Synthesis and Photochemistry of 2,2-Dimethyl-3(2H)-thiophenone, a Ketonic Tautomer of 3-Hydroxythiophene. Preliminary Communication

On irradiation (λ = 366 nm), the 4‐thia‐2‐cyclopentenone 3a behaves in complete analogy to the oxa‐enone 3c undergoing regio‐ and stereospecific cyclodimerization, regiospecific cycloaddition with 2‐methylpropene and cycloaddition with 2,3‐dimethyl‐2‐butene to afford cyclobutane derivatives. In contrast, the 4‐aza‐2‐cyclopentenone 3b does not undergo the above‐mentioned reactions but only slow photodecomposition.