Iron hydride radical reductive alkylation of unactivated alkenes

Iron-catalyzed hydrogen atom transfer-mediated intermolecular C−C coupling reactions between alkenes and tosylhydrazones, followed by in situ cleavage of the tosylhydrazine intermediates using Et3N, are described. The process involves a new strategic bond disconnection resulting in the reductive alkylation of nonactivated alkenes. The reaction is operationally simple, proceeds under mild conditions, and has a wide substrate scope

Four-Step Synthesis of (−)-4-epi-Presilphiperfolan-8α-ol by Intramolecular Iron Hydride Atom Transfer-Mediated Ketone-Alkene Coupling and Studies to Access trans-Hydrindanols with a Botryane Scaffold

From an (R)-(+)-pulegone-derived building block that incorporates the stereo-defined tertiary carbon bearing a methyl group, as found in the targeted sesquiterpenoid, a four-step synthesis of (−)-4-epi-presilphiperfolan-8-α-ol was achieved. The key processes involved are a ring-closing metathesis leading to a bridged alkene-tethered ketone and its subsequent FeIII-mediated metal-hydride atom transfer (MHAT) transannular cyclization. This synthetic method, implying an irreversible addition of a carbon-centered radical upon a ketone by means of a hydrogen atom transfer upon the alkoxy radical intermediate, was also applied in the synthesis of trans-fused hydrindanols structurally related to botrydial compounds.Financial support for this research was provided by the Grants PID2019-104188GB-I00 and PID2019-110008GB-I00 funded by MCIN/AEI/10.13039/501100011033. We also thank SGIker (UPV/EHU) for providing human and computational resources. B.B. acknowledges the Serra Hunter program (Generalitat de Catalunya)

Hydrogen Atom Transfer (HAT)-Triggered Iron-Catalyzed Intra- and Intermolecular Coupling of Alkenes with Hydrazones: Access to Complex Amines

A methodology for the coupling of alkenes with aldehyde- or ketone-derived Cbz-hydrazones to form a new C−C bond through a radical process is described. The sequence comprises an initial in situ generation of a putative iron hydride followed by a hydrogen atom transfer to an alkene, a coupling with a hydrazone, and a final reduction of the nitrogen-centered radical. Hydrogenation of the obtained hydrazines renders amines, including valuable tert-alkyl amines. KEYWORDS: HAT, iron catalysis, α-tert-amines, C−C bond formation, radical processes, synthetic method

Iron-Catalyzed Radical Intermolecular Addition of Unbiased Alkenes to Aldehydes

The intermolecular reductive radical coupling of aldehydes with nonactivated alkenes, employing metal hydride atom transfer (MHAT) catalysis with a combination of FeII and FeIII salts, is described. This constitutes the first use of aldehydes as viable acceptor groups in MHAT reactions. The insights gained in this study led to the reexamination of the previously reported intramolecular version of the reaction, and the addition of FeII salts allowed the development of a more efficient second-generation approach

Formal total synthesis of amphidinolide E

A formal total synthesis of the cytotoxic macrolide amphidinolide E is reported. The strategic steps are three Julia-Kocienski reactions (J-K), for the formation of the C5-C6, C9-C10, and C17-C18 double bonds, a Suzuki-Molander C21-C22 bond formation reaction, and a Kita-Trost macrolactonization. The 'instability' of the two dienic systems and of the stereocenter at C2 (allylic methine, alpha to the carboxy group) and the protecting groups at C17-OH and C18-OH have posed difficult challenges. Each Julia-Kocienski olefination has been systematically optimized to provide the highest possible E/Z ratios

Clinical and diagnostic aspects of feline cutaneous leishmaniosis in Venezuela

Abstract Background: Venezuela is an endemic area for human and canine leishmaniosis due to Leishmania infantum and parasites of the Leishmania braziliensis and L. mexicana complexes. Limited data are available on feline leishmaniosis (FeL) in this region. The aim of this study was to describe clinical and diagnostic aspects of FeL in Venezuela. Results: Thirty-one domestic cats from urban areas of Lara State in Venezuela were enrolled. Twenty-five were healthy. Six other cats had solitary or multiple nodular lesions, which were located on the nose; ears; ears and nose; and nose, ears, tail and lower limbs. Cutaneous lesions were characterized by diffuse pyogranulomatous infiltrate in all sick cats with numerous intracellular and extracellular amastigotes, and immunohistochemistry was positive for Leishmania in five sick cats. All healthy cats were seronegative for L. infantum and L. braziliensis antigens by ELISA. Two out of five sick cats yielded a positive ELISA result to both Leishmania antigens with higher antibody levels to L. braziliensis compared to L. infantum. Significantly higher antibody levels by ELISA as well as a higher number of bands by Western blot (WB) were found for L. braziliensis when compared to L. infantum antigens in all sera from Venezuelan sick and healthy cats. All healthy cats were blood Leishmania spp. qPCR negative while three out of six sick cats were blood qPCR positive. All paraffin-embedded skin biopsies (n = 4) as well as cutaneous cytology (n = 3) were positive by Leishmania spp. qPCR in sick cats. Leishmania speciation was obtained only from the cutaneous lesion samples from cytological preparations of two out of three sick cats which were identified as infected with L. mexicana or a closely related specie. Conclusions: FeL should be included in the differential diagnosis list of nodular-ulcerative lesions. The most reliable diagnostic technique in sick cats is cytological or histopathological examination along with immunohistochemistry, since blood PCR and serology by ELISA might be negative. WB appears to be more sensitive in detecting infection. Cats with leishmaniosis from Venezuela are most likely infected with species of L. mexicana or a closely related species or the L. braziliensis species complex and not with L. infantum

Direct Access to Mono-Protected Homoallylic 1,2-Diols via Dual Chromium/ Photoredox Catalysis

A dual catalytic strategy enables the efficient synthesis of mono-protected homoallylic 1,2-diols by coupling abundant aldehydes with simple (silyl) enol ethers, thus providing direct access to this important motif without the (super)stoichiometric use of prefunctionalized metal-allyl species. A variety of silyl- and alkyl-based protecting groups is shown and functional group tolerance, chemoselectivity and scalability are highlighted. </p

Hydrogen Atom Transfer (HAT)-Triggered Iron-Catalyzed Intra- and Intermolecular Coupling of Alkenes with Hydrazones: Access to Complex Amines

A methodology for the coupling of alkenes with aldehyde- or ketone-derived Cbz-hydrazones to form a new C−C bond through a radical process is described. The sequence comprises an initial in situ generation of a putative iron hydride followed by a hydrogen atom transfer to an alkene, a coupling with a hydrazone, and a final reduction of the nitrogen-centered radical. Hydrogenation of the obtained hydrazines renders amines, including valuable tert-alkyl amines. KEYWORDS: HAT, iron catalysis, α-tert-amines, C−C bond formation, radical processes, synthetic method

Formal Total Synthesis of Amphidinolide E

A formal total synthesis of the cytotoxic macrolide amphidinolide E is reported. The strategic steps are three Julia–Kocienski reactions (J–K), for the formation of the C5–C6, C9–C10, and C17–C18 double bonds, a Suzuki–Molander C21–C22 bond formation reaction, and a Kita–Trost macrolactonization. The “instability” of the two dienic systems and of the stereocenter at C2 (allylic methine, α to the carboxy group) and the protecting groups at C17-OH and C18-OH have posed difficult challenges. Each Julia–Kocienski olefination has been systematically optimized to provide the highest possible <i>E</i>/<i>Z</i> ratios