A new general route to thiophenophanes: synthesis and properties of [n](2,5)thiophenophane-1,n-diones.

A series of [n](2,5)thiophenophane-1,n-diones (5) (n = 9, 10, 12, 14, 16, and 20) were synthesized in a simple four-step route starting from the appropriate 1,omega-oligomethylenedicarboxylic acids. The bis(halomethylketones) (6), which were obtained by successive treatment of the diacids with SOCl2, diazomethane, and HBr or HCl, were cyclized by Na2S under high dilution conditions. The obtained monomeric cyclic diketosulfides (4) were condensed with glyoxal in MeOH by slowly adding dilute NaOMe affording 5. The thiophene-2,5-dicarbonyl moiety of 5 (n = 9) is significantly deformed as shown by X-ray crystallography, and the effect of the strain is reflected in the C=O stretching frequencies and the pi-pi* and the n-pi* absorptions.