Palladium chloride metal hydride reduction

Terminal monoalkenes were alkylated by stabilized carbanions (p a 10-18) in the presence of 1 equiv. of palladium chloride and 2 equiv. of triethylamine, at low temperatures (Scheme l).1 The resulting unstable hydride eliminate to give the alkene (path b), or treated with carbon monoxide and methanol to produce the ester (path c).2 As was the case with heteroatom nucleophiles, attack at the more substituted alkene position predominated, and internal alkenes underwent alkylation in much lower (=30%) yield. In the absence of triethylamine, the yields were very low (1-2%) and reduction of the metal by the carbanion became the major process. Presumably, the tertiary amine ligand prevented attack of the carbanion at the metal, directing it instead to the coordinated alkene. The regiochemistry (predominant attack at the more sub-... 

Other reactions studied include reduction of the triple bond of a-acetylenic esters and nitriles by tributyltin hydride in methanol electroreductive cyclization of acetylenic halides at a mercury cathode the trimerization and tetramerization of cyclo-octyne in the presence of various transition metals the kinetics of bromination of alka-l,3-diynes, of permanganate oxidation of acetylenedicarboxylic acid, and of iodination of propiolic acid the participation of the triple bond in reactions of various acetylenes of the general formula (225) and the trimerization of but-2-yne with tolyl-palladium chloride to give a [Pg.48]

Acid chlorides can be reduced to aldehydes either by catalytic hydrogenation or by reaction with a metal hydride. In both cases, the reagent and the reaction conditions are selected to avoid the further reduction of the aldehyde. The conversion of an acid chloride to an aldehyde can be carried out by the Rosenmund reduction, which uses hydrogen gas and a modified palladium catalyst. The palladium catalyst is altered to prevent further reduction of the aldehyde. To prepare the catalyst, the palladium is treated with quinoline, an aromatic heterocyclic amine, and is heated with sulfhr. 

The procedure outlined above describes the selective, retentive, p-coupling of (Z)-2,3-dibromopropenoic acid ethyl ester with (trimethylsilyl)acetylene employing the palladium-modified version of the Castro-Stephens reaction.4 5 The dibromide starting material is readily available by bromination of ethyl propiolate (Procedure A), as described by Trippett and Hall.2 The coupling product has been shown to be a versatile precursor for the synthesis of variously substituted enynes and enediynes. For example, a second acetylene may be introduced into the a-position under modified coupling conditions. Alternatively, reduction of the ester with diisobutylaluminum hydride and protection of the resultant alcohol with tert-butyldiphenylsilyl chloride affords a vinyl bromide that can be metalated and trapped with various electrophiles. These procedures have been used on the gram and multigram scale.5... 

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