Lindlar catalysts

Hydrogenation of alkynes may be halted at the alkene stage by using special catalysts Lindlar palladium is the metal catalyst employed most often Hydrogenation occurs with syn stereochemistry and yields a cis alkene... 

Total synthesis of motuporamide C is achieved by alkyne metathesis as a key step/ Diyne 133 is readily transformed into macrocyclic alkyne 134 with either catalyst. Lindlar reduction of 134 gives cycloalkene 135, which is further derivatized to motuporamine C-2HC1 (Scheme 47). 

Among the important reagents for which preparative procedures are given are 2,2 -bipyridine (by nickel directed and catalyzed dehydrogenation of pyridine p. 5), formamidine acetate (p. 39), phenyltrichloromethylmercury (p. 98), and trimethyl- and triethyloxonium fluoroborate (pp. 120, 113). The preparation of palladium catalyst ( Lindlar ) for the selective reduction of acetylenes is described (p. 89), as is the use of di-phenyliodonium-2-carboxylate, as a precursor of benzyne in the synthesis of 1,2,3,4-tetraphenylnaphthalene (p. 107). 

Hydrogenation Copper chromite (Lazier catalyst). Copper chromium oxide (Adkins catalyst). Lindlar catalyst (see also Lithium ethoxyacetylide, Malealdehyde, Nickel boride). Nickel catalysts. Palladium catalysts. Palladium hydroxide on carbon. Perchloric acid (promoter). Platinum catalysts. Raney catalysts, Rhenium catalysts. Rhodium catalysts. Stannous chloride. Tributylborane. Trifluoroicetic acid, Tris (triphenylphosphine)chlororhodium. 

Historically, the first synthesis of (Z)-isomers of carotenoids became possible after the introduction of a special palladium catalyst (Lindlar catalyst) for the partial hydrogenation of carbon-carbon triple bonds [4]. Thus (15Z)-P,P-carotene [(15Z)-3] [5] and (11Z,1 l Z)-p,13-carotene [(11Z,1 rZ)-3] [6-8] were obtained as intermediates in the synthesis of the (all- 3 target carotene. This partial hydrogenation of triple bonds, proceeding stereospecifically as a syn addition, is still a valuable method for the synthesis of disubstituted double bonds in the (Z)-configuration. The various reactions used to form carbon-carbon double bonds in the construction of the carotenoid skeleton generally proceed with variable stereoselectivity and result in ( 7Z)-mixtures (Chapter 2 Parts I, HI and IV). 

Many monoterpenes are desired fragrances in perfumery and flavors in food. They are produced on a larger scale from acetone (C3) and ethyne (acetylene C2) involving repetitive synthetic steps (Fig. 5). Initially, acetone is ethynylated by acetylene in the presence of a base (sodium hydroxide, amines with sodium carbonate) yielding 3-butyn-2-ol (C5) which is partially hydrogenated in the presence of deactivated catalysts (Lindlar catalysts) to 2-methyl-3-buten-2-ol. This can be converted to the key intermediate 6-methyl-5-hepten-2-one (Cg) via two pathways, either by transetherification with methylpropenylether and subsequent oxa-CoPE rearrangement, or by transesterification with methyl acetoacetate and subsequent Carroll decarboxylation. 

One such catalyst is frequently prepared by lead salt deactivation of palladium that has been deposited on calcium carbonate (CaCOs). It is called a Lindlar catalyst (Lindlar, H. Helv. Chim. Acta, 1952,55,446). 

There are many poisoned catalysts. One common example is called Lindlar s catalyst Lindlar s catalyst =, Pd / BaS04, CH3OH... 

Catalytic hydrogenation in the presence of a poisoned catalyst (Lindlar s catalyst or Ni2B) yields a c/s alkene. 

Boron trifluoride etherate is used as the condensation catalyst. Lindlar s procedure leads to the crystalline dihydrovitamin K, 1-monobenzoate, which can easily be purified and transformed to rac. vitamin K, of the hipest quality. 

Lindlar Catalyst ( Pd/BaS04/ quinoline)- partially poisoned to reduce activity will only reduce the most reactive functional groups. 

Hydrogenation with Lindlar s catalyst gives cis-olefins... 

Both objectives have been met by designing special hydrogenation catalysts The most frequently used one is the Lindlar catalyst, a palladium on calcium carbonate combi nation to which lead acetate and quinoline have been added Lead acetate and quinoline partially deactivate ( poison ) the catalyst making it a poor catalyst for alkene hydro genation while retaining its ability to catalyze the addition of H2 to the triple bond... 

The structure of quinoline is shown on page 460 In sub sequent equations we will simply use the term Lindlar Pd to stand for all of the components of the Lindlar catalyst... 

Lindlar catalyst (Section 9 9) A catalyst for the hydrogenation of alkynes to as alkenes It is composed of palladium which has been poisoned with lead(II) acetate and quino line supported on calcium carbonate... 

One of the important processes for manufacturing linalool is from the P-methylheptenone intermediate produced by the methods from petrochemical sources discussed earlier. For example, addition of sodium acetyUde to P-methylheptenone gives dehydrolinalool (4), which can be selectively hydrogenated, using a Lindlar catalyst, to produce linalool. 

Lindlar catalyst can be used for hydrogenation of l-[3-(2-phenylpyrazolo[1.5-a]pyridin-3-yl)propynoyl]-2-ethylpiperidine in ethyl acetate (38%) (Scheme 82 89EUP299209 92USP5102869) and l-(hetaryl)-4-alkynylpyrazole derivatives to the corresponding alkenes (96EUP703234). 

Hydrogenations with Lindlar catalysts frequently slow down or stop after absorption of 1 mol of hydrogen. Reduction of 4-hydroxydodec-2-ynoic acid stopped spontaneously when about 95% of the theoretical hydrogen had been absorbed 39). 

Amines (7a,12a), especially pyridine (75), have also been used as solvents in the hydrogenation of acetylenes. Hydrogenation of 3 over 5% Pd-on-BaS04 in pyridine gave df-cis-jasmanate (4) quantitatively (40). The authors comment that this combination for reduction of acetylenes was superior to the Lindlar catalyst in all cases examined. (See also Refs. 12 and 24 for similar conclusions.)... 

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