Cycloadditions carried out under reductive conditions can generally be effected with commercially available reducing agents, although a few reducing agents require special preparation. Reductive reactions employing iron carbonyl complexes should be carried out in a well-ventilated fume hood, as free carbon monoxide may be released. The optimal conditions for base-mediated cycloadditions vary somewhat, although polar media tend to give higher yields—fluorinated solvents are more effective than their non-fluorinated analogues, and alkoxide or amine bases work better than others.