Regio- and Stereoselective Synthesis of Functionalized Cyclopentene Derivatives via Mizoroki-Heck Reactions

Diastereoselective Synthesis of N-Methylspiroindolines by Intramolecular Mizoroki-Heck Annulations

Spiroindolines represent a privileged structure in medicinal chemistry, although stereocontrol around the spirocarbon can be a synthetic challenge. Here we present a palladium(0)-catalyzed intramolecular Mizoroki-Heck annulation reaction from (+)-Vince lactam-derived cyclopentenyl-tethered 2-bromo-N-methylanilines for the formation of N-methylspiroindolines. A series of 14 N-methylspiroindolines were synthesized in 59-81% yield with diastereoselectivity >98%, which was rationalized by density functional theory calculations and confirmed through X-ray crystallography. One spiroindoline was converted to an N- and C-terminal protected rigidified unnatural amino acid, which could be orthogonally deprotected.

Oxidative [2 + 1 + 1 + 1] Annulation of Aldehydes and Methylene Nitriles: Synthesis of Diastereoselective Polysubstituted Cyclopentenes

Herein, we report a green cascade approach to prepare a variety of diastereoselective polysubstituted cyclopentene derivatives through metal-free oxidative [2 + 1 + 1 + 1] annulation of aldehydes and methylene nitriles. Mechanistic studies demonstrated that the reaction underwent a four-step cascade reaction including air oxidation and Michael addition to obtain the final product. This reaction features readily available starting materials, transition metal-free, eco-friendly operations, gram-scale syntheses, and wide functional group tolerance. The methodology may be useful for the construction of polysubstituted cyano-cyclopentene heterocycles with potential biological activity.

Cascade Michael/aldol/rearrangement between phenacylmalononitriles and maleimides: highly diastereoselective access to functionalized bicyclic cyclopentenes containing a CN-substituted all-carbon quaternary center

A highly diastereoselective approach towards the synthesis of quaternary center-containing cyclopentenes was developed. The tandem Michael/aldol/rearrangement processes occurred under mild reaction conditions.

Recent Strategies in the Synthesis of Spiroindole and Spirooxindole Scaffolds

Spiroindole and spirooxindole scaffolds are very important spiro-heterocyclic compounds in drug design processes. Significant attention has been directed at obtaining molecules based on spiroindole and spirooxindole derivatives that have bioactivity against cancer cells, microbes, and different types of disease affecting the human body. Due to their inherent three-dimensional nature and ability to project functionalities in all three dimensions, they have become biological targets. Considering reports on spiroindole and spirooxindole-containing scaffolds in the past decades, introducing novel synthetic procedures has been an active research field of organic chemistry for well over a century and will be useful in creating new therapeutic agents. This review summarizes the pharmacological significance of spiroindole and spirooxindole scaffolds and highlights the latest strategies for their synthesis, focusing particularly on the past 2 years with typical examples. The spiroindole and spirooxindoles in this review are divided by the type and ring size of the spirocycle that is fused to indole or oxindole. Summarizing these procedures will be very beneficial for discovering novel therapeutic candidate molecules.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Regio- and Stereoselective Synthesis of Allylic Spiroethers (Spirobenzofuranes) via an Intramolecular Mizoroki-Heck Reaction

The palladium(0)-catalyzed intramolecular annulation of 12 1,3-disubstituted cyclopentenes, derived from (+)-vince lactam, resulted in 5-exo cyclizations which furnished a series of 2,5-dimethyl-1-((3R,4'S)-2H-spiro[benzofuran-3,1'-cyclopentan]-2'-en-4'-yl)-1H-pyrroles in excellent diastereoselectivities and useful isolated yields. The double bond migration process that followed the arylpalladium insertion was controlled by a fine-tuning of the reaction system, which provided regioselectivities of up to 98:2. The selective Mizoroki-Heck reaction was used as the key transformation for preparing two new spirocyclic monoprotected amino acids as single stereoisomers.

Diastereo- and Enantioselective Synthesis of Functionalized Cyclopentenes Containing a Quaternary Chiral Center via a Thiosquaramide-Catalyzed Cascade Michael-Henry Reaction

An efficient method for the highly diastereoselective synthesis of chiral quaternary center-containing cyclopentenes via a cinchona alkaloid-derived thiosquaramide VIII-catalyzed tandem Michael-Henry reaction of phenacylmalononitriles and nitroolefins was deleveloped. Meanwhile, up to 98% of enantioselectivity was observed. A mechanism involving thiosqaramide-catalyzed asymmetric Michael addition and assisted E2 elimination was proposed based on experimental data and preliminary theoretical analysis (Hartree-Fock calculations).

Mechanisms for C(sp2)-Si activation of aryltrimethylsilyl groups in palladium-catalysed couplings

Silyl-substituted aromatic compounds can participate as the electrophilic component in palladium-catalysed cross-couplings, and reactivity is enhanced by a neighbouring silyl-group. Products analogous to those obtained from C-H activation chemistry are accessible by this means with the additional benefit of regiochemistry defined by the site of silyl substitution. DFT studies described here show that the mechanism of C-Si cleavage is distinct from previously recognised mechanisms for C-H cleavage, with a cascade of silyl intermediates en route to a stable product. The amide directing-groups are involved only in the stabilisation of palladacyclic intermediates, and are never disposed to activate silicon directly. 5-Membered and 6-membered palladacycles are known to behave differently in coupling reactions and the calculations reveal underlying reasons in the cationic pathways studied here.

Selective Synthesis of Spirooxindoles by an Intramolecular Heck-Mizoroki Reaction

We report a highly diastereoselective synthesis of cyclopentene-spirooxindole derivatives via an intramolecular Heck-Mizoroki reaction using aryl bromides as precursors. The reactions were performed under dry conditions or in a DMF-water system. This protocol can be useful to introduce several functionalities to the aromatic nucleus of the spirooxindoles. DFT calculations were performed to rationalize the high antiselectivity. A functionalized spiroproduct was transformed into a cyclic amino acid derivative.