Access to Enantio-enriched Substituted α-Trifluoromethyl Azepanes from l-Proline

Synthesis of Functionalized Azepines via Cu(I)-Catalyzed Tandem Amination/Cyclization Reaction of Fluorinated Allenynes

An efficient method for the selective preparation of trifluoromethyl-substituted azepin-2-carboxylates and their phosphorous analogues has been developed via Cu(I)-catalyzed tandem amination/cyclization reaction of functionalized allenynes with primary and secondary amines.

Synthesis of Azocanes from Piperidines via an Azetidinium Intermediate

α-Trifluoromethyl azocanes are accessible from 2-(trifluoropropan-2-ol) piperidines by metal-free ring-expansion involving a bicyclic azetidinium intermediate. The opening of the azetidinium intermediate was achieved by various nucleophiles (amines, alcoholates, carboxylates, phosphonates, halides and pseudo-halides) with an excellent regio- diastereo- and enantioselectivity and in good yields. The relative configuration of the piperidines and azocanes were assigned and the deprotected azocanes offer opportunities for further derivatization.

Application of Oxidative Ring Opening/Ring Closing by Reductive Amination Protocol for the Stereocontrolled Synthesis of Functionalized Azaheterocycles

The current Account gives an insight into the synthesis of some N-heterocyclic β-amino acid derivatives and various functionalized saturated azaheterocycles accessed from substituted cycloalkenes via ring C=C bond oxidative cleavage followed by ring closing across double reductive amination. The ring-cleavage protocol has been accomplished according to two common approaches: a) Os-catalyzed dihydroxylation/NaIO4 vicinal diol oxidation and b) ozonolysis. A comparative study on these methodologies has been investigated. Due to the everincreasing relevance of organofluorine chemistry in drug research as well as of the high biological potential of β-amino acid derivatives several illustrative examples to the access of various fluorine-containing piperidine or azepane β-amino acid derivatives are also presented in the current Account.

1 Introduction

2 Olefin-Bond Transformation by Oxidative Ring Cleavage

3 Synthesis of Saturated Azaheterocycles via Oxidative Ring-Opening/Ring-Closing Double Reductive Amination

3.1 Importance of Fluorine-Containing Azaheterocycles in Pharmaceutical Research

3.2 Synthesis of Azaheterocyclic Amino Acid Derivatives with a Piperidine or Azepane Framework through Oxidative Ring Opening/Reductive Amination

3.2.1 Synthesis of Piperidine β-Amino Esters

3.2.2 Synthesis of Azepane β-Amino Esters

3.2.3 Synthesis of Fluorine-Containing Piperidine γ-Amino Esters

3.3 Synthesis of Tetrahydroisoquinoline Derivatives through Oxidative Ring Opening/Reductive Amination Protocol

3.4 Synthesis of Functionalized Benzazepines through Reductive Amination

3.4.1 Synthesis of Benzo[c]azepines

3.4.2 Synthesis of Benzo[d]azepines

3.5 Synthesis of Various N-Heterocycles via Ozonolysis/Reductive Amination

3.5.1 Synthesis of Compounds with an Azepane Ring

3.5.2 Synthesis of Piperidine β-Amino Acids and Piperidine-Fused β-Lactams

3.5.3 Synthesis of γ-Lactams with a Piperidine Ring

3.5.4 Synthesis of other N-Heterocycles

4 Summary and Outlook

5 List of Abbreviations

A general strategy for the synthesis of α-trifluoromethyl- and α-perfluoroalkyl-β-lactams via palladium-catalyzed carbonylation

β-Lactam compounds play a key role in medicinal chemistry, specifically as the most important class of antibiotics. Here, we report a novel one-step approach for the synthesis of α-(trifluoromethyl)-β-lactams and related products from fluorinated olefins, anilines and CO. Utilization of an advanced palladium catalyst system with the Ruphos ligand allows for selective cycloaminocarbonylations to give diverse fluorinated β-lactams in high yields.

Direct α-Alkenylation of Cyclic Amines with Maleimides through Fe(III)-Catalyzed C(sp3)-H/C(sp2)-H Cross Dehydrogenative Coupling

Presented herein is a novel and efficient α-C(sp³)-H alkenylation of cyclic amines with maleimides. Mechanistically, this C(sp³)-H/C(sp²)-H cross dehydrogenative coupling (CDC) reaction involves a cascade procedure including oxidative α-amino radical formation from the cyclic amine substrate and nucleophilic addition of the in situ formed α-amino radical onto the electron-deficient carbon-carbon double bond of maleimide followed by oxidation and β-elimination. Notably, this direct α-functionalization provides an effective alternative to the conventional ionic reaction mode, in which an imine or iminium intermediate is formed to react with electron-rich coupling partners other than electron-deficient ones. In general, this method features readily available and structurally diverse substrates, a green and economical catalyst, a unique reaction pathway, mild reaction conditions, high efficiency, and excellent atom economy. This new reaction enriches the application of Fe(III)-catalyzed C(sp³)-H activation and functionalization.

Asymmetric "Clip-Cycle" Synthesis of Pyrrolidines and Spiropyrrolidines

The development of an asymmetric "clip-cycle" synthesis of 2,2- and 3,3-disubstituted pyrrolidines and spiropyrrolidines, which are increasingly important scaffolds in drug discovery programs, is reported. Cbz-protected bis-homoallylic amines were activated by "clipping" them to thioacrylate via an alkene metathesis reaction. Enantioselective intramolecular aza-Michael cyclization onto the activated alkene, catalyzed by a chiral phosphoric acid, formed a pyrrolidine. The reaction accommodated a range of substitutions to form 2,2- and 3,3-disubstituted pyrrolidines and spiropyrrolidines with high enantioselectivities. The importance of the thioester activating group was demonstrated by comparison to ketone and oxoester-containing substrates. DFT studies supported the aza-Michael cyclization as the rate- and stereochemistry-determining step and correctly predicted the formation of the major enantiomer. The catalytic asymmetric syntheses of N-methylpyrrolidine alkaloids (R)-irnidine and (R)-bgugaine, which possess DNA binding and antibacterial properties, were achieved using the "clip-cycle" methodology.

Stereocontrolled Synthesis of Functionalized Azaheterocycles from Carbocycles through Oxidative Ring Opening/Reductive Ring Closing Protocols

Fluorine-containing organic scaffolds are of significant interest in medicinal chemistry. The incorporation of fluorine into biomolecules can lead to remarkable changes in their physical, chemical, and biological properties. There are already many drugs on the market, which contain at least one fluorine atom. Saturated functionalized azaheterocycles as bioactive substances have gained increasing attention in pharmaceutical chemistry. Due to the high biorelevance of organofluorine molecules and the importance of N-heterocyclic compounds, selective stereocontrolled procedures to the access of new fluorine-containing saturated N-heterocycles are considered to be a hot research topic. This account summarizes the synthesis of functionalized and fluorine-containing saturated azaheterocycles starting from functionalized cycloalkenes and based on oxidative ring cleavage of diol intermediates followed by ring expansion with reductive amination.

Synthesis of Highly Substituted Azepanones from 2 H-Azirines by a Stepwise Annulation/Ring-Opening Sequence

Bicyclic aziridines possessing a 1-azabicyclo[4.1.0]heptan-2-one core were prepared from 2 H-azirines by a stepwise annulation sequence involving a diastereoselective allylindanation, an N-acylation, and a ring-closing metathesis to construct the six-membered ring. After hydrogenation or functionalization of the olefin, regioselective ring opening of the resulting azabicyclic compounds with carboxylic acids (or sulfur nucleophiles) afforded highly substituted azepanones possessing an ester moiety or a trifluoromethyl group and a tetrasubstituted carbon at the α and β positions of the nitrogen atom, respectively.

Rapid Assembly of Saturated Nitrogen Heterocycles in One-Pot: Diazo-Heterocycle "Stitching" by N-H Insertion and Cyclization

Methods that provide rapid access to new heterocyclic structures in biologically relevant chemical space provide important opportunities in drug discovery. Here, a strategy is described for the preparation of 2,2-disubstituted azetidines, pyrrolidines, piperidines, and azepanes bearing ester and diverse aryl substituents. A one-pot rhodium catalyzed N-H insertion and cyclization sequence uses diazo compounds to stitch together linear 1,m-haloamines (m=2-5) to rapidly assemble 4 -, 5 -, 6 -, and 7 -membered saturated nitrogen heterocycles in excellent yields. Over fifty examples are demonstrated, including examples with diazo compounds derived from biologically active compounds. The products can be functionalized to afford α,α-disubstituted amino acids and applied to fragment synthesis.