In organic chemistry, the hexadehydro-Diels–Alder (HDDA) reaction is an organic chemical reaction between a diyne (2 alkyne functional groups arranged in a conjugated system) and an alkyne to form a reactive benzyne species, via a [4+2] cycloaddition reaction. This benzyne intermediate then reacts with a suitable trapping agent to form a substituted aromatic product. This reaction is a derivative of the established Diels–Alder reaction and proceeds via a similar [4+2] cycloaddition mechanism. The HDDA reaction is particularly effective for forming heavily functionalized aromatic systems and multiple ring systems in one synthetic step.
