James Redpath

Palladium Catalysed Tandem Cyclisation–Anion Capture Processes. Part 4: Organotin(IV) Transfer Agents

Abstract Palladium(0) catalysed cascade mono- and bis-cyclisation–anion capture involving a wide variety of starter species, terminating species and organotin(IV) anion capture reagents are reported leading to a range of bridged, fused and spirocyclic products. The diastereoselectivity of the bis-cyclisation processes is explained in terms of steric effects in the transition states.

Palladium catalysed cascade bis-cyclisation-anion capture processes proceeding via allenyl-palladium(II) starter species. 1-Vinyl-3-azabicyclo[3.1.0]hexanes

Abstract An additional starter species [allenylpalladium(II)] has been implemented for palladium catalysed cascade cyclisation-anion capture processes. Good yields of bis-cyclisation-anion products involving anionic (NaBPh4), neutral ( CO MeOH ) and organometallic (Bu3SnR) capture agents are reported.

X=y-ZH compounds as potential 1,3-dipoles. part 44.1 asymmetric 1,3-dipolar cycloaddition reactions of imines and chiral cyclic dipolarophiles

Abstract Metallo 1,3-dipoles generated in situ from both aryl and aliphatic imines of α-amino esters by the action of silver salts and tertiary amines undergo cycloaddition at room temperature to 5R-(1′R, 2′S, 5′R-menthyloxyl)-2(5H)-furanone and to N-acetyl-5R-isopropoxy-2(5H)pyrrolone giving homochiral cycloadducts in good yield in all cases. π-Interaction between the dipolarophile carbonyl group and the aryl group in the aryl imines is not required for good induction. The stronger the base the faster the cycloaddition with 2-t-butyl-1,1,3,3tetramethylguanidine > DBU > NEt 3 . X-Ray crystal structures of representative cycloadducts establish the absolute configuration of the pyrrolidine stereocentres.

X=Y−ZH compounds as potential 1,3-dipoles. Part 43. Metal ion catalysed asymmetric 1,3-dipolar cycloaddition reactions of imines and menthyl acrylate☆

Abstract Metallo-azomethine ylides, generated from imines by the action of amine bases in combination with LiBr or AgOAc, undergo cycloaddition with both 1R, 2S, 5R- and 1S, 2R, 5S-menthyl acrylate at room temperature to give homochiral pyrrolidines in excellent yield. The stronger the base the faster the cycloaddition and the greater the yield with: 2- 2-t-butyl-1,1,3,3-tetramethylguanidine > DBU > NEt 3 . X-Ray crystal structures of representative cycloadducts establish that the absolute configuration of the newly established pyrrolidine stereocentres is independent of the metal salt and the size of the pyrrolidineC(2)-substituent for a series of aryl and aliphatic imines.

Palladium catalysed cascade carbonylation-cyclisation-carbometallation-anion capture. Tetramolecular queuing processes

Abstract Palladium catalysed processes involving sequential carbonylation-cyclisation-carbometallation-anion capture from Sn(IV) and B(III) are described. These molecular queuing processes occur in good yield under 1 atm. of carbon monoxide. Reactivity/selectivity guidelines are delineated for carbopalladation, acylpalladation and anion capture.

Palladium Catalysed Tandem Cyclisation–Anion Capture. Part 5: Cascade Hydrostannylation-bis-cyclisation-intramolecular Anion Capture. Synthesis of Bridged- and Spiro-Cyclic Small and Macrocyclic Heterocycles

A series of O- and N-α,ω-enyne derivatives of 2-iodoarylethers and 2-iodoarylamides undergo palladium catalysed cascade hydrostannylation of the ω-alkyne moiety at 0–25°C followed by bis-cyclisation at 100–110°C terminating in intramolecular sp3–sp2 Stille coupling. These cascades provide a wide range of 5/6 and 5/12–17 membered bicyclic spiro- and bridged-ring heterocycles.

X=Y-ZH systems as potential 1,3-dipoles. Part 49. Catalytic palladium (II) mediated oxime-nitrone-isoxazolidine cascades

Abstract Bis(acetonitrile) palladium (II) chloride (10 mol %) effects cyclization of δ-alkenyl oximes to nitrones which undergo in situ 1,3-dipolar cycloaddition reactions with suitable dipolarophiles to afford a range of complex isoxazolidine derived heterocycles in high yield (81–85%).

Palladium catalysed cascade hydrostannylation-bis-cyclisation-intramolecular anion capture. Routes to bridged- and spiro-cyclic small and macrocyclic heterocycles

Palladium catalysed cascade hydrostannylation of terminal alkynes in α,ω-enynes at 0–25°C followed by bis-cyclisation initiated by insertion of Pd(0) into an aryl iodide at 100–110°C and terminating in an intramolecular Stille coupling provides a wide range of exo-methylene 56 and 512-17 membered spiro- and bridged-ring heterocycles.

Palladium (II) catalysed oxime-metallo-nitrone-isoxazolidine cascade reactions of α-imino aldoximes

Abstract Palladium (II) salts catalyse stereospecific and highly facially selective oxime-nitrone-isoxazolidine cascade reactions between α-imino aldoximes and N -methylmaleimide via intermediate N -metallo-aldonitrones. These processes occur at room temperature in a range of polar solvents through the chelation of both α-imino and aldoxime nitrogen atoms to the palladium (II) centre.

Homochiral cycloadducts derived from sugar aldoximes via nitrone intermediates

Abstract Tandem nitrone generation/cycloaddition reactions between simple sugar aldoximes and divinyl sulphone in refluxing toluene have been shown to occur regiospecifically and with high diastereoselectivity in the cycloaddition step to afford homochiral cycloadducts in good yield. The process is applicable to both furanose and pyranose aldoximes. Absolute stereochemistries of the products have been determined by NOE spectroscopy and X-ray crystallography.