Orthoformic----reaction with acetylene

They are colourless liquids with characteristic odours, and are prepared by the condensation of ketones with alkyl orthoformates in the presence of alcohols, or by the reaction of acetylenes with alcohols in presence of HgO and BF3. In some cases trichloroethanoic acid is used as the catalyst. They lose alcohol when heated and form vinyl ethers. Exchange of alcohol groups occurs when the ketals of the lower alcohols are boiled with alcohols of greater molecular weight. See acetals. 

Apart from the technical route described to p-apo-8 -carotenal, readily available vitamin A alcohol (Cjo) has served as an intermediate in the form of the phosphonium salt by reaction with the monodiethyl acetal of a Cio dial (ref. 54). The required Cjo monodiethylacetal was obtained (ref.5, p409) by the reaction of the mono aldehyde-protected derivative, the enol ether of methylmalonaldehyde, (C4) with the acetylenic Grignard reagent from trans 3-methyl-2-penten-4-yn-l-ol (C ) followed by acidic dehydration and partial reduction with Lindlar catalyst to give firstly 8-hydroxy-2,6-dimethylocta-2, 4,6-triene-l-al (Cio). Protection of the hydroxyl group by acetylation in pyridine solution with acetyl chloride and formation of the diethyl acetal with ethyl orthoformate followed by hydrolysis of the acetyl group and oxidation afforded the final CIO aldehyde component (D)shown in Scheme 15a. 

Without additional reagents Reaction of orthoformic acid amides with acetylene derivatives... 

Reaction of Metallated Acetylenes with Alkyl Halides, a-Halo-ethers, Epoxides and Alkyl Orthoformates... 

Other halides may be used in place of the bromo ester. Reaction of a pro-pargyl halide, for example, with various carbonyl compound gives y,d-acetylenic alcohols of type (6) in good yield.223 Also the carbonyl component may be replaced by an orthoformic ester, which leads to a malonic monoester monoaldehyde acetal of type (7) in 44-58% yield.224... 

The synthesis of 1 from the C 14-aldehyde 23 requires twenty reaction steps, including the preparation of the C6-acetal 37, and the formation of seven C-C bonds. Nevertheless, the process is economic because of the chemical and technological integration of the manufacturing process. Construction of the polyene chain, for example, only requires the simple chemicals acetylene, triethyl orthoformate, propenyl ethyl ether and vinyl ethyl ether. Five C-C bonds are formed with the aid of the enol ether condensation. This repetition of simple operations simplifies the process and allows even multistep syntheses to be carried out cost-effectively. 

---