Furans propargyl-Claisen rearrangement

In much the same way, but with improved yields, a gold(l)-catalyzed propargyl Claisen rearrangement affords tri-and tetrasubstituted furans in good to excellent yields (Equation 32) <2005OL3925>. 

Au-Catalyzed reaction of propargyl vinyl ethers furnished tri- and tetrasubstituted furans in high yields. The reaction proceeded through cyclization of 2-allenyl-13-dicarbonyl intermediates produced from propargyl-Claisen rearrangement <05OL3925>. 

SYNTHESIS OF FURANS AND PYRROLES VIA PROPARGYL CLAISEN REARRANGEMENT... 

Scheme 4 Furans synthesized via gold(l)-catalyzed propargyl Claisen rearrangement.

The pyrolytic reactions of pentafluorophenyl and heptafluoro-2-naphthyl propargyl ethers give product mixtures containing benzo- and naphtho[6]furan derivatives, resulting from initial Claisen rearrangement followed by further intra- and intermolecular reactions.31 34... 

For chirality transfer via a furan ring transfer reaction of tetrahydrobenzofuranyl allenyl ethers and Claiscn rearrangement see refs 675 and 676. The synthesis of cyclopropanes via Claisen rearrangements of propargylic alcohol derivatives is reported in ref 677 and for acetylene Claisen rearrangements of thio derivatives see refs 678 and 679. 

SCHEME 7.5 Conducting the Claisen rearrangement of the aryl propargyl ether in diethylanihne at elevated temperatures. Formation of the desired chroman product is accompanied by generation of furan by-product in successively increasing amounts. 

The related Gosteli-Claisen rearrangement of 2-alkoxycarbonyl-substituted propargyl vinyl ethers can also be catalyzed by cationic gold(I) complexes and provides highly substituted furan derivatives. ... 

This cyclization is likely to occur as a domino process consisting of Claisen rearrangement and heterocyclization. The Au(I)-catalyst activates the alkyne moiety of 109 for a thermal oxa-propargyl-CiAisEN rearrangement, which provides the allenyl carbonyl system 111 required for cyclization (probably via enol 112) to the furan-3-carboxylates 110. AgBp4 is necessary for activation of the Au(I)-catalyst. 

Kirsch et al. reported that vinyl propargyl ethers 36 could be converted into the densely substituted furans 38 via the Au(I)-catalyzed cycloisomerization reaction (Scheme 8.17) [125] A variety of substituted furans 38 (Table 8.1) could be obtained under very mild reaction conditions at only 2 mol% catalyst loading. It is believed that this cascade process begins vith the Au(I)-catalyzed Claisen-type rearrangement of 36 leading to the formation of skipped allenyl ketone 37, vhich, upon the Au(I)-catalyzed 5-exo-dig-cyclization, provides furan 38. 

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