Copper-assisted cycloisomerization

This system was described in one report and has been synthesized by a copper-assisted cycloisomerization of alkynyl imines. The authors proposed the following mechanism at first, 372 could undergo a base-induced propargyl-allenyl isomerization to form 373 next, coordination of copper to the terminal double bond of the allene (intermediate 374) would make it subjected to intramolecular nucleophilic attack to produce a zwitterion 375. The latter would isomerize into the more stable zwitterionic intermediate 376, which would be transformed to the thiazole 377 (Scheme 55) <2001JA2074>. 

Kel in et al. reported that the copper-assisted cycloisomerization of the alkynyl imines 320 gave the pyrroles 321 in high yields (Scheme 101).169 Mechanistic studies revealed that this reaction proceeded via the propargyl-allenyl isomerization of 320 to the... 

Gevorgyan describes a novel copper-assisted cycloisomerization of alkynyl imines 31 to 2,5-disubslituted pyrroles 32 as well as fused systems containing a pyrrole ring <01JA2074>. It was found that utilization of easily deprotectable N-substituents such as trityl or 3-(ethylbutyryl) (EB) groups allows for facile access to IV-unsubstituled pyrroles. 

---