The total synthesis of some monomeric Vinca alkaloids: dl-vincadine, dl-vincaminoreine, dl-vincaminorine, dl-vincadifformine, dl-minovine, and dl-vincaminoridine

Total Synthesis of (±)-Aspidospermidine, (±)-Aspidofractinine, (±)-Limaspermidine, and (±)-Vincadifformine via a Cascade and Common Intermediate Strategy

A concise strategy for the total synthesis of several Aspidosperma alkaloids is reported. A Suzuki-Miyaura cross-coupling provides access to a 2-vinyl indole that undergoes a Diels-Alder cascade reaction with butyn-2-one to deliver a pyrroloindoline intermediate. This undergoes cascade amidation, reduction, skeletal rearrangement, and intramolecular Michael addition to provide a common intermediate containing the full framework of the Aspidosperma alkaloids. The utility of this intermediate is shown in the synthesis of four different natural products.

A Concise Enantioselective Total Synthesis of (-)-Deoxoapodine

We have established a highly convergent 10-step route for the total synthesis of (-)-deoxoapodine, which is a hexacyclic aspidosperma alkaloid. The quaternary C5 center of the characteristic tetrahydrofuran ring was constructed by a chiral-phosphoric-acid-catalyzed enantioselective bromocycloetherification in a 5-endo fashion and subsequent allylation by using the Keck protocol. Construction of the aspidosperma skeleton features the formation of a nine-membered lactam by a catalytic C-H palladation/alkylation cascade at the indole 2-position and an iron-catalyzed oxidative transannular reaction at a late-stage of the synthesis.

Synthetic Approaches to Tricyclic Aminoketones in the Total Synthesis of Aspidosperma and Kopsia Alkaloids

Aspidosperma and kopsia alkaloids are significant functional molecules because of their potent biological activities. Their intricate structures present an intrinsic synthetic challenge and thus attract significant attention from synthetic organic academic community. Over the past decades, a series of elegant strategies has been developed, in particular, the Stork's original Fischer indolization of tricyclic aminoketones 1. Herein, we report a comprehensive review on various synthetic approaches access to tricyclic aminoketones 1 and provide a practical guidance to readers whose are interested in employing tricyclic aminoketones 1 as versatile building blocks in the realm of total synthesis of aspidosperma, kopsia and structurally related alkaloids.

Reductive ortho C–H cyanoalkylation of aryl(heteroaryl) sulfoxides: a general approach to α-aryl(heteroaryl) nitriles

A catalyst-free low-temperature cyanoalkylation has been developed as a general protocol for the synthesis of α-aryl(heteroaryl) nitriles.

Formal total syntheses of classic natural product target molecules via palladium-catalyzed enantioselective alkylation

Pd-catalyzed enantioselective alkylation in conjunction with further synthetic elaboration enables the formal total syntheses of a number of "classic" natural product target molecules. This publication highlights recent methods for setting quaternary and tetrasubstituted tertiary carbon stereocenters to address the synthetic hurdles encountered over many decades across multiple compound classes spanning carbohydrate derivatives, terpenes, and alkaloids. These enantioselective methods will impact both academic and industrial settings, where the synthesis of stereogenic quaternary carbons is a continuing challenge.

Biogenetically inspired synthesis and skeletal diversification of indole alkaloids

To access architecturally complex natural products, chemists usually devise a customized synthetic strategy for constructing a single target skeleton. In contrast, biosynthetic assembly lines often employ divergent intramolecular cyclizations of a polyunsaturated common intermediate to produce diverse arrays of scaffolds. With the aim of integrating such biogenetic strategies, we show the development of an artificial divergent assembly line generating unprecedented numbers of scaffold variations of terpenoid indole alkaloids. This approach not only allows practical access to multipotent intermediates, but also enables systematic diversification of skeletal, stereochemical and functional group properties without structural simplification of naturally occurring alkaloids. Three distinct modes of [4+2] cyclizations and two types of redox-mediated annulations provided divergent access to five skeletally distinct scaffolds involving iboga-, aspidosperma-, andranginine- and ngouniensine-type skeletons and a non-natural variant within six to nine steps from tryptamine. The efficiency of our approach was demonstrated by successful total syntheses of (±)-vincadifformine, (±)-andranginine and (-)-catharanthine.

Total synthesis of (-)- and ent-(+)-vindoline and related alkaloids

A concise 11-step total synthesis of (-)- and ent-(+)-vindoline (3) is detailed based on a unique tandem intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of a 1,3,4-oxadiazole inspired by the natural product structure, in which three rings and four C-C bonds are formed central to the characteristic pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural product in a single step. As key elements of the scope and stereochemical features of the reaction were defined, a series of related natural products of increasing complexity were prepared by total synthesis including both enantiomers of minovine (4), 4-desacetoxy-6,7-dihydrovindorosine (5), 4-desacetoxyvindorosine (6), and vindorosine (7) as well as N-methylaspidospermidine (11). Subsequent extensions of the approach provided both enantiomers of 6,7-dihydrovindoline (8), 4-desacetoxyvindoline (9), and 4-desacetoxy-6,7-dihydrovindoline (10).

Total synthesis of natural (+)- [corrected] and ent-(-)-4-desacetoxy-6,7-dihydrovindorosine [corrected] and natural and ent-minovine: oxadiazole tandem intramolecular Diels-Alder/1,3-dipolar cycloaddition reaction

Efficient and unusually concise total syntheses of both enantiomers of the Aspidosperma alkaloids 4-desacetoxy-6,7-dihydrovindorosine (12) and minovine (1) are detailed. A tandem intramolecular Diels-Alder/1,3-dipolar cycloaddition reaction of the 1,3,4-oxadiazole 8, in which three new rings, four new C-C bonds, and five stereocenters are formed, is a key step in the sequence. The availability of optically active material permitted an assessment of the enantiomeric integrity of minovine and the source of its reported unusual optical rotation. [Reaction: see text]