Compound (XIII) is disclosed in WO00/14085 as being useful as a PDE-IV inhibitor. A method for the preparation of a typical compound among compounds (XIII) disclosed in WO00/14085 is as follows:

However, this method is not practically satisfactory as a industrially applicable preparation method, because of (1) requiring multiple steps, (2) low overall yield, (3) requiring purification by silica-gel column chromatography, and the like.

REFERENCE EXAMPLE 1

Synthesis of cis-4-cyano-4-(2,3-dihydro-8-methoxy-1,4-benzodioxine-5-yl)cyclohexanecarboxylic acid

(1) Synthesis of cis-4-cyano-4-(2,3-dihydro-8-methoxy-1,4-benzodioxine-5-yl)cyclohexanecarboxylic acid ethyl ester

Under a nitrogen atmosphere, trifluoromethanesulfonic acid (2.25 g) and trimethylsilylcyanide (1.57 mL) were dissolved in benzotrifluoride (10 mL), and a solution of 4-(2,3-dihydro-8-methoxy-1,4-benzodioxine-5-yl)-3-cyclohexenecarboxylic acid ethyl ester (0.79 g) prepared according to the method described in EXAMPLE 1 in benzotrifluoride (10 mL) was added dropwise at −25° C. After being stirred for for one hour at −20° C., an aqueous saturated sodium hydrogen carbonate was added and the mixture was extracted with ethyl acetate. The organic layer was washed with brine and dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The residue was crystallized from ethanol (1 mL) to give a solid substance (0.64 g). The solid substance (0.030 g) was crystallized from a mixed solvent of diisopropyl ether and ethyl acetate (0.36 mL, diisopropyl ether/ethyl acetate=4/1) to give cis-4-cyano-4-(2,3-dihydro-8-methoxy-1,4-benzodioxine-5-yl)cyclohexanecarboxylic acid ethyl ester (0.019 g, 47.3%) as a solid.

Melting point 131° C.

¹H-NMR (CDCl₃, δ ppm) 6.84 (d, J=8.9 Hz, 1H), 6.49 (d, J=8.9 Hz, 1H), 4.39−4.33 (m, 4H), 4.17 (q, J=7.1 Hz, 2H), 3.88 (s, 3H), 2.44 (brd, J=12.6 Hz, 2H), 2.32 (tt, J=11.8, 3.8 Hz, 1H), 2.18−1.95 (m, 4H), 1.86 (dt, J=3.6, 12.6 Hz, 2H), 1.28 (t, J=7.1 Hz, 3H).

[0184] IR (KBr, cm⁻¹) 2953, 2228, 1722, 1607, 1504, 1460, 1381, 1325, 1281, 1117, 1043, 953, 787.

MS (m/z) 346(M+H)⁺.

 (2) Synthesis of cis-4-cyano-4-(2,3-dihydro-8-methoxy-1,4-benzodioxine-5-yl)cyclohexanecarboxylic acid

To a suspension of cis-4-cyano-4-(2,3-dihydro-8-methoxy-1,4-benzodioxine-5-yl)cyclohexanecarboxylic acid ethyl ester (397 g) prepared according to the method described (1) of REFERENCE EXAMPLE 1 in ethanol (1.99 L) was added a 6 ml/L aqueous potassium hydroxide (377 mL), and the mixture was stirred for 4 hours at room temperature. After water (2.03 L) was added to the reaction mixture, a 6 mol/L aqueous hydrochloric acid (576 mL) was added to crystallize and to give cis-4-cyano-4-(2,3-dihydro-8-methoxy-1,4-benzodioxine-5-yl)cyclohexanecarboxylic acid (366 g, 98.1%) as a solid.

Melting point 245° C.

¹H-NMR (DMSO-d₆, δ ppm) 12.26 (brs, 1H), 6.79 (d, J=8.9 Hz, 1H), 6.59 (d, J=8.9 Hz, 1H), 4.27 (dd, J=11.9, 5.0 Hz, 4H), 3.75 (s, 3H), 2.34−2.26 (m, 3H), 2.05−2.00 (m, 2H), 1.86−1.63 (m, 4H).

IR (KBr, cm⁻¹) 3287, 2932,1728, 1609, 1508, 1454, 1285, 1119, 953, 802, 764.

MS (m/z) 318(M+H)⁺.

Example 1.
4-Cyano-4-(8-methoxy-1,4-benzodioxan-5-yl) cyclohexanone (Compound 1)(Step A)
Synthesis of 2-(8-methoxy-1,4-benzodioxan-5-yl)acetonitrile (Compound 1a)
• To a solution of 12 g (62 mmol) of 8-methoxy-1,4-benzodioxane-5-carbaldehyde in 140 ml of acetonitrile was added 12 g (110 mmol) of lithium bromide, and then 12 ml (95 mmol) of trimethylsilyl chloride was dropwise added thereto. After 15 minutes, the mixture was ice-cooled, and 19 ml (110 mmol) of 1,1,3,3-tetramethyldisiloxane was dropwise added thereto, followed by stirring at room temperature for 2 hours. The mixture was diluted with methylene chloride, and then was filtered through Celite. The solvent was evaporated in vacuo from the filtrate to give a pale yellow oily substance. To a solution of the obtained crude 5-bromomethyl-8-methoxy-1,4-benzodioxane in 180 ml of DMF was added 9.2 g (190 mmol) of sodium cyanide, followed by stirring at room temperature for 60 hours. To the mixture was added water under ice-cooling, and a solid separated out therefrom was collected by filtration to give 6.8 g (53%) of Compound 1a as an ash-colored solid.
  Melting Point: 121 – 125 °C
  ¹H-NMR (CDCl₃, δ, ppm) 3.60 (s, 2H), 3.88 (s, 3H), 4.33 (s, 4H), 6.50 (d, J = 8 Hz, 1H), 6.86 (d, J = 8 Hz, 1H).
  MASS (m/z) 205 (M⁺).

(Step B) Synthesis of dimethyl 4-cyano-4-(8-methoxy-1,4-benzodioxan-5-yl)pimelate (Compound 1b)
• To a solution of 6.2 g (30 mmol) of Compound 1a obtained in Step A in 94 ml of acetonitrile were added 1.4 ml (3.0 mmol) of a 40% methanolic solution of Triton B and 27 ml (300 mmol) of methyl acrylate, followed by heating under reflux for 5 hours. The mixture was allowed to stand for cooling, and then poured into water, followed by extraction with ethyl acetate. The organic layer was washed with brine and dried over sodium sulfate, and the solvent was evaporated in vacuo. The residue was purified by silica gel column chromatography (eluted with hexane/ethyl acetate = 2/1) to give 6.4 g (56%) of Compound 1b as a pale yellow oily substance.
  ¹H-NMR (CDCl₃, δ, ppm) 2.05-2.37 (m, 4H), 2.39-2.59 (m, 2H), 2.62-2.82 (m, 2H), 3.60 (s, 6H), 3.87 (s, 3H), 4.20-4.40 (m, 4H), 6.48 (d, J = 9 Hz, 1H), 7.01 (d, J = 9 Hz, 1H).
  MASS (m/z) 377 (M⁺).

(Step C) Synthesis of 4-cyano-4-(8-methoxy-1,4-benzodioxan-5-yl)-2-methoxycarbonylcyclohexanone (Compound 1c)
• To a solution of 6.4 g (17 mmol) of Compound 1b obtained in Step B in 96 ml of 1,2-dimethoxyethane was added 2.0 g (50 mmol) of 60% sodium hydride. After heating under reflux for 3 hours, the mixture was allowed to stand for cooling, poured into ice water, acidified with a 6 mol/liter aqueous hydrochloric acid and extracted with ethyl acetate. The organic layer was washed with brine and dried over sodium sulfate, and the solvent was evaporated. The residue was purified by silica gel column chromatography (eluted with hexane/ethyl acetate = 2/1) to give 5.0 g (86%) of Compound 1c as a white solid.
  Melting Point: 129 – 132 °C
  ¹H-NMR (CDCl₃, δ, ppm) 2.21-2.50 (m, 3H), 2.61-2.89 (m, 2H), 3.11(d, J = 15 Hz, 1H), 3.79 (s, 3H), 3.89 (s, 3H), 4.37 (s, 4H), 6.49 (d, J = 9 Hz, 1H), 6.84 (d, J = 9 Hz, 1H), 12.2 (s, 1H).
  MASS (m/z) 345 (M⁺).

(Step D) Synthesis of Compound 1
• A mixture of 5.0 g (15 mmol) of Compound 1c obtained in Step C, 50 ml of DMSO, 5 ml of water, and 5.0 g of sodium chloride was stirred at 150°C for 5 hours. The mixture was allowed to stand for cooling, and water was added thereto, followed by extraction with ethyl acetate. The organic layer was washed with brine and dried over sodium sulfate, and the solvent was evaporated in vacuo. The residue was purified by silica gel column chromatography (eluted with hexane/ethyl acetate = 3/1) to give 3.6 g (86%) of Compound 1 as a white solid.
  Melting Point: 157 – 161 °C
  ¹H-NMR (CDCl₃, δ, ppm) 2.21-2.41 (m, 2H), 2.45-2.72 (m, 4H), 2.81-3.00 (m, 2H), 3.89 (s, 3H), 4.37 (s, 4H), 6.51 (d, J = 9 Hz, 1H), 6.88 (d, J = 9 Hz, 1H).
  MASS (m/z) 287 (M⁺).

Example 2. 4-Cyano-4-(8-methoxy-1,4-benzodioxan-5-yl)cyclohexanone ethyleneketal (Compound 2)
(Step A)Synthesis of 4-hydroxy-4-(8-methoxy-1,4-benzodioxan-5-yl)cyclohexanone ethyleneketal (Compound 2a)
• In 65 ml of THF was dissolved 10 g (41 mmol) of 5-bromo-8-methoxy-1,4-benzodioxane, and 28 ml (45 mmol) of a 1.59 mol/liter solution of n-butyl lithium in hexane was dropwise added thereto at -78°C. After 15 minutes, a solution of 9.6 g (61 mmol) of 1,4-cyclohexadione monoethyleneketal in 50 ml of THF was dropwise added thereto. The mixture was stirred for 1 hour, followed by stirring at room temperature for 20 minutes. Water was added thereto, the mixture was extracted with ethyl acetate, and the extract was washed with brine and dried over sodium sulfate. The solvent was evaporated therefrom, and the residue was purified by silica gel column chromatography (eluted with hexane/ethyl acetate = 1/1) to give 9.0 g (68%) of Compound 2a as a white solid.
  Melting Point: 94 – 96 °C
  ¹H-NMR (CDCl₃, δ, ppm) 1.58-1.72 (m, 2H), 1.88-2.28 (m, 6H), 3.57 (s, 1H), 3.86 (s, 3H), 3.90-4.07 (m, 4H), 4.35 (s, 4H), 6.46 (d, J = 9 Hz, 1H), 6.82 (d, J = 9 Hz, 1H).
  MASS (m/z) 322 (M⁺).
• (Step B) Synthesis of Compound 2
  • In 4.9 ml of methylene chloride was dissolved 0.49 g (1.5 mmol) of Compound 2a obtained in Step A, 0.26 ml (1.9 mmol) of trimethylsilyl cyanide was added thereto at -78°C, then 0.20 ml (1.6 mmol) of a boron trifluoride-ethyl ether complex was dropwise added thereto, and the mixture was stirred for 10 minutes, followed by stirring at room temperature for 10 minutes. A saturated aqueous solution of sodium bicarbonate was added thereto and the mixture was extracted with ethyl acetate. The extract was washed with brine and dried over sodium sulfate, and the solvent was evaporated. The residue was purified by silica gel column chromatography (eluted with hexane/ethyl acetate = 2/1) to give 0.30 g (61%) of Compound 2 as a colorless oily substance.
    ¹H-NMR (CDCl₃, δ, ppm) 1.79-1.95 (m, 2H), 2.06-2.20 (m, 4H), 2.30-2.46 (m, 2H), 3.87 (s, 3H), 3.90-4.07 (m, 4H), 4.36 (s, 4H), 6.48 (d, J = 9 Hz, 1H), 6.82 (d, J = 9 Hz, 1H).
    MASS (m/z) 331 (M⁺).

Example 3. Compound 1
• In 2.9 ml of acetone was dissolved 0.29 g (0.87 mmol) of Compound 2 obtained in Example 2, 1.2 ml (7.2 mmol) of a 6 mol/liter aqueous hydrochloric acid was added thereto, and the mixture was heated under reflux for 3 hours. The mixture was allowed to stand for cooling and poured into a saturated aqueous solution of sodium bicarbonate, the mixture was extracted with ethyl acetate, and the extract was washed with brine. The mixture was dried over sodium sulfate, and the solvent was evaporated to give 0.23 g (92%) of Compound 1 as a white solid.
Example 4. Methyl

cis-4-cyano-4-(8-methoxy-1,4-benzodioxan-5-yl)cyclohexanecarboxylate (Compound 3) and methyltrans-4-cyano-4-(8-methoxy-1,4-benzodioxan-5-yl)cyclohexanecarboxylate (Compound 4)(Step A) Synthesis of 2-[4-cyano-4-(8-methoxy-1,4-benzodioxan-5-yl)cyclohexylidene]-1,3-dithiane (Compound 3a)

• To a solution of 5.0 ml (26 mmol) of 2-trimethylsilyl-1,3-dithiane in 50 ml of THF was added dropwise 17 ml (26 mmol) of a 1.54 mol/liter solution of n-butyl lithium in hexane under ice-cooling. After 10 minutes, the mixture was cooled to -78°C, and a solution of 3.6 g (13 mmol) of Compound 1 obtained in Example 1 in 40 ml of THF was dropwise added thereto. After 10 minutes, to the mixture was added brine, followed by addition of water at room temperature. The mixture was extracted with ethyl acetate, the extract was dried over sodium sulfate, and the solvent was evaporated. The residue was purified by silica gel column chromatography (eluted with hexane/ethyl acetate = 4/1) to give 3.9 g (79%) of Compound 3a as a white solid.
  Melting Point: 164 – 166 °C
  ¹H-NMR (CDCl₃, δ, ppm) 1.70-1.92 (m, 2H), 2.05-2.24 (m, 2H), 2.28-2.53 (m, 4H), 2.89 (t, J = 6 Hz, 4H), 3.18-3.38 (m, 2H), 3.87 (s, 3H), 4.36 (s, 4H), 6.47 (d, J = 9 Hz, 1H), 6.79 (d, J = 9 Hz, 1H).
  MASS (m/z) 389 (M⁺).

(Step B) Synthesis of Compound 3 and Compound 4
• In 120 ml of methanol was suspended 3.9 g (10 mmol) of Compound 3a obtained in Step A, 1.7 ml (20 mmol) of 70% perchloric acid, and 4.3 g (16 mmol) of mercury chloride (HgCl₂) were added thereto, and the mixture was stirred for 4 hours. The mixture was diluted with methylene chloride and was filtered through Celite, the filtrate was poured into a saturated aqueous solution of sodium bicarbonate, and the mixture was extracted with methylene chloride. The organic layer was washed with brine and dried over sodium sulfate, and the solvent was evaporated. The residue was purified by silica gel column chromatography (eluted with hexane/ethyl acetate = 1/1) to give the crude Compound 3 as a white solid and also to give 0.18 g (5.5%) of Compound 4 as a colorless transparent oily substance. Compound 3 was further recrystallized from ethyl acetate to give 0.57 g (17%) of white crystals.
  Compound 3
  Melting Point: 123 – 124 °C
  ¹H-NMR (CDCl₃, δ, ppm) 1.75-2.22 (m, 6H), 2.27-2.51 (m, 3H), 3.71 (s, 3H), 3.88 (s, 3H), 4.36 (s, 4H), 6.48 (d, J = 9 Hz, 1H), 6.84 (d, J = 9 Hz, 1H).
  MASS (m/z) 331 (M⁺).
  Compound 4
  ¹H-NMR (CDCl₃, δ, ppm) 1.92-2.38 (m, 8H), 2.70-2.88 (m, 1H), 3.69 (s, 3H), 3.87 (s, 3H), 4.36 (s, 4H), 6.48 (d, J = 9 Hz, 1H), 6.81 (d, J = 9 Hz, 1H).
  MASS (m/z) 331 (M⁺).

Example 5.

cis-4-Cyano-4-(8-methoxy-1,4-benzodioxan-5-yl)cyclohexanecarboxylic acid (Compound 5)

• To a mixture of 0.55 g (1.7 mmol) of Compound 3 obtained in Example 4 and 3.3 ml of methanol was added 3.3 ml of THF to dissolve them. To the mixture was dropwise added 2.6 ml of a 1.3 mol/liter aqueous solution of potassium hydroxide, followed by stirring at room temperature for 1 hour. The mixture was poured into water, ethyl acetate was added thereto, and an aqueous layer was extracted. The aqueous layer was acidified with a 1 mol/liter aqueous hydrochloric acid, and the precipitated solid was collected by filtration and re-slurried with ethanol to give 0.45 g (86%) of Compound 5 as a white solid.
  Melting Point: 228 – 230 °C
  ¹H-NMR (DMSO-d₆ , δ, ppm) 1.59-1.90 (m, 4H), 1.94-2.10 (m, 2H), 2.20-2.45 (m, 3H), 3.75 (s, 3H), 4.27 (dd, J = 5, 12 Hz, 4H), 6.60 (d, J = 9 Hz, 1H), 6.79 (d, J = 9 Hz, 1H), 12.2 (br s, 1H).
  MASS (m/z) 317 (M⁺).

  Elemental analysis: C17H19NO5
  Found (%) C	64.09,	H : 6.01,	N : 4.51
  Calcd. (%) C	64.34,	H : 6.03,	N : 4.41

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