Addition to a Triple Bond

Hydrogen fluoride reacts readily with alkynes. The literature offers practically no details to cover the mode of operation, and most of the following observations are based upon the author s experience. 

Addition of Hydrogen Fluoride to Unsaturated Compounds Addition to a Triple Bond 

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KUCHEROV - DENIGES Hydration Water addition to a triple bond (Kucherov) or to a double borxl (Oeniges) under mercury salt catalysis... 

Alkenyl radicals generated by intramolecular addition to a triple bond can add to a nearby double bond, resulting in a tandem cyclization process. 

Intermolecular [3 + 2]-addition to a triple bond The [3+ 2]-addition reactions of acetylenes with nitrones never afford normal adducts instead, they produce the corresponding aziridines (381). An analogous situation is observed for most of nitronates (93, 95, 382 (Scheme 3.132). 

Nucleophilic addition to a triple bond serves to create the (3-al- Tips... 

The inversion in selectivity between the insertion into an H—Si bond favored by the intermediate in the dehalogenation and the addition to a triple bond favored by the intermediate formed upon silirane pyrolysis suggests that different reactive intermediates are formed. Since free silylene is implicated in the silirane pyrolysis, the lithium-induced deiodination probably involves a silylenoid such as a complex of the silylene with Lil or with THF. For a further discussion of this possibility, see Section II.E. 

There are two approaches for the preparation of alkenyl(phenyl)iodonium salts reaction of an activated alkene with an iodine(III) species and addition to a triple bond, either of simple alkynes or of alkynyl(phenyl)iodonium salts. 

Oxidation of diethyl a-benzylmalonate (25) by Mn(III) acetate in acetic acid at 70 °C in the presence of mono- or disubstituted alkynes leads to dihydronaphthalene derivatives (26) in moderate to good yields (equation 33). A mechanistic scheme involving the formation of the corresponding malonyl radical, its addition to a triple bond and intramolecular homolytic aromatic substitution of the vinyl radical adducts is discussed. Absolute rate constants, obtained from competitive studies, for the addition of a-benzylmalonyl radicals to a variety of alkynes cover few orders of magnitude e.g. the rate constants at 60 °C are 3x10 and 1 x 10 s for 4-octyne and phenylacetylene respectively. 

Addition of X to M = M in Reaction 1 represents a carbene-like addition to a triple bond. The moiety X could indeed be a carbene or... 

The pattern of adaptation of the orbital and energy structure of the alkyne molecule to the demands of the reaction of addition to a triple bond, shown in Fig. 6.3, is, in principle, retained also in addition reactions to heteronuclear triple bonds. This conclusion follows, for example, from the structure of the transition state V in the reaction of addition of hydrogen chloride to nitriles, which at the stage of the final product formation is characterized by the making of the bond C—Cl. The angle of nucleophilic attack is in the region of the transition strueture 126°. 

The key step in the total synthesis of e/ir-lycoricidine, recently accomplished by Keck and Wager [55] consisted of the thiy] radical addition to a triple bond of a suitable precursor followed by cyclization onto a pendant oxime moiety, as shown in Scheme 7. Then the alkoxyaminyl radical abstracts hydrogen from PhSH, when R=C02Me, or attacks intramolecularly the carbonyl moiety, when R = CHO. Following the former strategy, the target compound was obtained after two other transformations and in an overall yield of 11.1 % starting from lyxo.se, in 14 steps. 

In a recent report on directed regiodivergent additions to a triple bond (see 111) the change of reagents is combined with an interesting change from ionic to radical... 

Eisenstein, O., G. Procter, and J.D. Dunitz. 1978. Nucleophilic addition to a triple bond Preliminary ab initio study. Helv ChimActa 61 2538-2541. 

Komnick, P. and Sander, W., Intramolecular carbene addition to a triple bond matrix photochemistry of a-diazo-2-ethynylacetophenone, Liebigs Ann. Chem., 7, 1996. 

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