and the mixture was allowed to stir for 90 minutes the mixture was cooled to u2212 78 u00b0 c and treated with 4 n methoxy n methylcarboxamido 1 piperidinecarboxylic acid 1 1 dimethylethyl ester 9 20 g 33 8 mmol in thf 50 ml anhydrous via syringe the cooling dry ice acetone bath was removed and the mixture was allowed to come to room temperature after stirring for 3 hours saturated aqueous nh 4 cl was added and the mixture was allowed to stir overnight the layers were separated and the aqueous layer was extracted with ether the combined organic layers were washed with brine dried mgso 4 filtered and evaporated to afford an amber oil the oil was chromatographed on silica gel eluting with 20 etoac in hexane the appropriate fractions were combined and evaporated to an amber oil the oil was distilled to afford 4 2 3 dimethoxybenzoyl 1 piperidinecarboxylic acid 1 1 dimethylethyl ester as a colorless oil b p 225 250 u00b0 c 05 mm anal calcd for c 19 h 27 no 5 c 65 31 h 7 79 n 4 01 found c 65 04 h 7 92 n 4 11 4 2 3 dimethoxybenzoyl 1 piperidinecarboxylic acid 1 1 dimethylethyl ester 7 75 g 22 2 mmol was dissolved in trifluoroacetic acid 50 ml 650 mmol and stirred for 45 minutes.