A. Basak, S. S. Bag, A. K. Das
SHORT COMMUNICATION
Enediyne 5: Yield: 78%; yellow powder; m.p. 243 °C; λmax = 236
(s), 309 nm (w). H NMR (200 MHz): δ = 5.16 (s, 4 H), 7.33 (dd,
pearance of a new, weak absorption band at 345 nm (due
to partial transfer of π-electrons from the donor aromatic
system to the acceptor) in the UV/Vis spectra of these mate-
rials, relative to the spectra of the separate donor and ac-
ceptor groups, provides further evidence for the formation
of an intramolecular CT complex (Figure 5).[19]
Thus, we have successfully demonstrated that charge-
transfer or π-stacking interactions can enhance the cycliza-
tion kinetics. Repulsion between electron-deficient partners
raises the activation energy. While the D/A enediynes be-
come activated because of CT interactions, the enediynes
with D/D arms also show greater reactivity than the corre-
sponding A/A counterparts, possibly because of π-stacking
1
J = 3.5, 6.3 Hz, 2 H), 7.42 (dd, J = 2.7, 5.6 Hz, 2 H), 7.46 (d, J =
1.9 Hz, 2 H), 7.86 (dd, J = 2.0, 8.8 Hz, 2 H), 8.16 (d, J = 2.0 Hz,
2 H) ppm. 13C NMR (50 MHz): δ = 57.32, 84.15, 87.69, 105.91,
114.17, 116.10, 122.94, 129.15, 129.62, 132.34, 137.31, 147.22,
154.28 ppm. HRMS: calcd. for C26H14N4O6 478.0914; found
478.0917.
Enediyne 6: Yield: 75%; yellowish solid; m.p. 116 °C; λmax = 232
1
(s), 271 nm (w). H NMR (200 MHz): δ = 4.99 (s, 4 H), 7.27 (d, J
= 2.6 Hz, 2 H), 7.33 (d, J = 4.1 Hz, 2 H), 7.42 (dd, J = 2.3, 8.6
Hz, 4 H), 8.04 (d, J = 9.0 Hz, 2 H) ppm. 13C NMR (50 MHz): δ
= 57.33, 85.45, 86.99, 115.41 (CF3), 117.27, 118.97, 124.01, 124.41,
127.93, 129.03, 132.44, 141.31, 160.53 ppm. HRMS:calcd. for
interactions. It should be noted that in all the enediyne C26H14F6N2O6 564.0756; found 564.0758.
molecules the acceptor moieties are smaller than the donor
aromatic systems. Thus, if only steric effects are operating
we would expect the AA-enediynes to cyclize faster than
1
Enediyne 7: Yield: 82%; reddish oil; λmax = 240 (s), 303 nm (s). H
NMR (200 MHz): δ = 3.98 (s, 3 H), 4.18 (s, 2 H), 5.12 (s, 2 H),
6.74 (d, J = 8.3 Hz, 1 H), 7.01 (d, J = 8.3 Hz, 1 H), 7.24–7.34 (m,
their DD or DA counterparts. Since that is not happening, 6 H), 7.43 (dd, J = 3.6, 5.7 Hz, 2 H), 7.51 (dd, J = 1.7, 3.2 Hz, 2
H), 8.27 (d, J = 9.2 Hz, 1 H) ppm. HRMS: calcd. for C30H20N2O5
488.1373; found 488.1376.
it is clear that the steric effects in these systems are over-
shadowed by CT and π-stacking interactions. Current ef-
forts are aimed towards bringing down the activation bar-
rier further by inducing stronger CT interactions.
Enediyne 8: Yield: 81%; reddish-yellow oil; λmax = 236 (s), 268 (w),
1
307 nm (b). H NMR (200 MHz): δ = 3.95 (s, 3 H), 4.59 (s, 2 H),
5.07 (s, 2 H), 6.72 (d, J = 8.3 Hz, 1 H), 6.93 (dd, J = 2.7 Hz, 1 H),
6.98 (d, J = 3.2 Hz, 1 H), 7.26–7.31 (m, 3 H), 7.36–7.51 (m, 4 H),
7.86 (d, J = 9.0 Hz, 1 H), 8.23 (m, 2 H) ppm. 13C NMR (50 MHz):
δ = 55.70, 57.20, 57.42, 85.42, 85.51, 87.09, 88.84, 103.03, 106.00,
115.63 (CF3), 116.84, 121.77, 121.93, 124.12, 125.47, 125.97,
126.14, 126.40, 126.63, 127.83, 128.31, 128.87, 131.88, 132.14,
147.59, 150.26, 160.47 ppm. MS (EI): m/z = 531 [M+].
Experimental Section
General: All NMR spectra were recorded in CDCl3 unless other-
wise stated.
Enediyne 1: Yield: 82%; reddish crystalline solid; m.p. 116 °C; λmax
= 226 (s), 271 (w), 307 nm (w). H NMR (200 MHz): δ = 4.75 (s,
1
Enediyne 9: Yield: 78%; yellowish solid; m.p. 151 °C; λmax = 244
(s), 271 (w), 307 nm (s). 1H NMR (200 MHz): δ = 3.95 (s, 3 H),
4.57 (s, 2 H), 5.04 (s, 2 H), 6.69 (d, J = 8.4 Hz, 1 H), 6.85 (dd, J =
2.2, 7.2 Hz, 2 H), 6.94 (d, J = 8.3 Hz, 1 H), 7.25–7.32 (m, 2 H),
7.36–7.53 (m, 4 H), 8.09 (dd, J = 2.0, 9.3 Hz, 2 H), 8.15–8.25 (m,
2 H) ppm. 13C NMR (50 MHz, CDCl3 + CCl4): δ = 55.95, 57.12,
57.64, 85.89, 89.98, 103.19, 106.02, 115.21, 122.20, 122.33, 126.02,
126.29, 126.47, 128.58, 128.99, 132.21, 132.38, 140.64, 147.82,
162.34 ppm. HRMS: calcd. for C29H21NO5 463.1420; found
463.1424.
4 H), 7.16 (d, J = 2.6 Hz, 2 H), 7.19–7.27 (m, 4 H), 7.33–7.45 (m,
6 H), 7.71–7.80 (m, 6 H) ppm. 13C NMR (50 MHz): δ = 56.42,
85.65, 87.94, 107.60, 118.85, 123.95, 125.01, 126.47, 126.97, 127.68,
128.33, 129.22, 129.43, 132.10, 134.38, 155.66 ppm. HRMS: calcd.
for C32H22O2 438.1621; found 438.1624.
Enediyne 2: Yield: 82%; yellowish-white, crystalline solid; m.p.
120 °C; λmax = 233 (s), 273 (m), 305 nm (s). H NMR (200 MHz):
1
δ = 4.93 (s, 4 H), 7.10 (d, J = 9.0 Hz, 4 H), 7.30 (dd, J = 3.7, 5.4
Hz, 2 H), 7.42 (dd, J = 3.4, 8.7 Hz, 2 H), 8.23 (d, J = 9.0 Hz, 4 H)
ppm. 13C NMR (50 MHz): δ = 56.95, 86.18, 86.48, 114.97, 124.32,
125.77, 128.81, 132.27, 142.01, 162.44 ppm. HRMS: calcd. for
C24H16N2O6 428.1009; found 428.1011.
Enediyne 10: Yield: 68%; yellow powder; m.p. 153 °C; λmax = 258
1
(s), 351, 368, and 387 nm (s). H NMR (200 MHz): δ = 4.45 (s, 4
H), 5.53 (s, 4 H), 7.37–7.46 (m, 10 H), 7.62 (dd, J = 2.2, 5.6 Hz, 2
1
H), 7.95 (dd, J = 2.6, 5.5 Hz, 4 H), 8.37 (m, 6 H) ppm. H NMR
Enediyne 3: Yield: 87%; reddish-white, crystalline solid; m.p.
101 °C; λmax = 267 (w), 274 (w), 306 nm (bs). 1H NMR (300 MHz):
δ = 4.54 (s, 2 H), 5.01 (s, 2 H), 6.89 (dd, J = 2.1, 7.1 Hz, 2 H), 7.27
(m, 4 H), 7.37 (dd, J = 4.4, 6.9 Hz, 2 H), 7.45 (dd, J = 3.7, 5.2 Hz,
2 H), 7.77 (t, J = 8.9 Hz, 3 H), 8.14 (dd, J = 2.1, 7.2 Hz, 2 H) ppm.
13C NMR (50 MHz): δ = 56.53, 56.73, 85.64, 86.23, 86.42, 88.00,
107.62, 114.90, 118.78, 124.06, 124.34, 125.06, 125.70, 126.58,
126.92, 127.66, 128.40, 128.70, 129.21, 129.52, 132.03, 132.12,
134.31, 141.87, 155.64, 162.44 ppm. HRMS: calcd. for C28H19NO4
433.1314; found 433.1317.
(200 MHz, [D6]benzene): δ = 4.18 (s, 4 H), 5.45 (s, 4 H), 6.87 (dd,
J = 3.3, 5.7 Hz, 4 H), 7.15–7.29 (m, 4 H), 7.46 (dd, J = 3.4, 5.6
Hz, 4 H), 7.72 (d, J = 8.1 Hz, 4 H), 8.08 (s, 2 H), 8.48 (d, J =
8.7 Hz, 4 H) ppm. 13C NMR (50 MHz): δ = 58.24, 63.48, 85.46,
89.72, 124.24, 124.86, 125.41, 126.18, 127.90, 128.28, 128.51,
128.85, 131.04, 131.27, 132.25 ppm. HRMS: calcd. for C42H30O2
566.2247; found 566.2245.
Enediyne 11: Yield: 78%; liquid; λmax = 233 (s), 257 (w), 294 nm
(b). 1H NMR (200 MHz): δ = 5.29 (s, 4 H), 7.31–7.53 (m, 6 H),
8.47 (dd, J = 2.6, 9.2 Hz, 2 H), 8.75 (d, J = 2.6 Hz, 2 H) ppm. MS
(CI): m/z = 519 [MH+].
Enediyne 4: Yield: 89%; greenish, needle-shaped, crystalline solid;
m.p. 128 °C; λmax = 235 and 245 (s), 269 (w), 274 (w), 315 nm (s).
1H NMR (200 MHz): δ = 3.88 (s, 6 H), 4.91 (s, 4 H), 6.64 (d, J =
8.4 Hz, 2 H), 6.86 (d, J = 8.4 Hz, 2 H), 7.23–7.28 (m, 2 H), 7.41–
Enediyne 12: Yield: 78%; yellowish solid;m.p. 123 °C; λmax = 232
(s), 257 (s), 294 nm (b). 1H NMR (200 MHz): δ = 4.66 (s, 2 H),
7.52 (m, 6 H), 8.18–8.28 (m, 4 H) ppm. 13C NMR (50 MHz): δ = 4.76 (s, 2 H), 5.64 (s, 2 H), 6.95 (d, J = 9.3 Hz, 1 H), 7.28–7.55 (m,
55.63, 57.38, 85.52, 88.52, 103.03, 105.83, 121.79, 121.85, 125.15, 8 H, 4×Ph-H), 7.79 (dd, J = 2.6, 5.2 Hz, 1 H), 7.93 (d, J = 8.0 Hz,
125.81, 125.97, 128.22, 132.00, 135.59, 135.95, 147.89, 153.63 ppm.
HRMS: calcd. for C34H26O4 498.1832; found 498.1834.
2 H), 8.32 (d, J = 2.9 Hz, 1 H), 8.37 (d, J = 9.8 Hz, 2 H), 8.44 (s, 1
H) ppm. HRMS: calcd. for C33H22N2O6 542.1479; found 542.1481.
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2005, 1239–1245