Cascade Reactions Involving Formal [2+2] Thermal Cycloadditions: Total Synthesis of Artochamins F, H, I, and J

Boronic Ester Enabled [2 + 2]-Cycloadditions by Temporary Coordination: Synthesis of Artochamin J and Piperarborenine B

A strategy for the photosensitized cycloaddition of alkenylboronates and allylic alcohols by a temporary coordination is presented. The process allows for the synthesis of a diverse range of cyclobutylboronates. Key to development of these reactions is the temporary coordination of the allylic alcohol to the Bpin unit. This not only allows for the reaction to proceed in an intramolecular manner but also allows for high levels of stereo and regiocontrol. A key aspect of these studies is the utility of the cycloadducts in the synthesis of complex natural products artochamin J and piperarborenine B.

Recent Advances in [3+2]-Cycloaddition-Enabled Cascade Reactions: Application to Synthesize Complex Organic Frameworks

Many natural products and biologically important complex organic scaffolds have convoluted structures around their core skeleton. Interestingly, with just changing the outskirts, the core reflects new and unique degrees of various physical and chemical properties. A very common but intriguing core is a five-membered ring horning heaps of organic molecules crafts. The power of [3+2] cycloaddition reactions to generate five-membered ring systems allocate chemists to envision synthetic procedures of wonder molecules and if it is facilitating a cascade sequence, then the end product will imbibe significant level of complexity having applications in medicinal and pharmaceutical fields. This Account highlights the broad interest in assembling recent advances in cascade reactions involving [3+2] cycloaddition as the power tool in order to conceive breakthrough organic architectures reported in the last ten years. We foresee that our comprehensive collection of astonishing [3+2] cycloaddition enabled cascades will provide valuable insights to polycyclic molecular construction and perseverant approach towards nonconventional synthetic procedures to the organic community.

1 Introduction

2 Synthesis of Oxindoles Skeleton

3 Synthesis of Oxazoles Skeleton

4 Synthesis of Oxadiazoles Skeleton

5 Synthesis of Nitrogen-Containing Heterocycles

6 Synthesis via Formal [3+2] Cycloaddition

7 Synthesis of Miscellaneous Scaffolds

8 Conclusion

A comprehensive review: Biological activity, modification and synthetic methodologies of prenylated flavonoids

Prenylated flavonoids, a unique class of flavonoids which combine a flavonoid skeleton and a lipophilic prenyl side-chain, possess great potential biological activities including cytotoxicity, anti-inflammation, anti-Alzheimer, anti-microbial, anti-oxidant, anti-diabetes, estrogenic, vasorelaxant and enzyme inhibition. Recently, prenylated flavonoids have become an indispensable anchor for the development of new therapeutic agents, and have received increasing from medicinal chemists. The prenylated flavonoids have been outstanding developed through isolation, semi or fully synthesis in a very short period of time, which proves the great value in medicinal chemistry researches. In this review, research progress of prenylated flavonoids including natural prenylated flavonoids, structural modification, synthetic methodologies and pharmacological activities was summarized comprehensively. Furthermore, the structure-activity relationships (SARs) of prenylated flavonoids were summarized which provided a basis for the selective design and optimization of multifunctional prenylated flavonoid derivatives for the treatment of multi-factorial diseases in clinic.

Visible Light-Induced Pericyclic Cascade Reaction for the Synthesis of Quinolinone Derivatives with an Oxabicyclo[4.2.0]octene Skeleton

A photoinduced pericyclic cascade reaction has been developed to afford oxabicyclo[4.2.0]octenes. Mechanistic studies show that this reaction undergoes [2 + 2]-photocycloaddition, base-promoted elimination, retro-4π-electrocyclization, [1,5]-H shift, and 4π-electrocyclization procedures. This reaction features wide substrate scope, good functional group tolerance, and excellent diastereoselectivity.

Recent advances in the synthesis of gem-dimethylcyclobutane natural products

Covering: January 2000 to July 2018 gem-Dimethylcyclobutanes are a common motif found in a multitude of natural products, and thus these structures have captivated synthetic chemists for years. However, until the turn of the century, most synthetic efforts relied upon the use of widely available terpenes, such as pinene or caryophyllene, that already contain the gem-dimethylcyclobutane motif. This approach limits the scope of molecules that can be accessed readily. This review highlights recent syntheses in which the gem-dimethylcyclobutane is assembled via de novo approaches. An outlook on the future of this research area is also provided.

How cyclobutanes are assembled in nature--insights from quantum chemistry

Biosynthetic production of cyclobutanes leads to many complex natural products. Recently, theoretical work employing quantum chemical calculations has shed light on many of the details of cyclobutane-formation, in particular, for terpene natural products. Specific insights and general principles derived from these theoretical studies are described herein.

Denticulatains A and B: unique stilbene–diterpene heterodimers from Macaranga denticulata

Two novel heterodimers were isolated from the fronds of Macaranga denticulata. They possess an unprecedented stilbene–diterpene-type skeleton, which represents a unique class of prenylated stilbene.

An efficient route to highly strained cyclobutenes: indium-catalyzed reactions of enynals with alkynes

A catalytic method to synthesize the highly strained cyclobutene was developed. The reaction was believed to proceed through a formal indium-catalyzed [2+2] cycloaddition between electron-deficient enynals and a variety of alkynes.

Differentiating mechanistic possibilities for the thermal, intramolecular [2 + 2] cycloaddition of allene-ynes

Intramolecular [2 + 2] cycloaddition reactions of allene-ynes offer a quick and efficient route to fused bicyclic ring structures. Insights into the mechanism and regiochemical preferences of this reaction are provided herein on the basis of the results of quantum chemical calculations (B3LYP/6-31+G(d,p)) and select experiments; both indicate that the reaction likely proceeds through a stepwise diradical pathway where one radical center is stabilized through allylic delocalization. The influences of the length of the tether connecting the alkyne and allene and substituent effects are also discussed.

Pericyclic domino reactions: concise approaches to natural carbocyclic frameworks

This tutorial review highlights new research in the area of pericyclic domino reactions. It is directed towards chemists interested in cascading reactions and the total synthesis of natural products. Concise approaches to natural frameworks are described, as well as the application of domino reactions in the context of target-oriented synthesis and total synthesis.

Inspirations, discoveries, and future perspectives in total synthesis

The last one hundred years have witnessed a dramatic increase in the power and reach of total synthesis. The pantheon of accomplishments in the field includes the total synthesis of molecules of unimaginable beauty and diversity such as the four discussed in this article: endiandric acids (1982), calicheamicin gamma(1)(I) (1992), Taxol (1994), and brevetoxin B (1995). Chosen from the collection of the molecules synthesized in the author's laboratories, these structures are but a small fraction of the myriad constructed in laboratories around the world over the last century. Their stories, and the background on which they were based, should serve to trace the evolution of the art of chemical synthesis to its present sharp condition, an emergence that occurred as a result of new theories and mechanistic insights, new reactions, new reagents and catalysts, and new synthetic technologies and strategies. Indeed, the advent of chemical synthesis as a whole must be considered as one of the most influential developments of the twentieth century in terms of its impact on society.

A regiodivergent synthesis of ring a C-prenylflavones

Capitalizing on the use of orthogonal protecting groups and the development of a modified Robinson flavone synthesis that avoids harsh acidic conditions, a regioselective synthesis of 6- and 8-prenylflavones from the same prenylated disilylated phloracetophenone (9) has been developed, targeting cannflavin B (1d), the COX-inhibiting principle of marijuana, and its unnatural isomer isocannflavin B (1e) as model compounds.

Total synthesis of atrochamins F, H, I, and J through cascade reactions

A concise and efficient cascade-based total synthesis of artochamins F, H, I, and J is described. The potential biogenetic connection between artochamin F, or a derivative thereof, and artochamins H, I, and J, through an unusual formal [2+2] cycloaddition process, was shown to be feasible. An alternative mechanism for this transformation is also proposed.

Microwave dielectric heating in synthetic organic chemistry

First described more than two decades ago, microwave-assisted organic synthesis has matured from a laboratory curiosity to an established technique that today is heavily used in both academia and industry. One of the most valuable advantages of using controlled microwave dielectric heating for chemical synthesis is the dramatic reduction in reaction times: from days and hours to minutes and seconds. As will be explained in this tutorial review, there are many more good reasons why organic chemists are nowadays incorporating dedicated microwave reactors into their daily work routine.