J. Ito, H. Nishiyama, and K. Fujii
phebox–Ru complex 1c (6.1 mg, 0.010 mmol) and NaOAc (1.0 mg,
0.012 mmol) in dioxane (4 mL), at room temperature under an Ar atmos-
phere. After stirring at 1008C for 12 h, the reaction mixture was concen-
trated under reduced pressure. The crude product was purified by silica
gel column chromatography with hexane/ethyl acetate (20:1) as the
eluent to give 8aa (200 mg, 0.99 mmol, 99% yield). 1H NMR (300 MHz,
CDCl3, RT): d=7.40–7.37 (m, 2H), 7.29–7.26 (m, 3H), 4.19 (q, J=
7.0 Hz, 2H), 2.77–2.72 (m, 2H), 2.66–2.61 (m, 2H) 1.29 ppm (t, J=
7.0 Hz, 3H); 13C NMR (75 MHz, CDCl3, RT): d=171.6, 131.3, 128.0,
ꢀ
127.5, 123.3, 88.0, 81.1, 60.7, 33.8, 15.6, 14.4 ppm; IR (KBr): n˜ =2239 (C
C), 1736 cmÀ1 (C=O); HRMS (FAB): m/z calcd for C13H14O2+: 203.1072;
found: 203.1066 [M+H+].
Conjugate addition of 4a with 9 f: Phenylacetylene 4a (205 mg,
2.0 mmol) was added to a mixture of acrylamide 9 f (71 mg, 1.0 mmol),
phebox–Ru complex 1c (29.5 mg, 0.051 mmol) and NaOAc (4.2 mg,
0.051 mmol) in THF (4 mL), at room temperature under an Ar atmos-
phere. After stirring at 608C for 96 h, the reaction mixture was concen-
trated under reduced pressure. The crude product was purified by silica
gel column chromatography with chloroform/methanol (20:1) as the
1
eluent to give 10af (159 mg, 0.92 mmol, 92% yield). H NMR (300 MHz,
CDCl3, RT): d=7.41–7.36 (m, 2H), 7.29–7.25 (m, 3H), 3.04 (s, 3H), 2.98
(s, 3H), 2.80–2.74 (m, 2H), 2.67–2.63 ppm (m, 2H); 13C NMR (75 MHz,
CDCl3, RT): d=170.3, 131.0, 127.7, 127.1, 123.2, 88.8, 80.4, 36.8, 35.1,
Scheme 1. Proposed mechanism.
À1
ꢀ
32.3, 15.3 ppm; IR (KBr): n˜ =2245 (C C), 1649 cm (C=O); HRMS
(FAB): m/z calcd for C13H16NO+: 202.1232; found: 202.1228 [M+H+].
Conjugate addition of 4a with 11: Diethyl vinylphosphonate 11 (166 mg,
1.0 mmol) and phenylacetylene 4a (206 mg, 2.0 mmol) were added to a
mixture of phebox–Ru complex 1c (6.0 mg, 0.010 mmol) and NaOAc
(0.8 mg, 0.01 mmol) in dioxane (4 mL) at room temperature under Ar at-
mosphere. After stirring at 1008C for 12 h, the reaction mixture was con-
centrated under reduced pressure. The crude product was purified by
silica gel column chromatography with chloroform/methanol (20:1) as
the eluent to give 12 (179 mg, 0.67 mmol, 67% yield). 1H NMR
(300 MHz, CDCl3, RT): d=7.40–7.35 (m, 2H), 7.32–7.25 (m, 3H), 4.19–
4.07 (m, 4H), 2.76–2.67 (m, 2H), 2.15–2.04 (m, 2H), 1.38–1.32 ppm (m,
6H); 13C NMR (75 MHz, CDCl3, RT): d=131.2, 127.7 (d, J=110 Hz),
123.1, 88.1 (d, J=82 Hz), 81.0 (d, J=9.3 Hz), 61.7 ppm (d, J=25.0 Hz),
26.4, 24.5, 16.6 (d, J=22.8 Hz), 13.6 ppm (d, J=15.9 Hz); 31P NMR
then undergoes protonation to give the b-alkynyl compound.
Based on the R configuration of 14 obtained in the asym-
metric reaction with 13, the Re face at the b-carbon in 13 is
attacked by the Ru-ligated acetylide.
Conclusion
We have shown that NCN-pincer Ru-complexes containing
phebox ligands are potential catalysts for direct conjugate
addition of terminal alkynes to several types of a,b-unsatu-
rated carbonyl compounds. In particular, the phebox–Ru
complexes serve as good catalysts in the transformation of
a,b-unsaturated amides and phosphonates to g,d-alkynyl de-
rivatives. Asymmetric conjugate addition of an alkyne to an
a,b-unsaturated ketone was catalyzed by the chiral phebox–
Ru complex with enantiomeric induction. Further studies on
the asymmetric reaction are currently in progress in our lab-
oratory.
(121 MHz, CDCl3, RT): d=29.6 ppm; IR (KBr): n˜ =2221 cmÀ1 (C C).
ꢀ
HRMS (FAB): m/z calcd for C14H19NaO3P+: 289.0970; found: 289.0980
[M+Na+].
Conjugate addition of 4a with 13: phenylacetylene 4a (111 mg,
1.1 mmol) and 3-penten-2-one 13 (21 mg, 0.25 mmol) were added to a
mixture of phebox–Ru complex 1c (7.6 mg, 0.013 mmol) and NaOAc
(1.0 mg, 0.013 mmol) in THF (1 mL) at room temperature under an Ar
atmosphere. After stirring at 608C for 168 h, the reaction mixture was
concentrated under reduced pressure. The crude product was purified by
silica gel column chromatography with hexane/ethyl acetate (20:1) as the
eluent to give 14 (23 mg, 0.12 mmol, 49% yield). HPLC (Chiralcel OD-
H, 1% iPrOH in hexane, 0.5 mLminÀ1, 254 nm) Rt =23.5 (S), 29.1 min
(R). [a]2D8 =À23.0 (c=0.52, CHCl3) [lit.[8a] [a]D20 = +33.0 (c=0.82, CHCl3,
(S)]; 1H NMR (300 MHz, CDCl3, RT): d=7.39–7.35 (m, 2H), 7.29–7.24
(m, 3H), 3.19 (ddq, J=6.9, 7.2, 6.6 Hz, 1H), 2.79 (dd, J=16.5, 6.9 Hz,
1H), 2.59 (dd, J=16.5, 7.2 Hz, 1H), 2.22 (s, 3H), 1.29 ppm (d, J=6.6 Hz,
3H); 13C NMR (75 MHz, CDCl3, RT): d=206.1, 131.3, 128.0, 127.5,
Experimental Section
Conjugate addition of 4a with 5a: Methylvinylketone 5a (71.0 mg,
1.0 mmol) and phenylacetylene 4a (204 mg, 2.0 mmol) were added to a
mixture of phebox–Ru complex 1c (29.3 mg, 0.050 mmol) and NaOAc
(4.1 mg, 0.050 mmol) in THF (4 mL) at room temperature under Ar at-
mosphere. After stirring at 608C for 12 h, the reaction mixture was con-
centrated under reduced pressure. The crude product was purified by
silica gel column chromatography with hexane/ethyl acetate (20:1) as the
eluent to give 6aa (159 mg, 0.92 mmol, 92% yield) as a solid. 1H NMR
(300 MHz, CDCl3, RT): d=7.39–7.36 (m, 2H), 7.29–7.26 (m, 3H), 2.81–
2.76 (m, 2H), 2.70–2.65 (m, 2H), 2.22 ppm (s, 3H); 13C NMR (75 MHz,
ꢀ
123.3, 92.9, 80.8, 50.4, 30.6, 22.4, 21.1 ppm; IR (KBr): n˜ =2233 (C C),
1718 cmÀ1 (C=O); HRMS (FAB): m/z calcd for C13H15O: 187.1123;
found: 187.1117 [M+H+];
Acknowledgements
CDCl3, RT): d=206.2, 131.3, 128.0, 127.5, 123.3, 88.4, 80.9, 42.6, 30.1,
This research was partly supported by Grant-in-Aids for Scientific Re-
search from the Japan Society for the Promotion of Science (22245014,
24750084).
À1
ꢀ
14.1 ppm; IR (KBr): n˜ =2232 (C C), 1718 cm (C=O); HRMS (FAB)
calcd for C12H12O: 172.0888; found: 172.0891 [M+].
Conjugate addition of 4a with 7a: Ethyl acrylate 7a (103 mg, 1.0 mmol),
phenylacetylene 4a (205 mg, 2.0 mmol) were added to a mixture of
604
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 601 – 605