| Summary: | α,β-unsaturated carbonyl compounds are important organic intermediates in the manufacture of natural products having biological, pharmaceutical and cosmetic relevance. Isomerization of propargyl alcohols to their corresponding α,β-unsaturated carbonyls have been the subject of a large number of investigations. This transformation is called Meyer-Schuster rearrangement, which is a 1,3 shift of a hydroxyl moiety of secondary and tertiary α-acetylenic alcohols to form α,β-unsaturated carbonyls via an allenol intermediate. Numerous studies have been carried out involving transition metal catalyzed transformations, including gold and ruthenium. This study demonstrates that FeCl3, which is a more readily available and cheaper alternative, is an effective catalyst for promoting this type of reaction at milder conditions. Propargyl alcohols were first synthesized from various benzaldehydes and Grignard reagent, ethynyl magnesium bromide. The next step is isomerization of propargyl alcohols catalyzed by anhydrous FeCl3 to form their corresponding unsaturated aldehydes. Cinnamaldehyde, formed from benzaldehyde, gave the highest yield of 85%, followed closely by aldehydes with electon-donating (methyl and methoxy) groups on the para position. E/Z isomerism was observed only for aldehydes with electron donating substituents, with E isomer being the major product.
|
|---|