Expedient synthesis of highly substituted fused heterocoumarins.

[reaction: see text] Highly substituted fused coumarins can be prepared in two steps starting from the appropriate boronic acids and enol triflates. The synthesis of fused pyrano[2,3-d]pyrimidin-7-one (1) is a key example to demonstrate the potential of the method in the elaboration of new coumarin scaffolds.