E- and chemoselective thia-Michael addition to benzyl allenoate

Mechanistic Investigations on the Interaction of Morita–Baylis–Hillman Ketones with 2-Aminothiophenol

“…Furthermore, this critical experimental detail and the complete consumption of the MBH ketone prior to the addition of the base also pose a fundamental question. The thiol moiety of the 2-aminothiophenol is anticipated to be the dominant nucleophilic entity as against the amino group, which is also corroborated by reports that describe a preferential thia-Michael addition with various acceptors. − However, the product obtained, a dihydro-1,4-benzothiazine having a 2,2-disubstitution, apparently contradicts this aspect, because it corresponds to the occurrence of an aza-Michael addition. This intriguing paradox spurred us to undertake a deeper investigation to gain insight into the actual pathway, the findings of which are described herein.…”

“…Initial spectroscopic analysis of the crude product showed it to be a possible Michael adduct. Notably, the chemical shift values in the 1 H nuclear magnetic resonance (NMR) spectrum appeared to suggest the presence of -S-CH 2 and -NH 2 protons, 15 alluding to a thia-Michael addition. We needed to isolate and characterize the adduct in its pure form to be absolutely certain of its identity, but unfortunately, repeated attempts to purify it were in vain owing to its apparently low stability.…”