Direct Two Carbon Ring Expansion of 1-Indanones with Ynones: An Eco-Friendly, One-Flask Approach to Functionally Enriched 5H-Benzo[7]annulenes.

Direct 2C-ring expansion of 1-indanones with ynones to 5H-benzo[7]annulenes has been observed, and its generality has been gauged (19 examples). Overall, this simple and convenient cascade process to 5H-benzo[7]annulenes involves engagement of 1-indanone with two ynone moieties with formation of three new C-C σ-bonds, cleavage of C-C σ-bond, and concurrent functionality amplification. The resulting seven-membered ring, laced with an opportunistic disposition of four proximal functional groups, offers avenues for their further productive interplay. Our new approach embraces many green and eco-friendly features.

Indeno-Annulation of o-Formyl-Ynones, o-Bis-Ynones, and p-Bis-o-Formyl-Ynones with Dimethyl Acetone-1,3-Dicarboxylate: One Flask Cascade Synthesis of Functionally Endowed 9-Fluorenols and Indeno[1,2-b]fluorenols.

A mild, scalable, one-pot access to multifunctional 9-fluorenols from o-formyl-ynones and o-bis-ynones on reaction with dimethylacetone-1,3-dicarboxyate through tandem Michael addition-Aldol condensation cascade has been conceptualized and executed. The scope and utility of this synthetic approach have been further amplified for one-pot entry into functionally enhanced, higher order fluorenols like pentacyclic indeno[1,2-b]fluorene-6,12-diols and further to indeno[1,2-b]fluorene-6,12-diones through the implementation of "double indeno-annulation" tactic on p-bis-o-formyl ynones and dimethylacetone-1,3-dicarboxylate. Besides several green attributes, the current approach is also compatible with the emerging time and energy economy features and is a swift gateway to build complexity.

One-Pot Synthesis of Functionally Enriched Benzo[b]fluorenones: An Eco-Friendly Embedment of Diverse 1-Indanones into o-Bis-Ynones.

An efficient, base-promoted, one-pot, metal-free, open-flask synthesis of diverse, functionally enriched benzo[b]fluoren-11-ones has been discovered, and wide applicability of this exceptionally simple protocol with green flavors has been scoped. This synthesis proceeds via an unanticipated, tandem, double-aldol condensation between in situ-generated 1-indanone dianions and o-bis-ynones to furnish benzo[b]fluoren-11-ones harboring as many as six variegated substituents on their tetracyclic framework. This methodology has also been amplified to access heterocyclic analogues 2- and 4-azabenzo[b]fluorenones of benzo[b]fluoren-11-ones and extended to mixed linear-angular annulated pentacyclic dibenzo[a,h]fluoren-13-one.

In Situ-Generated Ammonia Mediates Deep Restructuring of o-Bis-Ynones through a Cascade Process: One-Pot Synthesis of 2-Azafluorenones.

One-pot synthesis of 2-azaflorenones from readily accessed o-bis-ynones through Michael addition, orthogonal aldol reaction, dehydrative isomerization, and a 6-endo-dig-cyclization cascade, triggered by in situ-generated ammonia in the presence of a Cu(I) catalyst, has been discovered and its generality scoped. A few selected reactions of a prototypical 2-azafluorenone have been explored for functionality augmentation in its core structure. Overall, this operationally convenient 2-azafluorenone synthesis involves the formation of five new bonds (3 C-N and 2 C-C) in one pot and embodies many green and sustainable features; notably, the reagent ammonia is subsumed into the reactant o-bis-ynones with atom economy, and the only by-product is water.

Recursive Anion-Triggered Tandem Reactions of ortho-Bis-ynones: Tunable Synthesis of 1-Indenones and Cyclopenta[a]inden-8(2H)-ones.

Recursive anion-mediated activation of o-bis-ynones sets off a Michael addition-aldol reaction-dehydrative rearrangement cascade, leading to the one-pot synthesis of 1-indenones via orthogonal interplay between the two ortho-ynone moieties. Repeating the recursive anion engagement with the 1-indenones unfolded access to a functionally embellished cyclopenta[a]inden-8(2H)-one core and its spiroannulated analogues either directly or stepwise through tandem 1,6-Michael-type addition-6π electrocyclization and an in situ oxidation sequence.

A BF3·Et2O catalyzed atom-economical approach to highly substituted indole-3-carbinols from nitrosobenzenes and propargylic alcohols.

The BF3·Et2O catalyzed reaction of nitrosobenzenes and an excess amount of propargylic alcohols was investigated to synthesize highly-substituted indole-3-carbinols. This reaction involves formal [3 + 2]-cycloaddition and the subsequent 1,3-rearrangement in a tandem manner via 3-alkylidene-3H-indole N-oxides. This methodology involves the sequential addition of propargylic alcohols and inexpensive Lewis acid catalyst, occurs in an open-air environment and is atom economical. The highly-substituted indole-3-carbinols were obtained in short time and the operational simplicity allows for a large scale experiment.