Palladium-Catalyzed Cyclization Reactions of Acetylene-Containing Amino Acids

Novel Approach to 5-Substituted Proline Derivatives Using a Silver-Catalyzed Cyclization as the Key Step

“…First of all, the reaction proceeds readily at room temperature, thus providing mild reaction conditions. Furthermore, in comparison with our previous cyclization examples, there is no protection of the nitrogen atom necessary. , Pleased with this result, we set out to gain insight in the scope and limitations of the observed cycloisomerization. Therefore, we prepared a variety of cyclization precursors via Sonogashira couplings of propargylglycine derivative 9 with several substituted aryl iodides.…”

“…Building on methodology that has recently been developed in our group, , we envisaged that the 2,5-disubstituted pyrrolines of type 3 will be accessible starting from optically active propargylglycine 6 . In this approach, the pyrrolines 3 (R = Me) might be obtained from the protected precursors 5 via cleavage of the Boc-group, followed by a metal-catalyzed intramolecular 5- endo - dig cyclization as the key step.…”

Synthesis of Fused Oxabicyclic Systems by Metal-Catalyzed Intramolecular Addition of 1,3-Cycloalkyldiones to Alkynes

“…The feasibility of activating alkynes by coordination to electrophilic transition metal complexes has led to the development of a variety of catalytic cycloisomerization reactions involving carbon−carbon or carbon−heteroatom bond formation . In the case of heterocyclizations, alcohols, amines, and carbocyclic acids have been widely employed as nucleophiles (essentially in palladium-catalyzed processes); however, carbonyl groups have only been used in the synthesis of furanes . Herein we show that readily available β-oxocyclohexa- and β-oxocyclopentanones can cyclize chemo- and regioselectively with pendant α‘-propargyl substituents to give fused dihydropyran or dihydrofuran systems.…”

Synthesis of Heterocycles via Palladium π-Olefin and π-Alkyne Chemistry

“…The Pd(II)-catalyzed cyclization of amino acid derivatives has been reported by Rutjes and co-workers (Scheme ) . Nitrogen-containing heterocycles can be obtained in good yields when the nitrogen functionality is protected as a sulfonamide.…”