RESEARCH FRONT
Photocycloaddition of 5-Methoxyoxazoles to Aldehydes and α-Keto Esters
exo-1-Ethyl-5-methoxy-3-methyl-7-phenyl-4,6-dioxa-
579
exo-1-Isopropyl-5-methoxy-3-methyl-7-phenyl-4,6-
dioxa-2-aza-bicyclo[3.2.0]hept-2-ene-7-carboxylic
2-aza-bicyclo[3.2.0]hept-2-ene-7-carboxylic Acid
tert-Butyl Ester (exo-4cd)
Acid tert-Butyl Ester (exo-4ed)
A solution of tert-butyl phenylglyoxylate (1.0 g, 5 mmol) and
A solution of tert-butyl phenylglyoxylate (1.0 g, 5 mmol) and 4-
isopropyl-2-methyl-5-methoxyoxazole (0.75 g, 5 mmol) in ben-
zene (50 mL) was irradiated for 24 h according to the above
general procedure to give 1.65 g of a yellow oil. Preparative
chromatography on silica gel yielded 0.74 g (42%) of the exo-
isomer and 0.46 g (26%) of the endo-isomer as colourless oils.
δH (300 MHz, CDCl3) 0.68 (d, J 6.8, 3H, CH3), 0.82 (d, J 6.8,
3H, CH3), 1.54 (s, 9H, 3CH3), 2.09 (s, 3H, CH3), 3.72 (s, 3H,
OCH3), 7.33–7.82 (m, 5H, Harom). δC (75.5 MHz, CDCl3) 14.2
(q, CH3), 15.9 (q, CH3), 16.7 (q, CH3), 25.9 (d, CH), 28.1 (q,
3CH3), 51.5 (q, OCH3), 82.9 (s, Cq), 85.8 (s, C1), 92.6 (s, C7),
123.2 (s, C5), 127.2 (d, CHarom), 128.0 (d, CHarom), 128.7 (d,
CHarom), 134.8 (s, Cq), 166.0 (s, C3), 168.3 (s, COO). m/z (EI,
4
-ethyl-2-methyl-5-methoxyoxazole (0.71 g, 5 mmol) in ben-
zene (50 mL) was irradiated for 24 h according to the above
general procedure to give 1.62 g of a yellow oil. Preparative
chromatography on silica gel yielded 0.72 g (41%) of the exo-
isomer and 0.38 g (22%) of the endo-isomer as colourless oils.
−1
νmax (film)/cm 2983, 2895, 1751, 1615, 1600, 1555, 1440,
1
085, 980, 770. δH (300 MHz, CDCl3) 0.73 (t, J 7.5, 3H, CH3),
1
.21 (m, 1H, CH), 1.46 (s, 9H, 3CH3), 1.60 (m, 1H, CH), 2.09
(
(
s, 3H, CH3), 3.65 (s, 3H, OCH3), 7.28–7.35 (m, 5H, Harom). δC
75.5 MHz, CDCl3) 7.4 (q, CH3), 14.8 (q, CH3), 21.8 (t, CH2),
2
7.9 (q, 3CH3), 51.6 (q, OCH3), 81.9 (s, C1), 82.9 (s, Cq), 91.4
(
s, C7), 123.4 (s, C5), 126.3 (d, CHarom), 127.5 (d, CHarom),
+
1
28.0 (d, CHarom), 134.9 (s, Cqarom), 166.5 (s, C3), 167.4 (s,
70 eV) 361 (M , 5%), 348 (45), 334 (35), 278 (40), 236 (20), 218
+
COO). m/z (EI, 70 eV) 347 (M , 10%), 310 (4), 264 (40), 222
(10), 173 (25), 130 (60), 105 (100), 102 (18), 91 (10), 77 (25),
+
(
7
25), 159 (75), 127 (40), 116 (100), 105 (80), 102 (38), 91 (10),
7 (25), 71 (28), 57 (60). (Found: M 347.1722. C19H25NO5
71 (28), 57 (60). (Found: M 361.1876. C20H27NO5 requires
+
361.1882.)
requires 347.1726.)
endo-1-Isopropyl-5-methoxy-3-methyl-7-phenyl-4,6-dioxa-
2
-aza-bicyclo[3.2.0]hept-2-ene-7-carboxylic Acid
endo-1-Ethyl-5-methoxy-3-methyl-7-phenyl-4,6-dioxa-
tert-Butyl Ester (endo-4ed)
2
-aza-bicyclo[3.2.0]hept-2-ene-7-carboxylic Acid
tert-Butyl Ester (endo-4cd)
δH (300 MHz, CDCl3) 0.86 (d, J 6.6, 3H, CH3), 1.24 (d, J
6
(
.8, 3H, CH3), 1.45 (s, 9H, 3CH3), 1.75 (s, 3H, CH3), 2.36
septet, J 6.6, 1H, CH), 3.72 (s, 3H, OCH3), 7.25–7.34 (m, 5H,
Harom). δC (75.5 MHz, CDCl3)14.3(q, CH3), 17.4(q, CH3), 17.7
q, CH3), 27.5 (d, CH), 27.8 (s, 9H, 3CH3), 51.8 (q, OCH3),
3.0 (s, Cq), 84.5 (s, C1), 92.4 (s, C7), 123.9 (s, C5), 126.7
δH (300 MHz, CDCl3) 0.93 (t, J 7.5, 3H, CH3), 1.44 (s, 9H,
3
3
CH3), 2.07 (s, 3H, CH3), 2.14 (m, 1H, CH), 2.18 (m, 1H, CH),
.69 (s, 3H, OCH3), 7.27–7.49 (m, 5H, Harom). δC (75.5 MHz,
(
8
CDCl3) 8.2 (q, CH3), 14.3 (q, CH3), 22.6 (t, CH2), 28.0 (q,
3
1
CH3), 51.9 (q, OCH3), 81.7 (s, C1), 83.1 (s, Cq), 90.9 (s, C7),
23.8 (s, C5), 126.3 (d, CHarom), 128.5 (d, CHarom), 129.0 (d,
(
(
d, CHarom), 127.7 (d, CHarom), 128.5 (d, CHarom), 135.4
s, Cqarom), 165.2 (s, C3), 168.5 (s, COO).
CHarom), 135.0 (s, Cqarom), 165.3 (s, C3), 168.1 (s, COO).
exo-1-Isobutyl-5-methoxy-3-methyl-7-phenyl-4,6-
dioxa-2-aza-bicyclo[3.2.0]hept-2-ene-7-carboxylic
Acid tert-Butyl Ester (exo-4gd)
exo-5-Methoxy-3-methyl-7-phenyl-1-propyl-4,6-dioxa-
2-aza-bicyclo[3.2.0]hept-2-ene-7-carboxylic Acid
tert-Butyl Ester (exo-4dd)
A solution of tert-butyl phenylglyoxylate (1.0 g, 5 mmol) and
A solution of tert-butyl phenylglyoxylate (1.0 g, 5 mmol) and 2-
methyl-4-propyl-5-methoxyoxazole (0.75 g, 5 mmol) in benzene
4
-isobutyl-2-methyl-5-methoxyoxazole (0.84 g, 5 mmol) in ben-
zene (50 mL) was irradiated for 24 h according to the above
general procedure to give 1.69 g of a yellow oil. Preparative
chromatography on silica gel yielded 0.75 g (40%) of the exo-
isomer and 0.39 g (21%) of the endo-isomer as colourless oils.
(
50 mL) was irradiated for 24 h according to the above general
procedure to give 1.68 g of a yellow oil. Preparative chromato-
graphy on silica gel yielded 0.84 g (47%) of the exo-isomer and
0
.41 g (23%) of the endo-isomer as colourless oils. δH (300 MHz,
CDCl3) 0.72 (t, J 6.8, 3H, CH3), 0.92 (m, 2H, CH2), 1.17 (m,
H, CH2), 1.46 (s, 9H, 3CH3), 2.08 (s, 3H, CH3), 3.64 (s, 3H,
OCH3), 7.25–7.69 (m, 5H, Harom). δC (75.5 MHz, CDCl3) 14.1
−1
νmax (film)/cm 2983, 2895, 1755, 1610, 1607, 1558, 1440,
1075, 980, 778. δH (300 MHz, CDCl3) 0.62 (d, J 6.6, 3H, CH3),
0.72 (d, J 6.6, 3H, CH3), 1.42 (s, 9H, 3CH3), 1.56 (m, 2H, CH2),
1.58 (m, 1H, CH), 2.04 (s, 3H, CH3), 3.64 (s, 3H, OCH3), 7.26–
7.52 (m, 5H, Harom). δC (75.5 MHz, CDCl3) 14.0 (q, CH3), 22.6
2
(
(
q, CH3), 14.8 (q, CH3), 16.4 (t, CH2), 27.9 (q, 3CH3), 30.9
t, CH2), 51.6 (q, OCH3), 81.6 (s, C1), 82.9 (s, Cq), 91.4 (s, C7),
(
q, CH3), 23.5 (q, CH3), 25.7 (d, CH), 27.9 (q, 3CH3), 36.5 (t,
CH2), 51.6 (q, OCH3), 82.4 (s, Cq), 86.7 (s, C2), 93.5 (s, C3),
23.3 (s, C5), 126.3 (d, CHarom), 127.3 (d, CHarom), 128.5 (d,
1
23.3 (s, C5), 126.3 (d, CHarom), 127.5 (d, CHarom), 128.5
(
d, CHarom), 134.9 (s, Cqarom), 166.0 (s, C3), 167.5 (s, COO).
1
CHarom), 134.2 (s, Cqarom), 165.5 (s, C3), 169.9 (s, COO). m/z
+
endo-5-Methoxy-3-methyl-7-phenyl-1-propyl-4,6-dioxa-
-aza-bicyclo[3.2.0]hept-2-ene-7-carboxylic Acid
tert-Butyl Ester (endo-4dd)
(EI, 70 eV) 375 (M , 10%), 348 (12), 320 (8), 292 (20), 274
2
(20), 187 (40), 168 (20), 144 (80), 105 (100), 102 (18), 91 (10),
77 (25), 71 (28), 57 (60). (Found: M 375.2034. C H NO
+
21 29 5
requires 375.2038.)
δH (300 MHz, CDCl3) 0.93 (t, J 7.5, 3H, CH3), 1.40 (m, 2H,
CH2), 1.44 (s, 9H, 3CH3), 1.77 (s, 3H, CH3), 1.79–1.83 (m,
endo-1-Isobutyl-5-methoxy-3-methyl-7-phenyl-4,6-dioxa-
-aza-bicyclo[3.2.0]hept-2-ene-7-carboxylic Acid
tert-Butyl Ester (endo-4gd)
2
H, CH2), 3.69 (s, 3H, OCH3), 7.27–7.48 (m, 5H, Harom). δC
75.5 MHz, CDCl3) 14.3 (q, CH3), 14.4 (q, CH3), 17.1 (t, CH2),
7.9 (q, 3CH3), 31.9 (t, CH2), 51.9 (q, OCH3), 81.3 (s, C1), 83.1
2
(
2
(
(
1
s, Cq), 91.0 (s, C7), 123.7 (s, C5), 127.2 (d, CHarom), 128.3
d, CHarom), 128.5 (d, CHarom), 135.1 (s, Cqarom), 165.1 (s, C3),
68.1 (s, COO).
δH (300 MHz, CDCl3) 0.79 (d, J 6.5, 3H, CH3), 0.92 (d, J 6.6,
3H, CH3), 1.18 (m, 1H, CH), 1.38 (m, 2H, CH2), 1.44 (s, 9H,
3CH3), 1.72 (s, 3H, CH3), 3.69 (s, 3H, OCH3), 7.26–7.80 (m,