RESUMO
Di- or tetrahydropyrans with a vinyl side chain are obtained by diastereoselective ring-closing metathesis or by addition of vinylmagnesium chloride to an appropriately functionalized tetrahydropyranone. The resulting allylic alcohols are converted to spirocyclic hemiacetals under hydroformylation conditions. Oxidation yields the corresponding lactones.
RESUMO
Supercritical carbon dioxide (scCO2) acts simultaneously as solvent and temporary protecting group during homogeneously rhodium-catalyzed hydroaminomethylation of ethyl methallylic amine. Cyclic amines are formed as the major products in scCO,, whereas the cyclic amide is formed preferentially in conventional solvents. Multinuclear high-pressure NMR spectroscopy revealed that this selectivity switch is mainly due to reversible formation of the carbamic acid in the solvent CO2, which reduces the tendency for intramolecular ring closure at the Rh-acyl intermediate. These results substantiate the general concept of using scCO2 as a protective medium for amines in homogeneous catalysis and demonstrate for the first time its application for selectivity control.
RESUMO
The title compound, C(16)H(26)O(2), (I), prepared by oxidation of (1R*,11R*)-12-hydroxybicyclo[9.4.1]hexadecan-16-one using pyridinium dichromate, has a trans configuration of the two fused rings and represents an interesting precursor for the synthesis of macrocyclic structures.
