The BF·EtO 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.

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.

An expedient method was demonstrated for the synthesis of 3-alkenyl-3-amino-2-oxindoles from readily available propargylic alcohols and isatin imines in the presence of BF 3 · Et 2 O as a catalyst under open-air atmosphere. The above reaction was time-dependent and further extended to the one-pot synthesis of highly substituted spiroindeneindolones via 1,3-amino group migration/ Friedel-Crafts cyclization. This methodology, which tolerates a broad variety of functional groups, offers versatile and atom-economical access to 3-alkenyl-3-amino-2-oxindole or spiro-indeneindolone derivatives in good yield at room temperature.

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.

An atom-economical synthesis of 3-alkylidene-3H-indole N-oxides has been developed via atandemreactionofp ropargylic alcoholsand nitrosobenzenes in the presenceo fb oront rifluoride etherate (BF 3 ·Et 2 O) as catalyst. This method offers great potential for the synthesis of biologically important 3-alkylidene-3H-indole N-oxides and related derivatives.