3,5-dimethylpyrrole-2-carboxaldehyde 616mg (5.00 mmol) and TOSMIC 1.070g(5.5 mmol) solution in anh THF 10mL was cooled to 0C and a solution of DBU 835mg (5.5 mmol) in anh THF 10mL was added dropwise over 5 min. The cooling bath was removed and stirring was continued at RT for 12 hours (overnight). The reaction mixture was applied onto a short column of silica in dichloromethane-ethyl acetate 20:1 and eluted with the same mixture. The bright-yellow band was collected. The purified material was re-crystallized from a mix of benzene 10mL and cyclohexane 40mL. Y=1.185g (79%) of a light-yellow soft crystalline solid.
1H(CDC3, 400MHz): 8.443(d, 1.6Hz, 1H), 8.158(d, 1.6Hz, 1H), 7.933(app d, 8.2Hz, 2H), 7.297(app d, 8.6Hz, 2H), 6.600(s, 1H), 2.487(s, 3H), 2.395(s, 3H), 2.363(s, 3H); 13C(CDCl3, 100MHz): 144.07, 137.82, 137.12, 135.91, 129.67(2C), 128.46(2C), 126.58, 122.44, 119.37, 115.97, 114.02, 21.92, 11.41, 10.55
Ten additional pyrrole-2-aldehydes provided these pyrrolopyrimidine sulfones with very good yields. From the available aldehyde set, the only pyrrole aldehyde that failed was methylester of 2-formylpyrrole-5-carboxylic acid. (The Me-ester in 4-position of 2-pyrrolecarboxaldehyde worked fine). TOSMIC can be replaced with methylester of isocyanoacetic acid but the yield is lower than with TOSMIC.
The sulphone group in these pyrrolopyrimidine cannot be displaced with a nucleophile but the Ts group can be reduced off with Na-Hg/K2HPO4.