One‐Pot Sequential Synthesis of Fused Isoquinolines via Intramolecular Cyclization/Annulation and their Photophysical Investigation

Pd(II)-Catalyzed Three-Component Synthesis of Furo[2,3-d]pyrimidines from β-Ketodinitriles, Boronic Acids, and Aldehydes

A Pd(II)-catalyzed three-component synthesis of 2,4,6-triarylfuro[2,3-d]pyrimidines from β-ketodinitriles, boronic acids, and aldehydes has been developed. The participation of both nitrile (-CN) groups led to the concurrent construction of furo-pyrimidine via the formation of C-C, C═C, C-O, C-N, and C═N bonds. The compounds show excellent photoluminescence properties with absorption maxima ranging from 348 to 387 nm and emission from 468 to 533 nm. The synthetic utility of the protocol was further demonstrated through a few postsynthetic manipulations.

Catalyst-Controlled C-H Allylation and Annulation of 2-Aryl Quinazolinones with 2-Methylidene Cyclic Carbonate

The site-selective modification of quinazolinone as a privileged bicyclic N-heterocycle is an attractive topic in medicinal chemistry and material science. We herein report the ruthenium(II)-catalyzed C-H allylation of 2-aryl quinazolinones with 2-methylidene cyclic carbonate. In addition, tandem C-H allylation and annulation are achieved under rhodium(III) catalysis, resulting in the formation of tetracyclic quinazolinones including a tertiary carbon center. Post-transformations of the synthesized products demonstrate the potential of the developed methodology. A series of mechanistic investigations were also performed.

Visible/solar-light-driven thiyl-radical-triggered synthesis of multi-substituted pyridines

A light-triggered synthesis of thio-functionalized pyridines is demonstrated using γ-ketodinitriles, thiols, and eosin Y as the photocatalyst. The reaction proceeds via the selective attack on one of the cyano groups by an in situ generated thiyl radical. The reaction also proceeds with nearly equal efficiency using direct sunlight. Large-scale synthesis and a few useful synthetic transformations of the substituted pyridines are also performed.

The Renaissance of Organo Nitriles in Organic Synthesis

In the arena of functional group-oriented organic synthesis, the nitrile or cyano functionality is of immense importance. The presence of nucleophilic N -atom, π-coordinating ability of the triple bond, and electrophilic C-center imparts unique and interesting reactivity. Owing to the ability of the nitrile to transform into various other functional groups or intermediates, the chemistry is very rich and diverse. In particular, the involvement of nitrile in numerous organic reactions such as inter- or intramolecular alkyne insertion, [2 + 2 + 2] cycloaddition with alkynes, [3 + 2] cycloaddition with azides, [4 + 2] cycloaddition with diene allow the synthesis of many important carbocycles and heterocycles. Furthermore, the nitrile serves as a directing group in many C-H bond functionalization reactions to introduce diverse functionality and participate as a radical acceptor in radical cascade strategies to obtain a large variety of functional molecules. This review mainly focuses on the reactivity and diverse synthetic application of the nitrile including C-H bond functionalization, alkyne insertion, cycloaddition, and thermal or photochemical cascade strategy. The objective of the current review aims at bringing out the striking collection of various nitrile-triggered organic transformations.

Pd(II)-Catalyzed Synthesis of Furo[2,3-b]pyridines from β-Ketodinitriles and Alkynes via Cyclization and N-H/C Annulation

A Pd(II)-catalyzed synthesis of furopyridines has been developed from β-ketodinitriles and alkynes via an unusual N-H/C annulation. The participation of both the nitrile groups and the concurrent construction of furan and pyridine rings through the formation of C-C, C═C, C-O, C-N, and C═N bonds are the important features. The synthetic applicability is further demonstrated through a series of postsynthetic alterations.

Cu(II)-Promoted Cascade Synthesis of Fused Imidazo-Pyridine-Carbonitriles

A Cu(II)-promoted synthesis of an aza-fused N-heterocycle having a benz-imidazopyridine scaffold is developed via an addition-cyclization reaction followed by an Ullmann-type C-N coupling between o-iodoanilines and γ-ketodinitriles. This protocol features a broad substrate scope, giving products in 32-84% yields. The compounds show excellent photoluminescence properties having two absorption maxima in the region between 270-280 and 338-350 nm and emission maxima in the range of 502-533 nm. The HOMO-LUMO energy gap of 3.49-3.57 eV was determined using Gaussian 09 at the B3LYP/6-31G (d, p) basis set level. We also demonstrated a few postsynthetic modifications.

An expedient route to tricyanovinylindoles and indolylmaleimides from o-alkynylanilines utilising DMSO as a one-carbon synthon

A Pd(ii)/Cu(ii) catalysed domino synthesis of tricyanovinylindoles has been achieved using DMSO as a one-carbon synthon. The reaction proceeds via the construction of 2-aryl-3-formyl indole followed by sequential addition of malononitrile and a CN resulting in two C-C, one C[double bond, length as m-dash]C and one C-N bonds in the final product. Furthermore, post-synthetic modification results in the unprecedented formation of 4-cyano-3-indolylmaleimides. Photophysical studies of selected compounds show emission in the visible range.

Construction of 2-pyridones via oxidative cyclization of enamides: access to Pechmann dye derivatives

An efficient protocol for the construction of structurally diverse 2-pyridone derivatives from imines and α,β-unsaturated acid chlorides in a single operation is reported. The target compounds, including coumarin-8-oxoprotoberbine analogues and lamellarin G isomers, were prepared via thermal cyclization of the in situ generated enamides followed by thermal dehydrogenation. The cyclization of enamides was achieved by the introduction of an electron-withdrawing group on the α-carbon of acid chlorides. This methodology allows quick access to polycyclic Pechmann dyes via rare double oxidative cyclizations of dienamides under mild conditions.

Synthesis of 1,6-Dihydropyridine-3-carbonitrile Derivatives via Lewis Acid-Catalyzed Annulation of Propargylic Alcohols with (E)-3-Amino-3-phenylacrylonitriles

A novel Lewis acid-catalyzed, highly efficient, practical, and atom-economical protocol for the synthesis of functionalized 1,2-dihydropyridine-3-carbonitrile derivatives in the presence of Bi(OTf)₃ (10 mol %) in tetrahydrofuran (2.0 mL) at 80 °C for 8 h in air is described, starting from readily accessed propargylic alcohols and (E)-3-amino-3-phenylacrylonitriles. This cycloaddition protocol, which is scalable and proceeds under mild conditions, is amenable to the gram-scale construction of valuable 1,2-dihydropyridine-3-carbonitriles. Furthermore, the good functional group compatibility and broad scope of this strategy were demonstrated by a broad range of propargylic alcohols and (E)-3-amino-3-phenylacrylonitriles, with yields ranging from 34 to 96%.