A Mechanistic Study of Hydroboration of 1-Octene with 1,3,2-Dithiaborolane and 1,3,2-Dithiaborinane. Part 2. A DFT Study of Disproportionation and Hydroboration

The hydroboration reactions of propene with 1,3,2-dithiaborolane and 1,3,2-dithiaborinane in their ground states have been studied using density functional theory (DFT) at the B3LYP/3-21+G and B3LYP/6-31+G(d) levels. Hydroboration and disproportionation transition states have been determined and activation energies for these transition states were compared. It has been shown that hydroboration reactions require slightly higher activation energies than disproportionation, and yield thermodynamically more stable products.Keywords: Hydroboration, disproportionation, DFT, transition states, potential energy surfacePDF and Supplementry file attache

The Evaluation of Novel Camphor-derived Ligands as Catalysts in the Asymmetric Henry Reaction

The evaluation of a series of camphor-derived ligands as catalysts in the asymmetric Henry reaction is reported. The synthesis of two novel derivatives is detailed and these molecules are also screened as catalysts in this reaction. The single crystal X-ray structure of one of the novel compounds is reported. The reaction is catalyzed with moderate to excellent yields and moderate enantioselectivity.Keywords: Camphor, asymmetric catalysis, Henry reaction, chiral ligand

Synthesis of Novel 3-Hydroxy-3-pyridylcamphor Derivatives

The synthesis of a series of five novel precursor compounds derived from (R)-(+)-camphor is reported. From these precursors, a further four novel pyridyl alcohol ligands were synthesized. The molecules represent the first reported examples where the pyridyl and hydroxyl moieties are pendant on the C3 position of the camphor skeleton. The regioselective synthesis was investigated and an efficient method was identified. The final ligands were obtained in moderate yield with absolute regio- and stereoselective control. The molecules were screened as catalysts in the alkylation of aldehydes with diethylzinc in order to compare the new arrangement of donor groups with previously reported results obtained with C2 pendant ligands. The results demonstrated a significant improvement for the synthesized C3 pendant ligands over previous C2 examples with moderate yields and up to 85 % ee being obtained.Keywords: Chiral, camphor ligands, pyridyl alcohols, asymmetric alkylation reactionsPDF and Supplementry file attache

Synthesis of Trishomocubane Amino Acid Derivatives

The synthesis of four novel trishomocubane amino acid derivatives is described. The hydantoin precursor and bis-Boc protected hydantoin (>95% yield) were previously reported. A mild hydrolysis of the bis-Boc hydantoin with lithium hydroxide at room temperature quantitatively yielded the corresponding novel cage amino acid. The cage amino acid was characterized as the Fmoc derivative. Although the Fmoc amino acid is partially deprotected after three weeks in a refrigerator, it is stable enough for use in Solid Phase Peptide Synthesis (SPPS). The Fmoc cage amino acid was converted to the acid fluoride with cyanuric fluoride. The acid fluoride is required for activation of the cage amino acid in SPPS. Esterification of the sterically hindered trishomocubane amino acid is also reported, indicating sufficient reactivity of the acid function for potential use in SPPS.Keywords: Trishomocubane amino acid, hydantoin, Fmoc protection, t-Boc protection, acid fluoride, esterification

Part II: Ab Initio and NMR Investigations into the Barrier to Internal Rotation of various Oxo- and Thio- Analogues of 2-Oxo-2H-chromen-7-yl Dimethylcarbamates

A range of 2-oxo-2H-chromen-7-yl dimethylcarbamates were synthesized as described in part I of this publication, containing either an oxygen or sulphur α to the carbonyl or thiocarbonyl group of the amide moiety. Variable temperature and exchange spectroscopy NMR was performed on these compounds and the barrier to free amide rotation was calculated. Each of these compounds were also modelled ab initio and the gas phase barrier to rotation calculated. These three sets of data were compared and the influence of the α-heteroatom on rotation for amides and thioamides evaluated.Keywords: Thiocarbonyl, amide, rotational barrie

The Evaluation of Novel Camphor-derived Pyridyl Ligands as Catalysts in the Asymmetric Diels-Alder Reaction of Cyclopentadiene with 3-Acryloyl-2-oxazolidinone

A series of camphor-derived pyridyl ligands were evaluated in the Diels-Alder reaction of 3-acryloyl-2-oxazolidinone 1 with cyclopentadiene 2. High yields with good endo:exo selectivity, but only moderate enantioselectivities (43 % ee), were obtained. The structures of the copper (II) complexes of the ligands were calculated using ONIOM density functional theory and the results suggest that chiral induction to the alkene functional group is indeed lacking. This explains the moderate experimental selectivities obtained.Keywords: Camphor ligands, asymmetric catalysis, Diels-Alder cycloaddition, computational modellingPDF and Supplementry file attache

Application of (S,S)-Pentacycloundecane bis(4-Phenyloxazoline) as a Novel Chiral Ligand for Catalysis of the Asymmetric Diels-Alder Reaction of Cyclopentadiene with 3-Acryloyl-2-oxazolidinone

The synthesis of the novel C1 symmetric (S,S)-pentacycloundecane bis(4-phenyloxazoline) ligand 5 and its evaluation as a chiral Lewis acid catalyst in the benchmark asymmetric Diels-Alder reaction between 3-acryloyloxazolidin-2-one (6) and cyclopentadiene (7) is reported. From the various metal salts screened the anhydrous magnesium perchlorate complex emerged as the best catalyst. The endo-cycloadduct product 8 was afforded in 81% enantiomeric excess with an endo:exo ratio of 98:2. An extensive screening of various metal ions as complexing agents was performed and is also reported.Keywords: Pentacycloundecane, oxazolines, chiral catalysis, Diels-Alder reactionPDF and Supplementry file attache

Synthesis and NMR Elucidation of Novel Octa-Amino Acid Resorcin[4]arenes Derivatives

The synthesis of nine novel protected amino acid cavitands is reported. All have four pendant n-undecyl chains and ‘headgroups’ connected by a two-carbon spacer at eight positions on the aromatic rings. The amino acids employed are glycine, alanine, phenylalanine, leucine, proline, tryptophan, serine, glutamine and lysine. The structures of the compounds were elucidated using one and two-dimensional NMR techniques which verified that all octa-substituted cavitands have symmetrical C2v conformation at room temperature. These compounds have potential synthetic ion channel applications.KEYWORDS Octa-amino acid resorcin[4]arenes, 1H-NMR, COSY, HSQC, C4v symmetry, C2v symmetry.PDF and Supp files attache

Synthesis of (S)-3-Aminoethyl- 1,2,3,4-Tetrahydroisoquinoline (TIQ-Diamine) via the Mitsunobu Protocol

The synthesis of (S)-3-Aminoethyl-1, 2, 3, 4-tetrahydroisoquinoline (TIQ-diamine) was successfully achieved via the Mitsunobu protocol. The method from earlier reports utilizing aminolysis of commercially available TIQ-amino methyl ester, and reduction of the amide, proved to be inadequate for preparation of TIQ-diamines. The modified route requires three additional steps and consequently rendered three novel intermediates, which were furnished under mild conditions.Keywords: Tetrahydroisoquinoline, TIQ-diamine, Mitsunobu Reactio

Comparison of Tetrahydroisoquinoline (TIQ) Thiazole and Oxazoline Ligands for Asymmetric Henry Reactions

A series of novel C1 symmetric thiazole ligands with a tetrahydroisoquinoline (TIQ) backbone were synthesized. Their application in the catalytic asymmetric Henry reaction was investigated with comparison to a corresponding TIQ oxazoline ligand. The Cu(II)-oxazoline complex was more reactive and furnished moderate enantioselectivities up to 61:36 (syn:anti) with 75:25 diastereomeric excess, while the Cu(II)-thiazole complexes had lower selectivity. This is the first example where a directcomparison between an N, N-type thiazole and oxazoline ligands has been studied.Keywords: Tetrahydroisoquinoline, thiazole, oxazoline, Henry reaction, enantioselectivit