CYCLOCARBONYLATION OF ACYCLIC 1,3-DIENES VIA THEIR TRICARBONYL IRON COMPLEXES - CYCLOPENTENE-2-ONES AND DICARBONYL CYCLOPENTADIENYL IRON HALIDES

Tricarbonyl iron complexes of acyclic 1.3-dienes can be converted to conjugated cyclopentenones by decomplexation with aluminium halides. Most complexes of simple dienes need drastic conditions for the cyclocarbonylation to occur (100 Atm CO, 100-degrees-C), with the exception of 1,1,3-trialkylbutadiene complexes which are nearly quantitatively converted into cyclopentenones at room temperature, even in the absence of a CO atmosphere. Under the same mild conditions, the other complexes lead in modest yields to cyclopentadienyl dicarbonyl iron halides by a cyclocarbonylation reaction followed by an aluminium halide promoted deoxygenation.