Iron-catalysed highly selective hydroalkoxycarbonylation of alkynes using CO as C1 source†

Though precious and rare, late-transition metals have been extensively used in metal-catalysed carbonylation reactions in organic transformations. On the other hand, base metals are abundant and cheap, but their practical utilization in carbonylation reactions is rarely explored. Here, we report iron-catalysed hydroalkoxycarbonylation of alkynes to α,β-unsaturated esters in one pot. A readily available iron precursor [Fe₂(CO)₉] in the presence of a diimine ligand L7 catalyzes the conversion of alkynes to α,β-unsaturated esters under 10 bar CO pressure. This operationally simple protocol tolerates various functional groups and allows facile access to about 40 α,β-unsaturated esters. The synthetic utility of the reaction has been demonstrated by scaling up the reaction to 1 g and by preparing sunscreen/antifungal agents. The kinetic study suggests that the reaction is an approximate 1st order with respect to the iron catalyst, and the initial rate of the reaction is 3.6 × 10⁻² M h⁻¹. Mechanistic investigations using NMR spectroscopy indicated the existence of an [Fe–H] intermediate, and control experiments using a radical trapping reagent and EPR revealed the absence of any radical species in the reaction.