We report the discovery of an anomalous reaction of 2‐(alkynonyl)alkynylbenzenes under AgI catalysis for the selective formation of isocoumarins. This reaction is previously undocumented for 2‐(alkynonyl)alkynylbenzenes in terms of the reaction me...
We report the discovery of an anomalous reaction of 2‐(alkynonyl)alkynylbenzenes under AgI catalysis for the selective formation of isocoumarins. This reaction is previously undocumented for 2‐(alkynonyl)alkynylbenzenes in terms of the reaction mechanism and the product formed. Water (H2O18) labeling studies suggested a possible mechanistic pathway in which the initial formation of a pyrylium ion is followed by hydrative dealkynylation, that is, water incorporation and alkyne expulsion, similar to a retro‐Favorskii reaction.
Silver strikes a new route: AgI promotes an unusual conversion of 2‐(alkynonyl)alkynylbenzenes to biologically relevant and structurally divergent isocoumarins (see scheme). Isocoumarin formation is highly dependent on the substituents present on the simple alkyne unit rather than the alkynone of 2‐(alkynonyl)alkynylbenzene. The mechanism involves a hydrative retro‐Favorskii‐reaction‐like dealkynylation process via an initial pyrylium ion intermediate.