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The communesin alkaloids are a diverse family of Penicillium-derived alkaloids. Their caged-polycyclic structure and intriguing biological profiles have made these natural products attractive targets for total synthesis. Similarly, the ascidian-derived alkaloid, perophoramidine, is structurally related to the communesins and has also become a popular target for total synthesis. This review serves to summarize the many elegant approaches that have been developed to access the communesin alkaloids and perophoramidine. Likewise, strategies to access the communesin ring system are reviewed.

A convergent synthetic route toward cytotoxic agent peloruside A that hinges on the use of an alkyne linchpin to assemble the natural product is described. Other highlights of this synthesis include an asymmetric desymmetrization reaction of a 1,3-diol, a one-pot conversion of a dibromoolefin to a stereodefined enone, and a diastereoselective aldol condensation. Misassignment of the absolute stereochemistry of the C18 stereocenter in our synthesis provided the natural product epimeric at the C18 ethyl stereocenter.

An enantioselective α-hydroxyacetate aldol reaction that employs N-acetyl pyrroles as activated ester equivalents and generates syn 1,2-diols in good yield and diastereoselectivity is reported. This dinuclear zinc–ProPhenol-catalyzed transformation proceeds with high enantioselectivity with a wide variety of substrates including aryl, alyl, and alkenyl aldehydes. The resulting α,β-dihydroxy activated esters are versatile intermediates for the synthesis of a variety of carboxylic acid derivatives including amides, esters, and unsymmetrical ketones.

A concise catalytic asymmetric synthesis of the proposed structure of trocheliophorolide B is reported. The synthetic sequence notably features an asymmetric acetaldehyde alkynylation, a Ru-catalyzed alder–ene reaction, and a Zn-ProPhenol ynone aldol condensation. Comparison with the reported data suggests a misassignment of the natural product structure.

A protocol for the enantioselective [3 + 2] cycloaddition of trimethylenemethane (TMM) with imines has been developed. Central to this effort were the novel phosphoramidite ligands developed in our laboratories. The conditions developed to effect an asymmetric TMM reaction using 2-trimethylsilylmethyl allyl acetate were shown to be tolerant of a wide variety of imine acceptors to provide the corresponding pyrrolidine cycloadducts with excellent yields and selectivities. Use of a bis-2-naphthyl phosphoramidite allowed the successful cycloaddition of the parent TMM with N-Boc imines, and has further permitted the reaction of substituted donors with N-tosyl aldimines and ketimines in high regio-, diastereo-, and enantioselectivity. Use of a diphenylazetidine ligand allows the complementary synthesis of the exocyclic nitrile product shown, and we demonstrate control of the regioselectivity of the product based on manipulation of the reaction parameters.

A new strategy for the synthesis of chiral β-alkynyl esters which relies on sequential Pd and Cu catalysis is reported. Terminal alkynes bearing aryl-, alkyl-, and silyl-groups can be employed without prior activation yielding a wide range of important chiral building blocks. The reaction sequence utilizes a robust Pd(II)-catalyzed hydroalkynylation of ynoates with terminal alkynes providing geometrically-pure ynenoates which are readily reduced by CuH. In contrast to previous reports, where additions to ynenoates proceed with marginal preference for the 1,6-pathway, this conjugate reduction occurs with high 1,4-selectivity yielding β-alkynyl esters with excellent levels of enantioselectivity. Importantly, the method tolerates a wide range of functionality, including allylic carbonates and carbamates, and thus allows for rapid elaboration of the β-alkynyl esters into a variety of chiral, substituted heterocycles.

Palladium-catalyzed asymmetric prenylation of oxindoles to selectively afford either the prenyl or the reverse prenyl product has been demonstrated. Control of regioselectivity in this transformation is governed by choice of ligand, solvent, and halide additive. The resulting prenylated and reverse prenylated products have been transformed into ent-flustramides and ent-flustramines A and B. Additionally, control in regio- and diastereoselectivity has been obtained using π-geranylpalladium complexes.

We report a full account of our work towards the development of an eight-step synthesis of anti-influenza drug (-)-oseltamivir (Tamiflu) from commercially available starting materials. The final synthetic route proceeds with an overall yield of 30 %. Key transformations include a novel palladium-catalyzed asymmetric allylic alkylation reaction (Pd-AAA) as well as a rhodium-catalyzed chemo-, regio-, and stereoselective aziridination reaction.

A robust route to 2,4-disubstituted pyrrole heterocycles relying upon a cascade reaction is reported. The reaction benefits from operational simplicity: it is air and moisture tolerant and is performed at ambient temperature. Control over the reaction conditions provides ready access to isopyrroles, 2,3,4- trisubstituted pyrroles and 3- substituted pyrollidin-2-ones.

A tricyclic core containing a 5,7-fused bicyclic unit of rameswaralide was prepared starting from a 1,6-enyne. The synthetic sequence involved (i) ruthenium-catalyzed [5+2]-cycloaddition of 1,6-enyne, (ii) an acyl radical based approach to construct the lactone, and (iii) a regioselective installation of the conjugated double bond by a concomitant sulfenylation-dehydrosulfenylation sequence.

We report that nitrogen heterocycles can serve as competent nucleophiles in the palladium-catalyzed dynamic kinetic asymmetric alkylation of vinyl aziridines. The resulting alkylated products were obtained with high regio-, chemo-, and enantioselectivity. Both substituted 1H-pyrroles and 1H-indoles were successfully employed to give exclusively the branched N-alkylated products. The synthetic utility of this process was demonstrated by applying this method to the preparation of several medicinal chemistry lead compounds and bromopyrrole alkaloids including longamide B, longamide B methyl ester, hanishin, agesamides A and B, and cyclooroidin.

A highly enantioselective method for the catalytic addition of terminal 1,3-diynes to aldehydes was developed using our dinuclear zinc ProPhenol (1) system. Furthermore, triphenylphosphine oxide was found to interact synergistically with the catalyst to substantially enhance the chiral recognition. The generality of this catalytic transformation was demonstrated with aryl, alpha,beta-unsaturated and saturated aldehydes, of which the latter were previously limited in alkynyl zinc additions. The chiral diynol products are also versatile building blocks that can be readily elaborated; this was illustrated through highly selective trans-hydrosilylations, which enabled the synthesis of a beta-hydroxyketone and enyne. Additionally, the development of this method allowed for the rapid total syntheses of several biologically important diynol-containing natural products.

Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio-, and enantioselective process for the synthesis of ketones bearing either a quaternary or a tertiary alpha-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic disubstituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium enolates, the DAAA reaction proceeds through an "outer sphere" S(N)2 type of attack on the pi-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the pi-allylpalladium cation must serve as the counterion for the enolate, the enolate probably exists as a tight-ion-pair. This largely prevents the common side reactions of enolates associated with the equilibrium between different enolates. The much milder reaction conditions as well as the much broader substrate scope also represent the advantages of the DAAA reaction over the direct allylation of preformed metal enolates.

Over the past decade, large strides have been achieved in the invention of methods for the direct enantioselective addition of alkynes and metal alkynylide nucleophiles into prochiral aldehydes, ketones, and imines. This review highlights and compares the available methods for these transformations.

Under dinuclear catalysis, the direct conjugate addition of 2(5H)-furanone to nitroalkenes involves the gamma-position of the nucleophile. The synthetically versatile Michael adducts are prepared in good yields, with high levels of diastereo- and enantioselectivity. A model is presented to rationalize the observed stereoselectivity.

The ideal in organic synthesis is to prepare complex molecules in the smallest possible number of steps. Also important is atom economy — limiting waste by ensuring that most of atoms present in the reactants end up in the product. Barry Trost and Guangbin Dong demonstrate these principles to good effect in a synthesis of the naturally occurring compound bryostatin 16 that takes about half as many steps as previous methods. A key reaction is the formation of a large ring, in a palladium-catalysed reaction between two alkynes (hydrocarbons containing carbon-carbon triple bonds). The bryostatins, a group of macrolide lactones originally isolated from coral-like marine organisms, display a range of biological activities including cytotoxicity, and have potential in anticancer and memory enhancement therapies. The ideal in organic synthesis is to prepare complex molecules using the smallest possible number of steps. Also important is atom economy, limiting waste by ensuring that most of atoms present in the reactants end up in the product. This paper demonstrates both of these principles to great effect in the synthesis of bryostatin 16, a biologically active, naturally occurring compound. The synthesis uses nearly half the number of steps of previously reported routes to bryostatins. Of the concepts used to improve the efficiency of organic syntheses, two have been especially effective: atom economy1 (the use of routes in which most of the atoms present in the reactants also end up in the product) and chemoselectivity2 (the use of reactions that take place only at desired positions in a molecule). Synthesis of complex natural products is the most demanding arena in which to explore such principles. The bryostatin family of compounds are especially interesting targets, because they combine structural complexity with promising biological activity3,4,5,6,7. Furthermore, synthetic routes to some bryostatins have already been reported9,10,11,12, providing a benchmark against which new syntheses can be measured. Here we report a concise total synthesis of bryostatin 16 (1), a parent structure from which almost all other bryostatins could in principle be accessed. Application of atom-economical and chemoselective reactions currently under development provides ready access to polyhydropyran motifs in the molecule, which are common structural features of many other natural products. The most notable transformations are two transition-metal-catalysed reactions. The first is a palladium-catalysed reaction of two different alkynes to form a large ring. The product of this step is then converted into a dihydropyran (the ‘C ring’ of bryostatins) in the second key reaction, which is catalysed by a gold compound. Analogues of bryostatin that do not exist in nature could be readily made by following this route, which might allow the biological activity of bryostatins to be fine-tuned.

The transition metal-catalyzed trimethylenemethane [3+2] cycloaddition provides a direct route to functionalized heterocycles. Herein, we describe a catalytic, asymmetric protocol for the reaction between 3-acetoxy-2-trimethylsilylmethyl-1-propene and various imines. The corresponding pyrrolidines were obtained in excellent yields and enantioselectivities making use of the novel phosphoramidite L10.

A Mannich-type addition of propargylic alcohols and N-methoxycarbonylimines has been achieved by using a vanadium catalyst. The reactivity of the vanadium catalyst could be modulated by modifying the silanol ligands to avoid the background reaction. The strategy described herein provides an atom-economical access to beta-aryl-substituted Z-enones with an allylic amino functional group, which are not readily accessible with other methods.

The use of imines bearing a hydrolyzable nitrogen substituent in direct asymmetric Mannich reactions with alpha-hydroxyketones is developed. Previous work focused on the use of N-arylimines or nonenolizable imines, and the latter with only methoxy-substituted alpha-hydroxyacetophenones. Using a dinuclear catalyst devised from 2,6-di-(S)-2'-diphenylhydroxymethylpyrrolidino-N-methyl)-4-methylphenol and diethylzinc, a broad array of hydroxyacetylated aromatics, including phenyl, 2-furyl, 1-naphthyl, and 2-naphthyl, react well. In addition, the reactions focused on the use of enolizable imines. With the N-diphenylphosphinoyl, the reactions are anti selective with enantiomeric excesses ranging from 83 to 99%, except for the reaction of the 2-methoxy-2'-hydroxyacetylbenzene. With the N-Boc-imines, the reactions were syn selective with enantiomeric excesses from 90 to 94%. The dependence of the diastereoselectivity on the nature of the N-substituent presumably arises from the steric demands of the diphenylphosphinoyl group.

A direct catalytic asymmetric aldol reaction of methyl vinyl ketone is described using our dinuclear zinc catalyst. The obtained aldol adduct functions as a bifunctional building block by utilization of the vinyl functionality. For example, convergent fragment coupling methods have been demonstrated via highly diastereoselective cycloaddition of nitrile oxide after reduction into 1,3-diol or via cross-metathesis reaction.