RESUMO
An aza-Robinson annulation strategy is described using a NaOEt-catalyzed conjugate addition of cyclic imides onto vinyl ketones, followed by a TfOH-mediated intramolecular aldol condensation to afford densely functionalized fused bicyclic amides. The potential use of these amides in the synthesis of alkaloids is demonstrated by the sequential conversion of appropriate precursors to (±)-coniceine and quinolizidine in two additional steps, thus allowing their preparation in overall 40 and 44% yields, respectively.
RESUMO
Considering the recent rapid advancement of synthetic technologies promoted by visible light in the last 15 years, the use of photocatalysts has been rightfully justified based on the fact that organic molecules generally do not absorb visible light. However, an increasing number of different classes of organic molecules is being identified as actually directly absorbing in this region of the electromagnetic spectrum. Among them, diazo compounds are possibly one of these classes whose chemistry has been more explored so far. Indeed, irradiation of these compounds with visible light has been introduced as a mild photolytic strategy generally leading to free carbene intermediates. This strategy not only allows for a more cost-economical approach revealing similar outcomes to some previously reported thermal, metal-catalyzed transformations; but it can also eventually lead to different reactivities. Herein, we will present the contributions of our laboratory and of other groups to this research area, along with some important elements of design behind the development of selected reaction profiles, aiming to provide the reader with an overall view of the current state of the art.
RESUMO
A reaction for H-F bond insertion into α-diazo carbonyl compounds is reported. The protocol describes a simple reaction setup employing commercially available HF·pyr (Olah reagent) as the fluorine source. The method is rapid and practical, and allows access to a broad range of α-fluorinated carbonyl compounds in generally good yields.
Assuntos
Compostos Azo , Flúor , Compostos Azo/química , Catálise , Flúor/químicaRESUMO
Two new visible-light-mediated strategies are described starting from aryldiazoacetates. The first approach describes their reaction with azides to afford the corresponding imines, and then reaction with aryldiazoketones produces alkyl 2-carboxylate-2,3,3-trisubstituted ß-lactams. The second approach describes the reaction with sulfoxides to afford the corresponding sulfoxonium ylides, followed by reaction with aryldiazoketones to produce 5-alkoxy-2,2,4-trisubstituted furan-3(2H)-ones. These protocols take advantage of the photolysis of aryldiazoacetates and the photochemically promoted Wolff rearrangement of aryldiazoketones.
RESUMO
A new visible-light-promoted reaction between aryldiazoacetates and 1,3-diketones allows good yields and selectivities for C-C bond insertions, leading to the corresponding 1,4-dicarbonyl compounds. This transformation is straightforward and highly practical. It tolerates air and moisture and does not require the use of any metals. Mechanistic investigations support the involvement of a key cyclopropanol intermediate derived from an intramolecular rearrangement.
RESUMO
The catalytic protonation of aryl diazoacetates by strong Brønsted acids, followed by a Friedel-Crafts alkylation reaction with electron rich aromatic compounds, is reported. The reaction provided in a direct fashion 24 geminal diarylacetates in yields of ≤92%.
RESUMO
A Brønsted acid catalyzed intramolecular cyclization of N-Cbz-protected diazoketones, derived from α-amino acids, is described. The reaction proceeds under metal-free conditions and is promoted by ecofriendly silica-supported HClO4 as the catalyst and methanol as the solvent. This transformation enables the short synthesis of various 1,3-oxazinane-2,5-diones under mild reaction conditions and in good yields (up to 90%). The set-up is very simple; by just mixing all reagents together with no work-up necessary before purification, this protocol takes a greener approach.
RESUMO
A one-pot alkylation-halogenation of ketosulfoxonium ylides in the presence of alkyl halides is described. The method furnishes several gem-difunctionalized haloketones (an alkyl and F, Cl, Br, or I) in good yields. Replacing alkyl halides with a mixture of electrophilic halogen species and various halide anions led to gem-dihalogenated ketones containing a combination of the same or two different halogens. Kinetic isotopic effects as well as reaction kinetic experiments give insight to the mechanism of these reactions.