Transformations of isoxazolidine and dihydropyran derivatives to optically active compounds
摘要:
Isoxazolidine and dihydropyran spiro derivatives can be easily transformed, by hydrolysis and hydrogenolysis, to give delta-keto esters, delta-keto acids, beta-amino esters, beta-amino acids and 3-amino alcohols in good yields, Starting from optically active compounds enantiomerically pure products are obtained, In some cases, reactions were induced by microwave irradiation.
Facial Selectivity in Cycloadditions of a Chiral Ketene Acetal under Microwave Irradiation in Solvent-Free Conditions. Configurational Assignment of the Cycloadducts by NOESY Experiments and Molecular Mechanics Calculations
摘要:
(R)-4-Phenyl-2-methylene-1,3-dioxolane (1) undergoes 1,3-dipolar and Diels-Alder cycloadditions under microwave irradiation within 3 min with excellent yields, a simple purification procedure, and an interesting facial selectivity. The stereochemistry of these cycloadducts has been inferred by NOESY experiments and molecular mechanics calculations. X-ray structure determination was required in one case. Thermal isomerization of the cycloadducts was performed affecting only the spiro-carbon. The Diels-Alder adducts in the presence of a slight amount of acid yield the corresponding open chain esters.