Propargylic esters, hydrogenation

Similarly, 1-halo-l-sulfonylallenes (139) have been prepared by heating in toluene at 80 °C of propargyl esters (138) via [2,3]sigmatropic rearrangement of the latter (Scheme 32) [51]. 1-Bromo-l-sulfonylallenes 139, when treated with bromine, undergo attack on central allenic carbon with formation of intermediate carbenium bromide followed by hydrogen bromide eUmination, and afford stereospecifically the 2,3-dibromo-l-sulfonyl-l,3-dienes 140. 

The reaction of propargylic esters with aldehydes and hydrogen sulfide in the presence of boron trifluoride etherate leads to 1,3-dithiins (86) (Equation (56)) <71T5753>. Dieckmann cyclization of suitably substituted acyclic 1,3-dithioacetals gives rise to l,3-dithian-5-ones (87) (Equation (57)) <59LA(624)79, 63LA(661)84>. 

The synthesis of substituted naphthylamine derivatives from propargyl esters by way of a carboannulation via a Pd(0)-catalysed [l,5]-sigmatropic hydrogen shift and cyclization has been reported (Scheme 134). ... 

Other indole syntheses of this type include the iridium-catalyzed hydrogen transfer of amine-substituted benzylic alcohols (130L3876), the intramolecular dehydrative coupling of tertiary amines with ketones (13OL6018), and the sequential alkylation/cyclization/isomerization of 3-(o-tri luoroacetamidoaryl)-l-propargylic esters (13T9494). 

Takasu, Ihara and coworkers described an efficient synthesis of ( )-paesslerin A (4-73) using a combination of a [4+2] and a [2+2] cycloaddition (Scheme 4.16) [25], Reaction of 4-71 and propargylic acid methyl ester in the presence of the Lewis acid EtAlCl2 led to 4-72 in 92 % yield, which was converted in six steps into the desired natural product 4-73 by transformation of one of the ester moieties into a methyl group, hydrogenation of one double bond, removal of the other ester moiety, and exchange of the TIPS group for an acetate. 

Hydride-promoted reactions are also well known, such as the acrylic and vinylacrylic syntheses (examples 7-10, Table VII). Some less-known compounds, which form in the presence of halide ions added to tetracar-bonylnickel, have been described by Foa and Cassar (example 11, Table VII). Reaction of allene to form methacrylates, and of propargyl chloride to give itaconic acid (via butadienoic acid), have been reported (examples 13 and 14, Table VII). 1,5-Hexadiene has been shown to be a very good substrate to obtain cyclic ketones in the presence of hydrogen chloride and tetracarbonylnickel (example 15, Table VII). The latter has also been used to form esters from olefins (example 16, Table VII). In the presence of an organic acid branched esters form regioselectivity (193). 

The boronic acid ester B was synthesized by transesterification of the corresponding pinacolester A with (lR,2R)-l,2-dicyclohexyl-l,2-dihydroxyethane. Stereoselective chlorination of B was carried out with (dichloromethyl) lithium and zinc chloride. Reaction of the obtained chloroboronic ester C with lithio 1-decyne followed by oxidation of the intermediate D with alkaline hydrogen peroxide afforded the propargylic alcohol E. Treatment with acid to saponify the tert-butyl ester moiety and to achieve ring closure, produced lactone F. Finally, Lindlar-hydrogenation provided japonilure 70 in an excellent yield and high enantiomeric purity. 

Methyl perfluoromethacrylate reacts with allyl and propargyl alcohols to give the Michael addition products 19 and 20, respectively these eliminate hydrogen fluoride in the presence of the boron trifluoride-triethylamine complex and rearrange to acyl fluorides 21 and 22. Hydrolysis of the acyl fluorides with base results in decarboxylation to give the 2-(trifluoromethyl) esters 23 and 24.11... 

REPPE PROCESS. Any of several processes involving reaction of acetylene (1) with formaldehyde to produce 2-butync-l,4-diol which can be converted to butadiene (2) with formaldehyde under different conditions to produce propargyl alcohol and, form this, allyl alcohol (3) with hydrogen cyanide to yield acrylonitrile (4) with alcohols to give vinyl ethers (5) with amines or phenols to give vinyl derivatives (6) with carbon monoxide and alcohols to give esters of acrylic acid (7) by polymerization to produce cyclooctatetraene and (8) with phenols to make resins. The use of catalysis, pressures up to 30 atm, and special techniques to avoid or contain explosions are important factors in these processes. 

An equimolar mixture of 3,4,5-trimethoxy phenyl iodide 157, lithium propargyl alkoxide 158, and diethyl ethoxymethylene malonate 159 was stirred at room temperature in the presence of a palladium catalyst. Then, to the resulting intermediate 161 potassium t-butoxide was added, and the ensuing base-promoted decarboxylative aromatization afforded tetrahydrofuran MCR adduct 162 in good yield. The ester was first reduced and the furan ring was hydrogenated with Raney nickel to furnish a diastereomeric mixture of products 163 in high yield. Further synthetic manipulations then provided a known precursor to the natural product. 

THF is useful in the malonic ester synthesis since it dissolves many sodio derivatives. Use of aqueous THF facilitates diazotization of salts of aminopolyphenyls which are sparingly soluble in water and is recommended also for the Schiemann reaction. It is superior to ether as solvent for coupling of an acetylenic Grignard reagent with a propargylic halide. Cremlyn and Chisholm found THF superior to dioxane or Cellosolve as solvent for the hydrogenation of cholesterol at ordinary temperature and pressure with perchloric acid as catalyst. 

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