A Claisen rearrangement route to the vineomycins

Anthrarufin is converted by a high yield route involving sequential Claisen rearrangements to an intermediate (3) suitable for the synthesis of vineomycins     

Nornicotine-organocatalyzed aqueous reduction of alpha,beta-unsaturated aldehydes

Nornicotine, a native component of tobacco and minor nicotine metabolite, was found to catalyze the chemoselective reduction of alpha,beta-unsaturated aldehydes under homogeneous aqueous conditions.     

Facile three-component coupling procedure for the synthesis of substituted tetrahydroisoindole-1,3-diones from alpha,beta-unsaturated aldehydes

[reaction: see text]. A new one-pot procedure for the efficient synthesis of a small library of amino-functionalized tetrahydroisoindole-1,3-dione derivatives was developed. This three-component coupling reaction comprises subsequent condensation and Diels-Alder reactions of ubiquitous available starting materials (alpha,beta-unsaturated aldehydes, amide, and maleimide). The synthesized compounds share a substituted tetrahydroisoindole motif in an endo fashion.     

Tandem addition beta-lithiation-alkylation sequence on alpha,beta-unsaturated aldehydes

A tandem reaction between (E)-cinnamaldehyde, 1a, and phenyllithium affording beta-substituted dihydrochalcones was recently reported. NMR spectroscopic studies on the reaction mixture, as well as isotopic exchange reactions and trapping of two intermediates, provide clues on the several mechanistic steps of this new reaction. Extended studies revealed that beta-alkyl-substituted alpha,beta-unsaturated aldehydes and aliphatic lithium reagents did not afford good yields of the tandem reaction products, while aromatic lithium reagents gave good results. The aggregation features of the aryllithium reagents and the extended charged delocalization effects are considered to promote beta-selectivity. This approach provides a convenient route for the synthesis of a wide variety of beta-alkyl-substituted dihydrochalcones.     

Oxazaborolidinone-catalyzed enantioselective Diels-Alder reaction of acyclic alpha,beta-unsaturated ketones

allo-Threonine-derived O-acyl-B-phenyl-oxazaborolidinones are demonstrated to be powerful and highly enantioselective Lewis acid catalysts for the Diels-Alder reaction of simple acyclic enone dienophiles, expanding the scope of ketone dienophiles and dienes. With 10 to 20 mol % of catalyst, the Diels-Alder adducts are obtained in 76-98% ee with high endo-selectivity. The catalyst exhibits high activity for the reaction with the less reactive beta-substituted dienophiles and the less reactive 1,3-cycohexadiene and 1,3-butadiene derivatives. The application of the catalysts to the Diels-Alder reaction of furan is also described.     

Dienamine catalysis: organocatalytic asymmetric gamma-amination of alpha,beta-unsaturated aldehydes

A new concept in organocatalysis is presented, the direct asymmetric gamma-functionalization of alpha,beta-unsaturated aldehydes. We disclose that secondary amines can invert the usual reactivity of alpha,beta-unsaturated aldehydes, enabling a direct gamma-amination of the carbonyl compound using azodicarboxylates as the electrophilic nitrogen-source. The scope of the reaction is demonstrated for the enantioselective gamma-amination of different alpha,beta-unsaturated aldehydes, giving the products in moderate to good yields and with high enantioselectivities up to 93% ee. Experimental investigations and DFT calculations indicate that the reaction might proceed as a hetero-Diels-Alder cycloaddition reaction. Such a mechanism can explain the "unexpected" stereochemical outcome of the reaction.     

Organocatalytic and direct asymmetric vinylogous Michael addition of alpha,alpha-dicyanoolefins to alpha,beta-unsaturated aldehydes

The first highly regio-, chemo-, diastereo- and enantioselective direct vinylogous Michael addition of alpha,alpha-dicyanoolefins to alpha,beta-unsaturated aldehydes is described, employing readily available chiral alpha,alpha-diarylprolinol salts as iminium organocatalysts.