Molecules 2019, 24, 2677
9 of 11
dried over Na2SO4, filtered, and concentrated in vacuo, giving a residue that was subjected to HPLC
to give 3a–c and 4a–c.
2-Allyl-2-(1,1-diphenylpropan-2-yl)malononitrile (3a): 1H-NMR (300 MHz, CDCl3)
δ 1.20 (d,
J = 6.8 Hz, 3H), 2.42–2.59 (m, 2H), 2.91–3.02 (m, 1H), 4.16 (d, J = 9.3 Hz, 1H), 5.28 (d, J = 17.6 Hz, 1H),
5.37 (d, J = 9.6 Hz, 1H), 5.76-5.92 (m, 1H), 7.21–7.40 (m, 10H) ppm; MS (EI) m/z = 41, 65, 77, 91, 102, 115,
128, 151, 165, 167, 193, 300 (M+).
1
2-Allyl-2-[1,1-bis(4-methoxyphenyl)propan-2-yl]malononitrile (3b): H-NMR (300 MHz, CDCl3)
δ
1.18 (d, J = 6.7 Hz, 3H), 2.44-2.60 (m, 2H), 2.80–2.91 (m, 1H), 3.76 (s, 3H), 3.78 (s, 3H), 4.08 (d, J = 9.2 Hz,
1H), 5.29 (d, J = 16.9 Hz, 1H), 5.36 (d, J = 10.0 Hz, 1H), 5.77–5.91 (m, 1H), 6.81–6.87 (m, 4H), 7.19–7.26
(m, 4H) ppm.
1
2-Allyl-2-[1,1-bis(4-chlorophenyl)propan-2-yl]malononitrile (3c): H-NMR (300 MHz, CDCl3)
δ
1.18 (d, J = 6.7 Hz, 3H), 2.52 (dd, J = 13.8, 7.5 Hz, 1H), 2.62 (dd, J = 13.9, 6.7 Hz, 1H), 2.88 (dq, J = 8.9,
6.7 Hz, 1H), 4.15 (d, J = 9.1 Hz, 1H), 5.31 (d, J = 16.9 Hz, 1H), 5.40 (d, J = 10.2 Hz, 1H), 5.76–5.91 (m, 1H),
7.19–7.36 (m, 8H) ppm; 13C-NMR (75 MHz, CDCl3)
δ 15.47, 41.40, 42.40, 42.79, 54.31, 114.18, 123.29,
128.44, 129.24, 129.27, 129.67, 129.93, 133.41, 133.76, 139.09, 139.24 ppm.
1
2-(1,1-Diphenylpropan-2-yl)malononitrile (4a): H-NMR (300 MHz, CDCl3)
δ
1.30 (d, J = 6.6 Hz,
3H), 2.95–3.06 (m, 1H), 3.64 (d, J = 3.3 Hz, 1H), 3.80 (d, J = 11.7 Hz, 1H), 7.21–7.36 (m, 10H) ppm; MS
(EI) m/z = 51, 63, 77, 83, 102, 128, 151, 165, 167, 193, 300 (M+).
1
2-[1,1-Bis(4-methoxyphenyl)propan-2-yl]malononitrile (4b): H-NMR (300 MHz, CDCl3)
δ
1.28
(d, J = 6.6 Hz, 3H), 2.82–2.95 (m, 1H), 3.66 (d, J = 3.3 Hz, 1H), 3.69 (d, J = 11.7 Hz, 1H), 3.77 (s, 6H),
6.83–6.89 (m, 4H), 7.18–7.24 (m, 4H) ppm.
2-[1,1-Bis(4-chlorophenyl)propan-2-yl]malononitrile (4c): 1H-NMR (300 MHz, CDCl3)
δ 1.29
(d, J = 6.6 Hz, 3H), 2.87-2.98 (m, 1H), 3.60 (d, J = 3.4 Hz, 1H), 3.78 (d, J = 11.8 Hz, 1H), 7.18–7.37
(m, 8H) ppm.
3.6. Resolution of Enantiomers
Resolutions of enantiomers of 3a and 4a were performed on a recycling preparative HPLC equipped
with Jasco PU-980 pump, Jasco UV-970 and CD-2095 detectors (Jasco Corporation, Tokyo, Japan),
Daicel CHIRALCEL OJ (3a) or OJ-H (4a) columns (Daicel Corporation, Osaka, Japan). Eluents were
hexane:2-propanol = 7:3 (3a) or 9:1 (4a). [3a] = 0.068 M, [4a] = 0.078 M. Both 3a and 4a were detected
by UV and CD detectors at 270 nm.
Resolutions of enantiomers of 3c and 4c were performed by using a SHIMADZU GCMS-QP5050
(Shimadzu Corporation, Kyoto, Japan) operating in the electron impact mode (70 eV) equipped with
SUPELCO GAMMA DEXTM 225 colu◦mn (Sigma-Aldrich Co., LLC, St. Louis, MO, USA). Detector
◦
temp = 215 C, injection temp = 220 C, inlet pressure = 93.7 kPa, flow rate = 1.0mL/min, linear
velocity = 28.1 cm/s, split ratio = 50, carrier gas = N2.
4. Conclusions
In summary, we found that photoreactions of prochiral 3,3-diaryl-1,1-dicyano-2-methylprop-1-enes
1a–c with allyltrimethylsilane, carried in the presence of enantiomerically pure chiral carboxylic acids,
generates photoallylation and photoreduction products with low but finite levels of enantioselectivity.
The percent enantiomeric excesses in the products of the process was highest (4.8 %ee) when
(S)-mandelic acid was used. Enantioselectivities in these reactions are a consequence of sterically
governed asymmetric proton transfer in intermediate complexes formed by π-π and OH-π interactions
between radical anions of the prochiral alkenes and the chiral carboxylic acids.
1
Supplementary Materials: The following are available online: H-NMR spectra of 1b
13C-NMR spectra of 1c and 3c.
, 1c, 3a, 3b, 3c, 4a, and 4c,
Author Contributions: Project administration, H.M.; investigation, M.I. and D.O.; supervision, K.M.