The enantioselective organocatalytic Michael addition in aqueous solution was compared with the reaction performed under solvent‐free ball‐milling conditions. A range of pyrrolidine‐derived organocatalysts were tested in the addition of aldehydes to nitroalkenes. Both procedures afforded good yields, diastereoselectivities, and enantioselectivities. The best catalyst in aqueous media was O‐lauroyl‐trans‐4‐hydroxyproline, whilst the ball‐milling technique was most‐efficient with α,α‐diphenyl‐2‐pyrrolidinemethanol trimethylsilyl ether.
Alkyl and aryloxyacetaldehydes add enantioselectively to various nitroalkenes. Addition products were isolated in good yield and high enantiomeric purity (up to 96 % ee) but
Ultrasound effect on the Pd(0) catalysed reaction of arylboronic acid with halobenzenes was investigated. The effect of catalyst, base as well as solvent was tested. Heterogenous reaction of iodoarenes with different arylboronic acids, catalysed by Pd/C and KF as the base in methanol:water mixture resulted in good yields of cross-coupling products. Reaction time of sonochemical reaction was 1 h, while 4 h of reflux was necessary to achieve comparable results. Bromobenzenes gave best results using aqueous solution of PdCl2 as the catalyst, potassium carbonate as the base in toluene:water two phase system using TEBA (benzyltriethylammonium chloride) as PT catalyst. Chlorobenzenes gave just feeble yields of cross-coupling products.
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