2H,6H-Thiin-3-ones

The absorption maximum around X 210 nm for simple dialkyl sulfides [11], corresponding to a n-o transition, experiences an important bathochromic shift for p-ketosulfides (X 240 nm) [12] due to a conjugative effect between the two functional groups. This interaction is illustrated in the spectra of 2H,6H-thiin-3-ones [13] and also of their corresponding 1-oxides [14], with the appearance of an additional absorption band around 275 nm that does not appear in the spectrum of e.g. 2fl, 6fl-pyran-3-ones [15] (Scheme 1). 

In contrast, the corresponding sulfoxides do undergo such a bond rupture between the allylic C-atom and the neighboring S-atom as a first chemical step after photoexcitation.As shown in Scheme 15, 2H,6H-thiin-3-one-l-oxides 47 photoisomerize to 3H,7H-l,2-oxathiepin-4-ones 48, which undergo a further thermal ring contraction to thietanone-1-oxides 49 via a 2,3-sigmatropic rearrangement. 

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