1,3-Diamine-Derived Bifunctional Organocatalyst Prepared from Camphor

Understanding divergent substrate stereoselectivity in the isothiourea-catalysed conjugate addition of cyclic α-substituted β-ketoesters to α,β-unsaturated aryl esters

The development of enantioselective synthetic methods capable of generating vicinal stereogenic centres, where one is tetrasubstituted (such as either an all-carbon quaternary centre or where one or more substituents are heteroatoms), is a recognised synthetic challenge. Herein, the enantioselective conjugate addition of a range of carbo- and heterocyclic α-substituted β-ketoesters to α,β-unsaturated aryl esters using the isothiourea HyperBTM as a Lewis base catalyst is demonstrated. Notably, divergent diastereoselectivity is observed through the use of either cyclopentanone-derived or indanone-derived substituted β-ketoesters with both generating the desired stereodefined products with high selectivity (>95 : 5 dr, up to 99 : 1 er). The scope and limitations of these processes are demonstrated, alongside application on gram scale. The origin of the divergent substrate selectivity has been probed through the use of DFT-analysis, with preferential orientation driven by dual stabilising CH⋯O interactions. The importance of solvation with strongly polar transition-states is highlighted and the SMD solvation model is demonstrated to capture solvation effects reliably.

Synthesis of Six-Membered N-Heterocyclic Carbene Precursors Based on Camphor

The endo- and exo-N-heterocyclic carbene precursors based on camphor were prepared diastereoselectively in five synthetic steps starting from (1S)-(+)-ketopinic acid. The obtained N-heterocyclic carbene precursors were investigated in an asymmetric benzoin reaction. All new compounds were fully characterized, and the absolute configurations were determined via X-ray diffraction and NOESY measurements.

Synthesis and Catalytic Activity of Bifunctional Phase-Transfer Organocatalysts Based on Camphor

Ten novel bifunctional quaternary ammonium salt phase-transfer organocatalysts were synthesized in four steps from (+)-camphor-derived 1,3-diamines. These quaternary ammonium salts contained either (thio)urea or squaramide hydrogen bond donor groups in combination with either trifluoroacetate or iodide as the counteranion. Their organocatalytic activity was evaluated in electrophilic heterofunctionalizations of β-keto esters and in the Michael addition of a glycine Schiff base with methyl acrylate. α-Fluorination and chlorination of β-keto esters proceeded with full conversion and low enantioselectivities (up to 29% ee). Similarly, the Michael addition of a glycine Schiff base with methyl acrylate proceeded with full conversion and up to 11% ee. The new catalysts have been fully characterized; the stereochemistry at the C-2 chiral center was unambiguously determined.

tert-Butyl 2-Amino-3-cyano-5-oxo-4-phenyl-5,7-dihydropyrano[2,3-c]pyrrole-6(4H)-carboxylate

Organocatalyzed synthesis of tert-butyl 2-amino-3-cyano-5-oxo-4-phenyl-5,7-dihydropyrano[2,3-c]pyrrole-6(4H)-carboxylate, prepared from Boc-tetramic acid and benzylidenemalononitrile, is disclosed. Two bifunctional noncovalent organocatalysts were employed, yielding the product as a racemic mixture in both cases. The structure of the new synthesized compound was confirmed by high resolution mass-spectrometry, 1H- and 13C-NMR, HSQC, and IR spectroscopy.

(S)-N1,N3-Dibenzyl-1-cyclohexyl-N1,N3-bis((R)-1-phenylethyl)propane-1,3-diamine

(S)-N1,N3-dibenzyl-1-cyclohexyl-N1,N3-bis((R)-1-phenylethyl)propane-1,3-diamine was prepared in good yield by the reduction of the corresponding amide, which was obtained by the addition of a chiral lithium amide to an α,β-unsaturated ester. The target compound was fully characterized by NMR (1H and 13C), high-resolution mass spectrometry and polarimetry.

1-{(1S,2S,4R)-7,7-Dimethyl-1-[(pyrrolidin-1-yl)methyl]bicyclo [2.2.1]heptan-2-yl}-1H-benzo[d]imidazole

A three-step synthesis of 1-{(1S,2S,4R)-7,7-dimethyl-1-[(pyrrolidin-1-yl)methyl]bicyclo[2.2.1]heptan-2-yl}-1H-benzo[d]imidazole, prepared from camphor derived diamine, is disclosed. The absolute configuration at the chiral center bearing benzo[d]imidazole moiety was confirmed by NOESY. The structure of a newly synthesized compound was confirmed by 1H- and 13C-NMR, 2D NMR, IR spectroscopy, and high resolution mass-spectrometry.

New bifunctional 1,3-diamine organocatalysts derived from (+)-camphoric acid for asymmetric Michael addition of 1,3-dicarbonyl compounds to nitroolefins

Novel 1,3-diamine-derived bifunctional thiourea and squaramide organocatalysts were synthesized from (+)-camphoric acid. These catalysts were easily obtained in up to two to five synthetic steps, in a flexible approach that facilitates their structure variation. Their catalytic activity was examined in the asymmetric Michael addition of 1,3-dicarbonyl compounds to several trans-β-nitrostyrenes. Yields up to 98% and enantiomeric excesses up to 74% and high diastereoselectivities when applicable (dr up to 93:7) were obtained in these reactions showing that 1,3-diamine-derived bifunctional thioureas are efficient organocatalysts.

Bifunctional squaramides with benzyl-like fragments: analysis of CH⋯π interactions by a multivariate linear regression model and quantum chemical topology

A multivariate linear regression model and quantum chemical topology are used for the quantitative description of non-covalent interactions in the transition state of the Michael addition catalyzed by bifunctional squaramides.

Double Spirocyclization of Arylidene-Δ2-Pyrrolin-4-Ones with 3-Isothiocyanato Oxindoles

Arylidene-Δ2-pyrrolin-4-ones undergo organocatalyzed double spirocyclization with 3-isothiocianato oxindoles in a domino 1,4/1,2-addition sequence. The products contain three contiguous stereocenters (ee up to 98%, dr up to 99:1, 12 examples). The absolute configuration of the major diastereomer was determined by single crystal X-ray analysis. Along with heterocyclic Michael acceptors based on oxazolone, isoxazolone, thiazolidinone, pyrazolone, and pyrimidinedione, the reported results display the applicability of unsaturated Δ2-pyrrolin-4-ones (pyrrolones) for the organocatalyzed construction of 3D-rich pyrrolone-containing heterocycles.

Stereodivergent Synthesis of Camphor-Derived Diamines and Their Application as Thiourea Organocatalysts

A series of 18 regio- and stereo-chemically diverse chiral non-racemic 1,2-, 1,3-, and 1,4-diamines have been synthesized from commercial (1S)-(+)-ketopinic acid and (1S)-(+)-10-camphorsulfonic acid. The structures of the diamines are all based on the d-(+)-camphor scaffold and feature isomeric diversity in terms of regioisomeric attachment of the primary and the tertiary amine function and the exo/endo-isomerism. Diamines were transformed into the corresponding noncovalent bifunctional thiourea organocatalysts, which have been evaluated for catalytic activity in the conjugative addition of 1,3-dicarbonyl nucleophiles (dimethyl malonate, acetylacetone, and dibenzoylmethane) to trans-β-nitrostyrene. The highest enantioselectivity was achieved in the reaction with acetylacetone as nucleophile using endo-1,3-diamine derived catalyst 52 (91.5:8.5 er). All new organocatalysts 48-63 have been fully characterized. The structures and the absolute configurations of eight intermediates and thiourea derivative 52 were also determined by X-ray diffraction.

Catalytic 1,2-Rearrangements: Organocatalyzed Michael/Semi-Pinacol-like Rearrangement Cascade of 1,3-Diones and Nitroolefins

New types of organocatalytic 1,2-rearrangements, which resemble the Smiles-like or semi-pinacol-like rearrangement, of Michael adducts of 1,3-dicarbonyl-2-alkyl compounds and nitroalkenes have been realized. Unlike the well-known conjugate addition, the reaction affords the 1-phenyl-1-nitroalkanes via unprecedented rearrangement and cascade reactions. Structures of the appropriate products were unambiguously characterized by X-ray crystallography.

Bifunctional thiourea-modified polymers of intrinsic microporosity for enantioselective α-amination of 3-aryl-2-oxindoles in batch and flow conditions

A multigram scale preparation of enantioenriched 3-aryl-3-amino-2-oxindoles promoted by a novel chiral bifunctional thiourea, readily prepared from polymers of intrinsic microporosity.

Conformational control of nonplanar free base porphyrins: towards bifunctional catalysts of tunable basicity

No metal needed: nonplanar free base porphyrins act as bifunctional organocatalysts revealing a new mode of action for porphyrins.

A homodinuclear cobalt complex for the catalytic asymmetric Michael reaction of β-ketoesters to nitroolefins

A homodinuclear Co₂/aminophenol sulfonamide complex has been developed for the asymmetric Michael reaction.

A DFT mechanistic study of the organocatalytic asymmetric reaction of aldehydes and homophthalic anhydride

The first study of the cycloaddition of benzaldehyde with homophthalic anhydride under the influence of an alkaloid-based, squaramide substituted bifunctional organocatalyst using DFT methodology is reported.