Preparation of β-hydroxyesters from isoxazolines. A selective Nibpy-catalyzed electrochemical method

An electrocatalytic method for the reductive N-O cleavage of isoxazolines is described. Ni⁰bpy, generated in situ, was used to promote selective ring opening of 3-methoxy-5-phenylisoxazoline (1a) and 3-methoxy-[4,5]cyclohexylisoxazoline (1b). DMF and NaI were used as solvent and supporting electrolyte, and β-hydroxyesters 2a and 2b were obtained in high yields respectively, after acid hydrolysis. β-Hydroxynitriles 3a and 3b were also identified as side products.     

Synthesis of an advanced intermediate for (+)-pillaromycinone. Staunton-Weinreb annulation revisited

Condensation of an orsellinate anion with a 2-cyclohexenone (Staunton-Weinreb annulation) afforded a linear tetracycle which was converted to a protected derivative of 12a-epipillaromycinone. Methodology for introducing a 12a-hydroxyl substituent into the tetracycle with correct (R) configuration is described.     

Conformational study of the intramolecular diels-alder reaction of a pentadienyl acrylate. Theoretical evaluation of kinetic and thermodynamic control

Acrylate 4, prepared from diacetylrhamnal, underwent intramolecular Diels-Alder cycloaddition to give the thermodynamically disfavored trans-fused gamma-lactone 15 as the major product, along with two stereoisomeric cycloadducts. A computational analysis of each of the four transition states arising from 4 and the corresponding cycloadducts permits an understanding of the contrasting requirements for kinetic versus thermodynamic control of the reaction.     

Conformational studies on 1,2-di- and 1,2,3-trisubstituted heterocycles. A spectroscopic and theoretical study of 3-acylaminopicolinic Acid derivatives and their N-oxides.

Theoretical studies involving minimization of model 3-propanoylaminopicolinic acids (10d-trans, 10d-cis), methyl ester (10a), and corresponding -N-oxide derivatives (10b, 10c-trans, 10c-cis) using AM1 gave conformations contrary to both sound chemical intuition and experimental data. RHF ab initio calculations using the 6-31G and 6-31G basis sets on the other hand corroborated spectroscopic data. 3-Amidopicolinic acid derivatives (7a-9a, 7b-9b, 7c-9c, 9d) were prepared and studied by NMR and IR spectroscopy. The results show that a strong intramolecular hydrogen bond between amide-H and the 2-carboxyl substituent results in a planar molecular conformation. This is particularly profound in the 3-acylaminopicolinic acid N-oxides (c-series). When the 2-substituent is a methyl ester on the other hand, repulsion between N-oxide and ester functions induces twisting of the carbomethoxy group out of the plane of the aromatic ring. The type of method used in molecular modeling can have profound impact on the final theoretical result in the case of the above-mentioned class of compounds. Our results indicate, that it is advisable to employ ab initio methods for modeling these types of compounds, and further, that the choice of basis set used for such calculations should depend on the type of information required. Thus, for most purposes pertaining to molecular conformation the 6-31G basis set provides sufficiently sound data in relatively short CPU time. For data related to electronic properties such as involvement of the N-oxide function or spectroscopic information such as IR frequencies or (1)H or (15)N NMR chemical shifts, the use of polarization functions as contained in the 6-31G basis set seems to be a must.