Brønsted Base-Catalyzed Formal Reductive [3+2] Annulation of 4,4,4-Trifluorocrotonate and α-Iminoketones

Asymmetric Auto-Tandem Catalysis with Chiral Organosuperbases: Intramolecular Cyclization/Enantioselective Direct Mannich-Type Addition Sequence

An enantioselective addition reaction of alkynyl esters with imines was developed under asymmetric autotandem catalysis with a chiral Brønsted base. A chiral bis(guanidino)iminophosphorane organosuperbase, which has much higher basicity than that of conventional chiral organic bases, efficiently promoted both the intramolecular cyclization for the construction of a benzofuran ring or a benzothiophene ring and the sequential enantioselective direct Mannich-type reaction of diarylmethane derivatives, affording enantio-enriched diarylalkane derivatives that are otherwise difficult to access.

Highly Efficient Darzens Reactions Mediated by Phosphazene Bases under Mild Conditions

The highly basic and poorly nucleophilic phosphazene base P1 -t-Bu promotes the Darzens condensation of α-halo esters with aromatic aldehydes affording α,β-epoxy esters in nearly quantitative yields under mild conditions and in short reaction times. The more basic P4 -t-Bu phosphazene was found useful with low reactivity aldehydes. These reactions can be performed in aprotic organic solvents of low polarity, thus minimizing the hydrolysis of α,β-epoxy esters which often accompanies the base-promoted Darzens condensations.

The organocatalytic synthesis of perfluorophenylsulfides via the thiolation of trimethyl(perfluorophenyl)silanes and thiosulfonates

The organic superbase t-Bu-P₄-catalyzed direct thiolation of trimethyl(perfluorophenyl)silanes and thiosulfonates was developed. Yields of perfluorophenylsulfides of up to 97% under catalysis of 5 mol% t-Bu-P₄ were achieved. This method was shown to provide an efficient way to construct the perfluorophenyl-sulfur bond under mild metal-free reaction conditions.

Formal Fluorinative Ring Opening of 2-Benzoylpyrrolidines Utilizing [1,2]-Phospha-Brook Rearrangement for Synthesis of 2-Aryl-3-fluoropiperidines

A ring expansion of 2-benzoylpyrrolidines, which involves the formal fluorinative ring opening utilizing the [1,2]-phospha-Brook rearrangement under Brønsted base catalysis and a subsequent intramolecular reductive amination, was developed. The operationally simple three-step protocol provides an efficient access to 2-aryl-3-fluoropiperidines. The methodology was further applied to the syntheses of azepanes and tetrahydroquinolines.

Preparation and Application of α-Imino Ketones through One-Pot Tandem Reactions Based on Heyns Rearrangement

α-Imino ketone is a useful building block for the preparation of α-amino ketones and α-amino alcohols. However, its preparation has been seldomly seen. Herein, a metal-free and operationally simple strategy has been developed to generate α-imino ketones with high regioselectivity. Meanwhile, the method allowed for the preparation of various N,O-ketals with high regioselectivities and diastereoselectivities through cascade reactions in one pot.

Organocatalytic aminocarbonylation of α,β-unsaturated ketones with N,N-dimethyl carbamoylsilane

Schwesinger's superbase can efficiently activate the Si–CONMe₂ bond and initiate the aminocarbonylation of α,β-unsaturated ketones and N,N-dimethyl carbamoylsilane.