The Research Of Gold-catalyzed Oxidation Of Alkynes And Substitution Of Propargylic Alchols

As a soft Lewis and π acid, gold complex can be used as catalyst for the activationof carbon carbon multibonds toward nucleophilic addition. As a result, gold-catalyzedreaction has been a hot research topic in the last decade. In addition, gold catalystsdisplayed several unique features, such as low air and moisture sensitivity, goodfunctional group tolerance and preference to protodeauration etc. Thus, goodchemoselectivity can be achieved in most cases. This paper mainly focuses onoxidation of alkynes and substitution of propargylic alcohols in the presence of goldcatalysts.1. Benzil derivatives and-keto imides are synthesized efficiently viagold-catalyzed oxidation of alkynes and ynamides. Substrates and3equivalents ofdiphenyl sulfoxide were treated with4mol%AuCl/AgSbF6in ClCH2CH2Cl at85℃.Most alkynes we investigated reacted smoothly to afford1,2-dicarbonyl compoundsin moderate to high yield. The CH3O-, F-, Cl-, Br-group are well-tolerated in thereaction. Furthermore,10equivalents of styrene were used to trap the hypothetic goldcarbenoid. No cyclopropane was synthesized which may suggest that no freecarbenoid was formed.2. Functionalized allenes are efficiently synthesized in moderate to high yieldsfrom gold-catalyzed reaction of propargylic alcohols and aromatic compounds. At thepropargylic position, the conjugated system was necessary for the formation of allenes.From the study of the electron withdrawing ability of the groups on benzene ring, wefound that the stronger electron withdrawing ability, the lower reaction rate and yield,substrate with NO2group can not work. Trisubstituted allenes can also be obtainedwhen tertiary propargylic alcohols were used. Substrate with triple bonds andpropargylic alcohol groups was also investigated, only the propargylic alcohol groupreacted, which led to allene product with a triple bonds substituent. There are two possible mechanisms of this type of reactions. Based on the reaction facts, an allenecarbocation mechanism was proposed. The regioselectivity of this type of reaction isvery interesting, and we believe that the mild nucleophilic ability of alkyl substitutedarene is the key factor.