[22754-96-7] · C2K2 · Dipotassium Acetylide · (MW 102.22)
Alternate Names: 1,2-ethynediyldipotassium; potassium acetylide; potassium carbide.
Solubility: low sol THF at 25 °C.3
Preparative Methods: dipotassium acetylide is prepared in situ and has not been isolated. Preparative routes include treatment of acetylene with potassium hydroxide in 1,2-dimethoxyethane or acetal solvents at temperatures between -10 °C and 20 °C,1 addition of acetylene to a solution of potassium t-pentoxide,2 and addition of 1 equiv of acetylene to 2 equiv of potassium t-butoxide in THF at 25 °C.3 Solutions produced by the above methods are then used immediately. The reaction of dipotassium acetylide with N,O-Bis(trimethylsilyl)acetamide affords bis(trimethylsilyl)acetylene (eq 1), which confirms the nature of the reactive species. Because dipotassium acetylide has not been isolated, there is little physical data that is available for it.
Treatment of androsta-4,9(11)-diene-3,17-dione with dipotassium acetylide (prepared from Acetylene (1 equiv) and Potassium t-Butoxide (2 equiv) in THF) afforded the propargyl alcohol derived from exclusive attack at C-17 (eq 2).3 Trapping experiments using Chlorotrimethylsilane revealed that the C-3 ketone was completely enolized, whereas the C-17 was only partially ionized. Apparently, the C-17 ketone was sufficiently ketonic at equilibrium to allow acetylide addition to proceed to completion.
In a related study, treatment of androsta-1,4-diene-3,17-dione with dipotassium acetylide afforded 17a-ethynyl-17b-hydroxyandrosta-1,4-dien-3-one (97%; eq 3). Again, the C-3 ketone was not alkylated.
Treatment of 9a-hydroxyandrost-4-ene-3,17-dione with dipotassium acetylide did not afford the desired 9a,17b-dihydroxy-17a-ethynylandrost-4-en-3-one, but rather gave a mixture of the rearranged steroids 4-methyl-19-norandrosta-4,9-diene-1,17-dione, 4ε-methyl-19-norandrosta-5(10),9(11)-diene-1,17-dione, the two corresponding C-17 hydroxyethynylated products, and the two C-10 diastereomers of 17a-ethynyl-17b-hydroxy-9,10-secoandrost-4-ene-3,9-dione (eq 4). Yields were not reported. The desired 9a,17b-dihydroxy-17a-ethynylandrost-4-en-3-one was prepared by treatment of 9a-hydroxy-3-methoxyandrosta-3,5-dien-17-one with Lithium Acetylide-1,2-Diaminoethane in dry THF, followed by acidic workup (eq 5).
Treatment of pivalaldehyde with dipotassium acetylide in p-dioxane/diethyl ether afforded the corresponding alkynic glycol after acidic workup (22%; eq 6). Hydrogenation of the alkynic glycol, followed by oxidation of the alcohols, afforded 2,2,7,7-tetramethyloctane-3,6-dione in 82% yield. In the same study, comparison was made with the dimetalloacetylides acetylenebismagnesium bromide and dilithium acetylide. Both of these acetylides afforded moderate yields of alkynic glycols upon condensation with aliphatic and aromatic aldehydes. In a direct comparison, treatment of acetylenebismagnesium bromide with pivalaldehyde afforded 2,2,7,7-tetramethyloctane-3,6-diol in 36% yield, while reaction of dipotassium acetylide with pivalaldehyde afforded the same diol in 22% yield.
Charles H. Winter
Wayne State University, Detroit, MI, USA