An enantioselective Bronsted acid-catalyzed N-acyliminium cyclization cascade of tryptamines with enol lactones to form architecturally complex heterocycles in high enantiomeric excess has been developed. The reaction is technically simple to perform as well as atom-efficient and may be coupled to a gold(1)-catalyzed cycloisomerization of alkynoic acids whereby the key enol lactone reaction partner is generated in situ. Employing up to 10 mol% bulky chiral phosphoric acid catalysts in boiling toluene allowed the product materials to be generated in good overall yields (63-99%) and high enantioselectivities (72-99% ee). With doubly substituted enol lactones, high diastereo- and enantioselectivities were obtained, thus providing a new example of a dynamic kinetic asymmetric cyclization reaction.
Abstract The reaction of 2-3- O -isopropylidene- d -glyceraldehyde ( 1 ) with active methylene compounds in the absence of a catalyst involves facile and reversible addition to the formyl group. The adducts are readily transformed into furan derivatives by acid hydrolysis. When the reaction is catalysed with piperidine, unsaturated products are also formed, including α,β- and β,γ-unsaturated dicarbonyl
Polyphenylene oxide compositions stabilized with beta-diketones
申请人:ENICHEM S.p.A.
公开号:EP0480383A2
公开(公告)日:1992-04-15
Disclosed are polymeric compositions having excellent thermal stability and containing polyphenylene ether or a blend thereof with at least one (co)polymer of styrene as well as at least one linear and/or cyclic beta-diketone.
Said beta-diketones are capable of endowing said compositions with a long-lasting thermal stability in the molten state and of ensuring sufficient fluidity, resulting in improved processability of said compositions.