Stereoselective organocascades: from fundamentals to recent developments

Reaction sequences where more bonds are sequentially formed (cascade reactions) may be started either by a stoichiometric or by a catalytic reagent, and proceed in an enantio- diastereo- or non-stereo- selective manner. A wide variety of such strategies has been developed, including both stoichiometric and catalytic ones.

Within the widely developed cascade reactions field, this chapter is not meant to be omni-comprehensive, but to offer an as much as possible complete overview on organocatalytic stereoselective methods. We embrace the more general definitions by Tietze and Denmark, considering as cascade reactions all those one-pot processes that involve two or more bond formations, where each subsequent step is enabled by a structural change caused by the previous one. We will include both two- and multi-component reactions where one or more organocatalysts may be responsible either for all or just some of the occurring transformations. Organocascades will be reported according to the number of involved catalytic cycles.

In the following paragraphs, only cascade reactions that are stereoselective by means of a chiral catalyst will be considered. It will be shown that multiple possibilities, relying on different catalysis modes, are available to achieve the same reaction sequence.

A single pot organocatalytic diastereoselective synthesis of fluorescent ring fused 2-pyridone decalines via a domino Knoevenagel/Michael/hydro-lactamisation sequence

A highly efficient one-pot triple cascade approach is developed to synthesise fluorescent, fused, octahydro-2-pyridone decalines in good to excellent yields using l-proline/PhCOOH as an organocatalyst.

Fluorine effects in organocatalysis - asymmetric Brønsted acid assisted Lewis base catalysis for the synthesis of trifluoromethylated heterocycles exploiting the negative hyperconjugation of the CF3-group

An efficient Brønsted acid assisted Lewis base catalysis protocol for the synthesis of enantiomerically pure trifluoromethylated dihydropyridazines starting from readily available hydrazones and α,β-unsaturated aldehydes has been developed. The reaction exhibits high tolerance towards many functional groups and is applicable to various aliphatic, aromatic and hetero-aromatic α,β-unsaturated aldehydes, and provides the products in good yields and with excellent enantioselectivities.

Recyclable Bi2WO6-nanoparticle mediated one-pot multicomponent reactions in aqueous medium at room temperature

Room temperature multicomponent reactions (MCRs) are reported using Bi₂O₃, BiVO₄, and Bi₂WO₆ (nanoparticle) as heterogeneous catalysts. Among these, Bi₂WO₆ (5 mol%) nanoparticles showed excellent reactivity for the synthesis of functionalized dihydropyridine, polyhydroquinoline, 4H-chromene and 2-amino-4H-benzo[b]pyran derivatives in aqueous medium.