Alkyne-propargylic acetates

In addition to the reactions discussed above, there are still other alkyne reactions carried out in aqueous media. Examples include the Pseudomonas cepacia lipase-catalyzed hydrolysis of propargylic acetate in an acetone-water solvent system,137 the ruthenium-catalyzed cycloisomerization-oxidation of propargyl alcohols in DMF-water,138 an intramolecular allylindination of terminal alkyne in THF-water,139 and alkyne polymerization catalyzed by late-transition metals.140... 

Palladium-catalyzed reduction of propargyl acetates is possible with Sml2 in the presence of a proton source (Scheme 3.17) [51]. The allene/alkyne selectivity is greatly influenced by the choice of the proton source. Propargyl phosphates were also converted into hydridoallenes by Pd-catalyzed reduction with Sml2 [52],... 

In contrast with olefins, alkoxy-alkoxycarbonylation of alkynes to give /J-alkoxyacrylic esters is not a common reaction, and has occasionally been observed as a side reaction of the main reaction pathway leading to maleates and fumarates [77,80]. However, with suitably functionalized alkynes bearing a coordinating group (such as o ,a -disubstituted propargylic acetates) it may become the major reaction course (Scheme 15) [88]. 

Reduction of propargylic compounds with Sml2 is possible in the presence of Pd catalysts. Propargylic acetates 233 are converted mainly to the allene 236 by Pd-catalysed reaction with Sml2 in the presence of a proton source [51]. In this reaction, the allenylpalladium 234 is reduced with Sm(II) to the allenyl anion 235, which is protonated to give allene 236. The alkyne 237 is a byproduct. 2,3-Naphthoquinodi-methane (240) as a reactive intermediate, can be generated by applying this reaction. 

Reduction of alkynes to cis-alkenes.1 This relatively stable copper hydride (1) reduces terminal alkynes at 25° internal alkynes are reduced at 80° to cis-alkenes exclusively. These reductions require 2 hydride equivalents of the complex, and 5-10 equiv. of H20 is necessary for satisfactory yields. Under these conditions, a tertiary propargyl acetate was converted to an allene (equation I). 

In addition to propargylic carbonates, propargylic chlorides react with terminal alkynes in the presence of triethylamine or diisopropylamine. 5-Butyldodeca-3,4-dien-6-yne (165) was obtained in 91% yield by the reaction of 3-chloro-4-nonyne (164) with 1-heptyne in diisopropylamine (Section 11-45). Coupling of the propargylic acetate 166 with 1-heptyne is possible in the presence of three equivalents of zinc chloride with or without cuprous iodide to give the l,2-alkadien-4-yne 167 [40]. 

Aldiough the Nicholas reaction is a reliable method for propargylation of silyl enolates, it requires a stoichiometric amount of alkyne-Co2(CO)6 complexes [260]. Recently, Matsuda et al. successfully used the Ir-catalyzed system for highly regioselective propargylation of silyl enolates with propargyl acetates (Scheme 10.97) [261]. 

Hydrostannylation. Regioselective conversion of 1-alkynes to 2-tributylstannyl-l-alkenes is accomplished with BuySnH in the presence of (r-BuNC)3Mo(CO)3/ By changing the catalyst to (p-02NC6H4NC)3W(C0)3 propargyl acetate furnishes a distannylated product. ... 

Furthermore, in 1998 Ube Industries, Ltd. expanded their research from doublebond compounds to triple-bond compounds and discovered that alkyne compounds such as methyl propargyl carbonate (13), propargyl acetate (14), and 2-butyne-l,4-diol dimethyl dicarbonate (15) suppress the decomposition of PC [53]. In 1999, the same company discovered that a mixture of methyl propargyl carbonate (13) and VC is capable of improving battery performance even further [27, 54]. 

Similar to alkynes, allenes can be converted to alkenes without over-reduction of the olefin. Thus, good yield of terminal olefin 18 was obtained from aUene 17 (Scheme 8). Allene 20 could in turn be prepared from propargyl cabonate 19 under slightly modified reaction conditions. For comparison, reactions using the corresponding propargyl acetates were much less satisfactory (Scheme 9). 

Diastereoselective addition of propargyl acetate to the aldehyde 61 followed by MOM protection of carbinol, removal of the acetate, and partial reduction of the alkyne furnished allylic alcohol 62. Allylic alcohol 62 on oxidation and reaction with CBr4/PPh3 was converted into (Z,Z) bromodiene 63a, which on subsequent regioselective ring opening of benzylidene acetal in 63a afforded alcohol 64. 

The expected cyclobutenes are not always formed and other pathways than [2+2] cycloadditions can occur from ruthenacyclopentene intermediate. For example, a cyclopropanation reaction of various bicyclic alkenes could be performed when secondary propargyhc alcohols were used as alkynes in the presence of the Cp RuCl(cod) catalyst in THF [84] or when tertiary propargylic acetates were reacted in the presence of the CpRuCl(PPh3)2 catalyst in dioxane [85] [Eq. (34)]. 

Konno reported a detailed study of the reaction of fluorine-containing propargyl acetates under Nicholas conditions with a variety of nucleophiles. Allylstannanes and allylsilanes provided moderate yields of the desired products, while enamines, silyl enol ethers, and silyl ketene acetals furnished the target compounds with excellent efficiency. In one example, cobalt-alkyne complex 25 reacts with silyl ketene acetal 26 in the presence of trimethylsilyl triflate to yield, after cobalt decomplexation, ester 27. ... 

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