Zur Stereochemie einiger neuer chiraler Bromverbindungen mit einem 2,4,8,10-Tetraoxaspiro[5.5]-undecan ? Ger�st
摘要:
New compounds containing the 2,4,8,10-tetraoxaspiro[5.5] undecanic skeleton, substituted with brominated groups, have been synthesized by a regioselective radicalic bromination reaction. The stereochemistry of the compounds was studied by high resolution NMR methods. The anancomericity or the flipping of the rings was inferred from the conformational analysis. The chirality of the spiranic skeleton was investigated by means of the diastereotopicity of hydrogen and carbon atoms.
A Facile, Selective Preparation of Monoketals from Pentaerythritol and Ketones
作者:Ricardo Grau、Marcelo Murguía、Santiago Vaillard
DOI:10.1055/s-2001-14569
日期:——
The selective preparation of monoketals 3a-f from pentaerythritol 1 and cyclic, acyclic, aromatic, and aliphatic ketones 2a-f was achieved by a facile method. The extreme polarity and low solubility of pentaerythritol in almost all organic solvents were the main difficulties to be overcome for the preparation of monoketals in good yields and high selectivity. A benzene-dimethylformamide (40:60) mixture proved to be excellent for the ketalization. The one-step procedure developed allowed the preparation of monoketals in good yields and good to excellent selectivity (higher than 90%).