Formation of Carboxylic Acids, Esters, and Amides

Một phần của tài liệu Palladium reagents and catalysts new perspectives for the 21st century tsuji (Trang 278 - 287)

3.5 Carbonylation and Reactions of Acyl Chlorides

3.5.2 Formation of Carboxylic Acids, Esters, and Amides

Aromatic and α,β-unsaturated carboxylic acids and esters are prepared from aryl and alkenyl halides.

+ CO + NU-H Pd(0) Nu

X

R

X

R

O

Nu O base

+ CO + NU-H Pd(0) base

Carbonylation of reactive iodides proceeds using PdCl2(PPh3)2 as a standard catalyst under mild conditions in the presence of a base. Several modified catalyst systems have been reported. For example, ligandless Pd charcoal is an active catalyst at 140◦C [1]. Uozumi reported that the amphiphilic phosphine-Pd complex (Pd-PEP) bound to PEG-PS resin is a very active and useful catalyst. Carbonylation

of iodobenzene proceeded in H2O without an organic solvent at room temperature and under atmospheric pressure of CO in the presence of Pd-PEP and K2CO3 to give benzoic acid in 97 % yield. No reaction occurred when Pd-PPh3, instead of Pd-PEP, was used under similar conditions. The catalyst can be recycled [2]. Pd- complex immobilized on PAMAM (polyamino amido) dendrimers supported on silica was found to be an active catalyst for efficient carbonylation of iodobenzene in MeOH at 100◦C and 7 atm to produce methyl benzoate and the catalyst was recycled four to five times without loss of activity [2a]. Phenyl benzoate was obtained in high yield from iodobenzene in the presence of phenol in DMF under 1 atm of CO. Addition of CuI accelerated the reaction [3]. Chlorides are difficult to be carbonylated. However, Beller carried out the carbonylation of chlorobenzene using the ferrocenyldicyclohexylphosphine XI-9 in the presence of Na2CO3 at 140◦C inn-BuOH, and obtained butyl benzoate in high yield [4]. Chloropyridines are active chlorides and butyl picolinate (2) was prepared by carbonylation of 2-chloropyridine at 130◦C. DPPF and DPPB were used as effective ligands [5].

Pd-PEP, K2CO3

DMF, 1 atm, 90 °C, 92%

PdCl2(PPh3)2, CuI, n-Bu3N

I CO2H

I

Me

CO2Ph

Me rt, 1 atm, 97%

+ CO + H2O

+ CO + PhOH

PdCl2(PhCN)2, DPPF Et3N, 25 atm, 130 °C, 95 % PdCl2(PhCN)2,XI-9 Na2CO3, MS 4a 1 atm, 145 °C, 97%

2

N Cl N CO2Bu

Cl CO2Bu

+ CO + n-BuOH

+ CO + n-BuOH

Alkenyl halides and triflates are easily carbonylated. Carbonylation of α-iodo enone 3 proceeded at 60◦C using Pd(OAc)2 and DPPP, and the ester 4 was obtained in 62 % yield [6]. The lactam 5 was converted to the vinyl triflate 6, which was carbonylated to afford the α,β-unsaturated ester 7 [7]. Carbonylation of the alkenyl iodide 8, possessing a labile peroxy group proceeded smoothly to give theα,β-unsaturated ester9under 1 atm of CO at 60◦C in DMF. The peroxy group remained intact [8].

Pd(OAc)2, DPPP, 2,6-lutidine THF, 50 atm, 60 °C, 62%

3 O 4

O

Me H

Me H

O MeO2C O

Me H

Me H

I

+ CO + MeOH

PdCl2(PPh3)2, Et3N, MeOH, 75%

5 6

7 R3SiO

NH O H

H

R3SiO

N OTf

H

H

CO2Me

TBDPSO

N CO2Me H

H

CO2Me

9 Pd(OAc)2, PPh3, Et3N,

DMF, 60 °C, 1 atm, 60%

8

I

O O OMe

CO2Me

O O OMe

+ CO + MeOH

Alkenyl iodides can be generated in situ by hydroalumination of alkynes, fol- lowed by iodination, and α,β-unsaturated esters are prepared by carbonylation without isolation of the iodide. As an example, the propargylic alcohol 10 was aluminated regio- and stereoselectively and converted to the alkenyl iodide 11.

The intramolecular carbonylation of11afforded the dibutenolide12in 81 % yield.

The reaction is a key step in the total synthesis of (+)-parviflorin [9].

+ CO

PdCl2(PPh3)2, NH2NH2, K2CO3 81%

10

11

12

3

3 3

1. Red-Al® 2. AcOEt 3. I2

3

O

O

OTBDPS

OTBDPS Me

Me OH

OH

O

O

TBPPSO

TBDPSO

O

O O

O

Me

Me TBDPSO

TBDPSO I

OH OH

I

Carbonylation is widely utilized for preparation of complex molecules of natu- ral products. As one example, Leighton constructed the fully elaborated tetracyclic

core of phomoiderides 16 efficiently by novel domino carbonylation–Cope rear- rangement of the vinyl triflate13as a key step [10]. The acylpalladium species14, generated by the carbonylation of the alkenyl triflate13, was trapped intramolec- ularly by the hemiketal OH group, which was formed from the hydroxy ketone as shown by14to afford the unsaturated lactone 15at 75◦C. The strained molecule of 15 underwent Cope rearrangement as shown by 15 to give 16 in 78 % yield simply by raising the temperature to 110◦C. Interestingly benzonitrile was used as the best solvent.

Pd(PPh3)4,i-Pr2NEt, PhCN, 54 atm 70~115°C, 78%

+ CO

13

14 O

R

Me

TESO

OTf

OTBDMS

OH OH

O R

TESO

OTBDMS

OH OH

Pd-X O

Cope rearrangement

15

16 R

Me

TESO

OTBDMS

OH O

O O

R

Me

TESO

OTBDMS

OH O

O O

R = (E)-MeCH=CH(CH2)5- O

O OTBDMS O

R Me

OH

OTES

In the total synthesis of ciguatoxins, the enol phosphate 18, derived from the nine-membered lactone 17, was carbonylated smoothly to give the unsaturated ester 19[11].

O

O O

(PhO)2(O)PO H O

OBn H

Ph

H H

Pd(PPh3)4, Et3N,

+ CO + MeOH O

O O

MeO2C H O

OBn H

Ph

H H 17

19

18

DMF, 50 °C, 70%

O

O O

H O

OBn H

Ph

H H O

Benzylic alcohols are reactive in the presence of an acid as an activator. Asym- metric carbonylation of 1-(6-methoxy-2-naphthyl)ethanol (20) by using DDPPI as a chiral ligand in the presence of CuCl2 and p-TsOH as activators afforded the methyl ester of (S)-naproxen (21) with 81 % ee [12]. Benzyl alcohol was carbony- lated to phenylacetic acid under somewhat harsh conditions in the presence of HI.

Presumably the carbonylation of benzyl iodide, generated by the reaction of benzyl alcohol with HI, occurred. 1,2-Di(hydroxymethyl)benzene (22) was carbonylated to give 3-isochromanone 25 in 88 % yield. In this reaction, one of the benzylic alcohols is converted to benzylic iodide23 and the lactone25 was obtained via acylpalladium24 [13].

20

21

Pd(PPh3)4, HI acetone-H2O + CO

90 atm, 90 °C 88%

+ Pd(0) + HI

22 23

24 25

O O OH

OH

OH I

OH O

PdI

+ CO + MeOH

PdCl2, CuCl2 DDPPI,p-TsOH

8 MPa, 100 °C 54%, 81% ee MeO

Me OH

MeO

Me H CO2Me

O O H

H PPh2

Ph2P DDPPI

CO

Pd-catalyzed reaction ofα-naphthol, isobutyraldehyde, and CO in the presence of CF3CO2H afforded naphthofuran-2(3H)-one 28 in 79 % yield. The reaction is explained by acid-catalyzed formation of 1-(2-naphthyl)butanol 27, followed by carbonylation of the benzylic alcohol. Although its reactivity is lower, the phenol derivative29reacted with acetaldehyde to generate the benzylic alcohol30, which was carbonylated to provide the benzofuranone31 in 54 % yield [14].

Pd(PPh3)4, CF3CO2H + CO + i -PrCHO

120°C, 5 atm, 79%

27 28 OH

O O

i -Pr OH

i -Pr 26

OH

CO

+ CH3CHO + CO

Pd(PPh3)4, CF3CO2H 125°C, 5 atm, 54%

29 OH

O O

OH

O O

OH Me

O O

O O

Me

30 31

CO

Although it is not a benzylic type, the mesylate 32 was carbonylated under normal conditions to give the methyl ester 33 as a precursor of camptothecin in high yield [15].

33

PdCl2(PPh3)2, Et3N N

N O

OMs

N

N O

O O HO Et 10 atm, 60 °C 84% from alcohol + CO + MeOH

camptothecin N

N O

CO2Me steps 32

Carbonylation in the presence of secondary amines provides either amides orα- keto amides by single and double carbonylations. Also, the corresponding α-keto esters are prepared. It was reported that ratios of single and double carbonylations depend mainly on the nature of the phosphine ligands. It was claimed that PMePh2

or DPPB is a suitable ligand for double carbonylation [16].

R2NH

Ar NR2 O

Ar NR2

O

O

Ar OR

O

Ar OR

O

O Ar-I + 2CO + NuH

+

ROH +

Later several ligands, including PPh3, were found to be effective depending on the substrate. Carbonylation of 2,5-dibromo-3-methylpyridine (34) in the presence of aniline produced the 2-picolinamide35regio- and chemoselectively when 2,2- bipyridine was used as a ligand. Poor yield and selectivity were obtained by the use of ubiquitous phosphine ligands. The monoamide 35 was isolated in 82 % yield in a chemical plant in 600 kg scale production [17].

+ CO + PhNH2

DBU, 65 °C, 5.5 atm, 90%

34 35 N

Br Me

Br N

Br Me

NHPh O PdCl2(PPh3)2, bipyridine

4-Pyridylglyoxamide37was prepared by double carbonylation of 4-iodopyridine (36). High selectivity and yield of37were obtained when PCy3 andi-PrOH were used as a ligand and nucleophile, respectively. When a primary amine,n-BuNH2, was used, the Schiff base of keto amide38was obtained in high yield [18]. Domino double carbonylation and hydrogenation of the Schiff base occurred in the reaction ofp-iodotoluene with cyclohexylamine under CO and H2pressure using ligandless Pd on charcoal to afford the α-amino amide 39in high yield [19].

55 atm 7 atm

36 37

Pd(OAc)2, PCy3 50°C, 60 atm, 90%

36 38

39 N

I

N

O

N-i-Pr2 O

N

I

N

N

NHBu O

Bu

I

Me

HN

NHBu O Cy

Me + CO + i-Pr2NH

+ CO + n-BUNH2

Pd(OAc)2, PCy3 50°C, 60 atm, 91%

+ CO + H2 + CyNH2

Pd/C, Et3N MS 4A 120 °C, 88%

Carbonylation of iodoferrocene 40 in the presence of morpholine gave rise to the amide 41 and the keto amide 42 by using PPh3 as a ligand [20]. A slight difference in temperature and pressure had a marked influence on the product ratios. The keto amide42was obtained as the main product with 80 % selectivity at 60◦C and 50 atm. The amide41 was obtained as a single product at 100◦C.

40 100 >99 : 1 Fe

I

Fe O

N O

Fe O

O N

O O

H N

100

41 : 42 40

+ CO + Pd(OAc)2, PPh3

+

temp. press. (atm) conv. % ratio

50 92 20 : 80

41

60

42

Carbonylation of a mixture of more reactive p-iodoacetophenone (44) and o- iodoaniline (43) occurred stepwise chemoselectively to give the amide 45, and further carbonylation of45 afforded 2-aryl-4H-3,1-benzoxazolin-4-one 46[21].

I

NH2

I + CO

+ Pd(PPh3)4, MeCN

K2CO3, 1 atm, 60 °C, 85%

I

NH

COMe O

N O

COMe O

43 44

45 46

O

CO

Carbonylation of iodobenzene in the presence ofN-benzylideneamine47 using DPPF as a ligand proceeded via formation of amide 48 by insertion of 47 to the acylpalladium bond, and 3-phenyl-2,3-dihydro-1H-isoindol-1-one (49) was obtained [22].

Direct preparation of primary amides by carbonylation in the presence of NH3

is not easy. As one solution, Indolese carried out carbonylation ofp-bromotoluene

+ CO + PdCl2(dppf), Et3N benene, 120 °C 20 atm, 46%

I PhN=CH

N Pd

O Ph

Ph X

N Ph Ph O

47

48

49

using formamide as an ammonia equivalent in the presence of Lewis bases such as DMAP or imidazole, and obtained toluamide (50) in good yield [23].

+ HCONH2+ CO

dioxane, 120 °C, 82%

PdCl2(PPh3)2, DMAP

50

Br CONH2

Me Me

Several attempts to find CO-free preparative methods of esters and amides have been carried out using alkyl formate or formamide as CO sources. Methyl ben- zoate (51) was obtained in 98 % yield by the reaction of iodobenzene with methyl formate in the presence of MeONa [24]. DMF can be used as an amide source.

Reaction of aryl iodides with DMF in the presence of 2 equivalents of POCl3

using ligandless Pd catalyst afforded the N,N-dimethylbenzamide 52. Formation of a Vilsmeier reagent from DMF and POCl3 is expected and the amide may be formed by Pd-catalyzed reaction of aryl iodide with the Vilsmeier reagent [25].

Aminocarbonylation of aryl bromides with DMF was carried out using Pd-DPPF as a catalyst in the presence of stoichiometric amounts of imidazole andt-BuOK to afford N,N-dimethylbenzamide 53[26]. Also, N,N-dimethylbenzamide (55) was prepared by the reaction of aryl bromide with carbamoylsilane 54, which is prepared from DMF [27].

+ HCO2Me + MeONa PdCl2(PPh3)2, CH2Cl2

40°C, 98%

+ HCONMe2 Pd2(dba)3, POCl3

120 °C, 87%

52 51

I CO2Me

I CONMe2

MeO MeO

+ HCONMe2 Pd(OAc)2, DPPF, imidazole t-BuOK, 180 °C, 15 min, 59%

+ Pd(PPh3)4, toluene

100°C, 88% +

54

53

55

Br CONMe2

Me Me

TMS NMe2

O Br CONMe2

DMF Me3SiBr

Một phần của tài liệu Palladium reagents and catalysts new perspectives for the 21st century tsuji (Trang 278 - 287)

Tải bản đầy đủ (PDF)

(664 trang)