Four-membered ring cyclic ketene –O,O–, –O,S–, –O,N–, –S,S–, –S,N–, and –N,N–acetals and their corresponding cations: a computational study

Facile access to thieno[2,3-b]thiophenes and poly-substituted thiophenes through divergent annulation of ketene 1,3-dithietanes

“…In the presence of AlCl 3 (20 mol%) and Tf 2 O (20 mol%), the reaction of 1a and 2m in a 1 : 2 molar ratio went well in DCE at 90 °C for 24 h under a nitrogen atmosphere, affording 3m in a higher yield of 78% (Table 1, entry 18). Significant solvent effects have also been observed, and DCE demonstrated superiority in this reaction over DMF, dioxane, Ac 2 O, EtOH and CH 3 CN (Table 1, entries [19][20][21][22][23]. Next, to demonstrate the effect of temperatures, the reaction was performed at 70 °C and 100 °C respectively.…”

“…17,18 In most studies, the ketene dithioacetal motif was generally designed to end with a five-or six-mem- bered ring system. 19,20 Thus, we envisioned whether a ketene dithioacetal (also named ketene 1,3-dithietanes) 21,22 anchoring to a more ring-strained four-membered ring would display viable synthetic potential. On one hand, it is thought that four-membered ring cyclic ketene 1,3-dithietanes retain the nucleophilic reactivity of ketene dithioacetals, displaying a versatile 1,3-dipole character.…”

Four-Membered Rings With Two Oxygen Atoms

“…Nevertheless, a computational study has been done on four-membered cyclic ketene-X,X-acetals (X being O, NMe or S heteroatoms) and their corresponding cations (Scheme 17). 57 Calculations with the MP2/cc-pvtz method indicated that 1,3-dioxetane 6 belongs to the C 2v symmetry group, whereas the cationic form 20 belongs to the C s symmetry group.…”