[acs symposium series] inorganic fluorine chemistry volume 555 (toward the 21st century) ||...

Chapter 18

Perfluorovinyl and Perfluoroaryl Zinc and Cadmium Reagents

Preparation, Stability, and Reactivity

Donald J. Burton

Department of Chemistry, University of Iowa, Iowa City, IA 52242

F-Vinyl iodides and bromides react directly with cadmium or zinc metal to stereospecifically produce the corresponding F-vinyl cadmium and zinc reagents. These vinyl cadmium and zinc reagents exhibit excellent thermal stability (> 100°C) and do not couple with F-vinyl halides. Metathesis with Cu(I) salts gives the analogous F-vinyl copper reagents. The F-vinyl copper reagents readily undergo stereospecific alkylation, coupling and acylation reactions. They also add stereospecifically syn to F-2-butyne to produce F-dienyl copper reagents. Acylation of the dienyl copper reagent gives a dienyl ketone which spontaneously undergoes electrocyclization to a pyran derivative. The F-vinyl zinc reagents couple to aryl iodides in the presence of Pd° and provide useful stereoselective routes to α,β,β-trifluorostyrenes and 1-arylperfluoropropenes. Similar Pd° catalyzed coupling of the F-vinyl zinc reagent with 1-iodoperfluoroolefins provides a stereospecific route to F-dienes. Reaction of bromopentafluorobenzene with cadmium metal gives the analogous F-aryl cadmium reagent, which readily undergoes metathesis with Cu(I) salts to give the F-aryl copper reagent essentially quantitatively. The F-aryl copper reagent also adds stereospecifically syn to F-2-butyne to give a vinyl copper reagent which is easily alkylated, arylated or acylated.

The low thermal stability of perfluoroalkenyl lithium and Grignard reagents has restricted their application for the synthesis of the fluorinated vinyl derivatives. Their preparation must be carried out at low temperatures and scale up processes are difficult. In addition, since both the preparation and reaction of these thermally labile organometallics must be accomplished at low temperatures, only reactive substrates can be utilized in functionalization reactions.

F2C=CFX + BuLi " i U U ^ » F2C=CFLi + BuX

X = H, CI, Br, I

0097-6156/94/0555-0297$08.00/0 © 1994 American Chemical Society

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8

In Inorganic Fluorine Chemistry; Thrasher, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

298 INORGANIC FLUORINE CHEMISTRY: TOWARD THE 21ST CENTURY

Therefore, we have attempted to develop a general route to stable F-vinyl organometallic compounds that would: (a) possess thermal stability at room temperature or above; (b) possess functionalization (or exchange) capability; and (c) be formed in one step (one-pot) from readily accessible precursors. The above properties would permit these reagents to be prepared with minimal experimental difficulty, easily scaled up, and readily utilized in preparative transformations to stereospecifically yield polyftinctionalized materials.

Thus, our initial attention focused on F-vinyl copper reagents. Miller (7) had reported the preparation of the stable copper reagent, E-CF3CF=C(CF3)Cu, from E-CF3CF=C(CF3)Ag. Although the generality of this approach was seriously limited by the regioselectivity and stereoselectivity of AgF addition to F-alkynes, the thermal stability of the vinyl copper reagent prompted us to develop a more general route to this class of fluorinated organometallics.

Initial Approaches

Our initial strategy was to utilize F-vinyl halides as precursors. Many of these compounds are readily available or easily prepared. Also, we anticipated that the formation of the organometallic reagent from the vinyl halide would occur stereospecifically, thus permitting preparation of the appropriate £- or Z-organometallic by proper choice of the E- or Z-vinyl halide.

Unfortunately, when either iodotrifluoroethene or Z-l-iodopentafluoropropene was reacted with copper metal (activated by various reported procedures), only diene products were detected. No vinyl copper reagent was observed in these reactions.

2 F2C=CFI 0 x 0 » F2C=CF-CF=CF2

CT3v ^ c = c

F ' N I

Ql° C F 3 s yF

C=C F

F ' S C F 3

Apparently, the slow step in diene formation is the formation of the vinyl copper reagent followed by rapid coupling of the vinyl copper reagent with additional vinyl halide.

F2C=CFT + 2Cu° slow [CF2=CFCu] + Cul

fast F,C=CFI

F2C=CF-CF=CF2 + Cul

Consequently, it is necessary to generate the vinyl copper reagent in the absence of vinyl halide to preclude coupling reactions (diene formation).

Perfluorovinyl Cadmium Reagents. In order to achieve the formation of the F-vinyl copper reagent in the absence of F-vinyl halide, we turned to the formation of a F-vinyl organometallic reagent that does not readily couple with vinyl halides. We

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8


18. BURTON Perfluorovinyl & Perfluoroatyl Zinc & Cadmium Reagents 299

initially selected F-vinyl cadmium reagents to study for the following reasons: (a) in the formation of F-aryl cadmium reagents from bromopentafluorobenzene and cadmium metal, we had not observed the formation of any F-biphenyl (coupled product); and (b) n i C d and 1 1 3 C d NMR active isotopes in the organometallic compound would allow us to monitor formation of the organometallic reagent by 1 9 F and 1 1 3 C d NMR and assist in the structural assignments of the mono and bis reagent

As expected, F-vinyl bromides and iodides readily reacted with cadmium metal in DMF to give stable F-vinyl cadmium reagents (mixture of mono and bis reagents) (2). In general, the vinyl iodides reacted at room temperature (mild exotherm) and the vinyl bromides required mild heating (RT-60°C). With Ε - and Z-vinyl halides (including diene precursors) stereospecificity was preserved in formation of the F-vinyl cadmium reagent.

RFCF=CFX + Cd RT-60°C » RFCF=CFCdX + (RFCF=CF)2M + CdX 2

DMF mono bis

X = Br, I R F = F, perfluoroalkyl,

perfluoroalkenyl

Table I summarizes typical examples of F-vinyl cadmium reagents.

Table I. Preparation of Alkenyl Cadmium Reagents from E-Vinyl Halides and Cadmium

RFCF=CFX + Cd P M F » RFCF=CFCdX + (RFCF=CF)2Cd + CdX 2 F RT-60°C F 2

Olefin Cadmium Reagent2 Yieldb

CF2=CFI CF2=CFCdX 99 Z-CF3CF=CFI Z-CF3CF=CFCdX 96 £-CF3CF=CFI E-CF3CF=CFCdX 92 Z-CF3(CF2)4CF=CFI Z-CF3(CF2)4CF=CFCdX 95 CF 3CF=CICF 3

C CF3CF=C(CF3)CdXd 91 CF3CF=C(Ph)CF=CFBre CF3CF=C(Ph)CF=CFCdXf 61 E-CF3C(Ph)=CFI E-CF3C(Ph)=CFCdX 77

a Mixture of mono and bis reagent; X = halogen or another F-alkenyl group. t> !9F NMR yield vs. PhCF3. CE/Z mixture; E/Z = 39/61 d£/Z = 37/63 *E, Z.Z, Ζ = 90/10 f E , Z:Z, Ζ = 90/10

Reproduced with permission from ref. 2. Copyright Elsevier 1986.

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8



The thermal stability of these vinyl cadmium reagents is remarkable. A solution of Z-CF3CF=CFCdX in dry DMF was stable for > 30 days at room temperature and lost only 25% activity at 123°C after 1.5 hours. The mono and bis cadmium reagents are involved in a Schlenk equilibrium; the bis reagent being the more volatile reagent. Thus, a short-path vacuum distillation of the reaction mixture followed by recrystallization from GfeCl^pentane (1:5) permits isolation of the bis reagent as a low-melting solvate (white solid). Thus, the DMF and triglyme (TG) solvates were isolated from F2C=CFI and Z-CF3CF=CFI (3).

CF 3 F CF 3 F c = c c = c

F ' % Cd»DMF F ' γ Cd^TG

m.p. 77-80°C m.p. 64-65°C

(F2C=CF)2Cd*TG

m.p. 20-25°C

As noted above, 1 1 3 C d NMR readily distinguishes the mono and bis reagents. Thus, for F2C=CFCdX (X = halogen or -CF=CF2), the mono reagent appears in the 1 1 3 C d NMR spectrum as a doublet of doublet of doublets, whereas the bis reagent appears as a triplet of triplet of triplets. Similarly, Z-CF3CF=CFCdX (X = halogen or -CF=CF2) shows a doublet of doublets for the mono reagent and a triplet of triplets for the bis reagent in the 1 1 3 C d spectrum (coupling to vinylic fluorines). These spectra and multiplicities are readily observable even in reaction mixtures and can be utilized to determine the mono-bis ratio directly.

Perfluorovinyl Zinc Reagents. Success in the formation of F-vinyl cadmium reagents (without coupling to vinyl halides) prompted us to examine formation of the corresponding zinc reagents. Thus, we found that zinc metal reacted readily with a

RFCF=CFX + Zn s o l v c n t » RFCF=CFZnX + (RFCF=CF)2Zn + ZnX 2

RT-60°C X = Br, I

R F = F, perfluoroalkyl perfluoroalkenyl

mono bis

variety of F-vinyl iodides and bromides to stereospecifically produce the corresponding mono and bis zinc reagents (4) - again without formation of any symmetrical diene. Unfortunately, zinc has no useful NMR active isotopes (like Cd); thus NMR could not be utilized to unequivocally assign mono and bis zinc reagents. However, in most cases the mono and bis zinc reagents were distinguishable by 1 9 F NMR. Thus, by enhancement of the signal for the mono reagent on addition of the appropriate zinc halide at the expense of the signal for the bis reagent, the mono/bis ratio could be determined.

(RFCF=CF)2Zn + ZnX 2 - 2RFCF=CFZnX

bis X = Br, I mono Table II summarizes typical F-vinyl zinc reagents prepared from zinc metal and F-vinyl halides.

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8


18. B U R T O N Perfluorovinyl & Perfluoroaryl Zinc & Cadmium Reagents 301

Table II. Preparation of Vinyl Zinc Reagents from E-Vinyl Halides and Zinc Metal

RFCF=CFX + Zn solvent/RT^ RFCF=CFZnX + (RFCF=CF)2Zn + ZnX2

Vinyl HaUde Solvent8 Zinc Reagent* Mono:Bis Yieldc

CF2=CFI DMF CF2=CFZnX 80:20 79% DMAc 84:16 97% MG 60% TG 68:32 95% TetG 67:33 85%

CF2=CFBr DMF CF2=CFZnX 95:5 72% CF2=CBr2 DMF CF2=CBrZnX 68:32 97% Z-CF3CF=CFI THF Z-CF3CF=CFZnX 68:32 98%

TG 65:35 96% DMF 74:26 100% CH3CN 81:19 90%

£-CF3CF=CFI TG £-CF3CF=CFZnX 59:41 100% Z-CF3CF2CF=CFI TG Z-CF3CF2CF=CFZnX 90% Z-CF3(CF2)4CF=CFBr DMF Z-CF3(CF2)4CF=CFZnX 77% Z-CF3(CT2)4CF=CTI TG Z-CF3(CF2)4CF=CFZnX 74% CF3C(Ph)=CFBrd DMF CF3C(Ph)=CFZnXd 94% CFsCCPh^CBrç DMF CF3C(Ph)=CBrZnXe 95% E-CF3C(Ph)=CFI THF £-CF3C(Ph)=CFZnX 67:33 78% Z-CF3(C6F5)C=CFI THF Z-CF3(C6F5)C=CFZnX 57:43 86% CF3CF=C(Ph)CF=CFBrf DMF CF3CF=C(Ph)CF=CFZnXf 71% E-CF3CH=CFI TG £-CF3CH=CFZnX 67:33 89% E-CF3CF=C(CF3)I TG E-CF3CF=C(CF3)ZnX 80:20 75%

a M G = monoglyme, TG = triglyme, TetG = Tetraglyme. b Mixture of mono and bis reagent; X = halogen or another F-vinyl group. c 19F NMR yield vs. PhCF3. d£/Z mixture; E/Z= 59/41 e£/Z = 67/33 f£,Z:Z, Ζ = 90:10

Reproduced with permission from ref. 4. Copyright Elsevier 1987.

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8



In contrast to the F-vinyl cadmium reagents, the F-vinyl zinc reagents can be prepared in a variety of amide, etheral, and nitrile solvents such as DMF, DMAC (Ν,Ν-dimethylacetamide), MG (monoglyme), TG (triglyme), TetG (tetraglyme), THF, and CH3CN (cf. Table Π). The ability to form the F-vinyl zinc reagents in etheral solvents is often important in functionalization reactions, since the functionalized derivative can react with amide solvents (5).

The F-vinyl zinc reagents exhibit excellent thermal stability. For example, Z-CF3CF=CFZnX in TG showed < 10% loss of activity after one month at room temperature and < 5% loss of activity after three days at 65°C. Thus, these reagents can be prepared on a large scale and stored for extended periods of time without any significant change in activity of the stock solution.

Perfluorovinyl Copper Reagents. The F-vinyl cadmium and zinc reagents outlined previously, could be readily prepared from F-vinyl halides without significant formation of dienes. Subsequent metathesis of the F-vinyl cadmium and zinc reagents in DMF with Cu(I) halides stereospecifically gives a solution of a stable F-vinyl

RFCF=CFX + M DMF » [RFCF=CFMX + (RFCF=CF)2M + M X J RT-60°C ι _

]Cu(I)Y [Y = I,Br,Cl] X = Br, I M = Cd, Zn t

[RFCF=CFCu]

copper reagent (6). Since no F-vinyl halide remains after formation of the intermediate F-vinyl cadmium or zinc reagents, no coupling results and the F-vinyl copper reagent survives. The stereochemical integrity is retained throughout the synthetic sequence and the F-vinyl copper reagent can be readily formed in either the E~ or Z-configuration from the appropriate E- or Z-F-vinyl halide or diene. Table ΙΠ summarizes some typical F-vinyl copper reagents prepared via this methodology.

Table III. Preparation of Vinylcopper Reagents olefin M RFCF=CFCu % yield"

CF2=CFI Cd CF2=CFCu 99% CF2=CFBr Zn CF2=CFCu 72% Z-CF3CF=CFI Cd Z-CF3CF=CFCu 92% Z-CF3CF=CFI Zn Z-CF3CF=CFCu 76% E-CF3CF=CFI Cd £-CF3CF=CFCu 83% Z-CF3(CF2)4CF=CFI Cd Z-CF3(CF2)4CF=CFCu 87% Z-CF3CC1=CFI Cd Z-CF3C(Ph)=CFCu 78% CF3C(Ph)=CFBr Zn CF3C(Ph)=CFCu 84% E/Z = 59/41 E/Z = 59/41 CF3CF=C(Ph)CF=CFBr Zn CF3CF=C(Ph)CF=CFCu 63% E/Z = 90/10 E/Z = 9010

aOverall 1 9 F NMR yield based on starting olefin. Reproduced from ref. 6. Copyright American Chemical Society, 1986.

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8


18. BURTON Perfluorovinyl & Perfluoroaryl Zinc & Cadmium Reagents 303

The F-vinyl copper reagents exhibit excellent stability at room temperature in the absence of moisture and/or oxygen. At higher temperatures (> 50°C) they undergo rapid decomposition.

The F-vinyl copper reagents participate in a variety of alkylation, coupling and acylation reactions as illustrated in Scheme I.

£-CF3CF-CFC(0)CH3 (77%) E,£-CT3CF=CFCF=C(Ph)CF3 (54%)

E-CF3CF=CFPh (56%) CH3C(0)C1

P h i

PhCH2Br

E-CF3C(Ph)=CFI £-CF3CF=CFCH2CH=CH2 (94%)

Z-CF3CF=CFCu

PhC(0)Cl

CH2=CHCH2Br

CH3I

£-CF3CF=CFCH3 (87%) E-CF3CF=CFCH2Ph (56%)

£-CF3CF=CFC(0)Ph (80%)

Scheme I Reproduced from ref. 6. Copyright American Chemical Society, 1986.

Stereospecific Addition of E-Vinyl Copper Reagents to E-Alkynes

Similar to their hydrocarbon analogues, the Ε-vinyl copper reagents add to alkynes. Although either syn or and addition is possible, only syn addition was detected in the

F2C=CF Cu C=C

CF, N C F 3

m syn addn.

F2C=CFCu anti • - X -

CF3C=CCF3 addn.

.CF, F2C=CF c=c

CF, Cu

addition of trifluorovinyl copper to E-2-butyne (3). When the copper/alkyne addition adduct is acylated, the corresponding dienyl ketone is not detected. Instead, the electrocyclization product is isolated.

F2C=CF ρχ C=C

CF, N C F 3

+ RC(0)C1

R = alkyl, aryl, perfluoroalkyl

CF2=CF XC-R

c=c CF 3 CF3

F F 2

ÇF3

,CF3

Λ

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8



If the F-vinyl copper reagent contains two bulky groups at the β-position, the electrocyclization process is not spontaneous and the dienyl ketone can be isolated. Subsequent heating of the dienyl ketone to 70°C promotes electrocyclization of the ketone to the heterocyclic product (3).

Palladium-Catalyzed Coupling Reactions of E-Vinyl Zinc Reagents

[A]: With Aryl Iodides

Pd° coupling reactions generally occur under mild conditions,with minimal side reactions and proceed with regiochemical and/or stereochemical control.

F-Vinyl zinc reagents readily react with aryl iodides in the presence of 1-3 mol % Pd (PPh3)4 to give excellent yields of 1-aryl-perfluorooleflns (7).

RFCF=CFZnX + Arl

£ o r Z R F = F, CF 3

P d ( P P h 3 > * > RpCF=CFAr 1-3 mol % Ά ί , *or Ε 60-80°C solvent

When Rp = F, the α,β,β-trifluorostyrenes are formed in good to excellent yields. Both electron-withdrawing and electron-releasing groups on the aryl ring can be utilized successfully. With 1,4-diiodobenzene, the bis-substituted compound is formed. Table TV summarizes typical preparations of trifluorovinyl styrenes via this methodology.

When Rp = CF3, the Pd° coupling reaction with aryl iodides proceeds with 100% retention of configuration with Z-CF3CF=CFZnX and > 92% retention of configuration with £-CF3CF=CFZnX. Table V illustrates typical examples with Z- and £-CF3CF=CFZnX.

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8


18. B U R T O N Perfluorovinyl & Perfluoroaryl Zinc & Cadmium Reagents 305

Table IV. Isolated Yields of α,β,β-Trifluorostyrenes Pd(PPh3)4

CF2=CFZnX + Arl i _ 3 M o l % » CF2=CFAr l-10h,60-80°C

α,β,β-Tifluorostyrene Solvent Isolated Yield, %

C6H5CF=CF2 DMF 74

o-N02C6H4CF=CF2 DMF 73 p-MeOC6H4CF=CF2 THF 61 o-(CH3)2CHC6H4CF=CF2 THF 70 2,5-Cl2C6H3CF=CF2 D M F 75 o-CF3C6H4CF=GF2 TG a 73 m-N02C6H4CF=CF2 T G a 81 p-ClC6H4CF=CF2 D M F 77 /7-CF2=CFC6H4CF=CF2b D M F 56

a TG = triglyme. bRoom temperature for 2 days.

Reproduced from ref. 7. Copyright American Chemical Society, 1988.

Table V. Isolated Yields of E-l-Arylperfluoropropenes and Z-l-Arylperfluoropropenesa

CF3CF=CFZnX + Arl Γ̂ΓΓ̂ 4 * CF3CF=CFAr

Λ 1-3 Mol % ° Ε or Z l-10h,60-80°C ΖοτΕ 1 -Arylperfluoropropene Isolated Yield, %

E-C6H5CF=CFCF3 80 £-p-CH3C6H4CF=CFCF3 65 £-p-ClC6H4CF=CFCF3 61 £-w-N02C6H4CF=CFCF3 80 Z-C6H5CF=CFCF3b 82 Z-p-CH3C6H4CF=CFCF3

c 70 Z-p-ClC6H4CF=CTCF3'' 74

a A l l preparations were conducted in triglyme with yellow Pd(PPh3)4 prepared in our laboratory. t>Z/E=97/3. cz/£ = 92/8.

Reproduced from ref. 7. Copyright American Chemical Society, 1988.

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8


306 I N O R G A N I C F L U O R I N E C H E M I S T R Y : T O W A R D T H E 21ST C E N T U R Y

The mechanism of the Pd° coupling presumably proceeded via the typical oxidative addition of die aryl iodide to Pd° to give a palladium (Π) intermediate. Subsequent metathesis of the Pd (Π) intermediate with the F-vinyl zinc reagent followed by reductive elimination gave the aryl-substituted olefin and regenerated the Pd° catalyst as summarized below for a typical palladium catalysis cycle.

ArR

PdL,

Pd°L2 ArX

ArPd N RL2

ZnXo

ArPd n XL 2

RZnX

[B]: With Perfluorovinyl Iodides

Previous work in our laboratory demonstrated that F-vinyl iodides could undergo oxidative addition to Pd°. Thus, utilization of the palladium catalysis cycle (with RpCF=CF- in place of Ar-) would provide a useful, stereospecific route to E-dienes.Thus, we found that the following dienes could be stereospecifically prepared via this approach (5).

F 3 C N F (1) C=C + F2C=CFI

F ZnX

1-3 Mol % (Ph 3P) 4Pd t

TG * 40°C 18 h

F 3 C X

c=c CF=CF2

(2) F2C=CFZnX + F 3 C X yl

c=c F ' S F

1-3 Mol % ρ c (Ph3P)4Pd | >

3 \

F' " S F

,GF=CF 2

TG 40°C 20 h 91%

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8


18. B U R T O N Petfluorovinyl & Perfluoroaryl Zinc & Cadmium Reagents 307

! ρ l-3Mol% ρ Γ _ ρ ρ ρ S • (Ph3P)4Pd /

(3) F2C=CFZnX+ C=C^ K ^ 4 » V c ^ F C 3 F 7 g j o ç F C3F7

15 h 86%

(4) F 3 C N F

c=c F ' NZnI

F 3 Q + c=c

1-3 Mol % ρ r (Ph3P)4Pd ^ 3 Ν

TG 95°C 6h

C=C y F ' W

F " S F

,CF3

71%

Perfluoro Aryl Copper Reagents

A previous report from our laboratory has demonstrated that F-aryl cadmium reagents could be readily formed at room temperature via reaction of cadmium powder with bromopentafluorobenzene (9).

The facile metathesis reaction of F-vinyl cadmium reagents with Cu(I) salts suggested that the F_-aryl copper reagent could be similarly prepared via metathesis of the F-aryl cadmium reagent. Indeed, this method works very well as summarized below (10):

C6F5Br + Cd D M F » [C6F5CdX] —£ϋΧ—»• [QFsCu] RT Y = Cl,Br 6 5

RT 100% X = Br, C 6 F 5

98%

Similar to the Ε-vinyl copper reagents, we have found that the F-aryl copper reagent also adds stereospecificially syn to E-2-butyne. The addition is slow (2-3 days) at room temperature but can be accomplished within a few hours at 40-60°C (10).

The alkyne addition adduct can be protonated, halogenated, arylated and acylated to give reasonable yields of highly substituted fluoroolefins as outlined in Scheme Π (yields in parentheses are based on CeFsBr).

CgFsCu + CF3C=CCF3 RT 2-3 days

Cu

c=c CF 3

C6F5

100%

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8



PhC(0)N

/ C = C \ CF 3

CF3 100(70)%

CH 3C(0)N JZeV5

/ C = C \ CF 3

CF3

24%

Scheme II

77(54)%

Acknowledgments. We thank the National Science Foundation and the Air Force Office of Scientific Research for support of this work.

Literature Cited (1) Miller, W.T. Abstracts of the 9th International Symposium on Fluorine

Chemistry, Avignon, France, p Ο 27. (2) Burton, D.J.; Hansen, S.W. J. Fluorine Chem. 1986, 31, 461. (3) Hansen, S.W. Ph.D. Thesis, University of Iowa. (4) Hansen, S.W.; Spawn, T.D.; Burton, D.J. J. Fluorine Chem. 1987, 35,

415. (5) Spawn, T.D.; Burton, D.J. Bull. Soc. Chim. Fr. 1986, (6), 876. (6) Burton, D.J.; Hansen, S.W. J. Am. Chem. Soc. 1986, 108, 4229. (7) Heinze, P.L.; Burton, D.J. J. Org. Chem. 1988, 53, 2714. (8) Nakamura, A. University of Iowa, unpublished results. (9) Heinze, P.L.; Burton, D.J. J. Fluorine Chem. 1985, 29, 359. (10) MacNeil, K. Ph.D. Thesis, University of Iowa.

RECEIVED April 6, 1993

Dow

nloa

ded

by P

EN

NSY

LV

AN

IA S

TA

TE

UN

IV o

n M

ay 2

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Apr

il 29

, 199

4 | d

oi: 1

0.10

21/b

k-19

94-0

555.

ch01

8


[acs symposium series] inorganic fluorine chemistry volume 555 (toward the 21st century) ||...

Documents