Although fire is now rarely used in synthetic chemistry, it was not until Robert Bunsen invented the burner in 1855 that the energy from this heat source could be applied to a reaction vessel in a focused manner. The Bunsen burner was later superseded by the isomantle, oil bath, or hot plate as a source for applying heat to a chemical reaction. In the past few years, heating and driving chemical reactions by microwave energy has been an increasingly popular theme in the scientific community. This nonclassical heating technique is slowly moving from a laboratory curiosity to an established technique that is heavily used in both academia and industry. The efficiency of "microwave flash heating" in dramatically reducing reaction times (from days and hours to minutes and seconds) is just one of the many advantages. This Review highlights recent applications of controlled microwave heating in modern organic synthesis, and discusses some of the underlying phenomena and issues involved.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.200400655

Controlled microwave heating in modern organic synthesis.

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Asymmetric 1,3-Dipolar Cycloaddition Reactions

The Diels-Alder reaction has both enabled and shaped the art and science of total synthesis over the last few decades to an extent which, arguably, has yet to be eclipsed by any other transformation in the current synthetic repertoire. With myriad applications of this magnificent pericyclic reaction, often as a crucial element in elegant and programmed cascade sequences facilitating complex molecule construction, the Diels-Alder cycloaddition has afforded numerous and unparalleled solutions to a diverse range of synthetic puzzles provided by nature in the form of natural products. In celebration of the 100th anniversary of Alder's birth, selected examples of the awesome power of the reaction he helped to discover are discussed in this review in the context of total synthesis to illustrate its overall versatility and underscore its vast potential which has yet to be fully realized.

https://www.ch.ic.ac.uk/local/organic/pericyclic/DA.pdf

The Diels--Alder reaction in total synthesis.

Introduction Cationic domino reactions Anionic domino reactions Radical domino reactions Pericyclic domino reactions Photochemically induced domino processes Transition metal catalysis Domino reactions initiated by oxidation or reduction Enzymes in domino reactions Multicomponent reactions Special techniques in domino reactions

Domino Reactions in Organic Synthesis

The cheletropic trapping of nitric oxide by the bis-ketene 1,2-dicarbonylcyclohexa-3,5-diene and the diene 3,4-diphenyl-2,5-dimethyl-2,4-hexadiene

The C-13 NMR data of five iminopropadienones R-N=C=C=C=O as well as carbon suboxide, C3O2, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31 +G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5-10 ppm. The computationally faster GIAO/HF/6-31 + G**//B3LYP/6-31 G* level is also adequate. (C) 2004 Elsevier B.V. All rights reserved.

Iminopropadienones R–NCCCO and carbon suboxide, C3O2. Theoretical and experimental 13C NMR spectra

Ethenedithione, S=C=C=S, has been generated in flash vacuum pyrolysis (FVP) reactions from isoxazolone and Meldrum's acid derivatives and characterized by IR, UV and mass spectrometry. Evidence for the existence of HN=C=C=S and its isomerization to thioformyl cyanide is also presented. The preparation and characterization of iminopropadienone derivatives RN=C=C=C=X (X = 0, S, or NR') from a variety of isoxazole compounds is described. These highly reactive cumulenes are formed via vinylidene, vinylnitrene, and ketenimine intermediates.

/pdf/the-use-of-1-2-shifts-in-carbenes-and-nitrenes-in-the-2rqw23h5wq.pdf

The use of 1, 2-shifts in carbenes and nitrenes in the generation of novel heterocumulenes

Matrix isolation and infrared spectrum of thioformyl cyanide

Abstract The mixture of 13C2-labelled naphthalenes obtained by flash vacuum thermolysis of [4,7-13C2] azulene (9) consists of [1,4-13C2]- (14) and [2,10-13C2] naphthalene (10) as major products and [1,3-13C2]naphthalene (11) as a minor product. Traces of [1,6-13C2]- (12) and [1,7-13C2] naphthalene (13) are also detectable. The recently proposed vinylidenenorcaradiene mechanism [5] correctly predicts the major products.

Curt Wentrup

Papers

The cheletropic trapping of nitric oxide by the bis-ketene 1,2-dicarbonylcyclohexa-3,5-diene and the diene 3,4-diphenyl-2,5-dimethyl-2,4-hexadiene

Iminopropadienones R–NCCCO and carbon suboxide, C3O2. Theoretical and experimental 13C NMR spectra

The use of 1, 2-shifts in carbenes and nitrenes in the generation of novel heterocumulenes

Matrix isolation and infrared spectrum of thioformyl cyanide

Azulen-Naphthalin-Umlagerung. Thermolyse von [4.7-13C2] -Azulen/ Azulene-Naphthalene Rearrangement. Thermolysis of [4,7-13C2] Azulene