Synthesis of β-Amino-Substituted Enones by Addition of Substituted Methyl Enones to Sulfinimines: Application to the Total Synthesis of Alkaloids (+)-Lasubine II and (+)-241D and the Formal Total Synthesis of (-)-Lasubine I

A Dual Role for the N-Perfluorobutanesulfinamide Auxiliary in an Asymmetric Decarboxylative Mannich Reaction

Herein, we demonstrate that the enhanced electrophilicity of N-perfluorobutanesulfinamide auxiliary-derived imines enables a highly selective decarboxylative Mannich reaction under mild conditions. The molecular sieves-mediated transformation tolerates a broad substrate scope and produces chiral β-amino thioesters in high yield. Additionally, we demonstrate that the N-perfluoroalkyl sulfinyl group can function as a phase tag for fluorous purification, thus enabling the rapid isolation of the chiral amine products by solid-phase extraction. The synthetic utility of this method is illustrated by the synthesis of sitagliptin, ruspolinone, and the natural product negamycin.

Diastereoselective Synthesis of trans-β-Amino Cyclohexyl Ketones and trans-3-Amino-4-acyl-tetrahydropyrans from Intramolecular C-Alkylation of ω-Halo-Substituted β-Sulfinamido Ketones

Reaction of ω-halo-substituted nonracemic β-sulfinamido ketones with NaH afforded the β-amino cyclohexyl ketones in excellent yields and diastereoselectivity, via an intramolecular C-alkylation, α to the carbonyl group. The reaction was found to be general and can be applied for the synthesis of different cyclohexyl amino ketones and tetrahydropyrans possessing amine and acyl substitutions.

Synthetic Access to α-Oxoketene Aminals by the Nucleophilic Addition of Enol Silane-Derived Palladium(II) Enolates to Carbodiimides

Synthetically important α-oxoketene aminal intermediates can now be accessed from readily available and inexpensive carbodiimides as starting materials via the nucleophilic addition of palladium enolates derived from enol silane precursors. This operationally simple method features mild reaction conditions, including open air atmosphere, ligand-free metal catalysis, broad substrate scope, and multi-gram scalability. Select synthetic applications that take advantage of the enamine character of α-oxoketene aminals and involve C-nucleophilic additions to electrophilic systems, including an α,β-unsaturated ester, an azo dicarboxylate, an aralkyl halide, and an aldehyde, are demonstrated.

The Ligand Free Palladium(II)-Catalyzed Regioselective 1,2-Addition of Enol Silanes to Quinones to Access 4-Hydroxy-4-(2-oxo-2-arylethyl)cyclohexadien-1-ones and Synthetic Applications

In contrast to the conventional 1,4-addition process, regioselective 1,2-addition of silyl enol ethers to quinones can now be achieved via a palladium(II) enolate pathway that provides access to 4-hydroxy-4-(2-oxo-2-arylethyl)cyclohexa-2,5-dien-1-one derivatives. This quinone alkylation protocol proceeds under mild reaction conditions at ambient temperature under open air and does not require either an external ligand for the palladium or the use of a base. Additionally, the cyclohexadienone products have been exploited as synthetic precursors for the construction of fused heteroaryl systems.

Double asymmetric intramolecular aza-Michael reaction: a convenient strategy for the synthesis of quinolizidine alkaloids

A new methodology to access the quinolizidine skeleton in an asymmetric fashion was devised. It involves two consecutive intramolecular aza-Michael reactions of sulfinyl amines bearing a bis-enone moiety, in turn generated by a monodirectional cross metathesis reaction. The sequence, which takes place with excellent yields and diastereocontrol, was applied to the total synthesis of alkaloids lasubine I and myrtine.

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

The synthesis of nitrogen-containing heterocycles, including natural alkaloids and other compounds presenting different types of biological activities have proved to be successful employing chiral sulfinyl imines derived from tert-butanesulfinamide. These imines are versatile chiral auxiliaries and have been extensively used as eletrophiles in a wide range of reactions. The electron-withdrawing sulfinyl group facilitates the nucleophilic addition of organometallic compounds to the iminic carbon with high diastereoisomeric excess and the free amines obtained after an easy removal of the tert-butanesulfinyl group can be transformed into enantioenriched nitrogen-containing heterocycles. The goal of this review is to the highlight enantioselective syntheses of heterocycles involving the use of chiral N-tert-butanesulfinyl imines as reaction intermediates, including the synthesis of several natural products. The synthesis of nitrogen-containing heterocycles in which the nitrogen atom is not provided by the chiral imine will not be considered in this review. The sections are organized according to the size of the heterocycles. The present work will comprehensively cover the most pertinent contributions to this research area from 2012 to 2020. We regret in advance that some contributions are excluded in order to maintain a concise format.

Chiral N-tert-Butylsulfinyl Imines: New Discoveries

In this account the reactions of chiral N-tert-butylsulfinyl imines with organometallic reagents such as organoalkaline (lithium, sodium, potassium and cesium derivatives), organomagnesium, organozinc, organoboron, organoaluminium, organoindium and organosilicon compounds is comprehensively described. The reactivity in all cases is derived to synthetic applications in order to prepare interesting organic nitrogenated molecules, especially in the field of alkaloid compounds.

Addition of Lithium Anion of (Acetylmethylene)triphenylphosphorane to Nonracemic Sulfinimines: Total Synthesis of (+)-241D and Formal Total Synthesis of (+)-Preussin

The addition of lithium anion of (acetylmethylene)triphenylphosphorane to nonracemic sulfinimines was investigated. It was found that the addition proceeded with good diastereoselectivity and further reaction of the formed sulfinimidophosphorane with several aldehydes afforded the β-sulfinamido substituted enones in good yields. The resultant enones were elaborated to the synthesis of alkaloid (+)-241D, to the formal total synthesis of (+)-preussin, and to the synthesis of aminocyclopentenol.

Stereoselective Synthesis of β-Amino Ynones by the Addition of Alkynones to Nonracemic Sulfinimines: Formal Total Synthesis of l-Xylo and l-Arabino Phytosphingosines

The addition of silyl enol ethers obtained from ynones to sulfinimines furnished the corresponding β-sulfinamido ynones in a very good yield and diastereoselectivity. The formed ynones serve as precursors amenable for the synthesis of bioactive compounds. This has been illustrated in the synthesis of l-xylo and l-arabino phytosphingosines.

The endo-aza-Michael addition in the synthesis of piperidines and pyrrolidines

Intramolecular endo-aza-Michael additions are categorised in various ways.

Transition-Metal-Free Reductive Hydroxymethylation of Isoquinolines

A transition-metal-free reductive hydroxymethylation reaction has been developed, enabling the preparation of tetrahydroisoquinolines bearing C4-quaternary centers from the corresponding isoquinolines. Deuterium labelling studies and control experiments enable a potential mechanism to be elucidated which features a key Cannizzaro-type reduction followed by an Evans-Tishchenko reaction. When isoquinolines featuring a proton at the 4-position are used, a tandem methylation-hydroxymethylation occurs, leading to the formation of 2 new C-C bonds in one pot.

Biomimetic Organocatalytic Approach to 4-Arylquinolizidine Alkaloids and Application in the Synthesis of (-)-Lasubine II and (+)-Subcosine II

An enantioselective, biomimetic organocatalytic synthesis of 4-arylquinolizidin-2-ones, key intermediates in the synthesis of several Lythraceae alkaloids, was developed. The methodology features S-proline-mediated Mannich/aza-Michael reactions of readily available arylideneacetones and Δ¹-piperideine. The total syntheses of (-)-lasubine II and (+)-subcosine II as well as the formal syntheses of structurally related Lythraceae alkaloids were achieved. The use of Δ¹-pyrroline in the Mannich/aza-Michael reaction provides enantiomerically enriched 5-arylindolizidin-7-ones, which are precursors to nonopiate antinociceptive agents.

Enantiodivergent Approach to the Synthesis of Cis-2,6-Disubstituted Piperidin-4-ones

Enantiopure β-amino ketone derivatives were synthesized by decarboxylative Mannich reaction of chiral N- tert-butanesulfinyl imines with β-keto acids and were subsequently transformed into cis-2,6-disubstituted piperidin-4-ones through an organocatalyzed condensation with aldehydes. Both enantiomers were accessible from the same precursors by inverting the order in the reaction sequence of the aldehydes involved in the imine formation and the intramolecular Mannich condensation. The synthesis of the piperidine alkaloids (+)-241D, (-)-epimyrtine, and (-)-lasubine II demonstrated the utility of this methodology.

Addition of the Lithium Anion of Diphenylmethanol Methyl/Methoxymethyl Ether to Nonracemic Sulfinimines: Two-Step Asymmetric Synthesis of Diphenylprolinol Methyl Ether and Chiral (Diphenylmethoxymethyl)amines

Addition of the lithium anion generated from diphenylmethanol methyl and methoxymethyl ether to nonracemic sulfinimines afforded the corresponding addition products in excellent diastereoselctivity and yields. Deprotection of the MOM as well as sulfinyl groups rendered the enantiopure (diphenylhydroxymethyl)amines in excellent yields. The procedure was applied for a two-step synthesis of diphenylprolinol, a privileged ligand in asymmetric catalysis.

Efficient Syntheses of Quinolizidine-Type Poison-Frog Alkaloids via Michael-Type Conjugate Addition

Efficient and flexible syntheses of 1,4-disubstituted quinolizidine-type poison-frog alkaloids using the highly stereoselective Michael-type conjugate addition reaction as the key step are described. The 1,4-disubstituted quinolizidine poison-frog alkaloids 233A, 235U and 251AA are reported.

Access to 2,6-Disubstituted 4-Oxopiperidines Using a 6-Endo-trig Cyclization: Stereoselective Synthesis of Spruce Alkaloid and (+)-241D

A synthetic route to cis-2-methyl-4-oxo-6-alkylpiperidines has been developed using a 6-endo-trig cyclization of (E)-enones. The base-mediated intramolecular cyclization was found to be general for both alkyl- and aryl-substituted enones, providing the corresponding 4-oxopiperidines in high yields (80-89%). Stereoselective reduction of the 2,6-cis-disubstituted 4-oxopiperidines then gave the 2,4,6-cis,cis-trisubstituted 4-hydroxypiperidines in high diastereoselectivity. The general nature of this approach was demonstrated with the synthesis of the natural products, spruce alkaloid and (+)-241D.

Synthesis of β-Amino Ketones by Addition of Aryl Methyl Ketones to Sulfinimines: Application to the Total Synthesis of HPA-12, Norsedamine, and Sedamine

Synthesis of β-sulfinamido ketones was accomplished by the addition of silyl enol ethers derived from arylmethyl ketones to chiral sulfinimines in excellent yield and selectivity. Application of the formed β-amino substituted ketones is exemplified in the total synthesis of sphingolipid HPA-12 and the sedamine alkaloids.

Asymmetric synthesis of δ-amino acid derivatives via diastereoselective vinylogous Mannich reactions between N-tert-butanesulfinyl imines and dioxinone-derived lithium dienolate

A diastereoselective vinylogous Mannich reaction between theN-tert-butanesulfinyl imines and dioxinone-derived lithium dienolate was developed.