Pyridine → 3-(N-Tosyl-L-alaninyloxy)-1-methyl-5-phenylpyrrole

Participants

Reaction Conditions

Reaction Steps

To a mixture of deoxygenated methanol (15.5 ml) and 3-acetoxy-1-methyl-5-phenylpyrrole (11) (1.3 g, 6.2 mmole), under argon, was added deoxygenated NaOH (2N, 12.5 ml). The reaction mixture was stirred in an ice-bath for 15 minutes. Then deoxygenated citric acid (2M, 7 ml) was added and the resulting mixture was stirred in an ice bath for 8 minutes. The reaction mixture was concentrated under reduced pressure, then 20 ml of water was added and was extracted twice with ethylacetate (EtOAc) (50 ml). The EtOAc layers were combined, dried over MgSO4, filtered and concentrated under reduced pressure to give 3-hydroxy-1-methyl-5-phenylpyrrole (12) as an orange residue. Under argon, a cold solution of anhydrous THF (12.4 ml), pyridine (0.6 ml, 7.4 mmole, 1.2 eq) and trifluoroacetic acid (1.2 ml, 15 mmole, 2.4 eq) was added to the orange residue, followed immediately by the addition of a solution of freshly prepared N-tosyl-L-alaninyl chloride (1.2 g, 7.4 mmole, 1.2 eq) in anhydrous THF (12.4 ml). The resulting mixture was stirred for one hr at 0° C. Then the reaction was quenched by the addition of aqueous citric acid (1M, 5ml) and EtOAc (30 ml). After a brief mixing, the layers were separated and the organic layer was successively washed with saturated NaCl solution, twice with 5% NaHCO3 solution and again with saturated NaCl solution. The EtOAc extract was then dried over MgSO4, treated with Norit 211, filtered and concentrated under reduced pressure to give the crude product (13) as an orange residue. This was dissolved in hexane: EtOAc (1:1) (5 ml) and chromatographed on a column (SiO2, 100 g) by elution with hexane:EtOAc (7:3) to give 1 g of (13) as a thick light orange oil. A portion of this crude product was further purified by semi-preparative HPLC (column, IBM silica, 1 cm×25 cm; mobile phase, hexane:EtOAc 8:2; flow rate, 4.0 ml/min; pressure, 0.2 psi) to yield a honey color thick oil (13).

Provenance & Evidence