Reaction mechanism alkynylation

Scheme 36 Possible reaction mechanism for the bismuth-catalyzed carbo-oxycarbonylation of alkynyl esters...

Significant mechanistic insights into the DABCO-catalysed isomerization of y-hydroxy-o ,/3-alkynyl esters to y-oxo-a,p-trans-alkenyl esters have been reported.33 The reaction mechanism involves cumulene formation, protonation with the conjugate acid of the amine, and protonation of the resulting allenol with water. 

Isotellurazoles 4 were obtained in low yields (3-11%) by the one-pot reaction of alkynyl ketones with hydroxylamino-O-sulfonic acid and K2Te in aqueous solution containing sodium acetate (83S824 87H1587). A plausible mechanism of the reaction includes formation of the oxime derivative and subsequent nucleophilic addition of telluride anion to the triple bond followed by cyclization to 4. The reaction is accompanied by the formation of telluro bis(alkenyl ketones) 5 in yields approximately equal to those of 4. When alkynyl aldehydes are used instead of ketones, the single reaction products are the tellurobis(alkenyl nitriles) 6 (83S824). 

Cascade migration of acyloxy and phosphatyloxy group/cyclization reaction of alkynyl ketones catalyzed by copper or silver provided trisubstituted furans in high yields. A study of the reaction mechanism was also reported <07JA9868>... 

When reactions of alkynyl tosylates with acids are carried out under arfhydrous conditions, 1,1-vinylic diesters 122 can be isolated (equation 15f. The regio- and stereoselectivity of this reaction (equation 75) is consistent with an Ad mechanism, which was proposed for the first step of the acidic hydrolysis of alkynyl esters (equation 74). Moreover, the consequent hydrolysis of 122 yields the same products as the hydrolysis of alkynyl tosylates. ... 

The mechanism of the neutral reaction is more unusual, and was investigated in detail for alkynyl benzoates. Neutral hydrolysis of propynyl benzoate (116) in aqueous acetonitrile leads to keto-ester 124 in 46% yield along with the expected propanoic and benzoic acids. The mechanism of this reaction involves an unusual cyclization pathway including the intermediate formation of dioxalene 123 (equation 76). This mechanism was unveiled by labeling studies in H2 as well as careful NMR studies. Further evidence for this mechanism comes from the isolation and characterization dioxalenes 125 from the reaction of alkynyl benzoates with anhydrous methanol (equation 77). ... 

Pd-catalyzed homocoupling of terminal alkynes proceeds in the presence of a catalytic amount of Cu(l) salts and amines. During this process a terminal alkyne reacts with copper(I) salt in the presence of an amine to give an alkynyl copper compound that reacts with the Pd catalyst. Therefore, the homocoupling of terminal alkynes falls into the category of homocoupling of organometals and follows the same reaction mechanism. 

Movassaghi and Hill developed a ruthenium-catalyzed cycloisomerization of 3-azadienynes to the corresponding pyridines [11]. The alkynyl imines were produced from a variety of iV-vinyl and iV-aryl amides by amide activation and nucleophilic addition of copper(I) (trimethylsilyl) acetylide sequence reaction. Then by Ru-catalyzed protodesilylation and cycloisomerization, the desired pyridine derivatives were formed selectively in good to excellent yields (Scheme 2.7). For the reaction mechanism, C-silyl metal vinylidene was found to be the key intermediate. 

The coupling of alkynyl metals with tertiary alkyl halides without the occurrence of elimination or other side-reactions has been achieved with the organo-alanes, which are prepared from the alkynyl-lithium by reaction with anhydrous AlCl3. Thus, reaction of (Bu C3C— )3A1 with 1-bromoadamantane gave (735 96%) two of the three acetylene units are not utilized and can be recovered nearly quantitatively. It appears that starting material savings caimot be made by using alkynyldialkylalanes since elimination processes tend to occur with t-alkyl halides. The reaction mechanism is not clear. 

The first catalytic asymmetric version of [2 + 2] cycloaddition reaction was realized by Narasaka in 1989 using chiral titanium catalyst derived from TADDOL. It was found that the reaction of ketene dithioacetal with acryloyloxazolidinone derivatives proceeded smoothly in the presence of 10 mol% of TADDOL-TiCl2 to give the cyclobutane derivatives in high yields (64-96%) and good to excellent enantioselectivities (80-98%) [183]. The reaction is presumed to proceed via a carbonyl substrate chelated TADDOL-TiCb intermediate although the exact reaction mechanism is unclear. Moreover, alkynyl, alkenyl, and 1,2-propadienyl... 

A reasonable reaction mechanism involves (a) coordination of the alkynyl moiety to the Au-catalyst (- 101), (b) domino nucleophilic attack ofROH and anti-endo-dig-cycHzation via oxirane oxygen to afford the organogold intermediates 101-103, and (c) protonation of 103 to regenerate the Au-catalyst and to produce dihydrofuran 104 followed by HOAc-elimination to the products 100. 

Cyclizations of alkynyl derivatives proved to be a synthetically convenient way to 2-(trifluoromethyl)quinolines. Indeed, the intramolecular cyclization of N-(a-trifluoromethyl)propargyl anilines 89 takes place with the gold(I) catalyst under extremely mild conditions to afford 2-trifluoromethylquinolines 90 (Scheme 36). The reaction mechanism has been suggested to involve cyclization and oxidation steps [57],... 

Scheme 2.5 Proposed reaction mechanism involving one bis(alkynyl)silane and three organonitriles...

Seo SY, Yu X, Marks TJ (2009) Intramolecular hydroalkoxylation/cyclization of alkynyl alcohols mediated by lanthanide Catalysts. Scope and reaction mechanism. J Am Chem Soc... 

The proposed reaction mechanism may be initiated by the formation of the 7i-alkynyl complex A by the complexation of the unsaturated triple bond to the Ir (1) catalyst. Subsequent addition of the alcohol, which was supposed to occur anti to the 71-complex A, would lead to a c—complex B, which is favored in polar protic solvents such as MeOH, through a transient zwitterionic intermediate. Proton transfer may then be followed by the intermolecular addition of MeOH to give the cyclic ketal (Scheme 31). 

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