Trifluoroacetic acid → 1-Benzyl-4-(3,4-difluoro-phenyl)-2,5-dihydro-1H-pyrrole-3-carboxylic acid

Participants

Reaction Steps

At r.t., trifluoroacetic acid (0.11 ml, 1.34 mmol, 0.1 eq.) followed by N-(methoxymethyl)-N-(phenylmethyl)-N-(trimethylsilyl)methylamine (4.89 g, 20.2 mmol, 1.5 eq.) were added dropwise to a stirred solution of (3,4-difluoro-phenyl)-propynoic acid ethyl ester (2.83 g, 13.5 mmol) in CH2Cl2 (80 ml). The yellow solution was stirred at r.t. for 18 h. Trifluoroacetic acid (0.034 ml, 0.44 mmol, 0.033 eq.) and N-(methoxymethyl)-N-(phenylmethyl)-N-(trimethylsilyl) methylamine (1.66 g, 6.73 mmol, 0.5 eq.) were added, and the solution was stirred for 1 h. It was evaporated to dryness, and the residue was dissolved in dioxane (40 ml). An aqueous solution of NaOH (18.7 ml, 37.4 mmol, 2.8 eq.) was added. The resulting emulsion was stirred at r.t. for 18 h, and the low boiling organic solvent was removed under reduced pressure. Water (40 ml) was added, and the aqueous layer separated and washed twice with TBME (50 ml). The organic layers were washed with the same portion of water (15 ml). The combined aqueous layers were acidified by addition of aqueous 3M HCl (12.4 ml). The resulting suspension was stirred for 48 h at r.t. The white precipitate was filtered off, washed with water and ethanol and dried under high vacuum to yield 4.25 g (58%) of IIc as a white solid.

Provenance & Evidence