Construction of Bicyclo[3.2.1]octanes with Four Stereogenic Centers by Organocatalytic Domino Michael/Aldol Reaction

Organo-catalysis as emerging tools in organic synthesis: aldol and Michael reactions

Organocatalysis has occupied sustainable position in organic synthesis as a powerful tool for the synthesis of enantiomeric-rich compounds with multiple stereogenic centers. Among the various organic molecules for organocatalysis, the formation of carbon–carbon is viewed as a challenging issue in organic synthesis. The asymmetric aldol and Michael addition reactions are the most significant methods for C–C bond forming reactions. These protocols deliver a valuable path to access chiral molecules, which are useful synthetic hybrids in biologically potent candidates and desirable versatile pharmaceutical intermediates. This work highlighted the impact of organocatalytic aldol and Michael addition reactions in abundant solvent media. It focused on the crucial methods to construct valuable molecules with high enantio- and diastereo-selectivity.

Copper-Catalyzed Asymmetric Synthesis of Bicyclo[3.n.1]alkenones

A series of highly strained bicyclo[3.n.1]alkenones have been successfully constructed in good-to-excellent enantioselectivities and moderate-to-good yields via copper-catalyzed formal [3+3] cycloaddition. The versatile chiral cycloadducts could be selectively converted into various valuable bridge systems, which hold considerable potential for the construction of natural and bioactive compounds containing a [3.n.1] moiety.

Organocatalysis: A Brief Overview on Its Evolution and Applications

The use of small organic molecules as catalysts has gained increasing importance recently. These substances, the so-called organocatalysts, present a lot of advantages, like being less toxic, less polluting, and more economically viable than the organometallic catalysts that dominate asymmetric synthesis. This work intends to briefly show some classic works and recent publications, explaining the advantages of organocatalysis and the different types of compounds used in this field, as well as their course of action.

A catalytic allylic cation-induced intermolecular allylation-semipinacol rearrangement

A catalytic intermolecular semipinacol rearrangement induced by allylic carbocations has been realized. This tandem reaction is highly efficient under the catalysis of ZnBr₂, generating a wide range of α-homoallyl substituted ketones which contain all-carbon quaternary centres in good to excellent yields (up to 98%) with moderate to high diastereoselectivities (up to >20 : 1). Synthetic application of this novel methodology in the construction of core structures of natural products is also reported.

Organocatalyzed Synthesis of [3.2.1] Bicyclooctanes

Organocatalysis constitutes one of the main research areas in organic chemistry from the last two decades. This chemistry has been applied to the synthesis of many natural products and structures in a manner that reduces the residues and so the ecological impact. In this review, we consider the work that has been done for the synthesis of bicyclo[3.2.1]octane framework. This structure is present in many natural products with very important biological activities.

Ligand-Effect in Gold(I)-Catalyzed Rautenstrauch Rearrangement: Regio- and Stereoselective Synthesis of Bicyclo[3.2.1]octa-3,6-dienes through Cyclodimerization of 1-Ethynyl-2-propenyl Esters

Gold(I) complexes bearing sterically demanding phosphine ligands such as ^tBuXphos catalyze the cascade Rautenstrauch rearrangement/[4 + 3] cycloaddition of 1-ethynyl-2-propenyl esters. The reaction provides an efficient and straightforward route to bicyclo[3.2.1]octa-3,6-dienes with high regio- and stereoselectivity. The formation of the [4 + 3] cycloadducts likely proceeds through the cycloaddition of a gold(I) carbenoid/gold-stabilized allyl cation intermediate with cyclopentadiene arising from Rautenstrauch rearrangement.

l-Phenylalanine potassium catalyzed asymmetric formal [3 + 3] annulation of 2-enoyl-pyridine N-oxides with acetone

A highly enantioselective formal [3 + 3] annulation of 2-enoyl-pyridine N-oxides with acetone was developed.

Stereoselective synthesis of bicyclo[3.n.1]alkenone frameworks by Lewis acid-catalysis

An indium-catalysed α,α′-annulation of cyclic ketones and alkynyl enones, leading to bicyclo[3.n.1]alkenones, is presented.

A switchable dual organocatalytic system and the enantioselective total synthesis of the quadrane sesquiterpene suberosanone

Switch it! The combination of aminocatalysis and N-heterocyclic carbene catalysis has been extended to a switchable dual catalytic system.

Octahedral Chiral-at-Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions

Octahedral iridium(III) complexes containing two bidentate cyclometalating 5-tert-butyl-2-phenylbenzoxazole (IrO) or 5-tert-butyl-2-phenylbenzothiazole (IrS) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5-5.0 mol % catalyst loading) for a variety of reactions with α,β-unsaturated carbonyl compounds, namely Friedel-Crafts alkylations (94-99% ee), Michael additions with CH-acidic compounds (81-97% ee), and a variety of cycloadditions (92-99% ee with high d.r.). Mechanistic investigations and crystal structures of an iridium-coordinated substrates and iridium-coordinated products are consistent with a mechanistic picture in which the α,β-unsaturated carbonyl compounds are activated by two-point binding (bidentate coordination) to the chiral Lewis acid.

Enantioselective synthesis of bicyclo[3.n.1]alkanes by chiral phosphoric acid-catalyzed desymmetrizing Michael cyclizations

2,2-Disubstituted cyclic 1,3-diketones containing a tethered electron-deficient alkene undergo chiral phosphoric acid-catalyzed desymmetrizing Michael cyclizations to give bridged bicyclic products in high enantioselectivities. Both bicyclo[3.2.1]octanes and bicyclo[3.3.1]nonanes are accessible using this methodology.

Base catalyzed synthesis of bicyclo[3.2.1]octane scaffolds

A base-catalyzed and time controlled reaction of 1,3-cyclopentanediones tethered to activated olefins afforded in high yields either bicyclo[3.2.1]octane-6,8-dione or bicyclo[3.2.1]octane-6-carboxylate derivatives.

Synthesis of highly strained bicyclic[3.n.1]alkenes by a metal-catalyzed Conia-ene reaction

A high yielding metal-catalysed Conia-ene reaction of 2-acetylenic ketones for the synthesis of bicyclo[3.n.1]alkenes has been developed.