One-Pot Synthesis of Multisubstituted Butyrolactonimidates: Total Synthesis of (−)-Nephrosteranic Acid

Stereodivergent Synthesis of 1,4-Dicarbonyl Compounds through Sulfonium Rearrangement: Mechanistic Investigation, Stereocontrolled Access to γ-Lactones and γ-Lactams, and Total Synthesis of Paraconic Acids

Although simple γ-lactones and γ-lactams have received considerable attention from the synthetic community, particularly due to their relevance in biological and medicinal contexts, stereoselective synthetic approaches to more densely substituted derivatives remain scarce. The in-depth study presented herein, showcasing a straightforward method for the stereocontrolled synthesis of γ-lactones and γ-lactams, builds on and considerably expands the stereodivergent synthesis of 1,4-dicarbonyl compounds by a ynamide/vinyl sulfoxide coupling. A full mechanistic and computational study of the rearrangement was conducted, uncovering the role of all of the reaction components and providing a rationale for stereoselection. The broad applicability of the developed tools to streamlining synthesis is demonstrated by concise enantioselective total syntheses of (+)-nephrosteranic acid, (+)-rocellaric acid, and (+)-nephromopsinic acid.

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.

New paraconic acids from the endophytic fungus Xylariaceae sp. J4

Three new paraconic acids, xylariacinics A-C (1-3), were isolated from the endophyte Xylariaceae sp. J4 harbored in the medicinal plant Blumea balsamifera. Their structures were elucidated on the basis of extensive spectroscopic data including HRMS, and NMR. The antibacterial efficacies of compounds 1-3 were evaluated against a panel of bacteria such as Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa. Their antifungal activities were also tested against Colletotrichum gloeosporioides. Unfortunately, all of them were inactive.

An efficient enantioselective approach to multifunctionalized γ-butyrolactone: concise synthesis of (+)-nephrosteranic acid

A short, efficient and novel approach for multifunctionalized γ-butyrolactone paraconic acids and its application to the total synthesis of (+)-nephrosteranic acid from readily available PMB (R)-glycidyl ether as a starting material are described. Key transformations include asymmetric Michael addition catalyzed by chiral diphenylprolinol silyl ether and stereoselective α-methylation.

Synthetic progress toward the marine natural product zamamiphidin A

An asymmetric synthetic approach to the octahydrofuro[3,4-b]pyridine framework of marine natural product zamamiphidin A has been described. The key steps include an asymmetric Michael addition of (R)-N-tert-butanesulfinyl imidate with enamidomalonate to install the C10 stereocenter, an intramolecular alkoxide exchange/Michael addition/hydrogenation sequence to construct the bicyclic ring system.

An asymmetric synthetic approach to the octahydrofuro[3,4-b]pyridine framework of marine natural product zamamiphidin A has been described.

Stereodivergent Synthesis of Chiral Paraconic Acids via Dynamic Kinetic Resolution of 3-Acylsuccinimides

A direct N-heterocyclic carbene (NHC) catalysis of maleimides with alkyl aldehydes is established for the synthesis of 3-acylsuccinimides. The first dynamic kinetic resolution of 3-acylsuccinimides is accomplished through asymmetric transfer hydrogenation. These two catalytic methodologies are utilized for the synthesis of each enantiomer of trans-paraconic acids in three steps and cis-paraconic acids in four steps with good yields and high stereoselectivities. This stereodivergent synthetic methodology is applied for the synthesis of seven bioactive paraconic acid natural products.

Diastereoselective α-Fluorination of N- tert-Butanesulfinyl Imidates

A diastereoselective α-fluorination of N- tert-butanesulfinyl imidates was developed. Deprotonation of N- tert-butanesulfinyl imidates with lithium hexamethyldisilazide generates aza-enolates that can be intercepted, with excellent diastereocontrol, by the inexpensive electrophilic fluorinating agent NFSI. This protocol was applied to the preparation of synthetically useful trans-2-fluoro-cyclohexamine with high enantiomeric purity (99.5% ee).

Diastereoselective α-Sulfenylation of N- tert-Butanesulfinyl Imidates

A diastereoselective α-sulfenylation of chiral α-aryl/alkyl N- tert-butanesulfinyl imidates has been developed. Suitable sulfur electrophiles can be used as sulfenylating reagents to intercept aza-enolates generated from imidate deprotonation, giving α-thiofunctionalized imidates in good yields with high diastereocontrol. This protocol for C-S bond formation can efficiently synthesize enantioenriched 1,2-sulfanyl amine derivatives such as sulconazole.

Construction of α-methoxyimidoyl ketonitrones via phosphite-mediated addition of α-keto N-tert-butanesulfinyl imidates to nitrosoarenes

A dimethyl phosphite-mediated addition of α-keto N-tert-butanesulfinyl imidates to nitrosoarenes was developed. Nitrosoarenes were successfully used as electrophiles to trap aza-enolate intermediates that were generated from nucleophilic addition of deprotonated phosphite to α-keto N-tert-butanesulfinyl imidates and following phospha-Brook rearrangement, allowing efficient construction of ketonitrones with excellent (Z)-geometries.

Diastereoselective α-Hydroxylation of N-tert-Butanesulfinyl Imidates and N'-tert-Butanesulfinyl Amidines with Molecular Oxygen

Diastereoselective α-hydroxylation using molecular oxygen has been achieved with chiral α-alkyl N-tert-butanesulfinyl imidates and α-aryl N'-tert-butanesulfinyl amidines. The aza-enolates generated from deprotonation of imidates/amidines can be intercepted by O₂ with excellent diastereocontrol and subsequently transformed into α-hydroxylation products in the presence of the reductant trimethyl phosphite.

Aldol Reaction of N-tert-Butanesulfinyl Imidates under Basic Conditions for Diastereoselective Synthesis of anti-Aldols

Diastereoselective aldol reaction of N-tert-butanesulfinyl imidates under typical hard enolization conditions is reported. Potassium bis(trimethylsilyl)amide (KHMDS) effectively promotes the aldol reaction of α-aryl- and α-alkyl-substituted imidates, providing anti-aldol adducts in high yields with good to excellent diastereoselectivities. In the case of α-aryl imidates, high conversion depends on adding trimethylsilyl chloride (TMSCl) to the reaction mixture. In the presence of a suitable Lewis acid, cyclohexanone is a good electrophile in the aldol reaction of imidates.

Diastereoselective Electrophilic α-Hydroxyamination of N-tert-Butanesulfinyl Imidates

Diastereoselective α-hydroxyamination of N-tert-butanesulfinyl imidates using nitrosoarenes is reported. A catalytic amount of base effectively promotes the hydroxyamination reaction of α-aryl-substituted imidates, and the resulting α-hydroxyamino imidates can be transformed into a range of synthetically useful intermediates.

A protecting-group-free synthesis of (+)-nephrosteranic, (+)-protolichesterinic, (+)-nephrosterinic, (+)-phaseolinic, (+)-rocellaric acids and (+)-methylenolactocin

A collective synthesis of a γ-butyrolactone class of paraconic acids such as (+)-methylenolactocin, (+)-phaseolinic acid, (+)-nephrosteranic acid, (+)-nephrosterinic acid, (+)-rocellaric acid and (+)-protolichesterinic acid is described.

Asymmetric Michael Addition Induced by (R)-tert-Butanesulfinamide and Syntheses of Chiral Pyrazolidinone Derivatives

A highly diastereoselective Michael addition of (R)-N-tert-butanesulfinyl imidates 8 to α,β-unsaturated pyrazolidinone 3a has been developed to afford pyrazolidinones 10 possessing three contiguous stereocenters with good to excellent yield and excellent diastereoselectivity. A two-step conversion of reduction and cyclization provides the bicyclic pyrazolopiperidine 12 in a good yield. A series of pyrazolopiperidine derivatives 18 with a quaternary carbon center at C-3a are stereoselectively synthesized via alkylation or Michael addition.

Diastereoselective synthesis of 2-methoxyimidoyloxiranes via dimethyl phosphite-mediated coupling of α-keto N-sulfinyl imidates with aldehydes

A dimethyl phosphite-triggered coupling of α-keto N-tert-butylsulfinyl imidates with aldehydes provides access to enantioenriched 2-methoxyimidoyloxiranes with excellent diastereoselectivities.

Total Synthesis of Lignan Lactone (-)-Hinokinin

This research paper is aimed at studying the total synthesis of pharmacologically active lignan (-)-hinokinin. The synthesis features a three-step cascade reaction involving highly stereoselective Michael addition, anion-oxidative hydroxylation, and oxygen anion cyclization to construct the pivotal butyrolactonimidate intermediate.

Total syntheses of (-)-isoschizogamine and (-)-2-hydroxyisoschizogamine

Total syntheses of (-)-isoschizogamine and (-)-2-hydroxyisoschizogamine are described. The synthesis employs two asymmetric Michael additions to establish chiral centers at C7 and the quaternary carbon C20. Regioselective reduction of the methylthioiminium cation rather than the enamine generates an isoschizogamine-type pentacyclic skeleton. Acidic hydrolysis of the isoschizogamine-type intermediate in the absence of oxygen provides natural (-)-isoschizogamine. Conducting the reaction in the presence of oxygen leads to a multistep oxidative hydrolysis cascade that affords unnatural (-)-2-hydroxyisoschizogamine.