Letters in Organic Chemistry - Volume 2, Issue 8, 2005

4,4-Bis(ethylthio)but-3-en-2-one 1a and 4,4-bis(benzylthio)but-3-en-2- one 1b have been investigated as non-thiolic and odorless thiol equivalents in thio-Michael addition. Promoted by acetyl chloride in methanol, the cleavage of compounds 1a and 1b commenced and the in-situ generated thiols underwent facile acid-catalyzed conjugate addition to α,β-unsaturated ketones 2 affording the corresponding β-keto sulfides 3 in good yields.

Chromium trioxide supported on NaHSO4.H2O can be used as an efficient reagent for the conversion of trimethylsilyl ethers to their corresponding carbonyl compounds in solution and under solvent free conditions.

Cerium(III) chloride heptahydrate adsorbed on silica gel (CeCl3.7H2O-SiO2) efficiently catalyzes the conversion of cyclic β-diketones to β-keto enol ethers in good yields. The catalyst is reusable and can be applied several times with little decrease in the yield of the reactions.

A solvent-free continuous bromination reaction of thiophene in a micro reactor rig was developed, using pure bromine and aromatic without any catalyst at room temperature processing. This micro-reactor operation led to high selectivities for the bromination of 2,5-dibromo-thiophene (at about complete conversion) and yields up to 86%, which is better than for self-made batch processing (77% yield) and literature data (50% yield). In addition, the reaction time could be reduced from about 2 hours to less than 1 second. Correspondingly, the space-time yields were higher by order of magnitude for the continuous microreactor process as compared to batch operation. The micro reactor allowed a fast parametric study and in this way to reliably find optimal operating conditions with regard to temperature and the bromine-to-thiophene molar ratio. The study was complemented by a comparison of two different micro mixers, a T-junction with minute internals, and batch processing under optimal conditions.