5-Bromophthalide

5-Bromophthalide is white to Pale Yellow Crystalline Solid

The synthesis of bromoacetal 6 from phthalimide (7) is shown in FIG. 11. Based on reactions described in the literature, these transformations were carried out on large scale, and some steps were improved. Nitration of 200 g of phthalimide (7) gives 146 g of 5-nitrophthalimide (8). Reduction of 8 by catalytic hydrogenation, according to the literature procedure, is a bottleneck in the synthesis because of the large volume of solvent needed. With a 2 L Parr hydrogenator pressure vessel, 30 g of 8 is converted to 25 g of amine 9. The next step is also a reduction; aminophthalide 10 is obtained quantitatively from 9 by copper-catalyzed reaction with zinc in aqueous base. Steps b and c could be combined by treating 8 with zinc dust and copper(II) sulfate in 2 M aq. sodium hydroxide. This variation, which is not shown in FIG. 11, removes the bottleneck, potentially allowing 100 g of 10 to be prepared in one step from 146 g of 9. The reaction conditions for the steps shown in FIG. 11 are as follows: a) HNO3, H2SO4, 0° C., 56percent ; b) 5percent Pd/C, H2, EtOAc, 97percent ; c) Zn, CuSO4, 6 M NaOH, 5° C. then heated at 70-80° C. 16 h, 100percent ; d) NaNO2, 4 M HBr, followed by CuBr at 0° C.; e) DIBAL, toluene, -42° C.; f) BF3 OEt2, MeOH, RT.Aminophthalide 10 is converted to bromophthalide 11 in 76percent yield by means of the Sandmeyer reaction. 36 g of 11 was prepared in one batch. Reduction of 11 with diisobutylaluminum hydride gives bromolactol 12, a novel compound in this series, in 77percent yield. Bromoacetal 6 was then prepared in 96percent yield by reaction of 12 with boron trifluoride etherate in methanol. 6 was also prepared on a 3 g scale. Overall, the synthesis of 6 shown in Scheme 3 is very effective, because the yields are generally high and only the last two steps (e and f) require chromatography for product purification.20 g (0.13 mol) of 5-aminoisobenzofuranone, 30 ml of 47percent HBr solution was added to a 250 ml three-necked flask, and the temperature was slowly controlled at 0 ° C.Then slowly adding 5 ml of an aqueous solution of sodium nitrite, wherein sodium nitrite contains 10.16 g (0.14 mol), and stirring for 1 h;20.56g (0.14mol) of cuprous bromide is dissolved in 5ml of 47percent hydrobromic acid solution, slowly added dropwise to the diazonium salt solution prepared above, and reacted at room temperature for 1h-3h;Filtration, washing with water and recrystallization from isopropanol gave a white powder, i.e., 5-Bromophthalide, 21.6 g, yield 76.8percent.Potassium bromate (3 mmol) in water (1.1 mL) was added to a solution of 4-bromo-2-methylbenzoic acid (1 mmol) in ethyl acetate (3 mL); then, a solution of sodium bisulfite (3 mmol) in water (3 mL) was slowly dripped. The resulting two-phase mixture was stirred at 20°C for 40 hours. After completion, the organic phase was separated, and the aqueous layer extracted with ethyl acetate (3 x 3 mL); the unified organic phases were dried over anhydrous sodium sulfate and concentrated in vacuo, affording the desired product as a white solid [5]. Yield: 59percent. TLC (cyclohexane – ethyl acetate 8:2): RTo a combined mixture of S17-1 (80 g, 0.37 mol, 1.0 eq.) in EtOAc (700 mL) and NaBrOGeneral procedure: A solution of Phthalic acid diethyl ester (1g, 4.5 mmol)in CH2Cl2 at -30°C was treated with DIBAL-H (11.25 mL, 11.25 mmol, 1 M solution in toluene). The reaction mixture was allowed to stir for next 1h at room temperature and quenched with saturated NH4Cl solution and 1 M HCl at 0°C. After warming up to room temperature more CH2Cl2 was added, organic layer was separated, washed with brine solution, dried over Na2SO4 and concentrated in vacuo.Chromatography on silica gel with hexane-EtOAc (1:1) asthe eluent afforded the phthalide 4a.Sodium borohydride (12.6 g, 330 mmol) was added to a mixed solvent of ethanol (300 mL) and water (50 mL)Add 5-bromophthalimide in 4 batches with stirring at 20-30 ° C(30.0 g, 132 mmol, stirred for 30 min after each addition).After the addition was complete, the reaction was incubated for 2h, hydrochloric acid solution (mass percent concentration 18percent, 180g, 883.5mmol) was added dropwise at 20-30 ° C, heated to 75-85 ° C after dropping, The reaction was incubated 3h, evaporated to ethanol under reduced pressure to give an aqueous white solid.Solid plus toluene (225ml), water (300ml), 45-55 ° C for 30min, to clarify the upper and lower.The layers were separated and the aqueous layer was extracted with toluene (150 mL * 1).The combined toluene layers were washed with saturated brine (150 ml * 1).Divided toluene layer, add water 225ml, sodium hydroxide (6g), stirred at 80 for 3h. The hot toluene is removed by hot section and extracted with toluene (50 ml * 1).Sub-water layer was cooled to 30 ° C dropwise hydrochloric acid (21.0g), heated to 75-85 ° C, incubated for 2-3h.Drop to 50 ° C and extract with toluene (225 ml * 1, 150 ml * 1).Toluene was combined and washed with water (50 ml * 1).Atmospheric pressure concentrated toluene layer to 5.5X, slowly cooled to 50 precipitated white crystals, 50 stirring 1h, then slowly cooled to 0-5 incubated 1h.Filtration and crystallization from ice-toluene (60 ml) gave a white 5-bromophthalide (13.7 g, 48.5percent yield) after drying in vacuo. HPLC: 98.0percent.The feed solution for the reaction was prepared by dissolving 455 g of 4-bromophthalic anhydride in 545 g of THF at 25° C. This solution was then added to the reducing agent, which was prepared as a slurry of 48 g of sodium borohydride in 450 g THF pre-cooled to 5° C prior to the addition of said solution. As the starting material was added to the reducing agent slurry, an increase in temperature from 5°C to 15°C was noted. After approximately 3 hours, all of the 4-bromophthalic anhydride had been added to the sodium borohydride slurry, and the reaction was allowed to continue, with stirring, for a further one hour at 25° C. Neutralisation of the excess sodium borohydride was performed by the careful addition of 300 g water and 150 g hydrochloric acid (as a 32percent aqueous solution). The pH of the neutralized reaction mixture dropped to pH 1-2, and the temperature rose from 25° C to 32° C. Phase separation was achieved by heating the mixture to 55° C, at which point two clearly distinguishable phases were observed: a heavy aqueous phase and a clear organic phase. The lower, aqueous, phase (600 g) was removed, following which the organic phase was washed with aqueous NaCl solution (400 g, 10percent w/w) to remove the residues of H3BO3 formed during the work-up, then the aqueous THF (750 g) was distilled off from the organic phase over a temperature range of 70 to 77° C in a reboiler. Aqueous ethanol (700 g, 95percent) and water (150 g) were added to the organic phase residue, which was heated to reflux. Crude 5-bromophthalide was then crystallized by controlled cooling of the solution from 75° C to 30° C over a period of one hour, following which the temperature was held constant at 30° C for a further one hour. The crystallized material was filtered and washed with 250 g aqueous ethanol (95percent). The filtration residue thus formed (272 g, LOD-23percent) was found to contain approximately 80percent 5-bromophthalide and 20percent 6- bromophthalide. In order to further purify the desired product, a slurry of 260 g of the wet, crude 5-bromophthalide was prepared in 540 g of ethanol containing 5percent water at 25° C. This slurry was then heated TO 70-80° C, and held at that temperature for one hour. Re-crystallization of the 5-bromophthalide was achieved by lowering the temperature from 80° C to 25°C over a period of one hour, and then holding at the lower temperature for a further one hour. The crystallized product was then filtered and washed with 150 g of aqueous 95percent ethanol, following which 180 g of wet residue was dried AT 80° C for a period of 2 hours. The dried product thus formed (145 g) was subjected to HPLC and NMR analysis, and was found to contain >98percent 5-bromophthalide. The yield was approximately 35percent.The feed solution for the reaction was prepared by dissolving 57 g of 4-bromophthalic anhydride in 53 g of DMF at 25° C. This solution was then added to the reducing agent, which was prepared as a slurry of 9.5 g of sodium borohydride in 100 g DMF, pre-cooled to 5° C prior to addition of said solution. After approximately 3 hours, all of the 4-bromophthalic anhydride had been added to the sodium borohydride slurry, and the reaction was allowed to continue, with stirring, for a further one hour. Neutralisation of the excess sodium borohydride was performed by careful addition of the reaction mixture to a solution of 200 g water and 62 g concentrated HC1. The precipitate, in the form of a paste, was filtered on a Buchner filter, and washed with 200 g water. 85 g of a wet mixture of isomers was obtained. It was impossible to crystallize 5-bromophthalide from DMF. However, the crystallization of the mixture was carried out in 140 g ethanol to give 30.9 g of the wet, crude product containing 70percent 5-bromophthalide. In order to further purify the desired product, a slurry of 30.3 g of the wet, crude 5-bromphthalide was prepared in 50 , G of ethanol at 25° C. This slurry was then heated to 75° C and held at that temperature for one hour. Re- crystallization of the 5-bromophthalide was achieved by lowering the temperature from 75 to 25° C over a period of one hour, and then holding at the lower temperature for a further one hour. The crystallized product was then filtered and washed with ethanol, prior to being dried at 80° C for a period of two hours. The dried product thus formed (8.1 g) was subjected to HPLC and NMR analysis, and was found to contain approximately 90percent 5-bromophthalide. The overall yield of 5-bromophthalide was approximately 15percent.The feed solution for the reaction was prepared by dissolving 227 g of 4-bromophthalic anhydride in 300 g of ethylene glycol dimethyl ether at 20° C. This solution was then added to the reducing agent, which was prepared as a slurry of 22.7 g of sodium BOROHDYRIDE in 200 g ethylene glycol dimethyl ether at 20°C. As the starting material was added to the reducing agent slurry, an increase in temperature from 20°C to 30°C was noted. After approximately 3.0 hours, all of the 4-bromophthalic anhydride had been added to the sodium borohydride slurry, and the reaction was allowed to continue, with stirring, for a further one hour at 26° C. Neutralisation of the excess sodium borohydride was performed by the careful addition of 200 g water and 70 g hydrochloric acid (as a 32percent aqueous solution). The pH of the neutralized reaction mixture dropped to pH 1-2, and the temperature rose from 26° C to 31° C. Phase separation was achieved by heating the mixture to 50° C, at which point two clearly distinguishable phases were observed: a heavy aqueous phase and a clear organic phase. The lower, aqueous, phase (223 g) was carefully removed, following which the organic phase was washed with aqueous NaCl solution (200 g, 15percent w/w) to remove the residues of H3BO3 formed during the work-up, then the aqueous ethylene glycol dimethyl ether (262 g) was partially distilled off from the organic phase over a temperature range of 74 to 91° C in a reboiler. Crude 5-bromophthalide was then crystallized from the organic phase residue by controlled cooling of said residue from 91°C to 25° C over a period of one hour, following which the temperature was held constant at 25° C for a further one hour. The crystallized material was filtered and washed with aqueous 50percent ethylene glycol dimethyl ether. The filtration residue thus formed was found to contain approximately 80percent 5-bromophthalide and 20percent 6-bromophthalide. In order to further purify the desired product, a slurry of 240 g of the wet, crude 5-bromophthalide was prepared in 240 g of aqueous 90percent ethylene glycol dimethyl ether at 25° C. This slurry was then heated to 85° C to obtain a solution, and re-crystallisation of the 5-bromophthalide was achieved by lowering the temperature from 85° C to 25°C over a period of one hour, and then holding at the lower temperature for a further one hour. The crystallized product was then filtered and washed with 90 g of aqueous 90percent ethylene glycol dimethyl ether, following which 97 g of wet residue was dried at 80° C for a period of 2 hours. The dried product thus formed (83 g) was subjected to HPLC analysis, and was found to contain >99percent 5-bromophthalide. The direct yield was approximately 38percent.The feed solution for the reaction was prepared by dissolving 197 g of 4-bromophthalic anhydride in 250 g of THF at 25° C. This solution (density = 1.15 g/ml) was then added to the reducing agent, which was prepared as a slurry of 18.5 g of sodium borohydride in 150 g THF pre-cooled to 5° C prior to the addition of said solution. As the starting material was added to the reducing agent slurry, an increase in temperature from 5°C to 15°C was noted. After approximately 2.5 hours, all of the 4-bromophthalic anhydride had been added to the sodium borohydride slurry, and the reaction was allowed to continue, with stirring, for a further one hour at 25° C. Neutralisation of the excess sodium borohydride was performed by the careful addition of 120 g water and 60g hydrochloric acid (as a 32percent aqueous solution). The pH of the neutralized reaction mixture dropped to pH 1-2, and the temperature rose from 25° C to 30° C. Phase separation was achieved by heating the mixture to 58° C, at which point two clearly distinguishable phases were observed: a heavy aqueous phase having a density of 1.15 G/ML, and a clear organic phase having a density of 1.03 g/ml. The lower, aqueous, phase (159 g) was carefully removed, following which the organic phase was washed with aqueous NaCl solution (140 g, 10percent w/w) to remove the residues of H3BO3 formed during the work-up, then the THF (267 g) was partially distilled off from the organic phase over a temperature range of 70 to 75° C in a reboiler. Crude 5-bromophthalide was then crystallized from the organic phase residue (317 g) by adding 30 g water and controlled cooling of said residue from 75° C to 30° C over a period of one hour, following which the temperature was held constant at 30° C for a further one hour. The crystallized material was filtered and washed with 100g THF. The filtration residue thus formed (113 g, LOD-25percent) was found to contain approximately 90percent 5-bromophthalide and 10percent 6-bromophthalide. In order to further purify the desired product, a slurry of 100 g of the wet, crude 5-bromophthalide was prepared in 140 g of THF containing 6percent water at 25° C. This slurry was then heated to 60° C, and held at that temperature for one hour. Re-crystallization of the 5-bromophthalide was achieved by lowering the temperature from 60° C to 25°C over a period of one hour, and then holding at the lower temperature for a further one hour. The crystallized product was then filtered and washed with 40 g of THF, following which 65 g of wet residue was dried at 80° C for a period of 2 hours. The dried product thus formed (53 g) was subjected to HPLC and NMR analysis, and was found to contain >98percent 5-bromophthalide. The direct yield was approximately 33percent. The filtrate contained approximately 21 g of a recoverable mixture of 5-bromophthalide (70percent) and 6- bromophthalide (30percent). The overall yield of this process (after recycling the mother liquor) was between 37 and 40percent.

5-Bromophthalide is a useful synthetic intermediate

Molecular Weight:213.03
XLogP3:1.5
Hydrogen Bond Acceptor Count:2
Exact Mass:211.94729
Monoisotopic Mass:211.94729
Topological Polar Surface Area:26.3
Heavy Atom Count:11
Complexity:181
Covalently-Bonded Unit Count:1
Compound Is Canonicalized:Yes