Sequential Cu(I)/Pd(0)-catalyzed multicomponent coupling and annulation protocol for the synthesis of indenoisoquinolines

Digitization and validation of a chemical synthesis literature database in the ChemPU

Despite huge potential, automation of synthetic chemistry has only made incremental progress over the past few decades. We present an automatically executable chemical reaction database of 100 molecules representative of the range of reactions found in contemporary organic synthesis. These reactions include transition metal–catalyzed coupling reactions, heterocycle formations, functional group interconversions, and multicomponent reactions. The chemical reaction codes or χDLs for the reactions have been stored in a database for version control, validation, collaboration, and data mining. Of these syntheses, more than 50 entries from the database have been downloaded and robotically run in seven modular ChemPU’s with yields and purities comparable to those achieved by an expert chemist. We also demonstrate the automatic purification of a range of compounds using a chromatography module seamlessly coupled to the platform and programmed with the same language.

Reversible C-C bond formation using palladium catalysis

A widely appreciated principle is that all reactions are fundamentally reversible. Observing reversible transition metal-catalysed reactions, particularly those that include the cleavage of C-C bonds, is more challenging. The development of palladium- and nickel-catalysed carboiodination reactions afforded access to the cis and trans diastereomers of the iodo-dihydroisoquinolone products. Using these substrates, an extensive study investigating the reversibility of C-C bond formation using a simple palladium catalyst was undertaken. Herein we report a comprehensive investigation of reversible C-C bond formation using palladium catalysis employing diastereomeric neopentyl iodides as the starting point. It was shown that both diastereomers could be converted to a common product under identical catalytic conditions. A combination of experimental and computational studies were used to probe the operative mechanism. A variety of concepts key to understanding the process of reversible C-C bond formations were investigated, including the effect of electronic and steric parameters on the C-C bond-cleavage step.

Divergent reaction pathways of homologous and isosteric propargyl amides in sequential Ru/Pd-catalyzed annulations for the synthesis of heterocycles

Cu-catalyzed three-component coupling of imines with benzoyl chloride and terminal arylalkynes followed by enyne ring-closing metathesis (RCM) and Heck cyclization afforded medicinally relevant benzoindolines, cyclopropane-fused indenopyridines, pyrroloquinolines, or 1,7-tetrahydrophenanthrolines via divergent cyclization pathways. Unexpectedly, the Pd-catalyzed cyclization of heterocyclic dienes proceeded via regiodivergent 5-exo or 6-endo pathways depending on the ring size (n = 1, 2) or the presence of isosteric groups (CH vs N). A one-pot protocol for the enyne-RCM/Heck annulation featuring a sequential addition of the Ru and Pd catalysts was developed maximizing the synthetic efficiency.

Application of sequential Cu(I)/Pd(0)-catalysis to solution-phase parallel synthesis of combinatorial libraries of dihydroindeno[1,2-c]isoquinolines

Parallel solution-phase synthesis of combinatorial libraries of dihydroindenoisoquinolines employing a sequential Cu(I)/Pd(0)-catalyzed multicomponent coupling and annulation protocol was realized. The scope and limitations of the protocol with respect to the substitution pattern in the aryl ring of the indene core, as well as the N-substituent have been defined, revealing that the methodology is compatible with a wide-range of aliphatic linear, branched, and ester functionalized N-substituents. Unexpectedly, the formation of regioisomers featuring a 1,2,3-contiguous substitution pattern in the aromatic ring of the indene core was observed. Three distinct combinatorial libraries with a total of 111 of members were synthesized, and 80 highly substituted dihydroindenoisoquinolines structurally related to known medicinal agents including some consisting of mixtures of two regioisomers were made available for biological activity testing.