Anions, alkyne

Terminal alkyne anions are popular reagents for the acyl anion synthons (RCHjCO"). If this nucleophile is added to aldehydes or ketones, the triple bond remains. This can be con verted to an alkynemercury(II) complex with mercuric salts and is hydrated with water or acids to form ketones (M.M.T. Khan, 1974). The more substituted carbon atom of the al-kynes is converted preferentially into a carbonyl group. Highly substituted a-hydroxyketones are available by this method (J.A. Katzenellenbogen, 1973). Acetylene itself can react with two molecules of an aldehyde or a ketone (V. jager, 1977). Hydration then leads to 1,4-dihydroxy-2-butanones. The 1,4-diols tend to condense to tetrahydrofuran derivatives in the presence of acids. 

Next ask, "What is an immediate precursor of 2-hexyne " We ve seen that an internal alkyne can be prepared by alkylation of a terminal alkyne anion. In the present... 

Terminal alkynes can be converted readily into alkynylsilanes by reaction of the corresponding alkyne anion or its metalloid equivalent with a suitable chlorosilane (/). The reverse reaction, that of liberation of the alkyne, is quite facile, being effected by several reagent combinations, including hydroxide ion, methanolysis, fluoride anion, silver(i) followed by cyanide anion, and methyl lithium-lithium bromide (2). 

The product of the rearrangement may be stable or may react further, depending on its nature (see also pp. 1396). An ab initio study predicts that a [l,2]-alkyl shift in alkyne anions should be facile. ... 

HEAVY ALKYNE ANION RADICALS The Only example of Compounds of this type, the anion radical of the valence isomer of distannyne 51-K, was recently synthesized by Power by the reduction of chlorostannylene 52 with potassium graphite in THF (Scheme 2.39). ... 

CuBr/QUINAP System The CuBr/QUlNAP system was initially used in the enan-tioselective synthesis of proparyl amines via the reaction of alkynes and enamines (Scheme 5.5). It was rationalized that the enamines reacted with protons in terminal alkynes in the presence of copper catalyst to form zwitterionic intermediates in which both the generated iminiums and alkyne anions coordinate to the copper metal center. After an intermolecular transfer of the alkyne moiety to the iminium ion, the desired products were released and the catalyst was regenerated. The combination of CuBr as catalyst and the chiral ligand QUEMAP is crucial for the good reactivities and enantioselectivities seen in the reaction. Another potential... 

The A1 atom is thought to coordinate with the oxygen of the epoxide in the first step of these reactions. The alkyne anion then reacts intramolecularly giving the product. 

After addition of the alkyne anion to the alkylborane, iodination facilitates alkyl group migration from boron to carbon in a transfer that resembles the one seen in the synthesis of (Z)-alkenes described in Section B4.1. Elimination to give the product alkyne occurs under the iodination reaction conditions (Figure B4.4). 

The benzoate ion is the product under the reaction conditions but the alkyne anion collects a oton from a water molecule, regenerating the second hydroxide ion, which therefore is a base... 

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