Page 205 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

asymmetric hydrogenation of carbon±carbon double bonds 193

Procedure

All reactions were carried out under argon in solution as above. Thus:
1. A solution of the appropriate substrate (1 mmol or 6 mmol) in degassed
methanol (2 mL to 5 mL) was added to the Ru(II) catalyst.
2. The glass vessel was placed under argon in a stainless steel autoclave, which
was then pressurized with hydrogen.
3. The reaction proceeded at 10 bar and 80 8C.
31
The enantiomeric excesses of the phosphonic acid was measured using P
NMR after treatment with (1S, 2S)-(ÿ)-N,N -dimethyl(diphenyl-ethylene)-
0
diamine in CDCl 3 and a catalytic amount of CD 3 OD.
1-Naphthylethenylphosphonic acid (R ˆ naphthyl)
1 H NMR (200 MHz, CDCl 3 ): d 9.0 (sl, 2H); 7.9±7.8 (m, 2H); 7.74±7.71 (d, J
7.7 Hz, 1H); 7.748±7.34 (m, 4H) 3.7 (qd, J 7.2 Hz, J 25.1, 1H); 1.3 (dd, J 7.1 Hz,
J 18.7 Hz, 3H).
31
P NMR (101 MHz, CDCl 3 ): d 32.2 ppm
The ee was measured by 31 P NMR (101 MHz, CDCl 3 ) in the presence of
0
1 equivalent of (1S, 2S)-(ÿ)-N,N -dimethyl(diphenylethylene)-diamine and 4 %
(vol.) of CD 3 OD.
d (ppm) 26.7 (R,S,S) and 26.3 ppm (S,S,S). Methyl ester [a] ˆ ‡94:2 (c 1.0,
D
CHCl 3 ) for ee 86 % (S).

12.6.4 SCOPE OF THE HYDROGENATION REACTION

The enantioselective ruthenium-catalysed hydrogenation reaction, which is ap-
plied above to vinylphosphonic acid derivatives [15] , has a much larger scope. It
has been shown that a number of olefins and functionalized carbonyl com-
pounds can be hydrogenated with very high selectivity by using the `in situ'
generated ruthenium catalyst [16] . For instance, b-ketoesters [16] , phospho-
nates [17] , sulfides [18] , sulfones [19] , sulfoxides and b-diketones [20] have been re-
duced to the corresponding alcohols in enantiomeric excesses approaching
100 %. Atropoisomeric ligands (BINAP, BIPHEMP, MeO-BIPHEP) but also
DuPHOS, DIOP, SKEWPHOS [21] , CnrPHOS [22] etc . . . can be used as chiral
auxiliaries. Selected results are given in the following table. Dynamic kinetic
resolution of a-chloro and a-acetamido-b-ketoesters have also been performed
by this method, leading to anti-a-chloro [23] and syn-a-acetamido-b-hydroxye-
sters [24] in 99 % enantiomeric excess.
All these hydrogenation reactions are quantitative, easy to perform on a
large scale, and thus represent an highly convenient approach to a number of
optically pure compounds. In most cases, it compares favourably with