Conjugated Ynones in Organic Synthesis

This review article will consider the preparation and application of ynones in synthetic organic chemistry. Concerning the preparation of these bifunctional compounds, several methodologies starting from propargyl alcohols, acyl derivatives, both by using alkynylmetal reagents or by transition metal (mainly palladium and copper) catalyzed alkynylations, carbon monoxide (carbonylation of terminal alkynes and alkenes), and other substrates will be discussed. The reactivity and synthetic applications of ynones will be focused on conjugate additions with boron-, carbon-, nitrogen-, oxygen-, and other heteroatom-containing nucleophiles, as well as radicals. Then, cycloaddition processes will include [2 + 2] cycloadditions, [3 + 2] 1,3-dipolar cycloadditions (with azides, nitrones, azomethine imines and ylides, nitrile oxides, diazo compounds, and other dipoles), and [4 + 2] cycloadditions (mainly Diels-Alder-type reactions). The reduction of the triple bond, addition to the carbonyl group (using carbon- and heteronucleophiles and reductions), and other not so commonly used processes (such as aldol reactions, cyclizations, and isomerizations) will be considered at the end.