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Scheme 5. Cyclic TS‡ in DC formation via Path A.
cyclic transition state, TS1‡, with the aid of intramolecular
H-bonding, as in Scheme 5. TS‡1 would lead to (8R, 10R) or
(8S, 10S) configuration, whereas TS‡2 leads to (8S, 10R) or
(8R, 10S) configuration. A steric effect may be involved
between the dimethyl groups of indoline and the forth-
coming phenolic oxygen moiety.
ethanol was refluxed for 8 h. The yellow precipitate was
filtered from the hot solution and washed thoroughly with
cold diethyl ether. Purification was carried out either by
recrystallization from acetone or by precipitation from
chloroform/diethyl ether. The product was identified by 1H
NMR and mass spectroscopy and gave satisfactory
elemental analysis.
This hypothesis is supported by the observation from the
X-ray data of DC-1, that the stereogenic centers C-8 and
C-10 have the RR or SS configuration. Thus the proton
locates at the same side of the pyranose ring oxygen in TS‡1.
Without this type of H-bonding, the epimeric proton on C-8
would not be steroselective. In addition, the fact that the
(8R, 10R) or (8S, 10S) DC isomer was formed stereo-
selectively may rule out the Path A formation mechanism
involving capture of the open merocyanine intermediate
prior to ring closure to the spiropyran, since stereo-
selectivity at C-10 could not be expected from the Michael
addition to the open merocyanine intermediate.
5.1.1. 4-(2-Methylene-1,3,3-trimethylindoline-20-yl)-6-
carboxylic-10,30,30-trimethyl-spiro[3,4-dihydro-2H-1-
benzopyran-2,20-indoline], DC-1. Yellow, yield 75%, mp
1
167 (dec 133) 8C, H NMR (400 MHz, CDCl3) d 1.25(s,
3H), 1.26 (s, 3H), 1.55 (s, 6H), 2.19 (dd, JZ14.2, 12.0 Hz,
1H), 2.43 (dd, JZ14.2, 4.20 Hz, 1H), 2.85 (s, 3H), 3.04 (s,
3H), 4.16 (d, JZ9.90 Hz, 1H), 4.27 (m, JZ12.4, 9.90,
4.20 Hz, 1H), 6.78 (t, 1H), 6.56 (d, 1H), 6.59 (d, JZ
7.50 Hz, 1H), 6.75 (d, JZ8.70 Hz, 1H), 6.86 (t, 1H), 7.10 (t,
1H), 7.18 (d, 1H), 7.15 (t, JZ7.50 Hz, 1H), 7.19 (d, 1H),
7.81 (d, JZ8.70 Hz, 1H), 8.06 (s, 1H); ES-Mass for
C32H34N2O3, Mw: 494; 105 (23.5), 158 (11.0), 174 (100),
494 (1.2) m/z (%); C, 77.7; H, 6.93; N, 5.66; O, 9.70
obtained C, 77.2; H, 7.10; N, 5.78, O, 9.92.
4. Conclusions
The results of X-ray structure determination for DC-1 as C
with (8R, 10R) or (8S, 10S) configuration are in complete
agreement with our earlier structural assignments based
solely on 1H NMR results for the series of DC compounds.15
The most plausible mechanism of DC formation involves
dehydration of the carbinol intermediate via the cyclic TS1‡
with the aid of intramolecular H-bonding (Path B in
Scheme 4), rather than capture of the open merocyanine
intermediate prior to ring closure to the spiropyran (Path A,
Scheme 4).
5.1.2. 4-(2-Methylene-1,3,3-trimethylindoline-20-yl)-6-
nitro-10,30,30-trimethylspiro[3,4-dihydro-2H-1-benzo-
pyran-2,20-indoline], DC-2. Yellow, yield 82%, mp 176
1
(dec 137) 8C, H NMR (400 MHz, CDCl3) d 1.31(s, 3H),
1.33 (s, 3H), 1.62 (s, 6H), 2.23 (dd, JZ14.3, 13.0 Hz, 1H),
2.85 (s, 3H), 3.00 (dd, JZ14.3, 4.87 Hz, 1H), 3.05 (s, 3H),
4.15 (d, JZ10.1 Hz, 1H), 4.32 (m, JZ13.0, 10.1, 4.87 Hz,
1H), 6.83 (t, 1H), 6.59 (d, 1H), 6.60 (d, JZ7.43 Hz, 1H),
6.75 (d, 1H), 6.86 (t, 1H), 7.06 (t, 1H), 7.07 (d, 1H), 7.09 (t,
JZ7.43 Hz, 1H), 7.11 (d, 1H), 7.96 (d, 1H), 8.23 (s, 1H);
ES-Mass for C31H33N3O3, Mw: 496; 118 (16.1), 132 (22.7),
174 (100) 323 (33.2), 496 (4.1) m/z (%); C, 75.13; H, 6.71;
N, 8.48; O, 9.68; found C, 74.9; H, 6.80; N, 8.57; O, 9.73.
5. Experimental
5.1. Materials
5.1.3. 4-(2-Methylene-1,3,3-trimethylindoline-20-yl)-6-
phenylazo-10,30,30-trimethyl spiro[3,4-dihydro-2HK1-
benzopyran-2,20-indoline], DC-3. Yellow, yield 73%, mp
Fischer base (2-ethylene-1,3,3-trimethylindoline) and
salicylaldehyde were available from Aldrich Chemical Co.
and were used without further purification.
1
170 (dec 142) 8C, H NMR (400 MHz, CDCl3) d 1.34 (s,
1H), 1.38 (s, 1H), 1.65 (s, 3H), 1.69 (s, 3H), 2.24 (dd, JZ
14.2, 12.0 Hz, 1H), 2.87 (s, 3H), 2.45 (dd, JZ14.2, 4.89 Hz,
1H), 3.06 (s, 3H), 4.26 (d, JZ10.0 Hz, 1H), 4.37 (m, JZ
12.0, 10.0, 4.89 Hz, 1H), 6.75 (t, 1H), 6.57 (d, 1H), 6.57 (d,
1H), 6.82 (d, JZ8.55 Hz, 1H), 6.85 (t, 1H), 7.08 (t, 1H),
7.19 (d, 1H), 7.09 (t, 1H), 7.22 (d, 1H), 7.79 (d, JZ8.55 Hz,
1H); ES-Mass for C37H38O, Mw: 554; 105 (35.4), 158
(16.4), 174 (100) 382 (22.9), 555 (0.5) m/z (%); C, 80.11; H,
The azoarylated salicylaldehydes were obtained from the
reaction of 1:1 molar ratio of commercially available
salicylaldehydes and the corresponding substituted benzene
diazonium salts, which were prepared from diazotization of
substituted anilines with nitrous acid.
For preparation of DC’s, a mixture of 5-substituted
salicylaldehyde and excess (2–3-fold) Fischer base in