Study of the pyrimidine nucleobase C5C6 bond reactivity under thio-michael/aldol tandem reaction conditions

Pyrimidine nucleobases can undergo a Michael/aldol tandem reaction triggered by a thiolate. In an intramolecular context, 5'-deoxy-2',3'-isopropylidene-5'-thiouridine affords the reminiscent Baylis-Hillman adduct after retro-Michael addition whereas its thymine counterpart is unreactive. In an intermolecular context, the conjugate addition-aldol reaction occurs only if the C5-C6 double bond is activated.