Chiral phosphoric acid-catalyzed enantioselective [5+1] cycloaddition reaction of C,N-cyclic azomethine imines with isocyanides

The first catalytic enantioselective [5+1] cycloaddition reactions of C,N-cyclic azomethine imines with isocyanides are reported herein. The method displays a broad substrate scope and atom-economy. A series of chiral tetrahydroisoquinoline containing indole skeletons were obtained in up to 90% yield with 95% ee under mild reaction conditions. A possible catalytic model was also proposed.

Divergent transformation of C,N-cyclic-N'-acyl azomethine imines by reaction with diazo compounds

C,N-cyclic-N'-acyl azomethine imines with isoquinoline skeletons were investigated for their reactivity with diazo compounds via two different pathways. During the reaction with ethyl diazoacetate, an α-diazoacetate moiety was introduced at the C1-position of the resulting tetrahydroisoquinolines. Alternatively, diazomethane or trimethylsilyldiazomethane was used to synthesize 3-benzazepine derivatives via ring expansion.

Syn-Stereoselective C3-Spirocyclization and C2-Amination of 3-(2-Isocyanoethyl)indole Using C,N-Cyclic Azomethine Imines

By utilizing an underexplored reaction mode of C,N-cyclic azomethine imines, a catalyst-free [1+2+3] cycloaddition/N-N bond cleavage sequential reaction for accessing spiroindolines with syn-stereoselectivity was developed. On the basis of experimental results and DFT calculations, peroxide and ethereal solvent were identified to trigger the hydrogen abstraction of the unstable [1+2+3] cycloaddition adducts, followed by homolytic cleavage of the N-N bond and hydrogen absorption.

Enantioselective Synthesis of Azetidines through [3 + 1]-Cycloaddition of Donor-Acceptor Aziridines with Isocyanides

The enantioselective [3 + 1]-cycloaddition of racemic donor-acceptor (D-A) aziridines with isocyanides was first realized under mild reaction conditions using a chiral N,N'-dioxide/Mg^II complex as catalyst, providing a facile route to enantioenriched exo-imido azetidines with good to excellent yield (up to 99%) and enantioselectivity (up to 94% ee). An obvious chiral amplification effect was observed in this system, and an explanation was elucidated based on the experimental investigation and X-ray crystal structure of the enantiomerically pure catalyst.

Divergent Reaction of Isocyanides with o-Bromobenzaldehydes: Synthesis of Ketenimines and Lactams with Isoindolinone Cores

A divergent reaction of isocyanides with o-bromobenzaldehydes for the synthesis of isoindolinone-derived ketenimines and lactams was disclosed. The reaction features readily available reactants, relatively mild conditions, and high yields of products. Ketenimines could be applied in further transformations for access to other functional molecules. A mechanism study showed that the palladium-migration/imine-insertion process was the key step in this reaction.

Divergent synthesis of α-functionalized amides through selective N-O/C-C or N-O/C-C/C-N cleavage of aza-cyclobutanone oxime esters

Herein, a novel sequential ring opening reaction of aza-cyclobutanone oxime esters with isocyanides is described. The reaction proceeded smoothly under redox-neutral and mild conditions, leading to a divergent synthesis of α-cyanomethylaminoamides, α-acyloxyamides and α-acylaminoamides. In these transformations, a selective N-O/C-C or N-O/C-C/C-N cleavage was achieved only by changing the iron-catalyst system. Among them, a rare sequential N-O/C-C/C-N cleavage process with a classical Passerini or Ugi multicomponent reaction can be executed in a single step. To the best of our knowledge, this work creates a novel reaction mode of cycloketone oximes and provides new opportunities for reaction design.

Asymmetric Synthesis of Tetrahydroisoquinoline Derivatives through 1,3-Dipolar Cycloaddition of C,N-Cyclic Azomethine Imines with Allyl Alkyl Ketones

A [3 + 2] 1,3-Dipolar cycloaddition of C,N-cyclic azomethine imines with allyl alkyl ketones has been achieved. The reaction proceeds under mild conditions and tolerates a wide range of functional groups. An array of tetrahydroisoquinoline derivatives is generally constructed with good diastereoselectivities and enantioselectivities (up to >25:1 dr, >95% ee). Moreover, the absolute configuration of the product was previously determined by using the quantum electronic circular dichroism calculation and ECD spectrum method.