Synthesis of Tetracyclic Benzoxazolo-indol-3-ones from Isatogens and Arynes through a [3 + 2]-Cycloaddition and Skeletal Reorganization.

The construction of an unprecedented tetracyclic benzoxazolo-indol-3-one scaffold has been executed through the [3 + 2]-cycloaddition of isatogens with arynes. The initially formed benzisoxazolo-indol-3-one intermediate undergoes a skeletal reorganization through a 1,3-sigmatropic shift/retro-Mannich reaction with the net formation of one C-N and two C-O bonds. The Lewis acid-catalyzed allylation of some of the resulting benzoxazolo-indol-3-ones resulted in oxazepino-indolones with promising photophysical properties.

Construction of the quinobenzoxazine core gold-catalyzed dual annulation of azide-tethered alkynones with anthranils.

A new catalytic method for the construction of the quinobenzoxazine core has been developed employing the gold-catalyzed cyclization of -azidoacetylenic ketones in the presence of anthranils. The overall process comprises of a gold-catalyzed 6- cyclisation of -azidoacetylenic ketone leading to a α-imino gold carbene and subsequent carbene transfer to anthranil leading to the 3-aryl-imino-quinoline-4-one intermediate, which undergoes 6π-electrocyclization and aromatization to form the central quinobenzoxazine core. This transformation provides a new approach to a diverse array of quinobenzoxazine structures, in addition to being scalable and having mild reaction conditions.

Rediscovering Bacon's hydrazine/phenylhydrazine mediated cyclization of 2,2'-dicarbonylbi(hetero)aryls: construction of (5-azo)-/indazolo[2,3-]quinolines.

Hydrazine/phenylhydrazine-mediated reductive dicarbonyl coupling reactions have been carried out under mild conditions to provide polycyclic aromatic compounds and azo-substituted polyaromatic compounds. This method has a broad substrate scope with good functional group compatibility.

Total synthesis of the pseudoindoxyl class of natural products.

The pseudoindoxyl sub-structural motif, amongst the large set of the indole class of alkaloids, represents a unique subset of the oxygenated indole class of the alkaloid family. A majority of this class of natural products contains complex bridged/polycyclic scaffolds with interesting biological profiles. They are thus attractive synthetic targets.

Intermolecular Interception of α-Oxo Gold Carbenes of Nitroalkyne Cycloisomerization with 1,2-Benzo[]isoxazole: Synthesis of Functionalized Quinazoline 1-Oxides.

The known nitrogen-transfer reagent 1,2-benzo[]isoxazole has been used to trap the postulated α-oxo gold carbene intermediate involved in the [Au]-catalyzed internal redox process of 2-alkynylnitrobenzenes. This process led us to develop a general convergent method for the synthesis of highly functionalized quinazoline 1-oxides.

Gold-Catalyzed Complementary Nitroalkyne Internal Redox Process: A DFT Study.

Gold-catalysis, in this century, is one of the most emerging and promising new areas of research in organic synthesis. During the last two decades, a wide range of distinct synthetic methodologies have been unveiled employing homogeneous gold catalysis and aptly applied in the synthesis of numerous natural products and biologically active molecules. Among these, the reactions involving α-oxo gold carbene/α-imino gold carbene intermediates are of contemporary interest, in view of their synthetic potential and also due to the need to understand the bonding involved in these complexes.

Gold-Catalysed Nitroalkyne Cycloisomerization - Synthetic Utility.

The gold-catalysed intramolecular redox cyclization of o-alkynylnitrobenzens documented by Professors Naoki Asao and Yoshinori Yamamoto is an important discovery that has opened two complementary research domains. Advancing this cyclization with other metals as well as developing new methods around the products that result from this reaction is one aspect that has seen growing interest. On the other hand, the idea of generating α-oxo gold carbenes via oxygen transfer to alkynes has established another important aspect in gold-catalysis.

Interrupting the [Au]-Catalyzed Nitroalkyne Cycloisomerization: Trapping the Putative α-Oxo Gold Carbene with Benzo[]isoxazole.

The [Au]-catalyzed nitroalkyne cycloisomerization of 2-alkynylnitrobenzenes leading to anthranils has been interrupted by possible trapping of the postulated intermediate α-oxo gold carbene with an external nucleophile such as benzo[]isoxazole (anthranil). At the outset, this provides a simple synthesis of highly functionalized 3-acyl-(2-formylphenyl)-2-indazoles with the sequential C-O, C-N, and N-N bond formations. This provides indirect support for the existence of α-oxo gold carbenes in the [Au]-catalyzed internal redox processes of nitroalkynes.

One-Pot Au[III]-/Lewis Acid Catalyzed Cycloisomerization of Nitroalkynes and [3 + 3]Cycloaddition with Donor-Acceptor Cyclopropanes.

A one-pot protocol for the synthesis of a tricyclic pseudoindoxyl scaffold from 2-nitroalkynylbenzenes, comprising of an Au(III)-catalyzed nitroalkyne cycloisomerization leading to isatogen and its [3 + 3]-cycloaddition with donor-acceptor cyclopropanes mediated by a suitable Lewis acid, has been developed.