COMMUNICATIONS

Oxidative Transfer Dehydrogenation of a,P-Unsaturated Carbinols to a,P-Unsaturated Ketones Catalyzed by Ruthenium Complexes

YOEL SASSON AND GARRY L. REMPEL I~zorgnnic Cl7emistr.y Laborutoq, Depurtmetlt ~f'Cl7ernicul Engineering, Unitjersity of' Waterloo,

Waterloo, Onturio, N2L 361

Received July 11, 1974

YOEL SASSON and GARRY L. REMPEL. Can. J. Chem. 52, 3825 (1974). The homogeneous competitive intermolecular and intramolecular hydrogen transfer from

unsaturated carbinols to vinyl ketones in the presence of a number of ruthenium complexes is reported. The oxotriruthenium complex, Ru,O(OOCCH,), was used in applying this process for the oxidative transfer dehydrogenation of unsaturated carbinols to unsaturated ketones.

YOEL SASSCN et CARRY L. REMTEL. Can. J. Chem. 52, 3825 (1974) On rapporte le transfert homogene d'hydrogene de carbinols non-satures a des vinyl cetones

en presence d'un certain nombre de complexes de ruthenium; la reaction implique une com- petition inter- et intramoltculaire. On a utilise le complexe oxotriruthCnium, Ru,O- (OOCCH,), afin d'appliquer ce processus a la dehydrogenation impliquant un transfert oxydant d'hydrogene des carbinols insatures en cetones non-saturees. [Traduit par le journal]

Recently we have investigated (1) the homo- geneous rearrangement of unsaturated secondary alcohols to the corresponding saturated ketones via an intran-iolecular hydrogen transfer (re- action 1).

[I] RCH=CHCH(OH)Rf -+ RCH2CHZCOR'

Reaction 1 was carried out in the presence of a number of ruthenium complexes; the oxotri- ruthenium acetate complex, Ru,O(OOCCH,),, being the most active and selective complex for the intramolecular hydrogen transfer process.

While studying the effects of various co- catalysts or potential inhibitors for reaction 1 we have found that in the presence of vinyl ketones reaction 1 is significantly inhibited and a competitive intermolecular hydrogen transfer process (reaction 2) is found to occur.

[2] RCH=CHCH(OH)Rf + CH,=CHCOR" -+

RCH=CHCOR' f CH,CH2CORr'

For example, when a mixture of 1-hexene-3-01 (0.5 g, 50 mmol) methyl vinyl ketone (0.35 g, 50 mmol), and RuCI,(P(C,FI,),), (19 mg, 2 x lo-' mmol) was maintained under nitrogen1 in

'The nitrogen atmosphere is not essential and reactions of this type also take place in the presence of air.

a sealed tube at 100 "C a clear reddish-orange solutiorl resulted. Analysis of the solution by g.1.c. after 4.5 h indicated that the mixture con- tained 0.285 g (28.5 mmol) hexene-3-one, 0.215 g (21.5 mrnol) 3-hexanone, 0.200 g (28.5 mmol) 2-butanone, and 0.150 g (21.5 mmol) of the remaining methyl vinyl ketone. Thus, in this case, 43% of the 1-hexene-3-01 reacted via the intramolecular route to yield 3-hexanone and 5 7 x yielded the intermolecular product 1- hexene-3-one.'

Results of siinilar experiments with a nurnber of catalysts under various conditions are sum- marized in Table 1.

As ktas found for the intramolecular process (I), Ru,O(OOCCH,), was also the most active and selective complex for the intermolecular reaction. The results in Table 1 indicate that the efficiency and selectivity of the catalyst depend on its concentration, donor: acceptor molar ratio, and reaction temperature. Highest yields of intermolecular transfer were obtained using 0.02 mM Ru,O(OOCCEI,), at 100 "C with a donor:

'It should be noted that after some I-hexene-3-one is formed it can itself be reduced to 3-hexanone via the intermolecular route. However, relative rate studies have indicated that this path is of minor importance.

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3826 CAN. J CHEM VOL. 5 2 , 1974

TABLE 1. Hydrogen transfer of I-hexene-01 in the presence of methyl vinyl ketone"

% Inter- % Intra- Concentration Molar ratio molecular molecular Tin~ef-

Catalyst (mM) donor/acceptor transfer transfer (h)

RuCI33Hz0 0.02f 111 56 3 8 4.0 R L ~ C ~ ~ ( P ( C ~ H S ) ~ ) ~ 0.02 111 57 43 4.7

0.08 111 5 8 42 4.3 0.02 115 64 3 6 14.0

R U H C I ( P ( C ~ H S ) ~ ) ~ 0.02 111 49 5 1 5.3 RL~H(OOCCH~)(P(C,H,),), 0.02 111 37 63 4.7 RhCl(P(C&s)3)3 0.02 11 1 24 76 1.5 Ru30(00CCH3), 0.0075§ 111 59 41 0.75

0.02 111 70 30 0.58 0.02 1 /5 89 1 I 0.42 0.02 118 8 8 12 0.42 0.005 115 87 13 1.17 0.0025 115 78 22 2.50 0.021 115 80 20 7 .5 0 .029 115 8 3 17 0.25

*Reaction conditions: 50 mmol I-llexene-3-01 plus apnropriare amount o f methyl vinyl ketone and the catalyst in a sealed tube under N2 at 100 'C. Separation o fp roduc t s on a 1 .8 m 10% Carbowax 20M o n chromosorb W columii a t 70 "C.

+Time required for complete disappearance o f I-hexene-3-01, t6Z of dehydrat~on and hydrogenoiysis products identified (2). #In all experiments where Ru,0(OOCCH,)7 \!as used, 0.5 ml ethylene glycol u a s added as co-solvent. The co-solvent played n o part in the

transfer reaction itself. I S 5 "C. 7115°C.

TABLE 2. Ox~dat~ve transfer dehydrogenat~on of unsaturated alcohols to unsaturated ketones u ~ t h methyl v~nyl ketone catalyzed by Ru30(OCCH3),"

Temperat~~re Time Y leld Alcohol Product PC) (h) (%I

*Reaction conditions: 50 mmol of alcoliol, 250 t n ~ n o l n?ethyl binyl ketone, 40 mg of Ru,0(OCCK3), in 0.5 ml ethylene glycol. Prodiicts \!ere separated o n a 1.8 m 1 0 Z Carbo\vax 20h1 on Chromosorb W Column at 70°C.

acceptor molar ratio of 115. It is of interest to note that RuCI,(P(C,H,)~), is quite different in its behavior when excess of acceptor is present; the selectivity for intern~olecular transfer is slightly improved but the reaction rate is very much lower.

Other common alcoholic donors (3) (i.e. benzyl alcohols) were not reactive for reduction of vinyl ketones. Also other potential acceptors (3, 4) (i.e. chalcone, benzalacetone, acetophe- none) also did not react with unsaturated alcohols under the conditions noted in Table 1. The combination of unsaturated alcohols as hydrogen donors and vinyl ketones as acceptors in the presence of Ru30(OOCCH3), or RuC1,- (P(C,M,),), is apparently the most reactive

homogeneous intermolecular hydrogen transfer system so far reported (3-6).

Although the intermolecular hydrogen trans- fer reaction may have some practical value for selective reduction of vinyl ketones to ethyl ketones, the major utiiity of the process is for the oxidative transfer dehydrogenation of un- saturated ~ a r b i n o l s . ~ In this manner we have oxidized some 1-alkene-3-01s to the correspond- ing 1-alkene-3-ones; other unsaturated alcohols requiring somewhat stronger conditions for oxidation. In Table 2, results of some of these oxidations are provided.

3Similar oxidation of diols have previously been reported (7).

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COMMUNICATIONS 3827

At present, no detailed mechanism can be deduced for the intermolecular hydrogen trans- fer, however, the following general remarks are applicable. The inhibition effect of the added vinyl ketone on the intramolecular route (reaction 1) suggests that coordination and activation of the acceptor (i.e. the vinyl ketone) occurs prior to the coordination of the donor. This fact is particularly evident in the case of the catalyst RuCl,(P(C,H,),), where in the presence of an excess of acceptor, the reaction rate is extremely slow; apparently due to blocking of the coordination sites on the catalyst by the unsaturated ketone. Since the competitive inter- molecular and intramolecular reactions proceed essentially at the same rate, they probably involve a similar rate determining step. Based on pre- vious related studies (4, 6, 8) it would appear that this step involves the breaking of the C-H bond a to the hydroxyl in the donor. The hydride is then transferred directly, or via a metal hydride intermediate, to the bound un-

saturated ketone or intramolecularly to the 3- position of the unsaturated alcohol.

We thank the National Research Council of Canada and the University of Waterloo for financial support, and Engelhard Industries for the loan of ruthenium.

1. Y. SASSON and G. L. REMPEL. To be published. 2. M. DEDIEU and Y. L. PASCAL. C. R. Acad. Sc. Paris

C, 277, 1257 (1973). 3. Y. SASSON and J. BLUM. Tetrahedron Lett. 2167 (1971). 4. Y. SASSON, P. ALBIN, and J. BLUM. Tetrahedron Lett.

833 (1974). 5. J. TROCHA-GRIMSHAW and H. B. HENBEST. Chem.

Commun. 544 (1967); M. GULLOTI and R. Uco. J. Chem. Soc(C), 139 (1971); T. N I ~ H I G L ~ H ~ and F. FUKUZUMI. BLIII. Chem. Soc. Jap. 45, 1656 (1972); T. NISHIGUCHI and K. Fueuzu\r~. J. Ani. Chen~. Soc. 96, 1893 (1974).

6. H. IMAI, T. NISHIGUCHI, and K. FLKUZUMI. J. Org. Chem. 39, 1622 (1974).

7. S. L. REGEP.~ and G. M. WHITESIDES. J. Org. Cheni. 37, 1832 (1972).

8. F. G. COWHERD and J. L, voh ROSENBERG. J. Am. Chem. Soc. 91, 2157 (1969): G. EADON and M. Y. SHIEKH. J. Am. Chem. Soc. 96,2289 (1974); Y . SASSON and J. BLUM. Chen~. Commun. 309 (1974).

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