Ynamines, hydration

Carboxylic esters, thiol esters, and amides can be made, respectively, by acid-catalyzed hydration of acetylenic ethers, thioethers,162 and ynamines, without a mercuric catalyst 163... 

Amides being formally hydrated ynamines would constitute cheap starting materials for the latter and many stratagems have been devised to achieve this goal. It must be kept in mind, however, that direct dehydration of amides is not feasible. One indirect approach has already been exemplified, namely the prior conversion of amides into thioamides. Another classical method involves halogen chloride elimination from amide chlorides. These versatile salts have received only scant attention prior to 1960. 

Ynamines are obtained by thiol elimination from ketene 5, A -acetals (1-aIkylthio-l-dialkylaminoalkenes) in 40-50% yields on treatment with LiNEt, at 20 °C or with NaNHo in boiling piperidine, or by leading them over solid NaNH.j at 150-165 °C. In the first two procedures the formed ynamines are fractionally distilled from the reaction mixture (equation 83) . When elimination is effected with KNHj in HMPT, aqueous work-up leads to the hydration of the ynamine. Therefore, 1,2-dibromo-ethane is added to the reaction mixture. It functions as a proton donor for the... 

---