1,4—enynyl acetates

Shi, F.-Q., Li, X., Xia, Y, Zhang, L. and Yu, Z.-X. (2007) DFT Study of the Mechanisms of In Water Au(I)-Catalyzed Tandem [3,3]-Rearrangement/Nazarov Reaction/[l,2]-Hydrogen Shift of Enynyl Acetates A Proton-Transport Catalysis Strategy in the Water-Catalyzed [l,2]-Hydrogen Shift. Journal of the American Chemical Society, 129, 15503-15512. 

Katsumata and colleagues reported the first electrochemically mediated Ni(I)-catalyzed tandem radical cyclization reactions [139]. A bromoacetaldehyde dienyl acetal or the corresponding enynyl acetal underwent tandem 5-exo/5-exo cyclization reactions in the presence of Ni(cyclam) complex 98a under electrochemical reductive conditions (see Part 2, Sect. 5.3.3, Fig. 68). Bicyclic esters were isolated in 35% and 72% yields as a mixture of two and four diastereomers, respectively. 

A solution of the diacetylenic glycol 1 (4.98 g, 30 mmol) [52] in THF (40 mL) was added dropwise to a solution of 1,2 5,6-di-O-isopropylidene-a-D-glucofuranose (3.9 g, 15 mmol) and potassium hydroxide (0.1 g) in THF (30 mL) maintained at 80°C under nitrogen. After 16 h at 80°C the mixture was cooled and filtered, and the filtrate concentrated to dryness. An aqueous solution of the residue was extracted with chloroform, and the organic extract was washed (H20), dried, and applied to a silica gel column. Elution with benzene-ethyl acetate 7 1, gave the mixed enynyl ethers 2 and 3 (4.46 g, 96%). 

Reddy s group reported a silver-catalyzed annulation of enynyl azides to pyridine derivatives in 2015 [8], 3,6-Disubstituted pyridines were prepared in good yields through Ag-mediated aza-annulation of 2-en-4-ynyl azides which were derived from MBH-acetates of acetylenic aldehydes. 5-Iodo-3,6-Disubstituted pyridines can be prepared from enynyl azides having an electron-rich substituent on the alkyne functionality with I2 as the promoter (Scheme 2.5). 

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