Synthesis of novel fused isoxazoles and isoxazolines by sequential Ugi/INOC reactions

Synthesis of Lactams via Isocyanide-Based Multicomponent Reactions

Lactams are very important heterocycles as a result of their presence in a wide range of bioactive molecules, natural products and drugs, and also due their utility as versatile synthetic intermediates. Due to these reasons, numerous efforts have focused on the development of effective and efficient methods for their synthesis. Compared to conventional two-component reactions, multicomponent reactions (MCRs), particularly isocyanide-based MCRs, are widely used for the synthesis of a range of small heterocycles including lactam analogues. Despite their numerous applications in almost every field of chemistry, as yet there is no dedicated review on isocyanide-based multicomponent reactions (IMCRs) concerning the synthesis of lactams. Therefore, this review presents strategies towards the synthesis of α-, β-, γ-, δ- and ε-lactams using IMCRs or IMCRs/post-transformation reactions reported in the literature between 2000 and 2020.

1 Introduction

2 Developments in Lactam Synthesis

2.1 α-Lactams

2.2 β-Lactams

2.3 γ-Lactams

2.3.1 General γ-Lactams

2.3.2 Benzo-Fused γ-Lactams

2.3.3 Spiro γ-Lactams

2.3.4 α,β-Unsaturated γ-Lactams

2.3.5 Polycyclic Fused γ-Lactams

2.4 δ-Lactams

2.5 ε-Lactams

3 Conclusions

Direct access to isoxazolino and isoxazolo benzazepines from 2-((hydroxyimino)methyl)benzoic acid via a post-Ugi heteroannulation

A diversity-oriented access to isoxazolino and isoxazolo benzazepines is elaborated via a post-Ugi heteroannulation involving intramolecular 1,3-dipolar cycloaddition reaction of nitrile oxides with alkenes and alkynes. This sequence offers an interesting multicomponent entry to a library of isoxazolino and isoxazolo benzazepines under mild reaction conditions in good to excellent yields.

Synthesis of Bicyclic Isoxazoles and Isoxazolines via Intramolecular Nitrile Oxide Cycloaddition

An efficient and straight forward procedure for the syntheses of bicyclic isoxazole/isoxazoline derivatives from the corresponding dimethyl-2-(2-nitro-1-aryl/alkyl)-2-(prop-2-yn-1yl)malonates or dimethyl 2-allyl-2-(2-nitro-1-aryl/alkyl ethyl)malonate is described. High yields and simple operations are important features of this methodology.

Construction of functionalized tricyclic dihydropyrazino-quinazolinedione chemotypes via an Ugi/N-acyliminium ion cyclization cascade

Dihydropyrazino-quinazolinedione chemotypes are complex and structurally challenging structures of biological interest, being found in the marine alkaloids such as brevianamide M-N and fumiquinazolines A-C. Herein we report the synthesis of this tricyclic system in three synthetic operations by means of an Ugi multi-component reaction (MCR) followed by a tandem N-acyliminium ion cyclization-intramolecular nucleophilic addition reaction sequence. Additional structural diversification for further library enrichment was also accomplished via sequential N-alkylation and N-acylation/sulfonation.

Synthesis of 4,5-dihydroisoxazoles by condensation of primary nitro compounds with alkenes by using a copper/base catalytic system

A new procedure for the synthesis of 4.5-dihydroisoxazoles by condensation of primary nitro compounds with olefins by using a copper/base catalytic system is described. The catalytic effect of copper(II) salts is evidenced by comparison of the reaction rates. Thus, activated nitro compounds react faster than with organic catalysis by tertiary amines, whereas nitroalkanes, unable to condense with dipolarophiles in the presence of the base alone, undergo the reaction on addition of a copper(II) catalyst. The observed occurrence of induction periods in most reactions is ascribed to an equilibrium preceding the rate-determining step, and gives a hint as to the proposed reaction mechanism. The results indicate that this method might be of practical and general utility for synthetic practice.

Topography-biased compound library design: the shape of things to come?

The design and synthesis of quality compound libraries is of critical importance to any pharmaceutical company that relies on high throughput screening efforts for the identification of lead compounds. In this perspective, we use a moment of inertia derived shape analysis to interrogate potential libraries for chemical synthesis. An analysis of known 'Rule of Five' compliant drug shapes using this methodology clearly highlights compound libraries that may be reasonably expected, shape wise, to interact with biologically relevant protein active site topography and those that, although being structurally diverse in shape, have little chance of being pharmacologically productive. The use of multicomponent reactions as a means of producing structurally novel, bioactive compounds in a synthetically expeditious manner is also highlighted.

Applications of Multicomponent Reactions for the Synthesis of Diverse Heterocyclic Scaffolds

A four-component coupling process involving sequential reactions of aldehydes, primary amines, acid chlorides, and nucleophiles has been developed to prepare multifunctional substrates that may be employed in subsequent ring-forming reactions to generate a diverse array of functionalized heterocyclic scaffolds. This new approach to diversity-oriented synthesis was then applied to the first total synthesis of the isopavine alkaloid (+/-)-roelactamine.

Rapid access to oxindoles by the combined use of an Ugi four-component reaction and a microwave-assisted intramolecular Buchwald-Hartwig amidation reaction

A two-step sequence involving an Ugi four-component reaction (Ugi-4CR) and a palladium-catalyzed intramolecular amidation of aryl iodide has been developed for rapid access to functionalized oxindole (1). Microwave heating was used to accelerate and to improve the efficiency of the intramolecular Buchwald-Hartwig reaction.

Synthesis of fused bicyclic imidazoles by sequential van Leusen/ring-closing metathesis reactions

[reaction: see text]. A new strategy employing the van Leusen three-component reaction and the ring-closing metathesis reaction in a sequential fashion to access fused bicyclic imidazole rings is reported. The two-step sequence generated compounds of significant molecular complexity from simple starting materials in an expedient fashion with excellent yields.