Jonathan Parr

Controlling stereochemistry in C-C and C-H bond formation with electronically asymmetric organometallics and chiral poisons

Air stable (cyclopentadienyl)Mo(NO)(halide)(q3-allyl) complexes add to aldehydes to yield homoallylic alcohols in high enantioselectivity and diastereoselectivity. A new strategy, chiral poisoning, is applied to asymmetric hydrogenation and the kinetic resolution of allylic alcohols using transition metal catalysts prepared from racemic bis-phosphine ligands. The activation afforded an organic moiety by complexation led to the extensive development of transition metal reagents for organic synthesis. The increased reactivity is influenced by differences in the steric and electronic nature of the metal and its ligands. Ultimately the environment at the metal can induce high stereoselectivity in reactions involving the coordinated ligands. Our aim has been the improvement of our understanding of the origins of selectivity in these reactions and the application of these principles to the rational design of reagents and catalysts. Our approach modifies the conventional emphasis on steric effects in catalyst design and focuses attention on electronically controlled selectivity. Our initial work emphasized the control which could be obtained with nucleophilic additions to chiral (CpMo(allyl)(NO)(CO))* cations, wherein the difference in electronic influences of the carbonyl and

Alkenyl tricarbonyl derivatives of α-amino acids as trielectrophiles. Formation of heterocyclic-substituted products

Abstract Alkenyl tricarbonyl esters have been prepared by reaction of mono aldehydes of dibasic amino acids with tricarbonyl esters. These systems undergo reaction with diamines and other dinucleophiles by a combination of Michael addition and nucleophilic attack at the electrophilic central carbonyl to form pyrrole derivatives. These monoaldehydes may also be used to incorporate imidazole and furan residues into the amino acid starting materials.

Nonrigid diastereomers: epimerization at chiral metal centers or chiral ligand conformations?

Variable temperature NMR studies of chiral metal complexes can reveal two diastereomers at lower temperatures. A caveat is presented regarding the possibility that chiral ligand conformations may be involved rather than epimeric chiral metal centers.

Alkynyl germatranes as alternative reagents for the preparation of biarylethynes

Arylalkynyl germatranes react with aryl chlorides and triflates to give the corresponding biarylethynes in good yield. The reaction proceeds under mild conditions in the presence of a palladium phosphine catalyst and fluoride ions.

α, β-Diketo nitriles as dielectrophiles. Formation of heterocyclic derivatives of amino acids

The reactions of mono Boc-protected amino monocarboxylic acids with phosphoranylideneacetonitrile yield ylido nitriles which on ozonolysis at low temperature form labile α,β-diketo nitriles. These derivatives may be used in situ for reaction with diamines or related dinucleophiles to yield hetero derivatives of interest as unnatural amino acid building blocks.

Half-sandwich complexes of ruthenium, rhodium and iridium with a chiral bisphosphine monoselenide

Monoselenation of the chiral bisphosphine (S)-(+)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyldi-t-butylphosphine gives the first enantiomerically pure chiral bisphosphine monoselenide prepared from a commercially available chiral bisphosphine. This bisphosphine monoselenide ligand is an effective chelating ligand that utilizes a [P,Se] donor set when forming chelates with half-sandwich complexes of ruthenium(II), rhodium(III) and iridium(III). These complexes have been characterised spectroscopically and, in some cases, crystallographically. The chirality of the ligand influences and controls the metal-centred chirality yielding one of two possible chelate complexes with high diastereoselectivity.

Vinyl vicinal tricarbonyl esters as trielectrophiles. Reactions with diamines and related trinucleophiles

The scope of the reactions of vinyl vicinal tricarbonyl esters with trinucleophiles has been extended in forming dipyrroles and novel polycyclic heterocyclic systems. In particular, diamines and analogs have been studied as polynucleophiles.

A convenient synthesis of cadmium chalcogenide quantum dots from cadmium acetate and bis(diphenylphosphino)methane monosulfide and –selenide or 1,4-bis(diphenylphosphino)butane monoselenide

GRAPHICAL ABSTRACT ABSTRACT The synthesis of both cadmium selenide and cadmium sulfide quantum dots has been effected using a synthetic protocol that avoids the use of volatile, toxic organocadmium reagents and alkyl phosphines.