Photosensitizer-Promoted Photoaddition Reactions of α-Silyl Group Containing N-Alkyl Glycinates to Dimethyl Acetylenedicarboxylate (DMAD)

Photosensitizer-promoted photoaddition reactions of N-α-trimethylsilyl-N-alkylglycinates with DMAD were conducted to explore the scope of glycinate substrates and how product distributions can be influenced by structural nature of glycinates. The results show that two competitive reaction pathways are involved, in which one route is cycloaddition of in situ formed azomethine ylides to DMAD to generate pyrroles and the other is Michael addition of in situ generated secondary amines to DMAD to produce enamino-esters. Importantly, product distributions patterns are dependent on structural nature of glycinates and kinds of photosensitizers. Especially, photoaddition reaction of cyclic glycinate took place chemoselectively to produce pyrrole adduct.