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To the Compound 2a (106 mmol) in anhydrous methanol (100 ml) was added methyl 3-aminocrotonate (106 mmol) and methyl acetoacetate (106 mmol) and the resulting solution heated at reflux under nitrogen for 4 days. The solvent was removed in vacuo to give a viscous yellow oil which was diluted in diethyl ether (75 ml) and then hexane (50 ml). After stirring overnight, a yellow solid was collected by filtration and purified by flash chromatography on silica gel eluted with hexane:diethyl ether (1:2) to give Compound 2b as a yellow solid (Rf =0.4, m.p. 140°-148°).

1. temperaturethe resulting solution heated
2. temperatureat reflux under nitrogen for 4 days
3. customThe solvent was removed in vacuo
4. customto give a viscous yellow oil which
5. filtrationa yellow solid was collected by filtration
6. custompurified by flash chromatography on silica gel
7. washeluted with hexane:diethyl ether (1:2)