Synthesis of simple diynals, diynones, their hydrazones, and diazo compounds: precursors to a family of dialkynyl carbenes (R(1)-C≡C-C-C≡C-R(2)).

A variety of substituted pentadiynols, -diynals, and -diynones have been prepared en route to precursors to dialkynyl carbenes (R(1)-C≡C-C-C≡C-R(2)). In light of the marginal stability associated with these simple systems, several strategies were required to assemble the carbon backbones. The requisite five-carbon skeletons were prepared using 4 + 1, 3 + 2, 2 + 2 + 1, and 2 + 1 + 1 + 1 coupling methodologies. The Dess-Martin periodinane serves as an excellent method for the oxidation of pentadiynols to diynals and diynones, although many of the oxidized products are sufficiently reactive that they were not isolated; rather, they were generated in situ and intercepted with nucleophiles such as tosylhydrazide or trisylhydrazide. The hydrazone derivatives are generally reliable precursors to diazo compounds and carbenes, although cyclization of the hydrazone to afford a pyrazole can be a complicating factor in certain instances.