The condensation of 6-acetyl-7-hydroxy-1,2,3,4-tetrahydronaphthalene (I) with allyl bromide (A) by means of K2CO3 in DMF gives 6-acetyl-7-allyloxy-1,2,3,4-tetrahydronaphthalene (II), which is isomerized to 5-allyl-7-acetyl-6-hydroxy-1,2,3,4-tetrahydronaphthalene (III) by heating at 200 C. Hydrogenation of (III) with H2 over Pd/C in ethanol affords 5-propyl-7-acetyl-6-hydroxy-1,2,3,4-tetrahydronaphthalene (IV), which is then cyclized with diethyl oxalate (B) by means of sodium ethoxide in refluxing etha-nol to yield ethyl 10-propyl-4-oxo-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (V) [an alternative way to prepare (V) is the cyclization of (III) with diethyl oxalate (B) by means of sodium ethoxide to give ethyl 10-allyl-4-oxo-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (VI), which is then reduced to (V) with H2 over Pd/C in ethanol]. The nitration of (V) with nitric acid in sulfuric acid gives ethyl 10-propyl-4-oxo-5-nitro-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (VII), which is reduced with H2 over Pd/C in ethanol-acetic acid to afford the corresponding amino derivative (VIII). Finally, this compound is diazotated with NaNO2 and H2SO4 and then treated with 50% H2SO4 at 120 C.

The condensation of 6-acetyl-7-hydroxy-1,2,3,4-tetrahydronaphthalene (I) with allyl bromide (A) by means of K2CO3 in DMF gives 6-acetyl-7-allyloxy-1,2,3,4-tetrahydronaphthalene (II), which is isomerized to 5-allyl-7-acetyl-6-hydroxy-1,2,3,4-tetrahydronaphthalene (III) by heating at 200 C. Hydrogenation of (III) with H2 over Pd/C in ethanol affords 5-propyl-7-acetyl-6-hydroxy-1,2,3,4-tetrahydronaphthalene (IV), which is then cyclized with diethyl oxalate (B) by means of sodium ethoxide in refluxing etha-nol to yield ethyl 10-propyl-4-oxo-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (V) [an alternative way to prepare (V) is the cyclization of (III) with diethyl oxalate (B) by means of sodium ethoxide to give ethyl 10-allyl-4-oxo-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (VI), which is then reduced to (V) with H2 over Pd/C in ethanol]. The nitration of (V) with nitric acid in sulfuric acid gives ethyl 10-propyl-4-oxo-5-nitro-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (VII), which is reduced with H2 over Pd/C in ethanol-acetic acid to afford the corresponding amino derivative (VIII). Finally, this compound is diazotated with NaNO2 and H2SO4 and then treated with 50% H2SO4 at 120 C.

The condensation of 6-acetyl-7-hydroxy-1,2,3,4-tetrahydronaphthalene (I) with allyl bromide (A) by means of K2CO3 in DMF gives 6-acetyl-7-allyloxy-1,2,3,4-tetrahydronaphthalene (II), which is isomerized to 5-allyl-7-acetyl-6-hydroxy-1,2,3,4-tetrahydronaphthalene (III) by heating at 200 C. Hydrogenation of (III) with H2 over Pd/C in ethanol affords 5-propyl-7-acetyl-6-hydroxy-1,2,3,4-tetrahydronaphthalene (IV), which is then cyclized with diethyl oxalate (B) by means of sodium ethoxide in refluxing etha-nol to yield ethyl 10-propyl-4-oxo-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (V) [an alternative way to prepare (V) is the cyclization of (III) with diethyl oxalate (B) by means of sodium ethoxide to give ethyl 10-allyl-4-oxo-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (VI), which is then reduced to (V) with H2 over Pd/C in ethanol]. The nitration of (V) with nitric acid in sulfuric acid gives ethyl 10-propyl-4-oxo-5-nitro-6,7,8,9-tetrahydro-4H-naphtho[2,3-b]pyran-2-carboxylate (VII), which is reduced with H2 over Pd/C in ethanol-acetic acid to afford the corresponding amino derivative (VIII). Finally, this compound is diazotated with NaNO2 and H2SO4 and then treated with 50% H2SO4 at 120 C.