Gold‐Catalyzed Oxidative Ring Expansions and Ring Cleavages of Alkynylcyclopropanes by Intermolecular Reactions Oxidized by Diphenylsulfoxide

Abstract

Ph2SO als Sauerstoffspender: Eine neue goldkatalysierte oxidative Ringerweiterung für nichtaktivierte Cyclopropylalkine mit Ph2SO wurde entwickelt (siehe Schema). Substrate mit einer Donorgruppe am Cyclopropanring gehen eine Ringöffnung ein, die zur Synthese von 2H‐Pyranen genutzt werden kann. L=P(tBu)2(o‐Biphenyl), Tf=Triflat.

Intermolecular and Selective Synthesis of 2,4,5‐Trisubstituted Oxazoles by a Gold‐Catalyzed Formal [3+2] Cycloaddition

“…(1), B-D, Ts = toluene-4-sulfonyl] have very recently been accessed by intermolecular attack of an O-or Nnucleophilic oxidant [4] or nitrene equivalent [5] to an electrophilically activated p system [Eq. The intermediates are quenched by the reaction with a functionality contained within the alkyne starting material (at R or R 1 ), [4,5] a [3 + 3] sigmatropic rearrangement at B, [6] or by further reaction with a nucleophilic oxidant [4c, 7] or nitrile [8] in the absence of faster intramolecular processes. The intermediates are quenched by the reaction with a functionality contained within the alkyne starting material (at R or R 1 ), [4,5] a [3 + 3] sigmatropic rearrangement at B, [6] or by further reaction with a nucleophilic oxidant [4c, 7] or nitrile [8] in the absence of faster intramolecular processes.…”

“…(1), A!B]. (1), B!C/D] may not proceed as a distinct step, [4] the overall reactivity patterns observed are reminiscent of electrophilic a-oxo-metal carbenoids (C/D), and thus allow CÀC triple bonds to be perceived of as simpler and direct alternatives to extensively used a-oxo-diazo compounds. Though elimination of the delivery system [Eq.…”

“…[16] Similarly convergent one-step or one-pot methods to prepare functionalized 1,3oxazoles are rare, [8] and often require the use of highly reactive species with consequent structural limitations. Cationic gold(I) complexes and gold tribromide (Table 1, entries [3][4][5] were similarly effective to [Au-I], though sodium tetrachloroaurate was slightly less active (Table 1, entry 6). Bn = benzyl, brsm = based on recovered starting material, Ms = methanesulfonyl.…”

Gold‐Catalyzed Oxidative Cyclizations on 1,4‐Enynes: Evidence for a γ‐Substituent Effect on Wagner–Meerwein Rearrangements

“…We employ these special 1,4-enynes, because their bridged cyclopropanes can stabilize carbocation F or F' with a "bisected" conformation, [11] in which the ketone group hinders the expansion of the cyclopropane ring. [12] A cyclopropyl group greatly enhances the electrophilicity of an alkyne in the presence of a gold catalyst. [12] Our experimental results disclose that only the cis-substituent R 1 at the alkene is transferable to give the observed cyclopentanone F selectively.…”

“…[12] A cyclopropyl group greatly enhances the electrophilicity of an alkyne in the presence of a gold catalyst. [12] Our experimental results disclose that only the cis-substituent R 1 at the alkene is transferable to give the observed cyclopentanone F selectively. Notably, this stereospecificity of the migration is unaffected when varying the R 1 and R 2 groups to methyl, alkyl, and aryl groups, thereby truly reflecting this significant g-effect.…”