Niyum Ramesar

Intramolecular Baylis-Hillman Reaction: A Pathway to Substituted Coumarins

Abstract The acrylate ester of salicylaldehyde, in the presence of DABCO, affords a crystalline coumarin salt. Formation of this derivative confirms a vital intermediate in the mechanism of the reaction. Salicylaldehyde, suitably protected, reacts with methyl acrylate to afford a novel coumarin not unlike the vasodilator chromonar.

Synthesis, resolution and assignment of absolute configuration of 2-(α-hydroxy)aryl acrylate esters

Abstract (−)(R,R)-2-Amino-1-(4-nitrophenyl)propan-1,3-diol 3 has been used to resolve racemic 3-hydroxy-2-methylene-3-phenylpropanoic acid 1a . Conversion of the laevorotatory enantiomer into anti and syn methyl 3-hydroxy-2-methyl-3-phenylpropanoate, 2a and 2b respectively, was achieved with Pd/H 2 . Correlation of the specific rotations of 2a and 2b with isomers of known configuration established the absolute configuration of 4a as R. This was confirmed independently by X-ray crystallography.

11,11-dimethyl-1,3,8,10-tetrahydroxy-9-methoxypeltogynan and three pentacyclic triterpenes from Cassine transvaalensis

Abstract From the root bark of Cassine transvaalensis a new peltogynoid,(+)-11,11-dimethyl-1,3,8,10-tetrahydroxy-9-methoxypeltogynan was obtained along with three pentacyclic triterpenes, canophyllol, canophyllal and 6β-hydroxy-lup-20(30)-en-3-one. The latter was fully characterized by X-ray analysis and high resolution NMR. The carbohydrate galactitol was also present in unusually high concentration.

Reaction of 2-Formyl Imidazole with Intermediates From the Baylis-Hillman Reaction

Abstract The reaction of formyl imidazole (in the presence and absence of DABCO, and with either THF or methanol as solvent) with α-hydroxylaryl derivatives of methyl acrylate affords novel synthetic intermediates. By controlling the reaction conditions, either allylic substitution products (THF, DABCO) or rearrangement (MeOH, no DABCO) products result.

Absolute configurations of all four stereoisomers of cryptocaryalactone and deacetyl cryptocaryalactone

Using information available in the literature and correlating this with physical data obtained for cryptocaryalactone stereoisomers isolated from C. myrtifolia and C. wyliei, it has been possible to assign the absolute configurations of the four stereoisomers of the title compound and its deacetyl analogue.

Stereostructure, conformation and reactivity of P- and a-gardiol from Burchellia bubalina

Abstract From the leaves of Burchellia bubalina (Rubiaceae) pure P- and a-gardiol have been isolated, the latter in crystalline form for the first time. X-ray analysis of P-gardiol establishes its relative configuration. Treatment of the tosyl derivative of P-gardiol with base affords a crystalline elimination product amenable to X-ray analysis. Evidence is presented for the partial conversion of a-gardiol to the epimeric P-gardiol at room temperature. Molecular dynamic studies at 1000 K on the two gardiols provide useful conformational information. In the case of P-gardiol, the analysis shows interesting correlations between conformations adopted at 1000 K and those present in the crystalline state at room temperature.

A novel tetrahydrofuran derivative via a tertiary ketol-type rearrangement

Abstract Hexahydro-3a, 7a-dihydroxy-3,7,7-trimethyl-2-phenyl-4H-furo [3,2-c]pyran-4-one 6 has been obtained from the reaction between tetrahydro-4, 4-dimethyl-2-oxo-3-furanyl propanoate 4 , benzaldehyde and base. The product is the result of a modified benzilic acid rearrangement.

Synthesis and X-ray crystal structure of cis-dichloro(cyclopentylamine) (dimethyl sulphoxide)platinum(II)

Summarycis-Dichlorocyclopentylamine(dimethyl sulphoxide)-platinum(II) is obtained, in addition to small quantities of the corresponding trans compound, by reaction of K2PtCl4 with cyclopentylamine in DMSO solution, where it is formed as the thermodynamically favoured isomer. An X-ray crystal structure analysis confirms the cis configuration. Coordination around the metal centre is square planar, and the ligand bond angles at the Pt atom are close to the expected values of 90 and 180°. The DMSO ligand is S-coordinated to Pt. The Pt-Cl bond lengths, 2.299(2) and 2.317(2) Å, are normal for structures of this type, as are the Pt-N and Pt-S bond distances, 2.059(5) and 2.191(2) Å, respectively.

Synthesis of thecis andtrans isomers oftert-butylaminedichloro-(dimethyl sulphoxide)platinum(II) and X-ray structure analysis of thecis compound

SummaryTreatment ofcis-dichlorobis(dimethyl sulphoxide)platinum(II) [1] with an excess oftert-butylamine in MeOH yieldstert-butylamine-trans-dichloro(dimethyl sulphoxide)-platinum(II) [(tr-5)], rather than thecis-diaminechloro-(dimethyl sulphoxide)platinum(II) cation expected by analogy with similar reactions reported in the literature. The correspondingcis isomer [(cis-5)] is prepared from the same reactants (and similarly from K2PtCl4 andtert-butylamine) in DMSO medium, in which the initially formedtrans compound partially isomerizes to the thermodynamically favouredcis complex. The molecular structure of (cis-5) is determined by X-ray analysis. The coordination around the Pt atom is square-planar, and the DMSO ligand is S-coordinated. The lengths of the Pt-Cl bondscis andtrans to the DMSO ligand are 2.296(11) and 2.321(10) Å, respectively, and are well within expected ranges. Interatomic distances within the amine and DMSO ligands are normal.

Metal-Mediated Reactions of α-Bromomethyl-Propenoate Esters

Abstract Methyl 2-bromomethylprop-2-enoate reacts with benzaldehyde and with salicylaldehyde via its Sn and Zn complexes under aqueous conditions to form α-methylene-γ-lactones in high yields. In the case of salicylaldehyde X-ray analysis proves conclusively formation of a five- rather than a seven-membered ring. Under the above conditions 2-bromomethyl-3-phenylprop-2-enoate does not afford any cyclic products.