Ethyl trifluoroacetate Celecoxib

With regard to the synthesis of celecoxib (1), several routes were described in the 1995 patent by G. D. Searle As shown in Scheme 1, dione 7 was prepared by the Claisen condensation of 4-methylacetophenone with ethyl trifluoroacetate in the presence of NaOMe in methanol under reflux. Subsequent diarylpyrazole formation from the condensation of dione 7 and 4-sulfonamidophenylhydrazine hydrochloride then delivered... 

Many continuous processes are used to prepare early pharmaceutical intermediates, but Pfizer recently presented a continuous process to prepare the API itself. A continuous process to prepare the anti-inflammatory drug celecoxib was described (Scheme 11.3) [6]. The batch process for celecoxib consists of two steps (1) a base-mediated Claisen reaction between 4-methylacetophenone and ethyl trifluoroacetate, and (2) an acid-mediated pyrazole condensation between enolate intermediate 8 and hydrazine 9 giving celecoxib (Scheme 11.4) [7]. Continuously flowing the Claisen reaction step 1 into the pyrazole condensation step 2 offers the advantages of directly telescoping continuous processing steps, as described in the introduction to this chapter. 

To a solution of ethyl trifluoroacetate (1.90 ml, 16.0 mmol) in 7 ml of methyl tert-butyl ether was added 25% NaOMe (3.62 ml, 16.8 mmol). Next 4-chloroaceteophenone (2.08 ml, 16.0 mmol) in 2 ml of methyl tert-butyl ether was added. The mixture was stirred at room temperature overnight. To above solution was added 100 ml of 90% EtOH, followed by 4 N HCI (4.0 ml, 16 mmol) and 4-sulphonamidophenylhydrazine hydrochloride (3.58 g, 16 mmol). The mixture was heated to reflux for 3 hours. The mixture was concentrated. When 30 ml of water was added, a solid formed. The solid was filtered and washed with 20 ml of 60% EtOH to give 4.50 g of white solid. The filtrate was evaporated and taken up in ethyl acetate (100 ml), washed with saturated NaHC03, and brine, dried over MgS04, and concentrated. Heptane was added at boiling point of the mixture. After cooling down to 0°C, 1.01 g more product was obtained. The combined yield of the 4-(5-(4-methylphenyl)-3-trifluoromethyl-N-pyrazol-l-yl)benzenesulfonamide (Celecoxib) was 86%. 

Celecoxib is prepared in a convergent synthesis by a classical condensation reaction, which gives a pyrazole from the corresponding 1,3-diketone and a hydrazine. [205] The hydrazine is obtained from aniline by sulfonation, diazotisa-tion and reduction. The 1,3-diketone is accessible in one step from 4-methylac-etophenone and ethyl trifluoroacetate. 

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