Chiral Spirophosphoric-Acid-Catalyzed Divergent Vinylogous Mannich and aza-Friedel-Crafts Reactions of 2-Methoxyfuran

The first enantioselective vinylogous Mannich reaction is developed using 2-methoxyfuran under chiral spirophosphoric acid catalysis. The strategy involves 4-isoxazoline derivatives as cyclic ketimine surrogates and provides γ-butenolide scaffolds (up to 97% ee and >20:1 dr). The mechanistic investigations suggest that an in situ generated water molecule plays a crucial role in delivering γ-butenolide, while the use of molecular sieves delivers aza-Friedel-Crafts products. The synthetic utility of γ-butenolide is shown toward obtaining piperidone skeleton via a lactone-lactam rearrangement.

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

An efficient approach to trans-4-hydroxy-5-substituted 2-pyrrolidinones through a stereoselective tandem Barbier process: divergent syntheses of (3R,4S)-statines, (+)-preussin and (−)-hapalosin

Natural products of (+)-preussin and (−)-hapalosin have been asymmetrically synthesized through the stereoselective tandem Barbier process.

A versatile access to vicinal diamine motifs by highly anti-selective asymmetric vinylogous Mannich reactions: an efficient total synthesis of (+)-absouline

An anti-stereoselective vinylogous Mannich reaction between 2-TBSO-pyrrole and N-tert-butanesulfinyl imines and its application to the efficient synthesis of (+)-absouline were reported.

The asymmetric total synthesis of (+)-N-acetyl norloline

The asymmetric total synthesis of (+)-N-acetyl norloline, the putative biogenic precursor of all known loline alkaloids, has been achieved in 12 steps from a commercially available compound.

Aza-Knoevenagel-type condensation of secondary amides: direct access to N-monosubstituted β,β-difunctionalized enamines

An efficient approach toN-monosubstituted β,β-difunctionalized enamines, a class of versatile building blocks for the synthesis of bioactive compounds, is reported.