Copper-Catalyzed Protoboration of 1,3-Diynes as a Platform for Iterative Functionalization

This paper presents the protoboration of 1,3-diynes as
a platform
for the iterative functionalization of various groups on enynes and
dienes. Synthetic approaches to targets with high complexity are directed
toward using small, modular building blocks similar to a “Lego”
construction using iterative chemistry and automated synthesis. Organoboron
compounds are currently in the spotlight for achieving these goals.
Here, we report an operationally simple, regioselective protoboration
of 1,3-diynes using a mixed diboron reagent and Cu(I)/phosphine catalyst
to provide enynylboronates in good yields. Under similar conditions,
diprotoboration of 1,3-diynes was also achieved to access bench-stable
1,4-diboryl-1,3-dienes in good yields and regioselectivities. The
iterative coupling capabilities of the products have been demonstrated
along with other downstream transformations offering a range of value-added
skeletons.