Asymmetric syn ‐1,3‐Dioxane Construction via Kinetic Resolution of Secondary Alcohols Using Chiral Phosphoric Acid Catalysts

Intramolecular Silanoxy-Michael Reactions with Pendant Nitroalkenes: Racemic and Enantioselective

We present the first racemic and scalemic examples of di-tert-butyl silanoxy-Michael additions. Our operationally simple protocol is selective for nitro-olefins and simply involves stirring the substrate with an appropriate hydrogen-bond donor catalyst without any special precautions to exclude air or moisture. For each substrate examined, we have developed complementary protocols that optimize yield and enantioselectivity. Our reactions scale well, and the products are valuable intermediates for further transformations, including for the preparation of enantioenriched vicinal amino alcohols.

Organocatalytic Access to Tetrasubstituted Chiral Carbons Integrating Functional Groups

Three-dimensional organic structures containing sp³ carbons bearing four non-hydrogen substituents can provide drug-like molecules. Although such complex structures are challenging targets in synthetic organic chemistry, efficient synthetic approaches will open a new chemical space for pharmaceutical candidates. This review provides an account of our recent achievements in developing organocatalytic approaches to attractive molecular platforms based on optically active sp³ carbons integrating four different functional groups. These methodologies include asymmetric cycloetherification and cyanation of multifunctional ketones, both of which take advantage of the mild characteristics of organocatalytic activation. Enzyme-like but non-enzymatic organocatalytic systems can be used to precisely manufacture molecules containing complex chiral structures without substrate specificity problems. In addition, these catalytic systems control not only stereoselectivity but also site-selectivity and do not induce side reactions even from substrates with rich functionality.

Dynamic kinetic resolution of transient hemiketals: a strategy for the desymmetrisation of prochiral oxetanols

Identification of an electron poor trifluoroacetophenone allows the formation of uniquely stable hemiketals from prochiral oxetanols. When exposed to a cobalt(ii) catalyst, efficient ring-opening to densely functionalized dioxolanes is observed. Mechanistic studies suggest an unprecedented redox process between the cobalt(ii) catalyst and the hemiketal that initiates the oxetane-opening. Based on this observation, a dynamic kinetic resolution of the transient hemiketals is explored that uses a Katsuki-type ligand for stereoinduction (up to 99 : 1 dr and 96 : 4 er) and allows a variety of 1,3-dioxolanes to be accessed (20 examples up to 98% yield).

Desymmetrization of prochiral oxetanols via an electron-deficient hemiketal intermediate is achieved. Key to this process is the catalyst's chiral recognition of one of the two hemiketal enantiomers enabling an efficient dynamic kinetic resolution.

Desymmetrization of gem-diols via water-assisted organocatalytic enantio- and diastereoselective cycloetherification

The first desymmetrization of gem-diols forming chiral hemiketal carbons was accomplished via organocatalytic enantio- and diastereoselective cycloetherification, which afforded optically active tetrahydropyrans containing a chiral hemiketal carbon and tetrasubstituted stereocenters bearing synthetically versatile fluorinated groups. The desymmetrization of silanediols was also demonstrated as an asymmetric route to chiral silicon centers.