1.3- Dithiolones intramolecular cycloadditions

An interesting example of an intramolecular cycloaddition reaction has been observed in the case of the mesoionic 1,3-dithiolone (97) which contains a non-activated alkyne in the same molecule. Thus, on heating (97) at 40-45 or 100 °C, the tricyclic thiophene derivative (99) is obtained via the non-isolable primary adduct (98) (81LA347). 

The observed regioselectivities during these cycloadditions have been explained in terms of qualitative frontier molecular orbital perturbation theory <78CB2028>. An intramolecular cycloaddition has been observed for the 1,3-dithiolone (111) to afford the tricyclic thiophene derivative (112) (Equation (13)) <81LA347>. 

Further examples including extrusion and ring expansion reactions <75JCS(Pi)632> as well as intramolecular [3 -I- 2] cycloadditions have been reported <81LA347>. In addition, the mesoionic 1,3-dithiolones (124) react with formaldehyde regiospecifically in a [3 -i- 2] cycloaddition reaction with formation of the 2-oxa-6,7-dithiabicyclo[2.2.1]heptanone derivative (125) (Equation (17)) <78CB3l7l>. Furthermore, upon reaction with the N=N bond of dimethyl azodicarboxylate, (126) is obtained (Equation (18)) <78CB3171>. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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