Thiazolium-catalyzed and -mediated reactions

The thiazolium-catalyzed addition of an aldehyde-derived acyl anion with a Michael acceptor (Stetter reaction) is a well-known synthetic tool leading to the synthesis of highly funtionalized products. Recent developments in this area include the direct nucleophilic addition of acyl anions to nitroalkenes using silyl-protected thiazolium carbinols 06JA4932 . In the presence of a fluoride anion, carbinol 186 is not cleaved to an aldehyde 

Benzotetramisole 213 has been identified as an effective catalyst for kinetic resolution of sec-benzylic and propargylic alcohols 214 to give 215 in excellent enantioselectivity O60L1351 06OL4859 . The benzotetramisole-catalyzed kinetic resolution has been extended to 2-oxazolidinone 217 via enantioselective /V-acylation 06JA6536 . 

The C2-symmetric bifunctional tridentate bis(thiazoline) 222 has been shown to promote the zinc(II)-catalyzed asymmetric Michael addition of nitroalkanes to nitroalkenes in high enantioselectivity 06JA7418 . The corresponding bis(oxazoline) ligand provides comparable enantioselectivity but higher product yield. The same bis(thiazoline) ligand has also been evaluated in the enantioselective Friedel-Crafts alkylation of indoles, but the enantioselectivity is moderate 06OL2115 . 

The thiazolium-mediated three-component reaction of thiazolium salts 201, aryl aldehydes and dimethyl acetylenedicarboxylate provides a facile synthesis of 2-amino-2-arylfurans 202 05OL1343 . The reaction pathway may involve the sequential nucleophilic addition of thiazol-2-ylidene 203 with the aldehyde and DMAD to form the spirocyclic intermediate 204 through the simultaneous formation of two C-C bonds and a C-O bond Selective ring opening of the spirocyclic intermediate 204 followed by hydrolysis leads to 3-aminofuran 202 via 205. 

---