Alkyne Cleavage and Selective Use of the Resulting Fragment as C1 Synthon

Catalytic cleavage of carbon-carbon triple bond and utilization of the resulting fragments for the synthesis of useful compounds is a challenging subject in organic synthesis. A cascade reaction, including a rhodium(III)-catalyzed oxidative (4+2) O-annulation of internal alkynes with α,β-unsaturated ketones via regioselective alkyne insertion, an in situ hydrolysis of the resulting pyrylium salts, and a dimeric copper(II)-catalyzed fragmentation reaction of the generated 1,5-diketone intermediates, was developed, enabling complete cleavage of internal alkynes and formally selective use of the resultant C1 fragments for the construction of synthetically useful furans. These results also expand the knowledge of rhodium(III) catalysis in which copper(II) acetate usually works as a terminal oxidant or cocatalyst to achieve rhodium(III) catalyst turnover rather than a catalyst to trigger the transformation of intermediate. Importantly, this synthetic protocol features broad substrate scope, late-stage functionalization, and diverse derivatizations and photochromism of the products and will have impact on multidisciplinary research.