhancesthis reaction and it has been suggestedthat phosphonium fluoride speciesform from triphenylphosphine, KF( HF),, and epoxide, and act as fluorinating agentsin this reaction.
Chemisr~
85 (1997)
147-149
149
References
[ I] G.H. Cady, .I. Am. Chem. Sot. 56 ( 1934) 1431. [2 I N. Yoneda, Tetrahedron 47 ( 1991) 5329. [31 M. Tamura, M. Shibakami, T. Arimura. S. Kurosawa, A. Sekiya, J. Fluorine. Chem. 70 ( 1995) 1. [ 41 M. Tamura, M. Shibakami. A. Sekiya, Synthesis ( 1995) 5 15. [ 5 1 S.J. Brown, J.H. Clark. J. Fluorine Chem. 30 ( 1985) 25 I. [ 61 H. Seto. Z. Qian, H. Yoshioka, Y. Uchibori. M. Umeno, Chem. Lett. (1991) 1185. [7] S. Yamamoto, K. Okuma, H. Ohata, Bull. Chem. Sot. Jpn. 61 ( 1988) 4476. [ 8 I D. Landini, M. Penso, Tetrahedron Lett. 3 1 ( 1990) 7209. [91 J. Ichihara. T. Hanafusa, J. Chem. Sot. Chem. Commun. ( 1989) 1848. [ IO] D. Landini, D. Albanese. M. Penso, Tetrahedron 48 ( 1992) 4163.
Journal of Fluorine Chemistry 85 ( 1997) 147-149
The effect of triphenylphosphine on ring-opening of aliphatic epoxides with potassium fluoride-poly (hydrogen fluoride) Masanori Tamura * , Motonari Shibakami, Akira Sekiya Natiunal
qf Mutrwls
Institute
and
Received
Chemical
Research.
10 January
1997;
I-I
Hi,rquhi.
Tsukubu,
Iburcrki
305.
Japan
accepted 19 May 1997
Abstract The ring-opening reaction of aliphatic epoxides with potassium fluoride-poly( hydrogen fluoride) triphenylphosphine. It is assumed that phosphonium fluoride species formed from triphenylphosphine reaction. 0 1997 Elsevier Science S.A. ~qw~~rr(s:
Pofawum
fluoride-poIy{
hydrogen
fluoride);
Fluorinating
agent; Ring openjn g; Epoxides:
1. Introduction
c-4
Potassiumfluoride-poIy( hydrogen fluoride) ( KF(HF),,) saltsare easy-to-handlesolid reagentswhich are easily prepared from potassiumfluoride and anhydrous hydrogen fluoride [ I]. From the viewpoint that they are poly( hydrogen fluoride) species,they are expected to be solid alternatives to anhydrous hydrogen fluoride or amine-HF. which are effective nucleophilic fluorinating agents [ 21. Recently, we have demonstratedthe utility of KF( HF), as nucleophilic fluorinating agentsfor the first time [ 3,4]. When KF( HF),> is usedfor ring-opening reactions of epoxides and for halofluorination of alkenes,the reactions proceedin a regio- and stereoselective manner to afford the corresponding fluorohydrins and halofluorides respectively. Especially, the stereoselectivity of the ring-opening reaction is quite unique, namely the reaction proceedsvia predominantly cis-addition of hydrogen fluoride to the epoxide. Concerning this ring-opening of epoxides, however, the substrate is limited
only to aromatic
epoxides, such as styrene
oxide. If aliphatic epoxides are reacted with KF(HF),, the yields of corresponding fluorohydrins are very low [ 31. In this study, we investigate the ring-opening of aliphatic epoxides with KF(HF), and find that a catalytic amount of triphenylphosphineenhancesthis reaction. * Corresponding Organic Chemistry. ccmail.nimc.go.jp 0022-I
139/97/$17.00
PUSOO22-1
author. Fluorine Chemistry Laboratory, Department of Tel./Fax: +81 298 54 4570; e-mail: mtamura@ 0 1997 Elsevier
139(97)00069-9
Science S.A. All rights reserved
is enhanced by a catalytic amount of work
as fluorinating
agents
in this
Triphenylphocphine
KF(HF),,
F
additive *
1
2 a : R = C,c,H2j
OH OH
R&
+
F
R A/ 3
-
b:R=PhOCH2-
Scheme I.
2. Results and discussion
The reaction of 1-dodeceneoxide (la) with KH,F, was initially attempted (Scheme 1). Without additives, although the ring-opening reaction proceededat 8O”C, the yields of corresponding fluorohydrins (2a and 3a) were very low becauseof undesirablesidereactions suchaspolymerization (Table I, entry 1) However, the yield was improved when the reaction was carried out in the presenceof a catalytic amount of trialkylphosphine (entry 2). And when triphenylphosphine( Ph3P) was usedasan additive, the fluorohydrins were obtained in 64% yield (entry 3). The effect of Ph,P on the reaction using other KF(HF), or substrateswas examined. When la was reacted with K2HsF7,the ring-opening reaction proceededat room temperature, but the combined yield of 2a and 3a wasonly 12% (entry 5). If a catalytic amount of Ph3P was used as an additive, the yield was improved to 44% (entry 6). And although the reaction of phenyl glycidyl ether (lb) with KH,F, did not proceedat all (entry 7), the reactionproceeded
148
M. Tumura
Table 1 The effect of phosphines Entry
on the ring-opening
Substrate
et al. /Journal
of aliphatic
epoxides
@‘Fluorine
Chenti.vtq
147-149
*
Additive
KF(HF),,
85 (1997)
Time (h)
Products
(2 +3)
Yield h (9%) 1 2 3 4 5 6 7 8
-
KW, KW,
la la la la la la lb lb
32 72 72 45 7 3 32
n-Bu,P Ph,P Ph,P’BrPh,P Ph,P
KHzF, K&F, WW, K&&F, KHzF, KHIF,
Selectivity
9’
72
h (2:3)
84:16
40 64 66 12”
‘73127 69:3 1 68:32 92:8
44 0’ 33 +
80:20 79:2 I
A Epoxide ( 1 mmol), KF( HF), (5 mmol), and an additive (0.1-0.2 mmol) were stirred at 80 “C in 1.2.dichloroethane. h Yield and selectivity were determined by ‘“F-NMR of the crude product (C,H,CF? was used as internal standard). ’ The substrate
(ca. 30%)
’ The reaction
was conducted
was recovered. at room
temperature.
’ The substrate ( 100%) was recovered. ’ The substrate (ca. 45%) was recovered.
in the presence of a catalytic amount of Ph,P and afforded 2b and 3b in 33% yield (entry 8). To consider the mechanism of this reaction, the reaction of la with KH2F3 was attempted in the presence of a catalytic amount of tetraphenylphosphonium bromide (Ph,P+Br) (entry 4). As a result, the corresponding fluorohydrins were obtained in 66% yield and the regioselectivity 2a:3a was 68:32, which was almost the same result as the reaction using Ph,P (entry 3). This result suggests that the mechanism of the reaction using Ph,P is similar to that using Ph,P+Br-. It has been reported that tetraphenylphosphonium fluoride species, such as Ph,P+HF;, form from Ph,P+Brand hydrogen fluoride [ 51, and that these phosphonium fluorides work as nucleophilic fluorinating agents [5,6]. Consequently, it is assumed that the ring-opening of epoxides with KH2F, in the presence of a catalytic amount of Ph,P+Brproceeds via formation of tetraphenylphosphonium fluoride species such as PhlP+F(HF); and that fluorination with the phosphonium fluoride follows, as shown in Scheme 2. Similarly, ring-opening reactions in the presence of Ph,P would also proceed by fluorination with phosphonium fluoride species. It is known that ring-opening of epoxides with Ph,P in the presence of acid readily occurs to form P-hydroxyalkyltriphenylphosphonium salts [ 71. Consequently. in the case of the ring-opening of epoxides with KF( HF), in the presKF(HF), PbP+Br
-
PbP+
F(HF);
Ph3P
+
(1) +Ph3
R’-
2
RCH(OH)CHzScheme
3.
ence of a catalytic amount of Ph,P, it is assumed that phydroxyalkyltriphenylphosphonium fluoride species such as RCH( OH)CH*-Ph3P+F( HF); are formed from epoxide, Ph3P, and KF(HF),. RCH(OH)CH,-Ph,P+F(HF); then fluorinates more epoxide to form RCH( OH)CH*Ph,P+F( HF);- ,, and RCH( OH)CH,-Ph,P+F( HF); is regenerated with KF( HF), (Scheme 3).
(1)
3. Experimental
Scheme
I
VWm-
details
A typical experimental procedure is as follows. To KHpF, (5 mmol) in a Teflon@ (PFA) vessel was added a solution of the epoxide ( 1 mmol) and an additive (0.1-0.2 mmol) in 1,2-dichloroethane (5 ml). The reaction mixture was stirred at 80 “C for a period indicated in Table 1, and quenched with aqueous sat. NaHCO,. After the usual work up, yields and selectivity of the products were determined by ‘“F-NMR of
M. Tnmuru
et al. /Journal
of Fhorinr
the crude product (C,H,CF, was usedasinternal standard). The products were purified and identified by comparisonof their IR, ‘H-NMR, and 19F-NMR spectra with those of authentic samples[S-10].
4. Conclusion We have demonstratedthe effect of triphenylphosphineon ring-opening reactionsof aliphatic epoxides with KF( HF),. A catalytic amountof triphenylphosphineenhancesthis reaction and it has been suggestedthat phosphonium fluoride speciesform from triphenylphosphine, KF( HF),, and epoxide, and act as fluorinating agentsin this reaction.
Chemisr~
85 (1997)
147-149
149
References
[ I] G.H. Cady, .I. Am. Chem. Sot. 56 ( 1934) 1431. [2 I N. Yoneda, Tetrahedron 47 ( 1991) 5329. [31 M. Tamura, M. Shibakami, T. Arimura. S. Kurosawa, A. Sekiya, J. Fluorine. Chem. 70 ( 1995) 1. [ 41 M. Tamura, M. Shibakami. A. Sekiya, Synthesis ( 1995) 5 15. [ 5 1 S.J. Brown, J.H. Clark. J. Fluorine Chem. 30 ( 1985) 25 I. [ 61 H. Seto. Z. Qian, H. Yoshioka, Y. Uchibori. M. Umeno, Chem. Lett. (1991) 1185. [7] S. Yamamoto, K. Okuma, H. Ohata, Bull. Chem. Sot. Jpn. 61 ( 1988) 4476. [ 8 I D. Landini, M. Penso, Tetrahedron Lett. 3 1 ( 1990) 7209. [91 J. Ichihara. T. Hanafusa, J. Chem. Sot. Chem. Commun. ( 1989) 1848. [ IO] D. Landini, D. Albanese. M. Penso, Tetrahedron 48 ( 1992) 4163.