Acylcobalt salophen reagents. Precursors to acyl radical intermediates for use in carbon-to-carbon bond-forming reactions to alkenes

Abstract

Acylcobalt salophen reagents (6) are conveniently synthesised from carboxylic acid chlorides following treatment with the sodium derivative (5) produced from reduction of cobalt(II) salophen with sodium amalgam in tetrahydrofuran at room temperature. The acylcobalt salophens (6) undergo homolytic cleavage in the presence of light from a conventional 300 W sunlamp to give acyl radicals (24) which then undergo additions to activated carbon-to-carbon double bonds, leading to enones, viz.(26)[following dehydrocobaltation from presumed organocobalt intermediates (25)], or saturated ketones, viz.(34)[following H-quenching of intermediates (25)]. Intramolecular cyclisations of the acylcobalt salophens (42a) and (42b) lead to the ylidenecyclopentanones (43) and (45), respectively.