Synthesis of 5-amino-N′-(9H-fluoren-9-ylidene)-8-nitro-7-aryl-1,2,3,7-tetrahydroimidazo[1,2-a]pyridine-6-carbohydrazide derivatives based on heterocyclic ketene aminals

Direct Benzylic C-H Functionalization with Fluorenones under Visible-Light Irradiation

An external photocatalyst-free benzylic C-H functionalization with fluorenones under visible-light irradiation has been achieved. This transformation provides an efficient synthetic approach to 9-benzylated fluorenols in ≤91% yield with 100% atom economy under mild conditions. Spectroscopic studies suggest that a reductive quenching of photoexcited fluorenones with toluene derivatives generates ketyl radicals and benzyl radicals, which undergo a cross-coupling to afford the desired fluorenols.

Crystal structure and Hirshfeld surface analysis of 5,7-diphenyl-1,2,3,5,6,7-hexa-hydro-imidazo[1,2-a]pyridine-6,6,8-tricarbo-nitrile methanol mono-solvate

In the title compound, C22H17N5·CH4O, the imidazolidine ring of the 1,2,3,5,6,7-hexa-hydro-imidazo[1,2-a]pyridine ring system is a twisted envelope, while the 1,2,3,4-tetra-hydro-pyridine ring adopts a twisted boat conformation. In the crystal, pairs of mol-ecules are linked by O-H⋯N and N-H⋯O hydrogen bonds via two methanol mol-ecules, forming a centrosymmetric R 4 4(16) ring motif. These motifs are connected to each other by C-H⋯N hydrogen bonds and form columns along the a axis. The columns form a stable mol-ecular packing, being connected to each other by van der Waals inter-actions. A Hirshfeld surface analysis indicates that the most significant contributions to the crystal packing are from H⋯H (43.8%), N⋯H/H⋯N (31.7%) and C⋯H/H⋯C (18.4%) contacts.

Fluorene-Based Multicomponent Reactions

Fluorene and fluorenone are privileged structures with extensive utility in both materials science and drug discovery. Here, we describe syntheses of those moieties through isocyanide-based multicomponent reactions (IMCRs) and the incorporation of the products in diverse and complex derivatives that can be further utilized. We performed six different IMCRs, based on the dual functionality of 9-isocyano-9H-fluorene, and we describe 23 unprecedented adducts.

An efficient synthesis of new imidazo[1,2-a]pyridine-6-carbohydrazide and pyrido[1,2-a]pyrimidine-7-carbohydrazide derivatives via a five-component cascade reaction

A highly efficient and straightforward synthesis of N-fused heterocyclic compounds including N'-(1-(4-nitrophenyl)ethylidene)imidazo[1,2-a]pyridine-6-carbohydrazide and N'-(1-(4-nitrophenyl)ethylidene)pyrido[1,2-a]pyrimidine-7-carbohydrazide derivatives is successfully achieved via a five-component cascade reaction utilizing cyanoacetohydrazide, 4-nitroacetophenone, 1,1-bis(methylthio)-2-nitroethylene and various diamines in a mixture of water and ethanol. The new efficient domino protocol involving a sequence of N,N-acetal formation, Knoevenagel condensation, Michael reaction, imine-enamine tautomerization and N-cyclization as key steps. The merit of this catalyst free approach is highlighted by its easily available starting materials, operational simplicity, clean reaction profile, the use of environmentally benign solvents and tolerance of a wide variety of functional groups.