Facile access towards a small library of unsymmetrical ammonium salt-tagged N-heterocyclic carbene gold(i) complexes is described, and their application as recyclable catalysts in cyclization reactions of acetylenic carboxylic acids and amides to lactones and lactams, respectively, in aqueous media is demonstrated. Catalyst was applied in the synthesis of 2-epi-clausemarine A ().
The total synthesis and characterization of ammonium‐salt‐tagged IMesAuCl complexes is described. Moreover, we have demonstrated their catalytic activity and recyclability in cycloisomerization reactions of allenic and acetylenic alcohols in water. The water‐soluble gold catalysts can be stabilized by the addition of LiCl.
Various [O,O]- and [N,O]-spiroacetals were synthesized by gold-catalyzed spirocyclization of suitable functionalized alkynes. Whereas simple spiroacetals with two heteroatoms were readily obtained by regioselective cyclization of acetylenic diols or aminoalcohols, hitherto unknown spirocyclic isoxazolidines and pyrazolidines bearing three heteroatoms were formed by three-component coupling of alkynols, aldehydes, and protected hydroxylamine or hydrazine derivatives. The sustainability of these spirocyclizations was improved by using recyclable gold catalysts in water or nanomicelles as reaction medium.
The title catalysts are applied in the cyclization reaction of acetylenic carboxylic acids and amides (I), (V) and (III) to lactones (II), (VI), and lactams (IV), respectively.
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