Addition of Alkynoates

While the Michael-addition of a,P-unsaturated carbonyl and related compounds constitutes one of the most important fundamental synthetic reactions in organic chemistry, the y-addition developed by Trost and Li of nucleophiles to 2-alkynoates catalyzed by a phosphine provides 

Fleming, L, Frontier Orbitals and Organic Chemical Reactions, John Wiley Sons, Chichester, 1976. 

Miranda, S., Lopez-Alvarado, P., Giorgi, G., Rodriguez, J., Aven-dano, C., Menendez, J., Synlett 2003, 2159. 

For an excellent review on this subject, see Hayashi, T., Synlett. 

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Enantiopure quinolizidinones and indolizidinones were obtained by Ma and Zhu in an intramolecular conjugate addition of the secondary amine of 293 to the alkynoate ester to provide the intermediate allenoate 294, which was subsequently trapped in a condensation reaction to afford 295 (Scheme 19.53) [62], In some instances, intermediate 296 was isolated, which could also be converted to 295. This quinolizidinone intermediate was then converted in a concise manner to lasubine II (297). 

Addition of a 2-alkynoic acid to alkali amide in liquid ammonia initially gives a solution of the alkali salt of the carboxylic acid. If an excess of alkali amide is present, the weakly basic salt is further deprotonated at a position next to the triple bond 183], This double deprotonation which may be compared with the formation of di-anions from 1,3-diketones and alkali amides [71], is essentially complete. The high kinetic stability of the alkynoic acid-dianion may be explained on the basis of resonance stabilization ... 

Mercury salts, such as mercury(II) acetate,521-525 mercury(II) oxide,524,526-528 metcury(II) trifluoroace-tate,529,530 mercury(II) sulfate524,531 and mercury(II) phosphate531 catalyze the addition of carboxylic acids to alkynes. Acetic anhydride in the presence of boron trifluoride etherate can also be effectively used in this reaction (equation 292).521,522 Alkynoic acids undergo mercury-catalyzed cyclization to lactones (equation 293).523,532,533... 

Michael-aldol reaction as an alternative to the Morita-Baylis-Hillman reaction 14 recent results in conjugate addition of nitroalkanes to electron-poor alkenes 15 asymmetric cyclopropanation of chiral (l-phosphoryl)vinyl sulfoxides 16 synthetic methodology using tertiary phosphines as nucleophilic catalysts in combination with allenoates or 2-alkynoates 17 recent advances in the transition metal-catalysed asymmetric hydrosilylation of ketones, imines, and electrophilic C=C bonds 18 Michael additions catalysed by transition metals and lanthanide species 19 recent progress in asymmetric organocatalysis, including the aldol reaction, Mannich reaction, Michael addition, cycloadditions, allylation, epoxidation, and phase-transfer catalysis 20 and nucleophilic phosphine organocatalysis.21... 

An improved one-pot access to a-substituted cinnamate esters (165) exploiting the addition of 1,3-diketones, /3-kclo esters, and malonates to alkynoates (164) catalysed by phosphines has been reported. Among the catalysts, n-BmP was found to be most effective, allowing the reaction to proceed under milder conditions and in a more general manner than with other phosphines.189... 

Isotope experiments revealed that D-atoms were incorporated to the vinyl position of adducts either in inter- or intramolecular reactions in d-TFA (Scheme 5) [3b, c]. Reaction of heteroarenes with alkynoates in AcOD gave similar results [4]. Also, addition of heteroaromatic C-D bonds to the C-C multiple bonds and the large isotope effect k,HlkD = 3) between pyrrole and ds-pyrrole in the reaction with ethyl phenylpropiolate were observed. 

Michael addition of thiophenols to fluorinated alkynoic acids under basic conditions affords the (Z)-3-arylthio-2-alkenoic acids which undergo an intramolecular Friedel-Crafts acylation to give 2-fluoroalkylated thiochromones 520 (Scheme 204) <1994JFC(68)25>. 

The regioselective anti-Markovnikov addition of benzoic acid to phenyl-acetylene has also been carried out with success at 111 °C in the presence of ruthenium complexes containing a tris(pyrazolyl)borate (Tp) ligand [RuCl(Tp)(cod), RuCl(Tp)(pyridine), RuCl(Tp)(N,N,Ar,AT-tetramethylethyl-enediamine )] with a stereoselectivity in favour of the (E)-enol ester isomer [22]. The o-enynyl complex Ru(Tp)[PhC=C(Ph)C=CPh](PMe/-Pr2) (C) efficiently catalyses the regioselective cyclization of a,cu-alkynoic acids to give en-docyclic enol lactones [23] (Eq. 2). 

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