Kinetic Resolution of Azaarylethynyl Tertiary Alcohols by Chiral Brønsted Acid Catalysed Phosphine-Mediated Deoxygenation

A chiral Brønsted acid catalysed phosphine-mediated deoxygenation protocol is reported. This metal-free method provides a precise kinetic resolution platform for azaarylethynyl tertiary alcohols, which are a broad category of biologically and synthetically important azaarene derivatives. In addition to providing an efficient method for the first asymmetric preparation of these tertiary alcohols, the strategy facilitates the construction of azaaryl-functionalized allenes with good to excellent enantioselectivities. The high selectivity factors (s up to 235), broad substrate scope, and ability to convert azaaryl compounds into both chiral tertiary alcohols and allenes robustly underscore the efficiency and promising utility of this method. The practicability is further validated by the successful synthesis of deuterated allenes with high ee values and substantial incorporation of deuterium using inexpensive D₂ O as the deuterium source.

Asymmetric α-Functionalization of 2-Alkyl Azaarenes: Synthesis of Tertiary Fluorides Having Vicinal Stereogenic Centers

An enantioselective approach for synthesizing fluorinated azaarenes containing vicinal quaternary-tertiary stereocenters is summarized. The chiral copper(I)-phosphine complex binds with the azaarenes followed by Michael addition to unsaturated acyl imidazoles, resulting in α-functionalized products with an excellent level of enantioselectivities (up to 99%), diastereoselectivities (>20:1), and yields (up to 97%). Furthermore, post-functionalization of the acyl imidazole part has also been demonstrated.

Stereodivergent Carbon-Carbon Bond Formation between Iminium and Enolate Intermediates by Synergistic Organocatalysis

We report here a stereodivergent method for the Michael addition of aryl acetic acid esters to α,β-unsaturated aldehydes catalyzed by a combination of a chiral pyrrolidine and a chiral Lewis base. This reaction proceeds through a synergistic catalytic cycle which consists of one cycle leading to a chiral iminium electrophile and a second cycle generating a nucleophilic chiral enolate for the construction of a carbon-carbon bond. By varying the combinations of catalyst enantiomers, all four stereoisomers of the products with two vicinal stereocenters are accessible with high enantio- and diastereoselectivity. The products of the Michael addition, 1,5-aldehyde esters, can be readily transformed into a variety of other valuable enantioenriched structures, including those bearing three contiguous stereocenters in an acyclic system, thus providing an efficient route to an array of structural and stereochemical diversity.

Kinetic resolution of racemic allylic alcohols via iridium-catalyzed asymmetric hydrogenation: scope, synthetic applications and insight into the origin of selectivity

Asymmetric hydrogenation is one of the most commonly used tools in organic synthesis, whereas, kinetic resolution via asymmetric hydrogenation is less developed. Herein, we describe the first iridium catalyzed kinetic resolution of a wide range of trisubstituted secondary and tertiary allylic alcohols. Large selectivity factors were observed in most cases (s up to 211), providing the unreacted starting materials in good yield with high levels of enantiopurity (ee up to >99%). The utility of this method is highlighted in the enantioselective formal synthesis of some bioactive natural products including pumiliotoxin A, inthomycin A and B. DFT studies and a selectivity model concerning the origin of selectivity are presented.

Asymmetric hydrogenation is one of the most commonly used tools in organic synthesis, whereas, kinetic resolution via asymmetric hydrogenation was less developed.

The organocatalyzed domino Michael–aldol reaction revisited. Synthesis of enantioenriched 3-hydroxycyclohexanone derivatives by reaction of enals with α,α′-diaryl-substituted acetone

The reaction of enals with α,α′-diaryl-substituted acetones (pK_a > 18) catalyzed by (S)-1-(2-pyrrolidinylmethyl) pyrrolidine provides direct access to enantioenriched 2,5,6-trisubstituted-3-hydroxy cyclohexanones.