Ag2CO3 catalyzed aza-michael addition of pyrazoles to α, β-unsaturated carbonyl compounds: A new access to N-alkylated pyrazole derivatives

Regio- and Stereoselective Switchable Synthesis of (E)- and (Z)-N-Carbonylvinylated Pyrazoles

“…Using other solvents such as toluene and 1, 4-dioxane, the reaction efficiency was not significantly improved (Table 1, entries 6 and 7). Because Ag + easily coordinates with both the nitrogen atom of imine and oxygen atom of the carbonyl group [35][36][37][38], we envisioned that the coordination guidance of Ag + probably favors the formation of (Z)-isomer 4a. Thus, with 10 mol% of readily available Ag 2 CO 3 as the catalyst, we proceeded the reaction in DCE at 60 • C and 20 • C, respectively.…”

“…In the presence of Ag2CO3, the reaction proceeded based on Path b. Since Ag + easily coordinates with both the nitrogen atom of imine and oxygen atom of the carbonyl group [35][36][37][38], it is clear that the reaction commenced from the coordination of Ag + to N 2 of 1aa and carbonyl of 2a to form intermediate I, in which 1aa and 2a are close enough and 2a is also fully activated. Subsequently, I occurs Michael addition to produce the intermediate II, in which pyrazolyl and acyl groups are positioned cis to each other by the coordination of Ag + .…”

“…In the presence of Ag 2 CO 3, the reaction proceeded based on Path b. Since Ag + easily coordinates with both the nitrogen atom of imine and oxygen atom of the carbonyl group [35][36][37][38], it is clear that the reaction commenced from the coordination of Ag + to N…”

“…Furthermore, by controlling the reaction conditions, the regioselective synthesis of isomeric 3-(1-substituted pyrazol-3(5)yl) indoles was also successfully realized when βethyltho-β-indolyl-α, β-unsaturated ketones reacted with monosubstituted hydrazines [34]. Subsequently, we developed the Ag 2 CO 3 -catalyzed aza-Michael addition of pyrazoles to α, βunsaturated carbonyl compounds, to afford a series of N-alkylated pyrazoles in excellent yields and with high regioselectivity [35]. As a continuation of our interest in the synthesis of pyrazole derivatives, most recently, we studied the regio-and stereoselective aza-Michael addition of pyrazoles and conjugated carbonyl alkynes for the switchable synthesis of (E)-and (Z)-Ncarbonylvinylated pyrazoles (Scheme 1D).…”