Synthesis and stereochemistry of new 1,3-thiazolidine systems based on 2-amino-2-(mercaptomethyl)propane-1,3-diol: 4,4-bis(hydroxymethyl)-1,3-thiazolidines and c-5-hydroxymethyl-3-oxa-7-thia-r-1-azabicyclo[3.3.0]octanes

Rationalization of Benzazole-2-carboxylate versus Benzazine-3-one/Benzazine-2,3-dione Selectivity Switch during Cyclocondensation of 2-Aminothiophenols/Phenols/Anilines with 1,2-Biselectrophiles in Aqueous Medium

“…Herein, the success of the 5- endo - trig cyclization was attributed to the soft nucleophilicity of sulfur. The thiol group (XH = SH, 1a ) attacks at the C2 (iminic carbon) of I - 1a , leading to the benzothiazoles through the 5- endo-trig pathway, in contrary to Baldwin’s rule ,− (Scheme ). However, in the case of 1,2-diaminobenzene (X = NH, 1d ) and 2-aminophenol (X = O, 1n ), the NH 2 and OH groups attack at the C1 (carbonyl carbon) of I - 1d / n , leading to the ring closure via 6- exo-trig pathway (Scheme ).…”

“…However, there are many reactions which do not follow Baldwin’s rule, and the revised and extended observations on Baldwin’s rule have been reported recently . For ring closure reactions that are not in compliance with Baldwin’s rule, density functional theory (DFT) has been widely used to rationalize the product selectivity with mechanistic insight. − Under the scope of multiple-site interactions for inter/intramolecular cyclocondensations, the local hard–soft acid–base (HSAB) principle provides the key insight to justify the unusual behavior of the reaction …”