Nucleophile acetylenic

Alkynyl derivatives of 9-BBN act as mild sources of nucleophilic acetylenic groups. Reaction occurs with both aldehydes and ketones, but the rate is at least 100... 

A synthesis of 5-(alkyn-l-yl)-l,2,4-triazines 77 has been developed, in which, by activation with the palladium-containing catalyst, acetylenes effectively react with 5-chloro- and 5-iodo-l,2,4-triazines 76 (Scheme 46) (84H2245). The synthesis of 5-((o-alkynyl)-l,2,4-triazines 79 has been described using as nucleophile acetylenes 78 featuring a nucleophilic group (e.g., hydroxy or CH-activated group) (Scheme 46). 

Since acetylenic esters of any type, but especially ones with a good leaving group, like sulfonates, were unknown until recently [4], early substrates for nucleophilic acetylenic substitutions [Sn-A] were primarily the haloacetylenes 1 [2, 3, 5]. Unfortunately, product yields in these reactions tend to be moderate at best, usually because of competing reactions including displacement of RC C via direct attack on the halogen itself. 

Formalistically, reactions 63 and 64 are nucleophilic acetylenic substitutions (Sa -A) with the corresponding anions (sulfonate, phosphate or carboxylate) acting as nucleophiles and alkynyliodonium species 97-99 as the electrophilic substrates. However, the actual details of the mechanism are considerably more complex (equation 66). 

The great majority of known2 reactions of acetylenes are with electrophiles either via the acetylide ions RC=C", or by way of electrophilic addition reactions to the triple bond. Nucleophilic acetylenic substitutions (Sat-A) are generally unfavorable2. Alkynyl(phenyl)iodonium species may serve as synthons for the electrophilic alkynyl... 

Acetylide anions are both strong bases and nucleophiles. acetylene serves as a two-carbon building block for the... 

If DMAD is the electrophilic acetylene of choice, the commercially available 1-diethylaminopropyne is one of the finest nucleophilic acetylenes, Ynamines show a pronounced affinity for [2 + 2] cycloaddition to carbonyl groups as well as to olefins. Thus tetrazine-3,6-carboxamides (135) react with (136) to give (137) as one product. ... 

The high acidity of superacids makes them extremely effective pro-tonating agents and catalysts. They also can activate a wide variety of extremely weakly basic compounds (nucleophiles) that previously could not be considered reactive in any practical way. Superacids such as fluoroantimonic or magic acid are capable of protonating not only TT-donor systems (aromatics, olefins, and acetylenes) but also what are called (T-donors, such as saturated hydrocarbons, including methane (CH4), the simplest parent saturated hydrocarbon. 

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. 

In stereoselective antitheses of chiral open-chain molecules transformations into cyclic precursors should be tried. The erythro-configurated acetylenic alcohol given below, for example, is disconnected into an acetylene monoanion and a symmetrical oxirane (M. A. Adams, 1979). Since nucleophilic substitution occurs with inversion of configuration this oxirane must be trens-conilgurated its precursor is commercially available trans-2-butene. 

The following acid-catalyzed cyclizations leading to steroid hormone precursors exemplify some important facts an acetylenic bond is less nucleophilic than an olelinic bond acetylenic bonds tend to form cyclopentane rather than cyclohexane derivatives, if there is a choice in proton-catalyzed olefin cyclizations the thermodynamically most stable Irons connection of cyclohexane rings is obtained selectively electroneutral nucleophilic agents such as ethylene carbonate can be used to terminate the cationic cyclization process forming stable enol derivatives which can be hydrolyzed to carbonyl compounds without this nucleophile and with trifluoroacetic acid the corresponding enol ester may be obtained (M.B. Gravestock, 1978, A,B P.E. Peterson, 1969). 

Anions of acetylene and terminal alkynes are nucleophilic and react with methyl and primary alkyl halides to form carbon-carbon bonds by nucleophilic substitution Some useful applications of this reaction will be discussed m the following section... 

In agreement with these analyses, it was found that conqiound S was unreactive toward base-catalyzed cyclization to 6, even though the double bond would be expected to be reactive toward nucleophilic conjugate addition. On the other hand the acetylene 7 is readily cyclized to 8 ... 

The 13-ethyl-17-ketones, i.e., (63), have been found to be considerably less reactive than their 13-methyl counterparts towards acetylenic nucleophiles. The difference is attributed to the additional steric hindrance provided by the ethyl group. An attempt to introduce an ethynyl group into mc- 2>-isopropyl-3-methoxygona-l,3,5(10)-trien-17-one was unsuccessful even in ethylenediamine at 50°. However ethynylation of rac-13-isopropyl-3-methoxygona-1,3,5(10),8(14)-tetraen-17-one proceeded smoothly at room temperature to afford the 17a-ethynyl compound in 60% yield. ... 

Disubstituted isotellurazoles 1 (4-11%) and bis((3-acylvinyl)tellurides 3 (3-10%) were isolated in very low yields from the reaction mixture as the products of nucleophilic addition of telluride anion to the triple bond of the initial ethynyl ketones (83S824). This method cannot be applied to the synthesis of 3//-isotellurazoles. When a-acetylenic aldehydes were used instead of ethynyl ketones, bis((3-cyanovinyl)tellurides 4 obtained in 14-20% yields were the only products (83S824). 

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