Stereochemically versatile synthesis of the C1-C12 fragment of tedanolide C

Development of the Synthesis of Desepoxy-Tedanolide C

We are presenting the development of our route for the total synthesis of desepoxy-tedanolide C. Through the obtained analytical data, the proposed structure of tedanolide C is questioned and a different configuration for this natural product is proposed. Key steps of the synthesis are a Kiyooka aldol reaction that builds up the tertiary alcohol flanked by three oxygenated carbon atoms and two aldol reactions used for fragment couplings. A Julia-Kocienski olefination was used for installation of the side chain. Besides the successful synthesis, the development for the protecting group setup of the southwestern hemisphere is described in detail as well as another retrosynthetic attempt for building up the target molecule.

Total Synthesis of Mycinamicin IV as Integral Part of a Collective Approach to Macrolide Antibiotics

The total synthesis of the 16-membered macrolide mycinamicin IV is outlined, which complements our previously disclosed, largely catalysis-based route to the aglycone. This work must also be seen in the context of our recent conquest of aldgamycin N, a related antibiotic featuring a similar core but a distinctly different functionalization pattern. Taken together, these projects prove that the underlying blueprint is integrative and hence qualifies for a collective approach to this prominent class of natural products. In both cases, the final glycosylation phase mandated close attention and was accomplished only after robust de novo syntheses of the (di)deoxy sugars of the desosamine, chalcose, mycinose and aldgarose types had been established. Systematic screening of the glycosidation promoter was also critically important for success.

Synthesis of Desepoxy-Tedanolide C

The synthesis of desepoxy‐tedanolide C was accomplished and provided experimental evidence on the configuration of tedanolide C. The reported chemical shifts and coupling constants point to a configuration different from the published structure and analogous to the structures of the other members of this family of natural products. The key step is a Kiyooka aldol protocol for the stereoselective synthesis of the tertiary alcohol flanked by three additional oxygenated carbon atoms. Furthermore, two additional aldol reactions and a Julia–Kocienski olefination were used to assemble the carbon framework.

Total Synthesis of Mycinolide IV and Path-Scouting for Aldgamycin N

Proof-of-concept is provided that a large estate of 16-membered macrolide antibiotics can be reached by a "unified" approach. The key building block was formed on scale by an asymmetric vinylogous Mukaiyama aldol reaction; its alkene terminus was then converted either into the corresponding methyl ketone by Wacker oxidation or into a chain-extended aldehyde by catalyst-controlled branch-selective asymmetric hydroformylation. These transformations ultimately opened access to two structurally distinct series of macrolide targets. Notable late-stage maneuvers comprise a rare example of a ruthenium-catalyzed redox isomerization of an 1,3-enyne-5-ol into a 1,3-diene-5-one derivative, as well as the elaboration of a tertiary propargylic alcohol into an acyloin by trans-hydrostannation/Chan-Lam-type coupling. Moreover, this case study illustrates the underutilized possibility of forging complex macrolactone rings by transesterification under essentially neutral conditions.

Polyoxygenated Tertiary Alcohols: A Kiyooka Approach

A Kiyooka aldol approach for the stereoselective synthesis of tertiary alcohols is presented. This approach allows for the incorporation of different substituents at all three remaining positions at the chiral center bearing the tertiary alcohol. To demonstrate the validity of this approach different chiral alcohols were depicted and the relationship of double bond geometry of the ketene acetal and the diastereoselectivity was established.

Diene hydroaminomethylation via ruthenium-catalyzed C-C bond forming transfer hydrogenation: beyond carbonylation

Under the conditions of ruthenium catalyzed transfer hydrogenation using 2-propanol as terminal reductant, 1,3-dienes engage in reductive C-C coupling with formaldimines obtained in situ from 1,3,5-tris(aryl)-hexahydro-1,3,5-triazines to form homoallylic amines. Deuterium labelling studies corroborate a mechanism involving reversible diene hydroruthenation to form an allylruthenium complex that engages in turn-over limiting imine addition. Protonolysis of the resulting amidoruthenium species releases product and delivers a ruthenium alkoxide, which upon β-hydride elimination closes the catalytic cycle. These transformations, which include enantioselective variants, represent the first examples of diene hydroaminomethylation.

Studies towards the synthesis of tedanolide C. Construction of the C13-epi C1–C15 fragment

An advanced intermediate on route towards tedanolide C has been synthesized using highly stereoselective substrate-controlled titanium-mediated aldol reactions.

The synthesis and biological evaluation of desepoxyisotedanolide and a comparison with desepoxytedanolide

The tedanolides are biologically active polyketides that exhibit a macrolactone constructed from a primary alcohol. Since polyketidal transformations only generate secondary alcohols, it has been hypothesized by Taylor that this unique lactone could arise from a postketidal transesterification. In order to probe this hypothesis and to investigate the biological profile of the putative precursor of all members of the tedanolide family, we embarked on the synthesis of desepoxyisotedanolide and its biological evaluation in comparison to desepoxytedanolide. The biological experiments unraveled a second target for desepoxytedanolide and provided evidence that the proposed transesterification indeed provides a survival advantage for the producing microorganism.

Rhodium-Catalyzed Hydroformylation of 1,1-Disubstituted Allenes Employing the Self-Assembling 6-DPPon System

A rhodium-catalyzed hydroformylation of 1,1-disubstituted allenes is reported. Using a Rh(I)/6-DPPon catalyst system, one can obtain β,γ-unsaturated aldehydes in high regio- and chemoselectivity. The Z-configured product is formed with up to >95% selectivity when unsymmetrically 1,1-disubstituted allenes are submitted to the reaction conditions. This is the first time that these interesting building blocks are accessible by hydroformylation of allenes. The utility of this methodology is demonstrated by further transformations of one of the obtained products.

Paraformaldehyde and methanol as C1 feedstocks in metal-catalyzed C-C couplings of π-unsaturated reactants: beyond hydroformylation

Ruthenium-catalyzed reductive couplings of paraformaldehyde with dienes, alkynes, and allenes provide access to products of hydrohydroxymethylation that cannot be formed selectively under the conditions of hydroformylation. In certain cases, the regioselectivity of the CC coupling can be inverted by using nickel catalysts. With iridium catalysts, methanol engages in redox-neutral regioselective hydrohydroxymethylations.

Enantioselective synthesis of the C1-C11 fragment of tedanolide C

A convergent synthesis of the protected C(1)-C(11) fragment 6 of the targeted enantiomer of tedanolide C is described. The key step of the synthesis is the Felkin-Ahn addition of vinyl iodide 7 to aldehyde 8 that proceeds in 80% yield with 4:1 diastereoselectivity.