Acetals hydride donors

Significantly better results in addition of non-stabilized nucleophiles have come from hydrogenolysis reactions using formate as a hydride donor as shown in Scheme 8E.46. The racemic cyclic acetate and prochiral linear carbonates were reduced in good enantioselectivities by monophosphine ligands (/ )-MOP (16) and (Zf)-MOP-phen (17), respectively [195]. The chirality of the allylsilane can be efficiently transferred to the carbinol center of the homoallylic alcohol by the subsequent Lewis acid catalyzed carbonyl addition reaction 1196], The analogous... 

Catalytic reduction of alkynes to ds-alkenes. This reduction is not possible with 10% Pd/C alone because this metal is too reactive and the alkane is formed readily. The selective reaction is possible if the Pd/C is deactivated by either Hg(0) or Pb(0), obtained by reduction of metal acetate with NaBH4. Sodium phosphinate, H2P02Na, is the preferred hydride donor. Since this donor is not soluble in the Organic solvents used, a phase-transfer catalyst, benzyltriethylammonium chloride, is added.3... 

The 1-adamantyl cation is also trapped by 1,1-dichloroethylene1921 and 1,1,3-trichloroethylene 193> to give 1-adamantyl acetic acid (Eq. (56)) and archloro- 1-adamantyl acetic acid (Eq. (57)), respectively, after hydrolysis, and by olefins in the presence of hydride donors such as hexane to give alkyl... 

Reductive cleavage of Aloe groups can be accomplished under Pd 0)-catalysis using various hydride donors such as formic acid,190 tributylstannane,191 phenyl-silane,192 sodium borohydride193 or various borane-amine complexes.194 The reaction gives metal carbamate derivatives and propene as the primary products With tributylstannane the reaction is usually conducted in the presence of acetic... 

In a similar fashion ethers, acetals and formic acid may serve as efficient hydride donors towards carbonium ions, aryldiazonium salts (reduction with loss of nitrogen occurs) and pyrylium salts. A review of this chemistry is available. ... 

In this experiment, we will conduct some modern organic chemistry using a palladium catalyst. It is a rare opportunity for students in undergraduate laboratories to experience this powerful chemistry. We will react the lodosubstituted aromatic compounds, shown below, with 1-pentyne, 1-hexyne, or 1-heptyne in the presence of the catalysts, palladium acetate and cuprous iodide, to yield 4-substituted-l-pentynyl, 4-substituted-l-hexynyl, or 4-substituted-l-heptynylaromatic compounds. This reaction is called the Sonogashira coupling reaction. The reaction will be carried out in refluxing 95% ethanol as the solvent. In addition, piperazine will be employed both as a base and as a hydride donor. 

Similarly, acetalic C-H bond could be exploited as hydride donor as well, and via ruthenium-catalyzed cyclization of linear alkynyl acetals 181, spirobicycles 182 could be furnished in fairly good yield (Scheme 69) [76], along with the formation of linear hydroxyester 183, which was generated by hydrolysis of intermediate I. Notably, rigid cyclic acetal afforded a higher yield of spiro compound in comparison to the linear acetals [96]. 

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