Intramolecular reactions gold-catalyzed acetylenic reaction

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. 

Toste has reported a gold(I)-catalyzed protocol for the intramolecular addition of an alkyl azide to an alkyne with loss of dinitrogen (acetylenic Schmidt reaction) to form pyrrole derivatives [19]. For example, treatment of homopropargyl azide 16 with a catalytic 1 2 mixture of (dppm)Au2Cl2 (dppm = l,2-bis(diphenylphosphino)meth-ane) and AgSbFfi in methylene chloride at 35 °C led to isolation of2,5-dibutylpyrrole in 82% yield (Eq. (11.13)). The method was also effective for the cyclization of a-unsubstituted homopropargyl azides and tolerated both alkyl and aryl substitution of the alkyne. 

Variation 8 Gold(I)-catalyzed Intramolecular Acetylenic Schmidt Reaction (Toste )... 

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