Pd-free, Sonogashira cross-coupling reaction. An update

The Sonogashira reaction is a cross-coupling reaction used in organic synthesis to form carbon-carbon bonds. In its classical form, it uses a Pd catalyst as well as copper co-catalyst and amines as the solvents or co-solvents to form a carbon-carbon bond between a terminal alkyne and an aryl or vinyl halide. Due to the relatively high price of Pd and its toxicity, the Pd-free catalyzed Sonogashira cross-coupling reaction has attracted much attention from synthetic organic chemists, both in academia and industry. Several successful attempts have been made, which were introduced in a review article published in 2016. Due to a plethora of relevant papers that appeared in the chemical literature, in this review, we try to underline the recent advances achieved in the Pd-free Sonogashira reaction from 2016 to date.