The use of ethylene glycol (15% v/v in toluene) as additive in the catalytic Pauson–Khand
reaction (PKR) is reported. In most cases both the yield and selectivity were enhanced
compared to standard protocols. Moreover, the immiscibility of ethylene glycol in
toluene allowed recycling of the catalyst (which remained mainly in the ethylene glycol).
The recycling allowed catalyst loading to be reduced to only 3 mol%. A gram-scale
reaction was also performed, allowing the use of only 1 mol% of Co2(CO)8, the lowest amount reported so far in intermolecular cobalt-catalyzed PKR.
Key words
Pauson–Khand Reaction - homogeneous catalysis - cyclization - cobalt - additives -
cyclopentenones - cycloaddition - catalyst recycling