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-phenylpropanamide, C22H18BrNOS, (1b); N-(4-bromo-2,6-dimethylphenyl)-3-phenyl-N-[phenyl(thiocarbonyl)]-propana mide, 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 gamma-hydrogen abstraction; short intramolecular O ... C(S) contacts (2.8 Angstrom) 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.