- Email: [email protected]
Selective reduction of α,β-unsaturated terpene carbonyl compounds using hydrosilane-rhodium(I) complex combinations
SELECTIVE REDUCTION OF O,;B-UNSATURATEDTIZRFENECARRONyL COMPOWDS USING HYDROSILANK-RHODIUM(I) COMPLEX COMRXNATI0NS
Iwao Ojima and Tetsuo Kogure Sagami Chemical Research Center, 4-4-l Nishi-Onuma, Sactamihara229 ;TAFAN and yoichiro Naqai Gunma University, Kiryu, Gunma, 376 JAFAR (&eived in JaFen27 October1972;noeived in UX for publiostion 6 lbmmber 1972) The reduction of Ci,p-unsaturatedcarbonyl compounds has been effected . chemically by dissolving alkali metals in liquid ammonia1 and amalsamated zinc hydrochloric acid2.
However, these reactions often cause undesired side re-
actions, because of the required stronqly basic or acidic conditions. Sodium borohydride also has been employed in certain cases, but lacks cteneralutility'. The homogeneous transition metal complex catalysed reduction of unsaturated campounds, most of which proved to involve metal hvdride comolex, is the subject of current interest4. However, there have so far been few attempts to sain selectivity for homogeneous reduction of &,&unsaturated carbonvl comoounds3,S . we wish to report in this paper a new selective reduction of U&unsaturated
carbonyl
compounds by means of hydrosilane-rhodium(I) comolex combinations under mild con-
The c&p-unsaturated carbonyl compounds involvinq an isolated double bond in the same molecule were chosen for,the substrates. A selective hvdroqenation of the double bond conjugated to carbonyl group in such compounds bv metal catalysed hydrogenation has not always afforded sufficient results because of a lack of consistent selectivity'. However, this hydrogenation can be easily achieved by the use of rhodium(I) complex catalysed hydrosilation without anv isomerisation of the remaining double bond. U-Ionone(l_)was treated with sliqht excess of triethylsilane in the presence
5035
50%
bo. 49
of a catalytic amount of (Ph9P')2RhCl (0.5 Mel %) under nitroqen at SO0 for 2 hr., was completely consumed. The reaultinq silvlenolether 2
thenU-ionone
(his.
solution and dihvdroionone 119O/O.4 mm) was hydrolysed by K2CC3-acetone-YeOH-I-T20 (3-1was obtained in 96 % yield (based on
A)“.
The nmr spectra of silvlenolether
2 and dihydroionone2 demonstrated that no isomerisation of the remaininq double bond had occurred during the reaction.
In a similar manner, citral(4) was hydrogenated to citronellal(2) in 97 % yield via silylenolether 5_ (hp. 76'/q.3 mm).
Citral has thus been hydrogenated in complete selectivity for the first time. It should be noted that the catalytic hydroqenation usinq the homoqeneous catalyst cannot be used to prepare citronella1 because of the extensive decarhonvlationll, while the hydrosilation can be achieved without anv deactivation bv such a side reaction.
f5?ib% tise_wo 3
1
(Ph3P)9PhCl
2
MeOH-HZ0
3
On the other hand, in the case of,9-ionone(7J which is one of the con4uqated dienones,
the formation of dihydro-&ionone(3;_0)and an alcohol(l1) was observed. -u The ratio of the ketone z to the alcohol 11 was found to be qreatlv affected bv the hydrosilane employed. For example, the ratio of the ketone 10 - versus the alcohol 1,1was 91/9 with phenyldimethylsilane; 12/s
= 44~36 with triethvlsila!M?:
O/l00 with diethyleilane and diphenylsilane. !fhus,the selective hvdroqenation of P-ionone(7J was achieved by phenyldimethylsilane-rhodium(I) complex combination in high selectivity, and the complete selective reduction of the carbonyl of!-ionone(7) was performed by hydrosilane-rhodium(S) comnlex combiantions. A similar trend was also observed in the case of the hydrosilation of pulegone(z). The ratio of the silylenolether 13 versus silylether 12 was found to be as follows: 13/14 = 75/25 with phenyldimethylsilane; SO/50 with triethylsilane ccand tri-n-propylsilaner O/l00 with diethylsilane and diphenylsilane.
Sodium borohydride reduction of conjugated carbonyl compounds was reported to result in the formation of almost equal amounts of the alcohol 15 and 1612, hr 'c often accompanied by an isomerization of the double bond13. Lithium aluminumhydride reduction of these compounds gave the alcohol 12 predominantly, but the conversion of the reaction was rather low13 .
Thus, the present results demon-
strated that the dihydrosilane-rhodium(I) complex combination in the reduction of $-ionone(7) and pulegone(l2) displayed an exceedingly hiqher selectivity than -
that of metal hydrides such as lithium aluminum hydride and sodium botohyariae.
Consequently, the hydrosilane-rhodium(I) complex combination may open a novel aevice for the selective hydrogenation or the reduction of
a &unsaturated
alaehyaes ana ketones in special of terpenes.
REFERENCES 1.
2. 3. 4.
5.
1) 6. 7. 8. 9. 10.
11. 12. 13.
A. J. Birch, Reactions in N. Y., 1968, J. G. St. C. (1969). K. Igbal and there in. For example,
Quart. Rev., Chem. Sot., 4_,69 (1950): U. Smith "nrqanic Liquid Ammania," R. L. Augstine, Ed., Marcel nekker, New York, p 65. Buchanan and P. D. Wooagate, Ouart. Rev., Chem. sot., 23, 522 W. R. Jackson, J. Chem. Sot., (C), 616 (1968) anilreferences M. E. Vol'pin and I. S. Kulomnikov, Puss. Chem. Rev., s,
273
(1969). J. Balpern, J. F. Harrod, and B. R. James, J. Amer. Chem. Sot., E, 51%') (1966); R. L. Augstine "Catalytic Hydrogenation," Marcel Dekker, Yew York, N. Y., 1965, p 60. R. Noyori, I.Umeda and T. Ishigami, J. Org. Chem., 37, 1542 (1972). I. Ojima, M. Nihonyanagi and Y. Nagai, Chem. Commun., 938 (1972). The nmr ma mass spectra, ana elemental analyses of all new comwunds were consistent with the assigned structures. M. Freifelder "Practical Catalytic Hydrogenation," Wiley-Interscience, a Division of John-Wiley L Sons, Inc., New York, 1971, p 155. Yielas were determined by glpc analyses. A. J. Birch and R. A. M. Walker, J. Chem. SOC., (Cl, 1894 (1966). M. R. Johnson and B. Rickborn, J. Org. Chem., S, 1041 (1970). J. W. Wheeler and R. Ii.Chung, ibid., 31, 1149 (1969).
Iwao Ojima and Tetsuo Kogure Sagami Chemical Research Center, 4-4-l Nishi-Onuma, Sactamihara229 ;TAFAN and yoichiro Naqai Gunma University, Kiryu, Gunma, 376 JAFAR (&eived in JaFen27 October1972;noeived in UX for publiostion 6 lbmmber 1972) The reduction of Ci,p-unsaturatedcarbonyl compounds has been effected . chemically by dissolving alkali metals in liquid ammonia1 and amalsamated zinc hydrochloric acid2.
However, these reactions often cause undesired side re-
actions, because of the required stronqly basic or acidic conditions. Sodium borohydride also has been employed in certain cases, but lacks cteneralutility'. The homogeneous transition metal complex catalysed reduction of unsaturated campounds, most of which proved to involve metal hvdride comolex, is the subject of current interest4. However, there have so far been few attempts to sain selectivity for homogeneous reduction of &,&unsaturated carbonvl comoounds3,S . we wish to report in this paper a new selective reduction of U&unsaturated
carbonyl
compounds by means of hydrosilane-rhodium(I) comolex combinations under mild con-
The c&p-unsaturated carbonyl compounds involvinq an isolated double bond in the same molecule were chosen for,the substrates. A selective hvdroqenation of the double bond conjugated to carbonyl group in such compounds bv metal catalysed hydrogenation has not always afforded sufficient results because of a lack of consistent selectivity'. However, this hydrogenation can be easily achieved by the use of rhodium(I) complex catalysed hydrosilation without anv isomerisation of the remaining double bond. U-Ionone(l_)was treated with sliqht excess of triethylsilane in the presence
5035
50%
bo. 49
of a catalytic amount of (Ph9P')2RhCl (0.5 Mel %) under nitroqen at SO0 for 2 hr., was completely consumed. The reaultinq silvlenolether 2
thenU-ionone
(his.
solution and dihvdroionone 119O/O.4 mm) was hydrolysed by K2CC3-acetone-YeOH-I-T20 (3-1was obtained in 96 % yield (based on
A)“.
The nmr spectra of silvlenolether
2 and dihydroionone2 demonstrated that no isomerisation of the remaininq double bond had occurred during the reaction.
In a similar manner, citral(4) was hydrogenated to citronellal(2) in 97 % yield via silylenolether 5_ (hp. 76'/q.3 mm).
Citral has thus been hydrogenated in complete selectivity for the first time. It should be noted that the catalytic hydroqenation usinq the homoqeneous catalyst cannot be used to prepare citronella1 because of the extensive decarhonvlationll, while the hydrosilation can be achieved without anv deactivation bv such a side reaction.
f5?ib% tise_wo 3
1
(Ph3P)9PhCl
2
MeOH-HZ0
3
On the other hand, in the case of,9-ionone(7J which is one of the con4uqated dienones,
the formation of dihydro-&ionone(3;_0)and an alcohol(l1) was observed. -u The ratio of the ketone z to the alcohol 11 was found to be qreatlv affected bv the hydrosilane employed. For example, the ratio of the ketone 10 - versus the alcohol 1,1was 91/9 with phenyldimethylsilane; 12/s
= 44~36 with triethvlsila!M?:
O/l00 with diethyleilane and diphenylsilane. !fhus,the selective hvdroqenation of P-ionone(7J was achieved by phenyldimethylsilane-rhodium(I) complex combination in high selectivity, and the complete selective reduction of the carbonyl of!-ionone(7) was performed by hydrosilane-rhodium(S) comnlex combiantions. A similar trend was also observed in the case of the hydrosilation of pulegone(z). The ratio of the silylenolether 13 versus silylether 12 was found to be as follows: 13/14 = 75/25 with phenyldimethylsilane; SO/50 with triethylsilane ccand tri-n-propylsilaner O/l00 with diethylsilane and diphenylsilane.
Sodium borohydride reduction of conjugated carbonyl compounds was reported to result in the formation of almost equal amounts of the alcohol 15 and 1612, hr 'c often accompanied by an isomerization of the double bond13. Lithium aluminumhydride reduction of these compounds gave the alcohol 12 predominantly, but the conversion of the reaction was rather low13 .
Thus, the present results demon-
strated that the dihydrosilane-rhodium(I) complex combination in the reduction of $-ionone(7) and pulegone(l2) displayed an exceedingly hiqher selectivity than -
that of metal hydrides such as lithium aluminum hydride and sodium botohyariae.
Consequently, the hydrosilane-rhodium(I) complex combination may open a novel aevice for the selective hydrogenation or the reduction of
a &unsaturated
alaehyaes ana ketones in special of terpenes.
REFERENCES 1.
2. 3. 4.
5.
1) 6. 7. 8. 9. 10.
11. 12. 13.
A. J. Birch, Reactions in N. Y., 1968, J. G. St. C. (1969). K. Igbal and there in. For example,
Quart. Rev., Chem. Sot., 4_,69 (1950): U. Smith "nrqanic Liquid Ammania," R. L. Augstine, Ed., Marcel nekker, New York, p 65. Buchanan and P. D. Wooagate, Ouart. Rev., Chem. sot., 23, 522 W. R. Jackson, J. Chem. Sot., (C), 616 (1968) anilreferences M. E. Vol'pin and I. S. Kulomnikov, Puss. Chem. Rev., s,
273
(1969). J. Balpern, J. F. Harrod, and B. R. James, J. Amer. Chem. Sot., E, 51%') (1966); R. L. Augstine "Catalytic Hydrogenation," Marcel Dekker, Yew York, N. Y., 1965, p 60. R. Noyori, I.Umeda and T. Ishigami, J. Org. Chem., 37, 1542 (1972). I. Ojima, M. Nihonyanagi and Y. Nagai, Chem. Commun., 938 (1972). The nmr ma mass spectra, ana elemental analyses of all new comwunds were consistent with the assigned structures. M. Freifelder "Practical Catalytic Hydrogenation," Wiley-Interscience, a Division of John-Wiley L Sons, Inc., New York, 1971, p 155. Yielas were determined by glpc analyses. A. J. Birch and R. A. M. Walker, J. Chem. SOC., (Cl, 1894 (1966). M. R. Johnson and B. Rickborn, J. Org. Chem., S, 1041 (1970). J. W. Wheeler and R. Ii.Chung, ibid., 31, 1149 (1969).