A palladium-catalysed reaction of conjugated enyne oxiranes with organoboron reagents is described. This method allows aryl-substituted vinylallenes containing a hydroxyl group on the allylic position to be synthesized, with good diastereomeric ratios, under mild conditions.
Acetate derivatives of 2-en-4-yne alcohols 1 and enyne oxiranes 4 regioselectively underwent 1,5-substitution (S N 2'')r eactions with Grignard reagents in the presence of an iron compound to provide vinylallenes exclusively with the (E)-configuration. An alkali salt was needed to avoid the hydride-promoted reductive1 ,5-substitutionp athway for 1, whereas no such additive was neededf or the effective conversion of 4 into the desired alkylated or arylated vinylallene structure.Scheme1.1,5-Substitution reaction of 1-(1-chloroethyl)-2-ethynylcyclohex-1ene with Grignard reagents (HMPA = hexamethylphosphoramide).Scheme2.1,5-Substitution of 2-en-4-ynea cetates with lithium organocuprates.
The rhodium‐catalysed carbonylation of 1,6‐enynes possessing an electron‐deficient alkenyl moiety in an alcohol reagent in the presence of a rhodium complex proceeded stereo‐ and chemoselectively to afford exocyclic α,β‐enoates.
The Rh-catalyzed reaction of arylboronic acids with internal alkynes under a CO atmosphere in the presence of an acid additive afforded a,b-unsaturated ketones as the major products. Hydroacylation of internal alkynes, except in the case of diaryl acetylenes, proceeded in syn fashion, yielding the E-configured isomer. A mixture of E-and Z-isomers was obtained with diphenyl acetylene. Reactions were also highly regioselective for various nonsymmetric alkynes.
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