Tetrahedron L.%m. Vol.31. No.29. pp4181-4184,1990 Printed in Grear Britain

oo40-4039/90 $3.00 + .oo

Pqgnm Re.ss pk

PALLADlUM(II)-CATALYZED OXIDATIVE REARRANGEMENT OF PROPARGYL ESTERS

ljjdeaki Kataoka, Kiyoshi Watanabe+ and Runiaki Goto*

Nippon Zeon Co.,Research & Development Center, 1-2-l Yako, Kawasaki 210, Japan

Abstract: Pmpargyl esters were converted to a-acyloxy-a$-unsaturated aklehydes by palladium (II) catalysts under oxygen atmosphere in good to excellent yields.

Since the discovery of the Wacker process, many oxidation reactions of olefm with homogeneous transition

metal catalysts under oxygen atmosphere have been reported. 1) However, similar oxidation of acetylenic

compounds has scarcely been studied. In the course of our studies to develop the practical palhulim-catalyxed

reactiotq2) we found that a propargyl ester was converted to an a-acyloxy-a&msatumted aldehyde by using a

palladium (II) catalyst under oxygen atmosphere (Scheme 1).3) In this paper, we wish to report the novel

palladium (II)-catalyxed oxidative rearrangement of propargyl esters in the presence of molecular oxygen.

Scheme- 1

As shown in Table 1, the 1-ethynyl-1-cyclohexanol esters 1 were converted to the a-acyloxy-a$-

unsaturated aldehydes 2 under various conditions. Several palladium (II) compounds were effective to the

reaction (Runs l-lo), and P~DQ was the best catalyst to give the aldehyde2 selectively. Selection of solvents

was also crucial to glve the aldehydes 2 in good yields, and in THF the aldehydes 2 were afforded in >80% yields

by using PdDrg as the catalyst. The structure of the ester moiety also influenced the yield of the aldehydes 2, and

the isobutymte fi and the benxoatek gave better results (92% and 89% mspectively) compared to the acetate h

(Runs 11,12).

A typical experimental procedure for the preparation of the aldehyde & is as follows: To a solution of the

isobutyratefi (99.Omg, 0.568mmol) in THF (2 ml) was added a catalytic amount of PdBr2 (8mg, 0.028mmol).

The reaction mixture was stirred at 65 Oc under 02 (1 atm) for 1 h. After the completion of the reaction, the

solvent was removed in vacua. The residue was chromatogmphed on silica gel (hexane : ether = 10: 1) to give the

aldehyde 2 (98.2mg, 9 1% yield).4)

The reaction was completed even with 2.5 mol% of the catalyst however it stopped alter 39% conversion

with 1 mol% of the catalyst (Runs 13,14). The reaction pmceeded even at 25oC under air atmosphere (Runs

1516).

4181

4182

Table 1. oxidative rcaKangement of the l-cthynyl-1~lokanOl estcml~

Run R Catalyst (mol%) Time(h) Additivckq.) Sohent Product yiehI(%)b~J

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15d

16”)

17

18

19

20 D

a n

n

n

”

n

”

n

I)

n

lPr

Ph

iPr n

”

n

9s

n

n

0

NazPdC4 (10) ”

”

n

”

PdQ (10)

Pdso4 (10)

pdh (10) n

W-q (10)

PdBrz (10) n

PdBr2 (2.5)

par2 (1)

P&r2 (7)

Par2 (7)

Par2 (5)

Par2 (1) n

PdBr2 (5)

6

1

5

2

4

6

7

1

1

1

1

1.5

8

80

9

11

80

3

3

1

none

Hz00 ” none CI-WN

I-W(5) - none DMP

”

” ”

n ”

2,CLa1tidiac(O. 1) n

35%HBr(O.5) W

36%HCl(O.5) W

t-BuGGH( 10) ”

48

26 (3O)d,

18

33 (IO)

15

50

42

81

65 (0) 71

92

89c)

87

30

97

95

21

56

57

62

a). All reactions were carried out at 65 Oc under oxygen atmosphere using 0.5mmol of the propargyl ester1 and

2ml of the aolventa unless otherwiac noted. b). Determined by G.C. using n-hcxadccaue m an internal SM.

c). AU the producta gave aatiafactory NMR, IR, and maas spcctm. d). Yield of the methyl ketone2 is indicated

inpnrcnthcsis. e). Isolated yield. f). C&crxion 39%. g). The reactionwascarricd outat 25%. II). The

reaction was carried out at 25 Oc under air. i). Conversion 64%. j). The reaction wan carried out under N2.

Addition of water resulted io the increase of the rate of the reaction; however the methyl ketones 2 were also

produced with Na#dC& catalyst (Runs 2,4). In the prcacncc of HCI or HBr, the reaction was completed for 1 h

evenwith 1 mol%ofthccatalyst(Runs 18,19). Ontheotherhand,addltionofbasedeacthratedUlecatalyst(Run

4183

17). The reaction also proceeded with t-BuCOH under nitrogen atmosphere (Run 20). When the absorption of

Ox during the reaction was measured, one molecular of 02 was found to be consumed for the production of two

mokculars of the aldehyde (Run 15).

Several examples of the oxidative rearmngement are demonstrated in Table 2. All reactions proceeded

smoothly to afford the cormspotuling a-isobutyryloxy-a$-uasanuated aldehydes in good to excellent yields.

Table 2. Oxidative rearrangement of pmpargyl esters catafyxed by PdBrg in TETP under oxygen atmosphere 3

Run Propargyl ester Time (h) Product b, Yield (%y)

1

2

1.5

9 OH

65

OH O&HMas

?!I

80

ACHM., 8o6)

P 5

+- \- CHO

43 e)

O$CHMo2

0

a) All mactions were carried out at 65 Oc in THP under oxygen atmosphere using 0.5mmol of the starting

material and 5mol% of PdBrx. b). All the products gave satisfactory NMR, IR, and mass spectra. c). Isolated

yield. d). These pmducts were about 1: 1 mixture of the olefdc isomers. e). only 2 isomer was detected.

A possible mechanism for the oxidative rearmngement is pmposed in Scheme 2. An active catalytic species is

considered to be a hydroperoxopakdium (II) 6 1) s&a which coordinates to the acetylenic bond to lead the

migration of the acyloxy group, followed by the internal addition of hydroperoxy moiety to give the httermediite

2. Then 2 decomposes to the aldehyde 2 and a hydroxy palladium Ip, which also works as an active catalyst and

catalyze the reaction to produce the second aldehydea and a palladium hydride u via the intemrediatel2. Piiy

a hydroperoxopalladium 4 is regenerated by the oxidation of fi with Ox. At the initial stage of the reaction, the

4184

catalytic species u would be produced from Pd&; however the me&a&m for the pmducticm of u from PdRrg

is unclear.

Scheme 2.

Further mechanistic studies and application of the present oxidative rearrangement for organic synthesis are

now in progress.

Acknowledgement: We would like to thank Prof.J.Tsuji, Okayama University of Science, and

Prof.K.Uneyama, Okayama University, for helpiirl comments and discussions.

References and Notea

(1) Recent works on transition-metal-catalyzed oxidation of oleiins under 02; (a) M.Rousscl, HMimoun,

J.Org.Chem, 45,5387, (1980). (b) J.Tsuji, HNagashima, K.Hori, Tetrahedron Leti., 23,2679 (1982). (c)

T.Hcaokawa, T.Uno, S.Inui, S.Murahashi, J.Am.Chem.Soc, 103, 23 18 (198 1). (d) KTakehira, H.Orita,

I.H.Ho, C.R.Leobardo, G.C.Martinez, M.Shimazu, THayakawa, T.Ishikawa, J.Mol.Catal.,42,247 (1987).

(e) D.E.HamiIton, RS.Dmgo, AZombeck, J.Am.Chem.soC., 109,374 (1987). (f) S.Inoki, T.Mukaiyama,

ChemLeft., 67 (1990). (g) T.Hosokawa, S.Mumhashi, Acc.Chem.Res., 23,49 (1990), and referencea cited

therein. (2) (a) HKataoka, T.Yamada, KGoto, J.Tsuji, Tetrahedmn, 43,4107 (1987). (b) T.Yamada,

K.Goto, Y.Mitsuda, J.Tsuji, Tetmhedmn btt., 28,4557 (1987). (3) The same type of compound was detected

in a related reaction. V.Rauten&auch, Tetdiedk I.&t, 25,3845 ( 1984). (4) Analytical data for the aldehyde

2h; 1H NMR (5OOMHz,CDCl3) : b 9.87 (s,lH,CHO), 2.70-2.82 (m,3H,allylic CH2 and CI-I), 2.25-2.32

(m,ZH,alIylic CHZ), 1.60-1.80 (m,6H,CHg), 1.29 (dJ=6.7Hz,6H,CH$; IR (neat) 1770, 1695, 1655, 1300,

1020,950,865,820 cm-t; MS calcd for t&I-It& 210.1256, found 210.1248.

(Received in Japan 11 May 1990)