Propargylic compounds allenic substrates

In addition to the 1,3-dienes, in situ formed allenes were applied as substrates and cyclized with 2-iodophenols as well. In 2007, Liang and co-workers reported a novel palladium-catalyzed intermolecular tandem reaction for the synthesis of tetracyclic compounds from propargylic compounds and 2-iodophenols. The corresponding tetracyclic compounds were isolated in moderate to good yields (Scheme 2.47). In respect of the reaction pathway, the possible reaction intermediate was isolated and applied. In detail, this transformation consists of two catalytic cycles. The steps are (a) initial decarboxylation of propargylic compound by palladium(O) to... 

Hydride-promoted reactions are also well known, such as the acrylic and vinylacrylic syntheses (examples 7-10, Table VII). Some less-known compounds, which form in the presence of halide ions added to tetracar-bonylnickel, have been described by Foa and Cassar (example 11, Table VII). Reaction of allene to form methacrylates, and of propargyl chloride to give itaconic acid (via butadienoic acid), have been reported (examples 13 and 14, Table VII). 1,5-Hexadiene has been shown to be a very good substrate to obtain cyclic ketones in the presence of hydrogen chloride and tetracarbonylnickel (example 15, Table VII). The latter has also been used to form esters from olefins (example 16, Table VII). In the presence of an organic acid branched esters form regioselectivity (193). 

The Claisen rearrangement of propargyl vinyl ethers directly delivers the allene no equilibrium is observed. This reaction was also successful with complex substrates in order to show this, of numerous examples [375, 513-536], the compounds 159 [537] and 161 [538] are depicted (Scheme 1.71). 

An interesting transformation involving the indole nucleus was found from propargylic carboxylates to give tetracychc compounds with Au(I) (equation 85). This reaction proceeds by an allene-gold complex in equilibrium with the aUcenyl-gold species, which reacts intramolecularly with the indole to form the product. When the reaction of these substrates is performed with dichloro(pyridine-2-carboxylato)gold(III) or Pt(II) as catalysts, products in equation (86) are obtained instead. This new reactivity can be explained by a formal [3 + 2] cycloaddition of 1,3-dipole... 

The zinc and cadmium reagents " " (R0)2P(0)CF2MBr have also proved useful as alkylation substrates for particularly reactive species, e.g. allylic, benzylic or propargylic halides with the last type, some rearrangement to allenic compounds is observed. Scheme 12 illustrates the use of such reagents in the synthesis of a-fluorinated alkylphosphonic acid derivatives. 

Alkoxypropargylation. The ambident character of the propargylic anion, which may be in equihbrium with the aUenic form, is responsible for its limited use in synthesis. In general the structure and reactivity of the ambident anion depend on the nature of the substrate, the counter cation, and the solvent. There is also an erythro-threo stereoselectivity problem when alkylated propargylic anions react with aldehydes or unsymmetrical ketones. In contrast, the zinc and titanium reagents derived from the title compound possess the allenic structure and, upon reaction with aldehydes, lead almost exclusively to the )8-acetylenic alcohol (eq 1), presumably by a chelate transition state (Sei process). The reaction also leads preferentially to the erythro diastereomer. The stereoselectivity is highest with titanium as the metal and THE as the solvent. ... 

---