Concise asymmetric total synthesis of lycopodine and flabelliformine via cascade cyclization reaction

The shortest asymmetric total synthesis of lycopodine (3) and the first asymmetric total synthesis of flabelliformine (4) were accomplished by a strategy that features a cascade cyclization of linear substrate (5) to construct tetracyclic structure (6).     

Iminium Ion Cascade Reactions: Stereoselective Synthesis of Quinolizidines and Indolizidines

A novel iminium ion cascade reaction has been developed that allows for the stereoselective synthesis of a variety of substituted aza-fused bicycles. The combination of amino allylsilanes and aldehydes (or ketones) was used to synthesize a number of quinolizidines and indolizidines in a one-pot reaction sequence. This technology has been used to effect the facile syntheses of several indolizidine and quinolizidine natural products including (±)-epilupinine, (±)-tashiromine, and (−)-epimyrtine. Substrate scope has been examined varying the type of amino allylsilanes (primary, secondary, and conjugated) and carbonyl compounds (aldehydes and ketones) to give a variety of fused ring structures. Varying the components chosen allows for the inclusion of synthetically useful functional groups at different positions on the core structure. The methodology has been used to construct the tricyclic core structures present in the cylindricine family and halichlorine.     

Efficient construction of the core framework of lysidicin A via three Claisen rearrangements including a cascade reaction

A model compound (6) with the core skeleton of lysidicin A was synthesized as a racemate. The key step (8→7) includes three Claisen rearrangements of the triether with phloroglucinols; two of which rearranged in a cascade manner and the other was a simple rearrangement. This one-pot reaction enabled the introduction of three phloroglucinol units at the correct positions and makes the synthetic approach significantly efficient.     

Synthesis of chiral isoindolinones via asymmetric propargylation/lactamization cascade

A Zn-mediated propargylation/lactamization cascade reaction with chiral 2-formylbenzoate derived N-tert-butanesulfinyl imines was realized, which provided a practical and efficient method for the synthesis of chiral isoindolinones. High diastereoselectivities (up to 97:3 dr) and good reaction yields were observed for most examined cases.     

Organocatalytic asymmetric cascade cyclization reaction of o-hydroxy cinnamaldehydes with diphenylphosphine oxide

A highly stereoselective asymmetric cascade cyclization reaction between o-hydroxycinnamaldehydes and diphenylphosphine oxide has been achieved with 84%-99% ee and 7:1-20:1 dr under the catalysis of L-prolinol silyl ether.     

NHC-catalysed retro-aldol/aldol cascade reaction enabling solvent-controlled stereodivergent synthesis of spirooxindoles

An N-heterocyclic carbene (NHC)-catalysed retro-aldol/aldol cascade reaction of spirooxindole-based β-hydroxyaldehyde has been developed. The ring opening-closure process enables the diastereodivergent synthesis of spirocyclopentaneoxindole products with four consecutive stereocenters by simply changing the reaction solvents (THF or DCE). The Michael/aldol/retro-aldol/aldol sequential protocol allows the diastereodivergent synthesis of spirocyclopentaneoxindoles from 3-substituted oxindole and α,β-unsaturated aldehyde under the relay catalysis of a chiral secondary amine and an NHC catalyst. Moreover, four stereoisomers of the product can be selectively provided by using different combinations of a chiral secondary amine and a solvent.     

Catalytic asymmetric reactions in alkaloid and terpenoid syntheses

Catalytic asymmetric induction is one of the most important methods in current synthetic organic chemistry for designing efficient and attractive synthetic routes. The efficient total synthesis of a natural product can be achieved through the identification of appropriate method and strategy. This Letter introduces the catalytic asymmetric syntheses of alkaloids and terpenoids based on an overview of four recently reported types of asymmetric reaction: (1) asymmetric decarboxylative allylation, (2) organocatalytic cascade reaction, (3) polyene cyclization, and (4) asymmetric [2+2]-photocycloaddition catalyzed by a chiral Lewis acid.     

A Negishi cross-coupling reaction enables the total synthesis of (+)-stachyflin

We present a full account on the development of the total synthesis of the antiviral meroterpenoid (+)-stachyflin. The decalin subunit is rapidly accessed by an exo-selective Diels–Alder reaction, whereas the isonindolinone was synthesized via a highly efficient and practical de novo route starting from dimedone. A challenging sp²–sp³ Negishi cross-coupling reaction enabled construction of the crucial C15–C16 bond that connects the arene with the decalin subunit. For the final installation of the cis-decalin framework, a Lewis acid-catalyzed cyclization was applied.     

Concise total syntheses of heliannuols B and D

Concise and efficient enantioselective total syntheses of heliannuols B and D have been accomplished using chirality transfer through a Lewis acid-promoted Claisen rearrangement for the construction of the C7 tertiary stereogenic center and a relay ring-closing metathesis for assembling the dihydrobenzo[b]oxepine backbone of the natural products as the key steps.     

Pyrrolo-dihydropteridines via a cascade reaction consisting of iminium cyclization and O-N Smiles rearrangement

The reactions of 5-pyrrolyl-pyrimidinyloxyacetaldehyde or methyl ketone with primary amines yielded hydroxymethylpyrrolopteridine derivatives via a cascade of iminium cyclization and O-N Smiles rearrangement. The present cascade exhibited a different profile compared to the previously reported ones, which consisted of N-N Smiles rearrangement. Lewis acid (TiCl₄) under carefully controlled conditions was employed to suppress the competing formation of imine dimers to give the desired heterocycles. A plausible mechanism involving the iminium cyclization and Smiles rearrangement is proposed. This methodology has been used to generate a series of 6-hydroxymethylpyrrolo[1,2-f]pteridine derivatives with potential biological activities.     

Formal synthesis of (−)-morphine from d-glucal based on the cascade Claisen rearrangement

The formal synthesis of (−)-morphine is described. The C-ring in morphine was prepared in an optically pure form from d-glucal using Ferrier’s carbocyclization reaction, and the vicinal tertiary and quaternary stereocenters in the C-ring were stereoselectively generated in a one-step reaction based on the cascade sequential Claisen rearrangement of an allylic vicinal diol derivative. After the one-step formation of the dibenzofuran structure, the intramolecular Friedel-Crafts type reaction effectively constructed the ABCE-phenanthrofuran skeleton. Introduction of a tosylamide function, followed by reductive cyclization furnished (−)-dihydroisocodeine, the known synthetic intermediate for (−)-morphine.     

Asymmetric formal total synthesis of the stemofoline alkaloids: the evolution,development, and application of a catalytic dipolar cycloaddition cascade

A formal synthesis of didehydrostemofoline and isodidehydrostemofoline has been accomplished by preparing an intermediate in the Overman synthesis of these alkaloids from commercially available 2-deoxy-d-ribose. The work presented in this account chronicles the evolution of our explorations to identify the optimal steric and electronic control elements necessary to generate the tricyclic core structure of these alkaloids in a single operation from an acyclic precursor. The key step in the synthesis is a novel dipolar cycloaddition cascade sequence that is initiated by cyclization of a rhodium-derived carbene onto the nitrogen atom of a proximal imine group to generate an azomethine ylide that then undergoes spontaneous cyclization via dipolar cycloaddition. The synthesis features several other interesting reactions, including a Boord elimination to prepare a chiral allylic alcohol, a highly diastereoselective Hirama–Itô cyclization, and a useful modification of the Barton decarboxylation protocol.     

Recent applications of gold-catalyzed cascade reactions in total synthesis of natural product

From the point of the view of the synthetic efficiency, the concept ‘step economy’ was required in total synthesis of natural product. Recently, versatile gold-catalyzed cascade reactions have been developed, and relating reports on practical applications in total synthesis has increased. This digest focuses and summarizes the gold-catalyzed reaction cascades in natural product synthesis during last five years with brief discussion on the reaction mechanism of the key gold-catalyzed cascade transformations.     

Highly chemo- and enantioselective vinylogous aldol/cyclization cascade reaction to construct chiral 5,6-dihydropyran-2-ones

An organocatalytic chemo- and enantioselective vinylogous aldol/cyclization cascade reaction between β,γ-unsaturated amides and β,γ-unsaturated α-keto esters was developed. With 5?mol% of chiral tertiary amine-thiourea catalyst C3, highly functionalized 5,6-dihydropyran-2-ones with a quaternary stereocenter were constructed in a straightforward manner with high yields (up to 99%) and excellent enantioselectivities (up to 98% ee).     

A Concise Total Synthesis of (+)‐Tetrabenazine and (+)‐α‐Dihydrotetrabenazine

Highly concise asymmetric total syntheses of (+)‐tetrabenazine ( 1 ), a drug for the treatment of chorea associated with Huntington’s disease, and of (+)‐α‐dihydrotetrabenazine ( 2 ), an active metabolite of 1 , have been accomplished. Our synthetic route features a trans‐selective enol etherification, followed by an unprecedented cation‐dependent aza‐Claisen rearrangement to establish the carbon framework and two stereogenic centers of tetrabenazine. The syntheses consist of seven steps (34 % overall yield) for (+)‐ 2 and eight steps (22 % overall yield) for (+)‐ 1 .     

Asymmetric total syntheses of (+)-goniopypyrone and (+)-9-deoxygoniopypyrone

Asymmetric total syntheses of (+)-goniopypyrone (1) and (+)-deoxygoniopypyrone (2) from methyl cinnamate (7) via (DHQ)2-PHAL-OsO4 catalyzed asymmetric dihydroxylation and highly stereoselective 2-furylcopper addition in eight steps and eleven steps with overall yield of 20% and 13%,respectively,are described.     

An asymmetric route to total synthesis of the furano lignan (+)-veraguensin

Total synthesis of the furano lignan (+)-veraguensin is described. The key steps involve a diastereoselective aldol-type condensation of an ester enolate having an α-chiral center with an aromatic aldehyde and a novel isomerization of the syn vicinal substituents on the furan ring via a ring opening-ring closing protocol.     

Generation of all carbon quaternary stereocenters at the C-3 carbon of piperidinones and pyrrolidinones and its application in natural product total synthesis

Methodologies regarding the construction of an all carbon quaternary stereocenters at C-3 of lactams have posed significant challenges in the total synthesis of natural products. This review summarizes the advancements for the construction of an all carbon quaternary stereocenters at C-3 of piperidinones and pyrrolidinones and its application in the total synthesis of biologically active and architecturally complex alkaloids.