Studies Directed toward the Total Synthesis of Lactonamycin: Control of the Sense of Cycloaddition of a Quinone through Directed Intramolecular Catalysis

The Castagnoli–Cushman Reaction

Since the first reports of the reaction of imines and cyclic anhydrides by Castagnoli and Cushman, this procedure has been applied to the synthesis of a variety of lactams, some of them with important synthetic or biological interest. The scope of the reaction has been extended to the use of various Schiff bases and anhydrides as well as to different types of precursors for these reagents. In recent years, important advances have been made in understanding the mechanism of the reaction, which has historically been quite controversial. This has helped to develop reaction conditions that lead to pure diastereomers and even homochiral products. In addition, these mechanistic studies have also led to the development of new multicomponent versions of the Castagnoli–Cushman reaction that allow products with more diverse and complex molecular structures to be easily obtained.

Highly Enantio- and Diastereoselective Catalytic Asymmetric Tamura Cycloaddition Reactions

The first broad-scope catalytic asymmetric Tamura cycloaddition reactions are reported. Under the influence of anion-binding bifunctional catalysis a wide range of α,β-unsaturated N-trityl imines undergo reactions with enolisable anhydrides to form highly synthetically useful α-tetralone structures with excellent enantio- and -diastereocontrol. In stark contrast to the previous literature benchmarks, doubly activated or highly electron deficient alkenes are not required. A facile two-step, high yielding sequence can convert the cycloadducts to α-haloketones (challenging to generate catalytically by other means) with the net formation of two new C-C bonds and three new contiguous stereocentres with exquisite stereocontrol. A DFT study has provided insight into the catalyst mode of action and the origins of the observed enantiocontrol.

The base-catalysed Tamura cycloaddition reaction: calculation, mechanism, isolation of intermediates and asymmetric catalysis

A combination of experimental and computational techniques has shown that the mechanism of the base-catalysed Tamura cycloaddition is not a concerted Diels–Alder process.

An Approach to the Core of Lactonamycin

A cascade reaction has been developed for the synthesis of lactonamycin. In this paper, we demonstrate that a transition-metal-free thermal ene-diyne cyclization can be used for the construction of the entire core of the antibiotic lactonamycin and anticancer agent lactonamycin Z.

The chemistry of isoindole natural products

This review highlights the chemical and biological aspects of natural products containing an oxidized or reduced isoindole skeleton. This motif is found in its intact or modified form in indolocarbazoles, macrocyclic polyketides (cytochalasan alkaloids), the aporhoeadane alkaloids, meroterpenoids from Stachybotrys species and anthraquinone-type alkaloids. Concerning their biological activity, molecular structure and synthesis, we have limited this review to the most inspiring examples. Within different congeners, we have selected a few members and discussed the synthetic routes in more detail. The putative biosynthetic pathways of the presented isoindole alkaloids are described as well.

Dynamic kinetic resolution during a vinylogous Payne rearrangement: a concise synthesis of the polar pharmacophoric subunit of (+)-scyphostatin

The diastereomeric epoxycyclohexenols 3a/b (obtained via a Wharton rearrangement of a bis-epoxycyclohexanone precursor) were shown to undergo interconversion via a facile vinylogous Payne rearrangement. Mechanistic issues were probed; the doubly O-deuterated analogues underwent this equilibration more slowly than the parent dihydroxy compounds. It was possible to kinetically resolve the mixture of 3a/b under equilibrating conditions by use of Amano PS. This DKR is additionally noteworthy because it sets four stereocenters in a single event.

Small molecule natural products in the discovery of therapeutic agents: the synthesis connection

Natural products have been a rich source of agents of value in medicine. They have also inspired, at various levels, the fashioning of nonnatural agents of pharmaceutical import. Hitherto, these nonnatural derivatives have been primarily synthesized by manipulating the natural product. As a consequence of major innovations in the subscience of synthetic methodology, the capacity of synthesis to deal with molecules of considerable complexity has increased dramatically. In this paper, we show by example some total syntheses which draw from strategy-enabling advances in methodology. Moreover, we show how these capabilities can be used to discover and develop new agents of potential pharmaceutical value without recourse to the natural product itself.

Studies on the total synthesis of lactonamycin: synthesis of the CDEF ring system

A concise and efficient synthesis of the tetracyclic CDEF ring system of lactonamycin (1) is described. The key step involved the Lewis acid mediated, intramolecular Friedel-Crafts acylation of carboxylic acid 6 to produce the tetracyclic CDEF core structure of target 1. The synthesis of 6 was carried out using a high-yielding Negishi coupling of benzyl bromide 7 with triflate 8, which was accessible in 11 steps and 31% overall yield on a multigram scale starting from trihydroxy acid 9.

Studies on the Total Synthesis of Lactonamycin: Construction of Model ABCD Ring Systems

Model studies on the synthesis of the tetracyclic ABCD ring system of lactonamycin (1) are described. The key step involved the double Michael addition reaction of alcohol 8 to propynoate esters to produce the BCD units 13 and 14 of the target 1. Alternatively, double Michael addition of alcohol 8 to di-tert-butyl acetylenedcarboxylate gave the corresponding BCD ring systems 36 and 37. Acid-mediated hydrolysis of the dihydroquinone monoketal units of 13 and 14 and 36 and 37 in the presence of air gave the corresponding quinones 7 and 39. These were converted into the tetracyclic ABCD units 6, 26a, 40, and 42 of lactonamycin (1) by either dihydroxylation or epoxidation and acid-catalyzed lactonization.

A nucleophile-catalyzed cycloisomerization permits a concise synthesis of (+)-harziphilone

Substantial structural transformations of much use in complex chemical synthesis can be achieved by channeling the reactivity of highly unsaturated molecules. This report describes the direct conversion of an acyclic polyunsaturated diketone to the HIV-1 Rev/Rev-responsive element inhibitor harziphilone under mild reaction conditions.