Diversity-oriented approach to spirooxindoles: application of a green reagent ‘rongalite’

Dithieno[3,2-b:2',3'-d]thiophene (DTT): an emerging heterocyclic building block for future organic electronic materials & functional supramolecular chemistry

Heterocyclic compounds being potent biochemical materials are ubiquitous molecules in our life. Amongst, the five membered aromatic ring systems, thiophene has emerged as a remarkable entity in organic electronics owing to its (i) high resonance energy, (ii) more electrophilic reactivity than benzene, (iii) high π-electron density, (iv) planar structure and, (v) presence of vacant d-orbital in addition to the presence of loosely bind lone-pairs of electrons on sulfur atoms. In recent past, thiophene-fused molecule namely, dithienothiophene (DTT) has attracted a tremendous attention of the researchers worldwide due to their potential applicability in organic electronics such as in solar cells, electrochromic devices (ECDs), organic field effect transistors (OFETs), organic limiting diodes (OLEDs), fluorescent probes, redox switching and so forth because of their (i) higher charge mobility, (ii) extended π-conjugation, and (iii) better tuning of band gaps, etc. In this particular review article, we envisioned to report the recent advancements made on the DTT-based architectures not only because of the potential applicability of this valuable scaffold in organic electronic but also to motivate the young researchers worldwide to look for the challenging opportunities related to this privileged building block in both material sciences and functional supramolecular chemistry.

Rongalite-Mediated Transition Metal- and Hydride-Free Chemoselective Reduction of α-Keto Esters and α-Keto Amides

A transition metal- and hydride-free protocol has been developed for the chemoselective reduction of α-keto esters and α-keto amides using rongalite as a reducing agent. Here, rongalite acts as a hydride-free reducing agent via a radical mechanism. This protocol offers the synthesis of a wide range of α-hydroxy esters and α-hydroxy amides with 85-98% yields. This chemoselective method is compatible with other reducible functionalities such as halides, alkenes, amides, and nitriles. The use of inexpensive rongalite (ca. $0.03/1 g), mild reaction conditions, and gram-scale synthesis are some of the key features of this methodology. Also, cyclandelate, a vasodilator drug, has been synthesized in gram scale with 79% yield.

Transition metal-free functionalization of 2-oxindoles via sequential aldol and reductive aldol reactions using rongalite as a C1 reagent

A sequential one-pot classical aldol, transition-metal and hydride-free reductive aldol reaction is reported here for C(sp3)- H functionalization of 2-oxindoles using the multifaceted reagent rongalite. Here, rongalite functions as a hydride-free reducing agent and double C1 unit donor. This protocol enables the synthesis of a wide range of 3-methylindoline-2-ones and 3-(hydroxymethyl)-3-methylindolin-2-ones from 2-oxindoles (65-95% yields), which are the synthetic precursors for many natural products. Some of the important aspects of this synthetic approach include one-pot methylation and hydroxymethylation, low-cost rongalite (ca. $0.03 per 1 g), mild reaction conditions and applicability to gram-scale synthesis.

Rongalite-induced transition-metal and hydride-free reductive aldol reaction: a rapid access to 3,3'-disubstituted oxindoles and its mechanistic studies

A transition-metal and hydride-free reductive aldol reaction has been developed for the synthesis of biologically active 3,3'-disubstituted oxindoles from isatin derivatives using rongalite. In this protocol, rongalite plays a dual role as a hydride-free reducing agent and a C1 unit donor. This transition metal-free method enables the synthesis of a wide range of 3-hydroxy-3-hydroxymethyloxindoles and 3-amino-3-hydroxymethyloxindoles with 79-96% yields. One-pot reductive hydroxymethylation, inexpensive rongalite (ca. $0.03/1 g), mild reaction conditions and short reaction time are some of the key features of this synthetic method. This protocol is also applicable to gram scale synthesis.

Tandem 1,6-addition/cyclopropanation/rearrangement reaction of vinylogous para-quinone methides with 3-chlorooxindoles: construction of vicinal quaternary carbon centers

A novel tandem 1,6-addition/cyclopropanation/rearrangement reaction of vinylogous para-quinone methides with 3-chlorooxindoles has been developed, providing dispirooxindole–cyclopentane–cyclohexadienones with vicinal quaternary carbon centers.

Modular Approaches to Cyclopentanoids and their Heteroanalogs

Cyclopentanoids and their derivatives are interesting targets in synthetic organic chemistry due to their extensive applications in various branches of chemical sciences like pharmaceuticals, natural and non-natural products. In view of these applications, several synthetic strategies have been developed in the past three to four decades. In this article, we describe our work towards the synthesis of cyclopentanoids and their heteroanalogs involving diverse synthetic strategies during the past two decades. Among these, photo-thermal olefin metathesis, ring-closing metathesis, ring-rearrangement metathesis, cyclopentane annulation, [2+2+2] cycloaddition and Diels–Alder reactions have been used to assemble cyclopentane rings of diverse architecture.

1 Introduction

2 Synthesis of Spiro[4.4]nonane (A1) Derivatives

3 Synthesis of Octahydropentalene (A2) Derivatives

4 Synthesis of Linear Triquinanes (A3)

5 Synthesis Spiro Triquinanes (A4)

6 Synthesis of Angular Triquinane (A5) Systems

7 Synthesis of Hexahydro-2′H-spiro[cyclopentane-1,1′-pentalene] (A6) Ring System

8 Synthesis of Dispiro[4.1.47.25]tridecane (A7) Ring System

9 Synthesis of Hexahydro-1H-3a,7a-propanoindene Ring System

10 Synthesis of Linear Tetraquinanes (A11 and A12)

11 Synthesis of Tetrahydro-1′H,3′H-dispiro[cyclopentane-1,2′-pentalene-5′,1′′-cyclopentane] (A13) Ring System

12 Synthesis of Decahydro-1H,8H-dicyclopenta[a,h]pentalene (A14) Ring System

13 Synthesis of Dodecahydro-1H-dicyclopenta[a,d]pentalene (A15) Ring System

14 Synthesis of Octahydro-1′H-spiro[cyclopentane-1,2′-cyclopenta[c]pentalene] (A16) Ring System

15 Synthesis of Decahydrospiro[cyclopentane-1,7′-cyclopenta-[a]pentalene] (A17) Ring System

16 Synthesis of Compact Tetraquinane (A18)

17 Synthesis of Higher Polyquinanes

18 Conclusions

19 Acronyms

Recent developments in photoredox-catalyzed remote ortho and para C-H bond functionalizations

In recent years, the research area of direct C-H bond functionalizations was growing exponentially not only due to the ubiquity of inert C-H bonds in diverse organic compounds, including bioactive natural and nonnatural products, but also due to its impact on the discovery of pharmaceutical candidates and the total synthesis of intricate natural products. On the other hand, more recently, the field of photoredox catalysis has become an indispensable and unparalleled research topic in modern synthetic organic chemistry for the constructions of challenging bonds, having the foremost scope in academia, pharmacy, and industry. Therefore, the development of green, simpler, and effective methodologies to accomplish direct C-H bond functionalization is well overdue and highly desirable to the scientific community. In this review, we mainly highlight the impact on, and the utility of, photoredox catalysts in inert ortho and para C-H bond functionalizations. Although a surge of research papers, including reviews, demonstrating C-H functionalizations have been published in this vital area of research, to our best knowledge, this is the first review that focuses on ortho and para C-H functionalizations by photoredox catalysis to provide atom- and step-economic organic transformations. We are certain that this review will act as a promoter to highlight the application of photoredox catalysts for the functionalization of inert bonds in the domain of synthetic organic chemistry.

Facile synthesis of aza-spirocyclopropanyl oxindoles by the reaction of 3-(2-bromoethyl)-indole with 2,3-dimethylimidazole-1-sulfonyl azide triflate

3-(2-Bromoethyl)indole reacts with 2,3-dimethylimidazole-1-sulfonyl azide triflate and then with an alcohol or amine to afford the corresponding aza-spirooxindole sulfonate and sulfonamide.