Sabyasachi Bhunia

Gold-Catalyzed Oxidative Cyclization of 1,5-Enynes Using External Oxidants**

Pd-catalyzed oxidative cyclizations of 1,6-enynes have found useful applications in organic synthesis, but such reactions with Au and Pt catalysis remain largely unexplored. Goldcatalyzed cycloisomerizations of 1,5and 1,6-enynes provide uncommon and useful carbocyclic frameworks. In the presence of organic oxidants, most enynes fail to produce oxidative cyclization products because oxidations of hypothetical gold–carbenoid intermediates are difficult. 5] Herein, we report two new oxidative cyclizations of 1,5-enynes via 5endo-dig and 5-exo-dig cyclizations, respectively; both reactions are implemented with Au and 8-methylquinoline Noxide. The success of such reactions relies on the prior oxidations of enyne form a-carbonyl carbenoids A and B, followed by their intramolecular cyclizations (Scheme 1). Terminal alkynes favor the oxidation at the C2 alkynyl carbon atom and aminoalkynes prefer the C1 carbon atom.

Gold-Catalyzed 1,2-Difunctionalizations of Aminoalkynes Using Only N- and O-Containing Oxidants

We report two viable routes for the 1,2-difunctionalization of aminoalkynes using only oxidants. In the presence of a gold catalyst, nitrones enable the oxoamination of aminoalkynes 1 to form 2-aminoamides 2. With a suitable gold catalyst, nitrosobenzenes implement an alkyne/nitroso metathesis of the same substrates to give 2-oxoiminylamides 3. These two novel oxidations also provide 1,2-aminoalcohols with opposite regioselectivity via NaBH(4) reduction in situ.

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 Azacyclic Compounds through a Redox/[2 + 2 + 1] Cycloaddition Cascade of Nitroalkyne Substrates

We report a new redox/cycloaddition cascade on readily available 1-alkynyl-2-nitrobenzenes that produces complex azacyclic compounds stereoselectively. The core structures of the resulting products are constructed through a formal [2 + 2 + 1] cycloaddition among α-carbonyl carbenoids, nitroso species, and external alkenes.

Gold‐Catalyzed Formal Cycloaddition of 2‐Ethynylbenzyl Ethers with Organic Oxides and α‐Diazoesters

A world of possibilities: Gold-catalyzed reactions of 2-ethynylbenzyl ethers with organic oxides and α-diazoesters gave 1,3-dihydroisobenzofuran and naphthalene derivatives, respectively (see scheme; EWG = electron-withdrawing group). Mechanisms for the formation of the formal cycloadducts were elucidated by isotope labeling.

Intermolecular Gold‐Catalyzed Diastereo‐ and Enantioselective [2+2+3] Cycloadditions of 1,6‐Enynes with Nitrones

Going for gold: The title reaction has been developed and demonstrates a wide substrate scope with respect to the 1,6-enynes and nitrones (see scheme; DCE = 1,2-dichloroethane, Tf = trifluoromethanesulfonyl). The results for the enantioselective versions are also presented.

Platinum-Catalyzed Oxoarylations of Ynamides with Nitrones

A new platinum-catalyzed oxoarylation of ynamides with nitrones is reported. Cascade sequences for the synthesis of indolin-2-ones via NaBH(3)CN reduction in situ of the initially formed oxoarylation products are also developed.

Access to molecular complexity via gold- and platinum-catalyzed cascade reactions*

We report recent progress on Au- and Pt-catalyzed cascade reactions to access complicated molecular frameworks. Reported reactions include new cyclization/cycloaddition cascades on carbonyl and epoxide substrates tethered with an allene, alkene, and alkyne. Such substrates enable Au-catalyzed cascade reactions comprising an initial cyclization to form reactive 1,n-dipole that undergoes subsequent cycloadditions with suitable dipolarophiles.