Visuvanathar Sridharan

X-Y-ZH Systems as potential 1,3-dipoles : Part 15. Amine generated azaallyl anios versus metallo-1,3-dipoles in cycloadditions of α-amino acid esters. Facile regio- and stereo-specific formation of pyrrolidines

Abstract Kinetic studies of the deprotonation of arylidene imines of alanine and phenylglycine esters by tertiary amines and pyridine and cycloaddition of the resultant 4π-azaallyl anions to N-phenylmaleimide show the expected dependance on the p-substituent in the aryl ring. e.g. p-NO2 > H > OMe >fs NMe2. A combination of metal salt (silver, lithium. or zinc) and triethylamine in THF, dipolar aprotic solvents (MeCN, DMSO, DMF) or N-methylacetamide effects regio- and stereo-specific or highly stereo-selective inter- and intra-molecular cycloaddition of imines of phenylglycine. alanine and glycine esters to a range of dipolarophiles probably via metallo-1,3-dipole formation at room temperature. Silver acetate is a more efficient and selective catalyst than lithium bromide and reactions in acetonitrile, DMSO or N-methylacetamide, are especially rapid (O.1–3.5h).

Palladium catalysed tandem cyclisation-anion capture processes.Hydride ion capture by vinylpalladium species.

Abstract A new palladium catalysed-anion capture process is proposed, Examples are provided involving cyclisation of o-(ω-acetylenic)-aryl iodides and 2-bromo-1,6-enynes to heterocyclic- and carbocyclic-vinylpalladium species followed by hydride ion capture.

Regiospecific palladium catalysed tandem cyclisation-anion capture processes. Stereospecific group transfer from organozinc and organoboron reagents

Abstract Vinyl-, alkyl- and π-allyl-palladium species arising from regiospecific palladium catalysed 5- or 6-exo-dig or -trig cyclisations onto proximate alkynes, alkenes or dienes can be intercepted stereospecifically by organozinc or organo boron reagents leading to carbo-and hetero-cyclic compounds in moderate to good yield.

Regiospecific palladium catalysed tandem cyclisation-anion capture processes. Stereospecific group transfer from organotin reagents.

Abstract Vinyl-, alkyl- and π-allyl-palladium species arising from regiospecific palladium catalysed 5- or 6-exo-trig cyclisations onto proximate alkynes, alkenes or dienes can be intercepted by organotin reagents with stereospecific transfer of an organic group from tin leading to carbo- and hetero-cyclic compounds in moderate to good yield.

Palladium catalysed tandem cyclisation-anion capture processes.Hydride ion capture by alkyl- and π-allyl-palladium species

Abstract Alkyl- and π-allyl-palladium species arising from 5-exo-trig cyclisations onto proximate alkenes or dienes can be intercepted by hydride ion sources leading to carbo- and hetero-cyclic compounds usually in good yield.

X=Y-ZH Systems as potential 1,3-dipoles : Part 13. Prototropic generation of azomethine imines from hydrazones

Abstract Hydrazones of aldehydes and ketones undergo intermolecular cycloaddition to electronegative olefins via azomethine imines, formed by a formal 1,2-prototropic shift, in low to moderate yield on heating in xylene or ethanol. In some instances the reaction is diverted to give products derived (at least formally) from an ene reaction. Similar intramolecular cycloadditions occur with unactivated terminal alkenes and alkynes.

X=Y-ZH systems as potential 1,3-dipoles. Part 21 activation of the ZH proton in imines.

Abstract A range of substituents is capable of inducing thermal 1,3-dipole formation in imines by activation of the CH proton as shown by trapping experiments with dipolarophiles.

X=Y-ZH Systems as potential 1,3-dipoles: Part 19. Intramolecular cycloadditions of non-stabilised azomethine ylides generated via the decarboxylative route from α- amino acids1

Abstract Heating a range of acyclic and cyclic secondary α-amino acids with aryl aldehydes containing a proximate terminal alkene or alkyne results in consecutive condensation and decarboxylation, followed by intramolecular cycloaddtion of the resultant non-stabilised azomethine ylides. Evidence is produced for syn-anti dipole equilibration and it is found that intramolecular cycloadditions to a terminal alkyne involve only the anti-dipole and proceed via an exotransition state to give a single cycloadduct. In contrast, intramolecular cycloaddition to a terminal alkene involves both anti- and syn-dipoles, with trapping of the former being slightly energetically preferred resulting in mixtures of two stereoisomeric cycloadducts. Intramolecular cycloadditions of terminal alkenes to anti-dipoles proceed via exo-transition states whilst analogous reactions of the syn-dipole involve endotransition states.

Regiospecific palladium catalysed tandem cyclisation-anion capture processes. Carbon-, nitrogen- and oxygen-centred nucleophiles

Abstract π-Allyl- and alkyl-palladium species arising from regiospecific palladium catalysed 5-exo-trig cyclisations onto a proximate diene or alkene can be intercepted regiospecifically by stabilised carbanions, secondary amines or acetate ion giving carbo- and hetero-cyclic compounds good to excellent yields.

The synthesis of spirocyclic compounds by regiospecific palladium catalysed cyclisation reactions

Abstract Enamides derived from o-iodobenzoic acid and Z-3-bromoacrylic acid undergo regiospecific palladium catalysed exo-trig cyclisation onto a proximate alkene to give spirocyclic products in good to excellent yield. Double bond isomerisation in the product is not usually observed and is retarded by the addition of tetraethylammonium chloride which also allows the reaction to be carried out under milder conditions.