Dimethyl acetylenedicarboxylate → 1,4-Dimethyl-7-aza-bicyclo[2.2.1]hepta-2,5-diene-2,3,7-tricarboxylic acid 7-tert-butyl ester 2,3-dimethyl ester

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Reaction Steps

A mixture of crude 2,5-dimethyl-pyrrole-1-carboxylic acid tert-butyl ester (prepared according to a literature (Haiser, H.-P.; et al. J. Org. Chem. 1984 49(22) 4203-4209); 500 mg) and dimethyl acetylenedicarboxylate (0.5 mL, ca 4 eq) was stirred at 120° C. under argon for 2 h. Purification by silica gel flash chomatography on SiO2 eluting with EtOAc/heptane (gradient from 1:20 to 1:2 ratio) gave compound 780A (166 mg, 50% yield) as a colorless liquid. HPLC: 90% at 3.67 min (retention time) (YMC S5 ODS-A column 4.6×50 mm eluting with 10-90% aqueous methanol over 4 mincontaining 0.2% phosphoric acid, 4 mL/min, monitoring at 220 nm).

Provenance & Evidence