Reduction ofalkynes

Reduction ofAlkynes. Alkynes are selectively reduced to (Z)-alkenes by a reduction catalyst prepared from NaH, t-CsHnOH, and Pd(OAc)2 (6 2 1) in THE The reactions, carried out in the presence of quinoline under near atmospheric pressure of H2, are self-terminating at the semihydrogenated stage, and are more selective than the corresponding reductions catalyzed by Lindlar s catalyst. Omitting the f-CsHnOH gave a catalyst that effected complete reduction. 

Reduction ofAlkynes. Internal alkynes have been found to undergo either partial or full reduction upon treatment with sodium methoxide in the presence of Pd(OAc)2. The extent of reduction can be controlled by altering the solvent used and the partial reduction process affords the Z-alkene as the major reaction product (eq 126). 36... 

The proposed reaction mechanism (Scheme 7-2) comprises (1) oxidative addition of ArSH to RhCl(PPh3)3 to give Rh(H)(Cl)(SPh)(PPli3)n, (2) coordination ofalkyne to the Rh complex, (3) ris-insertion of alkyne into the Rh-H bond with Rh positioned at terminal carbon and H at internal carbon, (4) reductive elimination of 16 from the Rh(III) complex to regenerate the Rh(I) complex. 

Reduction of acetylenic alcohols made by addition ofalkynes to aldehydes or ketones... 

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