Expeditious and Divergent Total Syntheses of Aspidosperma Alkaloids Exploiting Iridium(I)-Catalyzed Generation of Reactive Enamine Intermediates

Total synthesis of alkaloids using both chemical and biochemical methods

A chemoenzymatic approach to synthesize structurally complex natural alkaloids (tetrahydroisoquinoline antibiotics, indole diterpenes, and monoterpene indole alkaloids) has been reviewed.

Directed ortho-metalation-nucleophilic acyl substitution strategies in deep eutectic solvents: the organolithium base dictates the chemoselectivity

Directed ortho metalation (DoM) or nucleophilic acyl substitution (S_NAc) can be efficiently programmed on the same aromatic carboxylic acid amide, in a choline chloride-based eutectic mixture, by simply switching the nature of the organolithium reagent. Telescoped, one-pot ortho-lithiation/Suzuki-Miyaura cross-couplings have also been demonstrated for the first time in Deep Eutectic Solvents.

Approach to Fully Substituted Cyclic Nitrones from N-Hydroxylactam Derivatives: Development and Application to the Total Synthesis of Cylindricine C

An approach to cyclic nitrones from N-hydroxylactam derivatives is documented. The nucleophilic addition of an organolithium reagent to an N-OSEM [SEM=2-(trimethylsilyl)ethoxymethyl] lactam forms a five-membered chelated intermediate, which undergoes both elimination and deprotection to give a fully substituted nitrone in a one-pot process. When combined with the N-oxidation of easily available chiral lactams, this method becomes especially useful for the quick synthesis of chiral nitrones in enantio-pure form, enabling the concise total synthesis of cylindricine C.

Iridium-Catalyzed Reductive Nucleophilic Addition to Secondary Amides

An iridium-catalyzed reductive nucleophilic addition to secondary amides is reported. After the iridium-catalyzed reduction, the resulting imines can undergo the Strecker reaction, the Mannich reaction, allylation, and [3 + 2]-cycloaddition. The method shows high chemoselectivity in the presence of other functional groups such as methyl ester.

Iridium-catalyzed reductive Ugi-type reactions of tertiary amides

Amides are ubiquitous in the fine chemical, agrochemical and pharmaceutical industries, but are rarely exploited as substrates for homologous amine synthesis. By virtue of their high chemical stability, they are essentially inert to all but the harshest of chemical reagents and to the majority of chemical transformations routinely used in organic synthesis. Accordingly, the development of chemoselective carbon−carbon bond-forming methodologies arising from the functionalization of the amide functionality should find widespread use across academia and industry. We herein present our findings on a series of Ugi-type reactions of tertiary amides enabled by an initial chemoselective iridium-catalyzed partial reduction, followed by reaction with isocyanide and (thio)acetic acid or trimethylsilyl azide, thus providing a multicomponent synthesis of α-amino (thio)amide or α-amino tetrazole derivatives. The reductive Ugi-type reactions are amenable to a broad range of amides and isocyanides, and are applicable to late-stage functionalization of various bioactive molecules and pharmaceutical compounds.

Chemical transformation of amides is normally occurring under harsh conditions. Here, the authors report a mild iridium-catalyzed reductive Ugi-type coupling of tertiary amides, isocyanides and (thio)acetic acid or trimethylsilyl azide to give homologous, bioactive amine products.

Cycloaddition/annulation strategies for the construction of multisubstituted pyrrolidines and their applications in natural product synthesis

Pyrrolidines are privileged substructures of numerous bioactive natural products and drugs.

Total synthesis of complex alkaloids by nucleophilic addition to amides

This mini review focuses on the recent progress of total synthesis of complex alkaloids based on the nucleophilic additions toN-alkoxyamides, tertiary amides and secondary amides.

Total synthesis of natural productsviairidium catalysis

An overview of the highlights in total synthesis of natural products using iridium as a catalyst is given.

Unified Total Synthesis of Stemoamide-Type Alkaloids by Chemoselective Assembly of Five-Membered Building Blocks

A unified total synthesis of stemoamide-type alkaloids is reported. Our synthetic approach features the chemoselective convergent assembly of five-membered building blocks via stemoamide as the common precursor to tetracyclic natural products. The synthesis consists of two successive coupling reactions of the three five-membered building blocks. The first coupling reaction is the vinylogous Michael addition/reduction sequence, which enables the gram-scale synthesis of stemoamide. The second coupling reaction is a chemoselective nucleophilic addition to stemoamide. While the lactone-selective nucleophilic addition to stemoamide affords saxorumamide and isosaxorumamide, the lactam-selective reductive nucleophilic addition leads to the formation of stemonine. Both chemoselective nucleophilic additions enable direct modification of stemoamide, resulting in highly concise and efficient total syntheses of the stemoamide-type alkaloids.

A Gold-Catalyzed Domino Cyclization Enabling Rapid Construction of Diverse Polyheterocyclic Frameworks

We report herein an efficient gold(I)-catalyzed post-Ugi domino dearomatization/ipso-cyclization/Michael sequence that enables access to libraries of diverse (hetero)arene-annulated tricyclic heterocycles. This process affords novel complex polycyclic scaffolds in moderate to good yields from readily available acyclic precursors with excellent chemo-, regio-, and diastereoselectivity. The power of this strategy has been demonstrated by the rapid synthesis of 40 highly functionalized polyheterocycles bearing indole, pyrrole, (benzo)furan, (benzo)thiophene, pyrazole, and electron-rich arene groups in two operational steps.

Enantioselective Total Synthesis of (-)-Deoxoapodine

The first enantioselective total synthesis of (-)-deoxoapodine is described. Our synthesis of this hexacyclic aspidosperma alkaloid includes an efficient molybdenum-catalyzed enantioselective ring-closing metathesis reaction for the desymmetrization of an advanced intermediate that introduces the C5-quaternary stereocenter. After C21-oxygenation, the pentacyclic core was accessed by electrophilic C19-amide activation and transannular spirocyclization. A biogenetically inspired dehydrative C6-etherification reaction proved highly effective to secure the F-ring and the fourth contiguous stereocenter of (-)-deoxoapodine with complete stereochemical control.

Tertiary amine synthesis via reductive coupling of amides with Grignard reagents

A new iridium catalyzed reductive coupling reaction of Grignard reagents and tertiary amides affording functionalised tertiary amine products is described.

A new iridium catalyzed reductive coupling reaction of Grignard reagents and tertiary amides affording functionalised tertiary amine products via an efficient and technically-simple one-pot, two-stage experimental protocol, is reported. The reaction – which can be carried out on gram-scale using as little as 1 mol% Vaska's complex [IrCl(CO)(PPh₃)₂] and TMDS as the terminal reductant for the initial reductive activation step – tolerates a broad range of tertiary amides from (hetero)aromatic to aliphatic (branched, unbranched and formyl) and a wide variety of alkyl (linear, branched), vinyl, alkynyl and (hetero)aryl Grignard reagents. The new methodology has been applied directly to bioactive molecule synthesis and the high chemoselectivity of the reductive coupling of amide has been exploited in late stage functionalization of drug molecules. This reductive functionalisation of tertiary amides provides a new and practical solution to tertiary amine synthesis.

Mild Reductive Functionalization of Amides into N-Sulfonylformamidines

The development of a protocol for the reductive functionalization of amides into N‐sulfonylformamidines is reported. The one‐pot procedure is based on a mild catalytic reduction of tertiary amides into the corresponding enamines by the use of Mo(CO)₆ (molybdenum hexacarbonyl) and TMDS (1,1,3,3‐tetramethyldisiloxane). The formed enamines were allowed to react with sulfonyl azides to give the target compounds in moderate to good yields.

Iridium-Catalyzed Reductive Strecker Reaction for Late-Stage Amide and Lactam Cyanation

A new iridium-catalyzed reductive Strecker reaction for the direct and efficient formation of α-amino nitrile products from a broad range of (hetero)aromatic and aliphatic tertiary amides, and N-alkyl lactams is reported. The protocol exploits the mild and highly chemoselective reduction of the amide and lactam functionalities using IrCl(CO)[P(C₆ H₅ )₃ ]₂ (Vaska's complex) in the presence of tetramethyldisiloxane, as a reductant, to directly generate hemiaminal species able to undergo substitution by cyanide upon treatment with TMSCN (TMS=trimethylsilyl). The protocol is simple to perform, broad in scope, efficient (up to 99 % yield), and has been successfully applied to the late-stage functionalization of amide- and lactam-containing drugs, and naturally occurring alkaloids, as well as for the selective cyanation of the carbonyl carbon atom linked to the N atom of proline residues within di- and tripeptides.