Organics

The direct chlorination, bromination and azidation of beta keto esters, 2-acetyl-1-tetralone and methyl 1-oxo-2,3-dihydro-1H-indene-2-carboxylate is achieved utilizing anion-coordinated hypervalent iodine benziodazoles derived from hypervalent iodine macrocycles. This reaction, which introduces the halogen, azido or cyano group at the alpha carbon atom of beta keto esters, is accomplished in chloroform at 60 °C and results in the formation of a chiral center. Depending on the structure of the benziodazole reagent, the reaction can have mild enantioselectivity. The reaction between 2-acetyl-1-tetralone and phenylalanine-derived hypervalent iodine benziodazoles results in the chlorinated product with 26% enantiomeric excess.

The synthesis of a small library of fused Cyclic Aryl Amino Carbon (f-CArAC) carbene precursors in the form of 1,1,2,4-tetraaryl-1H-isoindol-2-ium triflate (6), (7-R) (R = ^tBu, CF₃) or 3,3-dimethyl-2,8-bis-arene-substituted-3,4-dihydro-isoquinolin-2-ium hydrogen-dichloride (8) and 2,4,8-tri(substituted)-isoquinolin-2-ium tosylate salts (12) has been achieved. All of them feature an arene incorporated on the annulated benzene ring of the corresponding heterocycle, introduced at the early stages of their synthesis via the Suzuki cross-coupling reaction between 2,6-dibromo-benzaldehyde and the desired aryl boronic acid. The terphenyl-2′carbaldehyde by-products of this Suzuki reaction are useful starting points for the preparation of two new iminium iodide salts (10-R) (R = H, CF₃) as potential precursors to access ACyclic Amino Carbon (ACAC) carbenes. Compounds (6) and (7-^tBu) react readily with hydroxide either in THF or in a biphasic Et₂O/aqueous OH⁻ solution to produce the substituted isoindolinols (13) and (14), respectively. The thermal dehydration of the former generates the corresponding f-CArAC carbene in situ, which is trapped by Cu(I)Cl furnishing, a rare example of a two-coordinate Cu(I) complex (15) supported by this new ligand scaffold.

High-Throughput Experimentation has undergone an outstanding evolution in the past two decades and has proven to be a game-changer in the acceleration of reaction discovery and optimization. Despite a good implementation in the pharmaceutical industry and a demonstrated accessibility to the technology, the generalization of High-Throughput Experimentation as a standard method for optimizing reactions is not yet observed. The perspective aims at discussing the necessity of generalizing such technologies, supported by the case study: the optimization by High-Throughput Experimentation of a key step in the synthesis of Flortaucipir, an FDA-approved imaging agent for Alzheimer’s diagnosis.