6-(p-Dimethylaminophenylazo)-4-methyldihydrofuro[2,3-h]coumarin-9-one (5). The compound
was obtained by the method [9] with a yield of 80%; mp 190°C (chloroform).
4-Methyl-6-phenylazodihydrofuro[2,3-h]coumarin-9-one (9). The compound was obtained by the
method [9]. The yield was 90%; mp 248-250°C (DMSO).
6-Amino-4-methyldihydrofuro[2,3-h]coumarin-9-one (11). Mixture of compound 9 (1 g, 3 mmol),
isopropyl alcohol (200 ml), and glacial acetic acid (20 ml) was stirred with an excess of zinc (15 mmol) for 2 h
at 60°C and was then poured into water. The formed precipitate was filtered off. Yield 0.03 g (40%);
decomp. 280°C (DMF).
6-Acetamido-4-methyldihydrofuro[2,3-h]coumarin-9-one (14). Mixture of compound 11 (0.1 g,
0.4 mmol) and acetic anhydride (5 ml) was heated for 10 min and cooled until precipitation occurred. The
precipitate separated was recrystallized from acetic acid. Yield 0.1 g (90%); mp 279-281°C.
6-Formamido-4-methyldihydrofuro[2,3-h]coumarin-9-one (19). Compound 11 (0.1g, 0.4 mmol) was
dissolved in formic acid (5 ml). The precipitate that separated after 2 days was filtered off and recrystallized
from acetic acid. Yield 0.1 g (90%); mp 279-281°C.
4-Methyldihydrofuro[2,3-h]coumarin-9-one-6-yldiazonium Chloride (23). 6-Aminocoumarin-9-one
11 (2.31 g, 10.0 mmol) was dissolved by heating in concentrated hydrochloric acid (20 ml). The solution was
cooled to 0-2°C, and sodium nitrite (0.77 g, 12.0 mmol) was added in the form of 30% solution. The mixture
was stirred for 30 min and filtered, and the solution was used for the further reactions.
6-Azido-4-methyldihydrofuro[2,3-h]coumarin-9-one (25). To the solution of diazonium chloride 23
we added sodium azide (0.72 g, 11 mmol) in the form of 30% solution. The precipitate was filtered off, washed
several times with water, dried, and recrystallized from DMF. Yield 0.3 g (40%); decomp. 204°C.
6-Chloro-4-methyldihydrofuro[2,3-h]coumarin-9-one (24). To a solution of diazonium chloride 23
(~10 mmol) under stirring we slowly added solution of cuprous chloride (2 g, 10.0 mmol). The precipitate was
filtered off and dried. Yield 0.5 g (20%); mp 258-260°C (chloroform).
Reduction of Dihydrofuro[2,3-h]coumarin-9-ones (General Procedure). To suspension of the
respective dihydrofuro[2,3-h]coumarin-9-one (10 mmol) in methanol (200 ml) we added sodium borohydride
(0.74 g, 20 mmol). The mixture was stirred at room temperature for 2 h, after which it was poured into water.
The precipitate was filtered off and recrystallized.
6-(p-Dimethylaminophenylazo)-4-methyldihydrofuro[2,3-h]coumarin-9-ol (7). Yield 80%; decomp.
200°C (alcohol).
6-(p-Dimethylaminophenylazo)-4-methyldihydrofuro[2,3-h]coumarin (6). This compound was
obtained simultaneously with compound 7 and isolated by column chromatography on aluminum oxide with
1
), δ, ppm,
chloroform as eluent. Yield 10%; decomp. 230°C (alcohol). H NMR spectrum (DMSO-d6
J (Hz): 1.45
(2H, m, 9-CH2); 2.47 (3H, d, 4-Me, JMe,3 = 1.1); 3.13 (6H, s, Me2N); 2.52 (2H, m, 8-CH2); 6.18 (1H, d, 3-H,
J
3,Me = 1.1); 6.75 (2H, d, 2'-H, 6'-H, J2',3' = J6',5' = 9.2); 7.78 (2H, d, 3'-H, 5'-H, J3',2' = J5',6' = 9.2); 8.05 (1H, s, 5-H).
Found, %: C 68.70; H 5.40; N 12.00. M+ 349 (45%). C20H19N3O3. Calculated, %: C 68.75; H 5.48; N 12.03.
6-Amino-4-methyldihydrofuro[2,3-h]coumarin-9-ol (12). Yield 90%; decomp. 219-221°C (alcohol).
6-Acetamido-4-methyldihydrofuro[2,3-h]coumarin-9-ol (17). Yield 60%; mp 238-240°C (alcohol).
6-Formamido-4-methyldihydrofuro[2,3-h]coumarin-9-ol (20). Yield 55%; mp 207-210°C (alcohol).
6-Azido-4-methyldihydrofuro[2,3-h]coumarin-9-ol (26). Yield 70%; decomp. 205°C (alcohol).
6-(p-Dimethylaminophenylazo)-4-methylangelicin (8). To solution of compound 7 (0.5 g, 1.37 mmol)
in dioxane (10 ml) we added excess of 20% sulfuric acid. The mixture was heated for 1 h, and the solution was
poured into water. The formed precipitate was filtered off. Yield 0.31 g (65%); mp 230-232°C (chloroform).
6-Amino-4-methylangelicin (13). Solution of compound 12 (2.33 g, 1 mmol) in excess of 20% sulfuric
acid was heated for 1 h, and solution of sodium carbonate was added until a precipitate separated. The
precipitate was filtered off and recrystallized from DMF. Yield 1.54 g (70%); mp 229-231°C.
291