Titanocene-Catalyzed Cyclocarbonylation of o-Allyl Aryl Ketones to γ-Butyrolactones

A method for the transformation of o -allyl aryl ketones to γ-butyrolactones using a catalytic amount of Cp 2 Ti(PMe 3 ) 2 or Cp 2 Ti(CO) 2 is described. This catalytic “hetero Pauson−Khand”-type process proceeds via the carbonylation of an oxatitanacycle followed by thermally-induced reductive elimination to form a γ-butyrolactone and to regenerate the catalyst. We have investigated the scope and limitations of this catalytic methodology. Our results are consistent with the view that the key step in this catalytic cycle is formation of a charge transfer complex or involves reversible electron transfer between the catalyst and the substrate.