Photochemical and thermal (2+2)-cycloaddition of thioxanthenethione to some aliphatic pentatetraenes

Reaction of thioxanthene-9-thione 1 with the alkyl substituted pentatetraenes 2a-g gives mixtures of the thietanes 3a-g and 4a-g. The ratio $\text{3}\text{4}$ in the thermal reaction is strongly dependent on the substituents. In the case of 2a thermal rearrangement of the product leads to a stable thiete.