Synthesis of 7a-Substituted Hajos−Wiechert Ketone Analogues

Organocatalyst Design for the Stereoselective Annulation towards Bicyclic Diketones and Analogues

The Wieland–Miescher ketone, Hajos–Parrish–Eder–Sauer–Wiechert ketone, and their analogues are bicyclic diketones essential as building blocks for the synthesis of several natural and bioactive molecules. For this reason, since 1971, when Hajos and Parrish and Eder, Sauer, and Wiechert reported the stereoselective synthesis of these compounds promoted by L-proline, numerous methodologies and organocatalysts have been studied over the years with the aim of identifying increasingly efficient asymmetrical syntheses of these bicyclic ketones. This review will outline the methodological and stereochemical features of the organocatalytic stereoselective synthesis of these bicyclic scaffolds based on the different organocatalysts employed from 1971 until today. Particular emphasis will be given to the structural features of the catalysts and to the reaction conditions.

Intercepted-Knoevenagel condensation for the synthesis of unsymmetrical fused-tricyclic 4H-pyrans

4H-Pyrans (4H-Pys) and 1,4-dihydropyridines (1,4-DHPs) are important classes of heterocyclic scaffolds in medicinal chemistry. Herein, an indium(III)-catalyzed one-pot domino reaction for the synthesis of highly functionalized 4H-Pys, and a model of 1,4-DHP is reported. This alternative approach to the challenging Hantzsch 4-component reaction enables the synthesis of fused-tricyclic heterocycles, and the mechanistic studies underline the importance of an intercepted-Knoevenagel adduct to achieve higher chemoselectivity towards these types of unsymmetrical heterocycles.

Ruthenium-catalysed C-alkylation of 1,3-dicarbonyl compounds with primary alcohols and synthesis of 3-keto-quinolines

Mono alkylation of 1,3-dicarbonyls is now possible with alcohols and catalytic amount of Hantzsch ester under Ru catalysis.

Asymmetric organocatalytic desymmetrization of 4,4-disubstituted cyclohexadienones at high pressure: a new powerful strategy for the synthesis of highly congested chiral cyclohexenones

A highly diastereoselective and enantioselective method for the asymmetric desymmetrization of 4,4-disubstituted cyclohexadienones at high pressure was developed.

Metal-free aerobic C–H oxidation of cyclic enones

A metal-free procedure is described for the aerobic and complete C–H methylene oxidation of Hajos–Parrish enones to versatile dihydroindenediones.

Direct methoxypyridine functionalization approach to magellanine-type Lycopodium alkaloids

A concise enantioselective approach to the tetracyclic core of the magellanine-type Lycopodium alkaloids is reported. Key to this approach is the use of the Hajos-Parrish reaction to set a challenging quaternary stereocenter, thereby guiding the stereoselectivity for the remainder of the synthesis, as well as the use of a palladium-mediated direct pyridine functionalization reaction to forge the tetracyclic core.