Gold -catalyzed furan synthesis

Carbonyl compounds also react with allenes and, in fact, the first example of a gold-catalyzed addition of a nucleophile to allenes was the formation of lurans from allenones. The reaction was applied by Gevorgyan to the synthesis of substituted furans and in the case of bromide-substituted allenes halide migration was observed. Similar additions of... 

Another example concerning furan synthesis by gold-catalyzed cyclization was also reported. Reaction of (Z)-enynols using AuClj furnish fully substituted furans in high yields under mild reaction conditions <050L5409>. 

Various other acetylenic substrates can also be used for the synthesis of furans by intramolecular gold-catalyzed C-O bond formation. Thus, acetylenic diols gave a variety of monosubstituted, disubstituted, or trisubstituted fiirans by dehydrative cyclization in the presence of 2 mol% Au[P(r-Bu)2(o-biphenyl)]Cl/AgOTf or AuCl at 0 °C (Scheme 4-8In the latter case, the catalyst loading can be decreased to 0.05 mol% by scavenging water with activated molecular sieves and conducting the reaction in refluxing THF. 

Liu, Y, Song, F., Song, Z., Liu, M. and Yan, B. 2005. Gold-catalyzed cyclization of (Z)-2-En-4-yn-l-ols Highly efficient synthesis of fuUy substituted dihydrofurans and furans. Org. 

Recently, a highly selective gold-catalyzed synthesis of anelated phenol derivatives (e.g., 31) from 8-alkynyl furans (e.g., 30) was developed [14] ... 

Scheme 1.11 Synthesis of phenols via gold-catalyzed intramolecular reaction of furanes and alkynes...

Hydrofunctionalization of allenes also can be promoted by ketones in the presence of [Au(PPh3)]OTf to form furans [192]. This gold-catalyzed synthesis of furans proceeds by a novel [l,2]-alkyl shift (Scheme 33). Gold(III) porphyrin-catalyzed cycloisomerization of allenones gave the corresponding furans in good to excellent yields (up to 98%) [193]. 

Gold(I)-catalyzed synthesis of dihydrobenzo[ >]furans from aryl allyl ethers was reported as depicted below <06SL1278>. Highly efficient AuCl3/AgOTf-catalyzed atom-economical annulation of phenols with dienes was developed. This annulation generated various dihydrobenzo[ >]furans under mild conditions <06OL2397>. 

The first carbon addition to allenes catalyzed by gold was described by Hashmi and was the addition of furans to allenones, a reaction that is discussed as a conjugate addition to carbonyls. Then the annulation of 2-allenyl indoles was described (equation 111)and an enantioselective version was later developed for terminal allenes. Then Nelson described the cyclization of an N-substituted pyrrol in the synthesis of (—)-Rhazinilam (equation 112). In that case, gold notably improved the yields and selectivities obtained with Pd(II) or Ag(l), and gave complete retention of the chiral information of the allene. The most recent report is on the hydroarylations of allenes with gold-covered substituted benzenes as substrates. ""... 

Kim, S. and Lee, H. 2008. Cyclization of allenyne-l,6-diols catalyzed by gold and silver salts An efficient selective synthesis of dihydrofuran and furan derivatives. Adv. Synth. Catal. 350 547-551. 

Suhre, M. H., Reif, M. and Kirsch, S. F. 2005. Gold(I)-catalyzed synthesis of highly substituted furan. Org. Lett. 7 3925-3927. 

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