Carbonyl compounds with alkynes

Alkylation of alkynes. The reaction of alkynes with carbonyl compounds in lolucne-aqueous NaOH is markedly accelerated by catalytic amounts of tetra-n-butylammonium bromide. 

Propargylic akohols Condensation of alkynes with carbonyl compounds is simply accomplished by treatment with Galj-BUjN in THF at room temperature (16 examples, 49-88%). 

Table 2.62 Nucleophilic Additions of Terminal Alkynes With Carbonyl Compounds ...

Recently, four-component coupling reactions of aldehydes, alkynes, dienes, and dimethylzinc catalyzed by a nickel complex have been reported (Equation (78)).435 Similarly, l,c< -dienynes react with carbonyl compounds and dimethylzinc in the presence of an Ni catalyst to afford the corresponding cyclized products. 

Isosydnones (146) react with alkynes to give pyrazoles (150). For example, 4,5-diphenylisosydnone (146, R = R = Ph) and ethyl phenyl propiolate gives 4-ethoxycarbonyl-l,3,5-triphenylpyrazole (150, R = R = R = Ph, R = CO Et) identical with the product from 4,5-diphenylsydnone (1, R = R = Ph). The rate of 1,3-cycloaddition for isosydnones (146) is relatively slow in comparison with sydnones (1).2o, 04 number of other cycloaddition reactions of isosydnones with alkenes, alkynes, and carbonyl compounds have been reported. ... 

Similarly, l-bromo-l,l-difluoro-2-alkynes, which were prepared by the reaction of lithium acetylides with CF2ClBr [284] or CF2Br2 [285], also reacted with carbonyl compounds in the presence of zinc to afford the corresponding a,a-difluoropropargyl alcohol [285]. This reaction has been utilized for the preparation of 3-fluoro-2,5-disubstituted furans [286] and other fluorinated biologically active compounds [285,287] (Scheme 99). 

Hydration of alkynes yields carbonyl compounds and the ketone used in pyrylium syntheses has been successfully replaced by an alkyne (65CB334). Phenylacetylene, for example, reacts with 3-chloro-l-phenylprop-2-en-l-one to yield the 2,6-diphenylpyrylium salt. 

Resin-bound amines can be converted into imines [710,711] or enamines by reaction with carbonyl compounds (Entries 6 and 7, Table 3.39). Resin-bound enamines have also been prepared by Michael addition of resin-bound secondary amines to acceptor-substituted alkynes [712], by Hg(II)-catalyzed addition of resin-bound secondary amines to unactivated alkynes [713], by addition of C-nucleophiles to resin-bound imino ethers [714], and by chemical modification of other resin-bound enamines [712,713,715], Acceptor-substituted enamines ( push-pull alkenes) are not always susceptible to hydrolytic cleavage by TFA alone and might require aqueous acids to undergo hydrolysis [716]. 

Organozinc reagent prepared from the 2-(trimethylsilyl)allyl bromide 156 and zinc react with alkynes or carbonyl compounds as well as nitriles to give the corresponding coupling products in moderate to good yields (equation 130)225. 

Calculations of reactions of simple nucleophiles such as H with carbonyl compounds show that, in the gas phase, there is no barrier. Activation energies in solution arise from desolvation of the nucleophile. However, reactions of a nucleophile with an alkene or an alkyne do have a barrier in the gas phase. 

Oxidation of alkenylboranes by alkaline hydrogen peroxide gives aldehydes or ketones depending on the substituent pattern of the alkenyl group thus, when alkaline hydrogen peroxide oxidation is combined with alkyne hydroboration, the resulting two-step process is a procedure for converting alkynes to carbonyl compounds (Equations B2.7 and B2.8). 

Oppolzer has classified intramolecular ene reactions into type I, II and III depending on whether the tether is attached to carbon 1,2 or 3 of the ene component (see equations 4, S and 6). Type IV reactions, which are a variation of type I in which the tether is attached to the terminal rather thim internal end of the enophile, are occasionally observed (see equation 7). Type I reactions with alkenes or alkynes as enophiles have been extensively studied. Only a few examples of type II, III and IV reactions with alkenes or alkynes as enophiles are known. Numerous examples of intramolecular type I, II and III reactions with carbonyl compounds as enophiles are discussed in Volume 2, Chapter 2.1. 

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