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Keywords
- 1,2,4-Dithiazole (1)
- 1,2-Dithiole (1)
- 2-Alkylidene-4-oxothiazolidine (1)
- 4-Oxothiazolidine (1)
- CH center dot center dot center dot O hydrogen bonds (1)
- Condensed thiazolidines (1)
- Density functional calculations (1)
- Diastereoselectivity (1)
- Push-pull character (1)
- Quantum chemical calculations (1)
- Rearrangement to trithiaazapentalene (1)
- Sulfoxide (1)
- Trithiapentalene (1)
- Vinylogous N-acyliminium ion (1)
- endo-Mode cyclization (1)
Institute
Syntheses of thiazolidine-fused heterocycles via exo-mode cyclizations of vinylogous N-acyliminium ions incorporating heteroatom-based nucleophiles have been examined and discussed. The formation of (5,6)-membered systems was feasible with all nucleophiles tried (O, S and N), while the closing of the five-membered ring was restricted to O- and S-nucleophiles. The closure of a four-membered ring failed. Instead, the bicyclic (5,6)-membered acetal derivative and the tricyclic system with an eight-membered central ring were obtained from the substrates containing O and S nucleophilic moieties, respectively. The reaction outcome and stereochemistry are rationalized using quantum chemical calculations at B3LYP/6-31G(d) level. The exclusive cis-stereoselectivity in the formation of (5,6)- and (5,5)-membered systems results from thermodynamic control, whereas the formation of the eight-membered ring was kinetically controlled.