Propargylic acetates, addition

The unsaturated c.vo-enol lactone 17 is obtained by the coupling of propargylic acetate with 4-pentynoic acid in the presence of KBr using tri(2-furyl)-phosphine (TFP) as a ligand. The reaction is explained by the oxypalladation of the triple bond of 4-pentynoic acid with the ailenyipailadium and the carbox-ylate as shown by 16, followed by reductive elimination to afford the lactone 17. The ( -alkene bond is formed because the oxypalladation is tnins addition[8]. 

Propargylic acetates, halides, and sulfonates usually react with a double-bond shift to give allenes.34 Some direct substitution product can be formed as well. A high ratio of allenic product is usually found with CH3Cu-LiBr-MgBrI, which is prepared by addition of methylmagnesium bromide to a 1 1 LiBr-Cul mixture.35... 

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... 

An alternative, but related, route to allenic titanium reagents from propargylic esters has been reported recently. Reaction of titanocene dichloride with BuMgCl and Mg yields a reactive titanocene intermediate, formulated as Cp2Ti. This reduced Ti species reacts in situ by oxidative addition to propargylic acetates. The allenyltitanium reagents thus produced add to aldehydes and ketones, as expected, to afford homopropargylic alcohols (Table 9.27) [43]. 

Similarly, the benzannulated enyne-allenes 172 and 173 were prepared from the propargylic acetates 171 by cuprate addition or by Pd-catalyzed addition of arylzinc chloride (Scheme 20.35) [49]. The presence of a butyl group and a p-anisyl group at the allenic terminus of 173a and 173b permits competition between a formal ene reaction and a formal Diels-Alder reaction leading to 174 and 175, respectively. 

A higher oxidation state product is obtained by the analogous cyclization of propargylic acetals.Unfortunately, the location of the additional unsaturation cannot be controlled. 

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]. 

Propargyl acetates, on addition of alkyl Grignard reagents in the presence of a catalytic amount of Cu , afford exclusively the 5 2 product namely, the allenic derivatives by an rtnr/-process [80], as shown in Eq. (80). 

Propargyl acetates undergo reductive isomerization to give terminal allenes. Conjugate additions. Interesting preparations pertain to the synthesis of 3-tri-fluoromethyl-3-hydroxyalkanoic acids, 3-aminomethylcycloalkanones, and 4-vinyl-2-acetoxy-2-cyclobutenones. Compounds of the last type give catechol derivatives on thermolysis. 

This reaction has been adapted to primary acetylenic alcohol by treatment of the mixture of propargyl acetate and water with mercury(II) trifluoromethanesulfonate [mercuric triflate, Hg(Tf)2] to give vinyl ketones under very mild conditions. In addition, this reaction has been carried out at high temperatures without the addition of an acid catalyst. ... 

The Pd(0)-catalysed addition of enolates of 2-oxocyclohex-3-enecarboxylates (46) to propargylic acetates (44) has been reported to produce 7-methylenebicyclo[3.2.1]-oct-3-en-2-ones (48). The proposed mechanism involves the initial nucleophilic attack at the central carbon of the intermediate tt-propargylic Pd-complex (45), followed by... 

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