Doubly Decarboxylative Synthesis of 4-(Pyridylmethyl)chroman-2-ones and 2-(Pyridylmethyl)chroman-4-ones under Mild Reaction Conditions.

The doubly decarboxylative Michael-type addition of pyridylacetic acid to chromone-3-carboxylic acids or coumarin-3-carboxylic acids has been developed. This protocol has been realized under Brønsted base catalysis, providing biologically interesting 4-(pyridylmethyl)chroman-2-ones and 2-(pyridylmethyl)chroman-4-ones in good or very good yields. The decarboxylative reaction pathway has been confirmed by mechanistic studies. Moreover, attempts to develop an enantioselective variant of the cascade are also described.

Hydroxyl-group-activated azomethine ylides in organocatalytic H-bond-assisted 1,3-dipolar cycloadditions and beyond.

1,3-Dipolar cycloaddition constitutes a powerful means for the synthesis of five-membered heterocycles. Recently, the potential of this field of chemistry has been expanded by the employment of organocatalytic activation strategies. One group of substrates, namely imines derived from salicylaldehydes, is particularly useful. Additional activation via intramolecular H-bonding interactions offered by the presence of an ortho-hydroxyl phenolic group in their structure results in increased reactivity of these reactants. Furthermore, it can be utilized in subsequent reactions creating chemical and stereochemical diversity. This minireview provides a summary of the recent progress in this field of organocatalysis and indicates other important applications of hydroxyl-group-activated azomethine ylides in asymmetric organocatalysis.

Enantioselective Synthesis of Chromanones Bearing an α,α-Disubstituted α-Amino Acid Moiety via Decarboxylative Michael Reaction.

In this manuscript, a novel, decarboxylative Michael reaction between α-substituted azlactones and chromone-3-carboxylic acids is described. The reaction proceeds in a sequence Michael addition followed by decarboxylative deprotonation, and it results in the formation of chromanones bearing an azlactone structural unit. The possibility of transforming an azlactone moiety into a protected α,α-disubstituted α-amino acid derivative is also demonstrated.

Decarboxylative, trienamine mediated cycloaddition for the synthesis of 3,4-dihydrocoumarin derivatives.

In this Communication, a new approach for trienamine chemistry is described. It is based on the application of carboxylic-acid-activated dienophiles that undergo spontaneous decarboxylative protonation after the initial [4 + 2]-cycloaddition step. The utilization of such a novel cascade reaction for the synthesis of biologically relevant 3,4-dihydrocoumarins has been demonstrated. High levels of enantiocontrol and excellent yield of the cascade reaction have been achieved by the use of diphenylprolinol diphenylmethylsilyl ether.

Organocatalytic Synthesis of cis-2,3-Aziridine Aldehydes by a Postreaction Isomerization.

An unprecedented organocatalytic cis-selective aziridination of α,ß-unsaturated aldehydes is described. The strategy utilizes postreaction isomerization as a key step. Our study demonstrates that by a proper choice of structural features of reagents and the catalyst the outcome of well-established reactions can be altered, leading to the formation of normally inaccessible diastereomers. The usefulness of the developed approach has been confirmed in the syn-selective formal aminohydroxylation of α,ß-unsaturated aldehydes.