Alkylation of alkynyl anions

Making alkenes by addition to alkynes offers two distinct advantages. Firstly, although the reaction is not connective in the sense that the Wittig and Julia reactions are, the starting materials can often be made straightforwardly by alkylation of alkynyl anions. Secondly, the same alkyne can be used to make either E- or Z-alkene—an advantage shared with the Peterson reaction but here the... 

Preparation of Aikynes by Alkylation of Alkynyl Anions A synthesis of internal aikynes starting from terminal aikynes. 

Preparation of Alkynes by Alkylation of Alkynyl Anions The other major alkyne preparation is based on the easy accessibility of nucleophilic carbanions from terminal alkynes (Section 13-2). So, a wide variety of internal alkynes may be made from any terminal alkyne, via the sehenie... 

The two basic methods used to prepare alkynes are double elimination from 1,2-dihaloalkanes and alkylation of alkynyl anions. This section deals with the first method, which provides a synthetic route to alkynes from alkenes Section 13-5 addresses the second, which converts terminal alkynes into more complex, internal ones. 

Attempted alkylation of alkynyl anions with secondary and tertiary haUdes leads to F.2 products because of the strongly basic character of the nucleophile (recall Section 7-8). Ethyne itself may be alkylated in a series of steps through the selective formation of the monoanion to give mono- and dialkyl derivatives. 

Electrophilic attack on the 3-carbon of alkynyl ligands (Equation 12.50) is common and is a route to vinylidene complexes introduced in Chapter 3. Examples of protonation and electrophilic alkylation of an anionic acetylide complex at the 3-carbon are shown in Equation 12.51. Attack of two protons on an anionic carbyne complex generates a new carbyne complex, as shown in Equation 12.52. ° This reaction, presumably, occurs by initial formation of a vinylidene complex. 

Carbanions are negatively charged organic species with an even number of electrons and the charge mainly concentrated on a carbon atom. In alkyl, alkenyl, and alkynyl anions all of the... 

Alkynyl anions are more stable = 22) than the more saturated alkyl or alkenyl anions (p/Tj = 40-45). They may be obtained directly from terminal acetylenes by treatment with strong base, e.g. sodium amide (pA, of NH 35). Frequently magnesium acetylides are made in proton-metal exchange reactions with more reactive Grignard reagents. Copper and mercury acetylides are formed directly from the corresponding metal acetates and acetylenes under neutral conditions (G.E. Coates, 1977 R.P. Houghton, 1979). 

Acetylenedimagnesium bromide, 66, 84, 137 Acyl-alkyl diradical disproportionations, 299 Acyl-alkyl diradical recombination, 296 Alkaline hydrogen peroxide, 10, 12, 20 Alkylation of formyl ketones, 93 Alkylation via enolate anions, 86 17a-Alkynyl steroids from 17-ketones, 67 2a-Al]yl-17jS-hydroxy-5a-androstan-3 -one, 9 5 Allylic acetoxylation, 242 Allylmagnesium bromide, 64 17 -Aminoandrost-5-en-3 -ol, 145 17 a-Aminomethy 1-5 a-androstane-3, 1718-diol, 387... 

Anionic complexes of boron (boronates, borinates, etc.) have been introduced as convenient reagents in cross-coupling reactions of broad scope, particularly interesting for the transfer of alkynyl and primary alkyl residues, which cannot be accomplished using the standard protocols of the Suzuki-Miyaura reaction. Readily available Ph4BNa can be used as a convenient reagent for phenylation in place of the much more expensive PhB(OH)2, and all four phenyl groups can be utilized when the reaction is carried out with a phosphine-free catalyst in aqueous solutions.244... 

The most convenient pathway to this important class of compounds is the reaction of alkynes RG=GH with salts of the bis(acetylacetonato)gold anion.71 This reaction leads to almost any type of target compounds, including those with R = H, alkyl, alkenyl, alkynyl, aryl, heteroaryl, etc. (Q = metal or quaternary or PPN cation Equation (22)). 

Substitution of one dimethylamino group by alkyl, aryl, or alkynyl groups in complexes [M =C=C=C(NMe2)2 (CO)5] (M = Cr, W 51) has also been described [9]. The process occurs through an initial addition of the anionic carbon nucleophile to the Cy atom of 51 and subsequent abstraction of one dimethylamido... 

The unique reactivity pattern of alkynyl iodonium salts discussed in Sections II,A.2 and II,D,la can also serve as two-carbon conjunctive reagents in the synthesis of pyrroles, dihydropyrroles, and indoles. Feldman et al. found that combination of alkyl or aralkyl tosylamide anions 101 with phenyl(propynyl)iodonium triflate (102) furnishes the corresponding dihydropyrroles 103 (95JOC7722) (Scheme 28). 

Alkynyliodonium ions, 1 and 2, are hypervalent iodine species in which one or two alkynyl ligands are bound to a positively charged iodine(III) atom. They are sensitive to nucleophiles, especially at the /1-carbon atom(s) of the alkynyl ligand(s), and for that reason, the isolation of stable alkynyliodonium salts generally requires the incorporation of nucleofugic anions. A list of known alkynyliodonium compounds (i.e. as of 4/1/94), containing 134 iodonium salts derived from 103 iodonium ions, and references (5-45) to their preparation and characterization are presented in Table 1. Among these compounds, alkynyl(phenyl)iodonium sulfonates and tetrafluoroborates are the most common, while alkynyl(alkyl)iodonium salts of any kind are unknown. 

A synthesis could start with the same bromoketone as the one above reduction gives an alcohol, but alkylation of an alkynyl anion with this compound is not possible, because the anion will just deprotonate the hydroxyl group. 

Metallation of various 1-alkynyl sulfides, followed by alkylation of the resulting anion leads exclusively to a-alkylated allenyl sulfides (Scheme 39). 

The addition of anionic heteroatom-centered nucleophiles (HO, MeO, pyr-azolate, etc.) and carbanions (CN , enolates, alkyl or alkynyl reagents) to the cationic allenylidenes Ru(/75-C9H7)(=C=C=CR R2)(PPh3)2l PF6l [125-128,... 

The alkynyl anion can act as a nucleophile. Reaction with primary alkyl halides will lead to alkylation (by an SN2 mechanism) and the introduction of an alkyl group on the terminal carbon atom of the alkyne. 

Alkylations and silylations. Moderately stabilized allylic and propargylic anions are readily generated by treating substituted alkenes and alkynes with BuLi. l-(Benzotriazol-l-yl)propargyl ethyl ethers are a convenient source of alkynyl ketones by virtue of their facile alkylation. 

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