Deepak B. Huple

Gold-catalyzed oxidative cyclizations of cis-3-en-1-ynes to form cyclopentenone derivatives.

the corresponding oxidative cyclizationremains undocumented. Herein, we report new gold-cata-lyzed oxidative cyclizations of cis-3-en-1-ynes to give cyclo-pentenone skeletons using 8-methylquinoline oxide (Sche-me 1b). Notably, the mechanistic transformation of this C Hactivation is proven to proceed through a noncarbene route,thus excluding the intermediacy of the a-carbonyl carbeneA.

Gold-Catalyzed Stereoselective Synthesis of 9-Oxabicyclo(3.3.1)nona-4,7-dienes from Diverse 1-Oxo-4-oxy-5-ynes: A Viable Formal (4 + 2) Cycloaddition on an s-trans-Heterodiene Framework

We report a highly stereoselective Au-catalyzed synthesis of 9-oxabicyclo[3.3.1]nona-4,7-dienes from diverse 1-oxo-4-oxy-5-ynes. Formation of these highly strained anti-Bredt oxacycles implies the workability of an unprecedented 1,4-dipole of s-trans-methylene(vinyl)oxonium. This work reveals the feasibility of a formal [4 + 2] cycloaddition on an s-trans-heterodiene framework.

Gold-catalyzed diastereoselective [2+2+2]-cycloaddition of 1,7-enynes with carbonyl compounds

We report a gold-catalyzed [2+2+2]-cycloaddition of 1,7-enynes with carbonyl species; our experimental data suggest that the resulting oxacyclic cycloadducts arose from an interception of gold-containing cyclobutenium intermediates with carbonyl species.

Gold‐Catalyzed Oxidative Cycloadditions to Activate a Quinoline Framework

Going for gold! Gold-catalyzed reactions of 3,5- and 3,6-dienynes with 8-alkylquinoline oxides results in an oxidative cycloaddition with high stereospecificity (see scheme; EWG = electron-withdrawing group); this process involves a catalytic activation of a quinoline framework. The reaction mechanism involves the intermediacy of α-carbonyl pyridinium ylides (I) in a concerted [3+2]-cycloaddition with a tethered alkene.

Zn(II)- or Ag(I)-Catalyzed 1,4-Metathesis Reactions between 3-En-1-ynamides and Nitrosoarenes

Catalyst-dependent metathesis reactions between 3-en-1-ynamides and nitrosoarenes are described. Particularly notable are the unprecedented 1,4-metathesis reactions catalyzed by Ag(I) or Zn(II) to give 2-propynimidamides and benzaldehyde derivatives. With 3-en-1-ynamides bearing a cycloalkenyl group, 1,4-oxoimination products were produced efficiently. We have developed metathesis/alkynation cascades for unsubstituted 2-propynimidamides and benzaldehyde species generated in situ, to manifest 1,4-hydroxyimination reactions of 3-en-1-ynes. Both 1,4-oxoiminations and 1,4-hydroxyiminations increase the molecular complexity of products.

Zinc(II)‐Catalyzed Intermolecular Hydrative Aldol Reactions of 2‐En‐1‐ynamides with Aldehydes and Water to form Branched Aldol Products Regio‐ and Stereoselectively

This work describes zinc(II)-catalyzed hydrative aldol reactions of 2-en-1-ynamides with aldehydes and water to afford branched aldol products regio- and stereoselectively. The anti and syn selectivity can be modulated by the sizes of sulfonamides to yield E- and Z-configured zinc(II) dienolates selectively. This new reaction leads to enantiopure aldol products by using a cheap chiral sulfonamide. The mechanistic analysis reveals that the sulfonamide amides of the substrates can trap a released proton to generate dual acidic sites to activate a carbonyl allylation reaction.

Corrigendum: Alkene-Directed N-Attack Chemoselectivity in the Gold-Catalyzed [2+2+1]-Annulations of 1,6-Enynes with N-Hydroxyanilines.

Kinetically unstable nitrones are generated from gold-catalyzed reactions of 1,6-enynes with N-hydroxyanilines, and subsequently trapped by tethered alkenes to furnish [2+2+1]-annulations. Our experimental data reveal that such nitrones arise from atypical N-attack chemoselectivity that is triggered by tethered alkenes to facilitate the key protodeauration reaction.

Gold‐catalyzed Intermolecular Oxidations of 2‐Ketonyl‐1‐ethynyl Benzenes with N‐Hydoxyanilines to Yield 2‐Aminoindenones via Gold Carbene Intermediates

Gold-catalyzed oxidations of 2-ketonyl-1-ethynyl benzenes with N-hydroxyanilines yield 2-aminoindenone derivatives efficiently. Experimental data suggests that this process involves an α-oxo gold carbene intermediate, generated from the attack of N-hydroxyaniline on furylgold carbene intermediate, rather than the typical attack of oxidants on π-alkynes.

One‐Pot Stereocontrolled Synthesis of Bicyclic Pyrrolidine Derivatives by a Platinum–Brønsted Acid Relay Cascade Reaction

Metal-catalyzed reactions commonly form one chemical bond, and extra steps are required to construct a complicated molecular framework. Catalytic cascade reactions can generate two or three chemical bonds in a single operation, thus becoming a powerful tool to access products with molecular complexity. The development of Ptand Au-catalyzed cascade reactions has emerged as a rapidly growing field; many useful carboand heterocyclic frameworks can be constructed efficiently from readily available alkynes A and external p-bond motifs according to the protocol depicted in Equation (1) In these systems, Au or Pt catalysts activate initial cyclizations of alkyne substrates A to form alkenylmetal species B or B’, which bear 1,n-dipole properties to react with p-bond motifs to afford new cycloadducts. Patil and Yamamoto first reported such cyclization/cycloaddition cascades in several formal [4+2]-cycloadditions of 2-alkynylbenzaldehydes (Nu = CHO) with pbond motifs such as alkynes, alkenes, and ketones. This method has been extensively developed by many groups by using diverse functionalized alkynes including 1,n-enynes (n = 5 and 6), oxoalkynes, iminoalkynes, nitroalkynes, epoxyalkynes, alkynyl nitrones, and alkynyl hydroxyamines. These catalytic cascade reactions have been applied to the synthesis of several naturally occurring compounds to manifest their utility. Beyond these cyclization/cycloaddition cascades, few instances are known to access bicyclic heterocycles by using other alkyne substances.