Trichloroacetimidates are useful reagents for the synthesis of esters under mild conditions that do not require an exogenous promoter. These conditions avoid the undesired decomposition of substrates with sensitive functional groups that are often observed with the use of strong Lewis or Brønsted acids. With heating, these reactions have been extended to benzyl esters without electron donating groups. These inexpensive and convenient methods should find application in the formation of esters in complex substrates.
Air-stable iron carbonyl compounds bearing cyclopentadienone ligands with varying substitution were explored as catalysts in dehydrogenative diol lactonization reactions using acetone as both the solvent and hydrogen acceptor. Two catalysts with trimethylsilyl groups in the 2-and 5-positions, [2,5- 2), were found to be the most active, with 2 being the most selective in the lactonization of diols containing both primary and secondary alcohols. Lactones containing five-, six-, and seven-membered rings were successfully synthesized, and no over-oxidations to carboxylic acids were detected. The lactonization of unsymmetrical diols containing two primary alcohols occurred with catalyst 1, but selectivity was low based on alcohol electronics and modest based on alcohol sterics. Evidence for a transfer dehydrogenation mechanism was found, and insight into the origin of selectivity in the lactonization of 1°/2°diols was obtained. Additionally, spectroscopic evidence for a trimethylamine-ligated iron species formed in solution during the reaction was discovered.
Tertiary benzylic alcohols react with oxoammonium salts, undergoing a tandem elimination / allylic oxidation to provide an allylic ether product in a single step. This mode of reactivity provides a...
4-Acetamido-2,2,6,6-tetramethyl-1-oxopiperidinium tetrafluoroborate (Bobbitt's salt) effectively activates electron rich alkenes and promotes the addition of anilines. This transformation provides a direct, transition metal free method for amino-oxidation of alkenes under mild conditions. The relative stereochemistry of the amino-oxidation is influenced by solvent effects, with both the syn and anti amino-oxidation products being accessible from identical starting materials.
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