Synthesis of Benzofuranones via Malonates Desymmetrization: Yield Increase by the Portion-wise Addition of Quinones

Asymmetric Synthesis of Benzofuranones with a C3 Quaternary Center via an Addition/Cyclization Cascade Using Noncovalent N-Heterocyclic Carbene Catalysis

An asymmetric addition/cyclization cascade of amidoesters and iminoquinones is developed using noncovalent N-heterocyclic carbene (NHC) catalysis. The process enables access to various functionalized benzofuranones with an all-carbon quaternary stereocenter with high yields and ee values. The reaction displays a broad substrate scope. Via product modifications, enantioenriched synthesis of biologically relevant spirocyclic lactones and lactams is achieved. Substrate activation via noncovalent interaction with NHC is suggested for the process.

Synthesis of functionalized 3-aryl-3H-benzofuranone derivatives from aryl acetate via [3 + 2] annulation of 1,4-dihydroxy-2-naphthoic acid ester

A novel [3 + 2] cascade reaction of aryl acetate with 1,4-dihydroxy-2-naphthoic acid ester by cooperative catalysis of isothiourea and vanadium is developed. The key step of the reaction is that the C1-ammonium enolates generated from aryl acetate will cycloadduct to 1,4-naphthoquinone intermediates. 3-Aryl-3H-benzofuranone derivatives can be prepared in medium to good yields under mild conditions.

Green Chemistry Meets Asymmetric Organocatalysis: A Critical Overview on Catalysts Synthesis

Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (EG factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process.

Organocatalytic Synthesis of Benzazetidines by Trapping Hemiaminals with Protecting Groups

Benzazetidines are highly strained and inherently unstable heterocycles. There are only few methodologies for assembling these compounds. Here, a protocol is presented to trap an elusive cyclic, four-membered hemiaminal structure. This method affords several benzazetidines in moderate to good yields (up to 81%), and it uses inexpensive materials and does not require catalysts based on transition metals. The high ring strain energy of these benzazetidine systems was estimated by density functional theory calculations to be about 32 kcal mol^-1. This synthesis can be applied also on gram scale with reaction yield essentially unchanged.

Organocatalysis and catalyst aggregation: a study using the asymmetric synthesis of benzofuranones as a test reaction

A common problem encountered in enantioselective organocatalysis is the aggregation of the catalyst, which can result in a relevant decrease of the efficiency and selectivity of the process. In the asymmetric synthesis of chiral benzofuranones, recently reported by us, we noted a remarkable increase of the reaction yield upon the addition of one of the reagents in a portionwise manner rather than in a single addition. We investigated this phenomenon by several experimental techniques such as 1D and 2D NMR experiments, UV-Vis spectroscopy, circular dichroism and dynamic light scattering. In addition, we studied the kinetic profile of this reaction using a simple numerical model and carried out in silico investigations. All these different approaches point to the conclusion that in the reaction medium a supramolecular polymerization/aggregation phenomenon, based on weak interactions, occurs and such a process is promoted by a quinone, which is one of the reagents of the benzofuranone synthesis. The portionwise mode of addition is a known strategy which can improve the performance of many synthetic procedures and this strategy is commonly adopted on account of empirical experience. However, our results provide an explanation, based on a chemical kinetic model, of the reason why the portionwise addition affects in such a dramatic way the yield of the benzofuranone synthesis catalyzed by Cinchona alkaloids.