Modified Julia–Kocienski Reagents for a Stereoselective Introduction of Trisubstituted Double Bonds: A Formal Total Synthesis of Limazepine E and Barmumycin

Concise access to C2-ethylidene pyrrolo[1,4]benzodiazepine natural products

A 3-step route toward pyrrolo[1,4]benzodiazepine (PBD) antitumor antibiotic class members oxo-prothracarcin and boseongazepine B has been developed. This methodology also enables preparing oxo-tomaymycin in only 4 linear steps representing the shortest total synthesis known to date. The synthesis features an olefination with sterically demanding Julia-Kocienski reagents as the key step.

Stereoselective Olefination with Sterically Demanding Julia-Kocienski Reagents: Total Synthesis of Oxo-prothracarcin, Oxo-tomaymycin, and Boseongazepine B

Total syntheses of three pyrrolo[1,4]benzodiazepine anticancer antibiotic family members oxo-prothracarcin, oxo-tomaymycin, and boseongazepine B are described. The total syntheses feature late-stage stereoselective olefination employing modified Julia-Kocienski reagents that can be conveniently prepared in only two steps and allows for a significant reduction in the number of linear steps. Detailed density functional theory (DFT) studies explain the stereochemical outcome of the key step.

Bioinspired Palladium-Catalyzed Intramolecular C(sp3 )-H Activation for the Collective Synthesis of Proline Natural Products

Bioinspired palladium-catalyzed intramolecular cyclization of amino acid derivatives containing a vinyl iodide moiety by C-H activation enabled rapid access to a wide range of functionalized proline derivatives with an exocyclic olefin. To demonstrate the practicality of this methodology, the functionalized prolines were used as intermediates for the synthesis of several natural products: lucentamycin A, oxotomaymycin, oxoprothracarcin, and barmumycin.

The influence of α-coordinating groups of aldehydes on E/Z-selectivity and the use of quaternary ammonium counter ions for enhanced E-selectivity in the Julia-Kocienski reaction

Modified reaction conditions for improved E-selectivity of olefins in the Julia-Kocienski reaction of aldehydes having α-coordinating substituents are demonstrated. The chelating groups in aldehydes are expected to stabilize the syn-transition state with metal ions, whereas the weakly coordinating quaternary ammonium ions are devoid of all possible chelating interactions to enhance E-selectivity. A systematic investigation is presented to study the size of the neighbouring protecting groups of aldehydes and their chelation effect on E/Z-selectivity in the Julia-Kocienski reaction.

Enantiospecific Total Synthesis and Absolute Configuration Assignment of Chabrolobenzoquinone H

Chabrolobenzoquinone H (1), a meroditerpene metabolite with cytotoxic activity, is synthesized via a stereoselective Julia-Kocienski olefination between a chiral pool derived aliphatic PT-sulfone and a benzoquinone aldehyde partner. The latter was obtained via consecutive chain extension steps involving a Stille coupling and a stereospecific olefin cross-metathesis reaction followed by malonic ester synthesis and a Krapcho decarboxylation. Furthermore, this total synthesis securely determined the absolute configuration of the targeted natural product.

Toward the synthesis of the hypoxia selective anticancer agent BE-43547 A2

A short and enantioselective synthesis of the 19-epi-BE-43547 A2 chiral framework has been achieved in a high yield. The challenging key C15 tertiary stereocenter was derived from D-glucose. The synthetic strategy involves a Julia-Kocienski olefination to install the lipophilic side chain. An efficient protocol for Z to E isomerization of olefin was developed using a novel UV flow reactor. In addition, an unprecedented oxygen mediated hydroboration and the Krapcho decarboxylation of β-keto lactone were observed.

Isolation, chemistry, and biology of pyrrolo[1,4]benzodiazepine natural products

The isolation of the antitumor antibiotic anthramycin in the 1960s prompted extensive research into pyrrolo[1,4]benzodiazepines (PBD) as potential therapeutics for the treatment of cancers. Since then, nearly 60 PBD natural products have been isolated and evaluated with regard to their biological activity. Synthetic studies and total syntheses have enabled access to PBD analogues, culminating in the development of highly potent anticancer agents. This review provides a summary of the occurrence and biological activity of PBD natural products and covers the strategies employed for their total syntheses.

Stereoselective Synthesis of Trisubstituted (Z)-Alkenes from Ketones via the Julia-Kocienski Olefination Using 1-Methyl- and 1-tert-Butyl-1H-tetrazol-5-yl Alkyl Sulfones

1-Methyl-1H-tetrazol-5-yl (MT) alkyl sulfones 1b, 3b, and 7b react with various unsymmetrical ketones in the presence of LiHMDS in THF at low temperature to give trisubstituted (Z)-alkenes in good yields stereoselectively (Z/E = 91:9 to 99:1). For sterically less demanding ketones, olefination using t-Bu reagents 1d and 3d generated (Z)-alkenes with higher stereoselectivity (93:7-99:1).

Enantioselective total synthesis of pyrrolo-[2,1-c][1,4]-benzodiazepine monomers (S)-(−)-barmumycin and (S)-(+)-boseongazepine B

An efficient enantioselective total synthesis of pyrrolo-[2,1-c][1,4]benzodiazepine (PBD) monomers (S)-(−)-barmumycin and (S)-(+)-boseongazepine B was achieved through a stereocontrolled strategy, which relies on a proline catalysed asymmetric α-amination and ester α-ethylenation.