Asymmetric isochalcogenourea-catalysed (4 + 2)-cycloadditions of -quinone methides and allenoates.

Chiral isochalcogenoureas ( isothioureas and isoselenoureas) catalyse the asymmetric (4 + 2)-cycloaddition of various allenoates with -quinone methides. This approach provides straightforward access to different chromane derivatives with high enantioselectivities, good yields, and control of the configuration of the exocyclic double bond. Furthermore, some of the novel -quinone methides used herein were successfully integrated into the Mayr reactivity scale by determining their electrophilicity parameter.

Enantioselective α-heterofunctionalization reactions of catalytically generated C1-Lewis base enolates.

Chiral Lewis base (LB) organocatalysis has emerged as a powerful covalent catalysis concept which allows for highly selective asymmetric C-C and C-heteroatom bond formations. Considering significant recent progress in the development of strategies to access α-heterofunctionalized carboxylic acid derivatives under chiral LB catalysis, we wish to summarize the most significant concepts and advances in this field within this mini review now.

Enantioselective Syntheses of 3,4-Dihydropyrans Employing Isochalcogenourea-Catalyzed Formal (4+2)-Cycloadditions of Allenoates.

We herein successfully demonstrate the use of chiral isochalcogenoureas as Lewis Base catalysts for a variety of (4+2)-cycloaddition reactions of allenoates and different Michael acceptors. In all cases the same structural key-motive, a dihydropyran with a (Z)-configurated exocyclic double bond could be accessed as the major regio- and diastereoisomer in an enantioselective manner. Furthermore, these chiral dihydropyrans were successfully engaged in different follow-up transformations.

Photochemical Wolff Rearrangement Initiated Generation and Subsequent α-Chlorination of C1 Ammonium Enolates.

The enantioselective synthesis of α-chlorinated carboxylic acid esters with er up to 99:1 and yields up to 82% was achieved via a one-pot multistep protocol starting from α-diazoketones. This process proceeds via a photochemical Wolff rearrangement, trapping of the generated ketene with a chiral Lewis base catalyst, subsequent enantioselective α-chlorination, and a final nucleophilic displacement of the bound catalyst. The obtained products were successfully utilized for stereospecific nucleophilic displacement reactions with - and -nucleophiles.