Propargyl vinyl ethers, transformation

Vidhani, D. V., Krafft, M. E., Alabugin, I. V. (2014). Rh(I)-Catalyzed Transformation of Propargyl Vinyl Ethers into , Z)-Dienals Stereoelectronic Role of trans Effect in a Metal-Mediated PericycUc Process and a Shift from Homogeneous to Heterogeneous Catalysis During a One-Pot Reaction. Journal of Organic Chemistry, 79, 352-364. 

The transformation of propargyl vinyl ethers into 2f/-pyrans is also possible with electrophilic iodine or bromine as demonstrated recendy by Xin and co-workers (Scheme 22) (15TL401). Firstly, propargylic alcohols 65 and bis-acceptor-substituted alkynes 66 are converted in situ into propargyl vinyl ethers.While no transition metal-catalysts are involved, the cychzation is induced by the initial formation of a halonium ion. The halonium ion is then attacked by the internal vinyl group and, after deprotonation, the product 67 is formed. The halogenated 2H-pyrans 67 were obtained in good yields under mild conditions. 

In a series of striking reports, Tejedor, Garcia-Tellado and co-workers were able to demonstrate that propargyl vinyl ethers 87 can be transformed into 1,2-dihydropyridines 88 with no transition metals being involved. Using microwave-assisted thermal heating, expensive and somewhat toxic metal... 

In an analogous manner, propargyl vinyl ethers with a pendant alcohol group as internal nucleophile gave 5,6- or 6,6-spiroketals with excellent diastereoselectivity (Scheme 4-49). This transformation is an example for efficient center-to-axis-to-center chirality transfer. 

In a convenient one-pot process, easily accessed propargyl vinyl ethers and aromatic amines are effectively converted into tetra- and pentasubstituted 5-methylpyrroles, which can fnrther be transformed into 5-formylpyrroles via 2-iodoxybenzoic acid (IBX)-mediated oxidation (Binder and Kirsch 2006). The cascade reaction proceeds through a silver(l)-catalyzed propargyl Claisen rearrangement, an amine condensation, and a gold(l)-catalyzed 5-exo-dig heterocyclization, as shown in Schane 11.4. 

Kirsch has reported the conversion of propargyl vinyl ethers to form pyrroles via a multi-step transformation involving the silver-catalyzed propargyl Claisen rearrangement to form the a-allenyl P-keto ester, condensation with a primary aryl amine. 

The propargyl Claisen rearrangement affords functionalized allenes through the [3,3]-sigmatropic transformation of propargyl vinyl ethers (Scheme 35)." ... 

The extention of radical cyclization of (bromomethyl)dimethylsilyl allyl ethers to propargyl analogs 17 has been studied by Malacria and coworkers. The intermediate exocyclic vinyl radical 18 can be either trapped by the hydrogen atom to give, after simple chemical transformations, the trisubstituted alkene 19 (equation 25) or can be added intramolecularly to give cyclic products when suitably located double bonds are present (equations 26 and 27). An attempt to apply this methodology to the stereoselective synthesis of angular and linear triquinane has also been performed. When = t rt-butyl,... 

In 2012, Fukuyama s group reported a novel synthesis route to the spiro-p-lactonic sesquiterpene (-)-anisatin, and they also relied on the construction of a bicyclo[2.2.2]octane system via a DIB-mediated methoxylative phenol dearomatization followed by an intramolecular Diels-Alder reaction [127]. The homochiral phenolic dihydrobenzofuran propargyl ether 231 thus afforded, via the ort/io-quinone monoketal 232 and treatment of its intramolecular [4+2] epimeric cycloadducts with camphorsulfonic acid in MeOH, the bicyclo[2.2.2] octanedienone 234 as a single diastereomer (Fig. 56). Further transformation of 234 gave the vinyl 235, whose trisubstituted double btmd bridge was oxidatively cleaved by mild ozonolysis to furnish the ketoaldehyde 236, en route to (-)-anisatin [127]. 

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