Regioselectivity of conjugate addition of secondary amines and thiols to α-substituted enyne aldehydes

Abstract

The reaction of 2,5-disubstituted (Z,E)-pent-2-en-4-ynals with secondary amines and thiols has been studied. It is found that only the triple bond is subjected to nucleophilic attack. The interaction of polyunsaturated aldehydes with piperazine leads to a mixture of addition products at the triple bond with the participation of one or both NH-groups. Organogermanium enynal - 2-(butylthio)-5-(triethylgermyl)pent-2-en-4-ynal, gives products of addition at the triple bond with pyrrolidine both with retention and with cleavage of the triethylgermyl group. The regioselectivity of the addition of nucleophiles to α-substituted enyne aldehydes is explained within the framework of DFT methods by comparing both the reactivity indices for competing electrophilic centers (electrophilic Parr functions) and the thermodynamic stability of the resulting products.