Reactivity of sarcosine and 1,3-thiazolidine-4-carboxylic acid towards salicylaldehyde-derived alkynes and allenes

Catalyst- and Additive-Free Methodical Ring Expansion Protocol to Access Benzooxepino-Fused Pyrroles

An efficient metal-free, additive-free synthetic method was developed to access benzooxepino-fused pyrrole derivatives from alkynyl substituted aziridines. In this organic transformation, two new C-C bonds were formed via initial cleavage of C-C bond of aziridine ring by in situ generated azomethine ylides. Moderate to excellent yields of benzooxepino-fused pyrroles were obtained atom economically in the presence of t-BuOH in one-pot.

Synthesis of Spiro[chromene-imidazo[1,2-a]pyridin]-3'-imines via 6-exo-dig Cyclization Reaction

A transition-metal-free postmodification of the Groebke-Blackburn-Bienaymé (GBB) reaction for the synthesis of spiro[chromene-imidazo[1,2-a]pyridin]-3'-imine was discovered. The unusual transformation represents the first example of activation and the reaction of the imidazole carbon atom. In this postcondensational modification, KOt-Bu acts as a base, which, after the isomerization of an alkyne moiety to allene, causes the next unique nucleophilic reaction of the imidazole carbon atom that results in spirocyclic structures. The proposed reaction mechanism was confirmed based on the DFT calculations.

Gold(iii)-catalyzed synthesis of aroylbenzo[b]oxepin-3-ones from ortho-O-propargyl-1-one substituted arylaldehydes

An efficient gold-catalyzed intramolecular cyclization of ortho-O-propargyl-1-one substituted arylaldehydes has been achieved for the generation of substituted aroylbenzo[b]oxepin-3-one derivatives in moderate to good yields. This synthetic transformation proceeds via gold-catalysed oxidation of the internal alkyne moiety followed by an intramolecular condensation leading to seven-membered oxacycles.