Photocleavage Reactions of Monothioimides

The photochemistry and crystal structures of four monothioimides have been studied: N-phenyl-3-phenyl-N-[phenyl(thiocarbonyl)]propanamide, C₂₂H₁₉NOS, (1a); N-(4-bromophenyl)-N-[phenyl(thiocarbonyl)]-3-phenyl-propanamide, C₂₂H₁₈BrNOS, (1b); N-(4-bromo-2,6-dimethylphenyl)-3-phenyl-N-[phenyl(thiocarbonyl)]propanamide, C₂₄H₂₂BrNOS, (1c); and N-[4-methoxyphenyl(thiocarbonyl)]-N-phenyl-3-phenylpropanamide, C₂₃H₂₁NO₂S, (1d). All four molecules adopt similar (E_S,Z_O) conformations, which are not suitable for photochemical γ-hydrogen abstraction; short intramolecular O...C(S) contacts (2.8 Å) suggest a new mechanism with nucleophilic attack by the carbonyl O atom on the C=S double bond; the presence of water is also essential for the reaction to proceed.

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