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 The Bunsen burner was later superseded by the isomantle, oil bath, or hot plate as a source for applying heat to a chemical reaction.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

This review describes the applications of tandem mass spectrometry methodologies for the preparation and identification of ionized and neutral heterocumulenes S=C=(C) n =C=X in the gas phase.

Mass Spectrometry of S:C:(C)n:C:X Cumulenes

Transforming Triplet Vinylnitrene into Triplet Alkylnitrene at Cryogenic Temperatures.

Synthesis of Isoxazolo(4,5-d)pyrimidinones, and Their Isomerization into Oxazolo(4,5-d)pyrimidinones on Flash Vacuum Pyrolysis.

There is only one crystal structure of a 2-pyridylformamide found in the literature to date, viz. dimeric 2-pyridylformamide (Bock et al., 1996). In the monomeric title compound, (I), atom Cl31 forces the formamide group to be trans, thus preventing the hydrogen bonding which forms the dimer in the unchlorinated compound through the equivalents of N1 and N21. The torsion angle for N1—C2—C21—C22 is 5.3 (7) .

N-(3,5-dichloro-2-pyridyl) formamide

Dicarbalkoxyketenes 8a and 8b are obtained by photolysis of diazo esters 7 in cryogenic matrices or by FVT of 7 followed by matrix isolation. The photochemical Wolff rearrangement of diazomalonates 1 in Ar matrix at temperatures as low as 6.5 K produces alkoxy(alkoxycarbonyl)ketenes 3, also obtained by FVT of 1. Photolysis of 1 in CO matrix at greater than or equal to 6.5 K produces the dicarbalkoxyketenes 8. Ketenes 3, 8, and 12 react with pyridine above 40 K to produce ketene-pyridine ylides (zwitterions) 9, 10, and 13, respectively.

Reactivity of Carbenes and Ketenes in Low-Temperature Matrices. Carbene CO Trapping, Wolff Rearrangement, and Ketene-Pyridine Ylide ( Zwitterion) Observation.

Curt Wentrup

Papers

Mass Spectrometry of S:C:(C)n:C:X Cumulenes

Transforming Triplet Vinylnitrene into Triplet Alkylnitrene at Cryogenic Temperatures.

Synthesis of Isoxazolo(4,5-d)pyrimidinones, and Their Isomerization into Oxazolo(4,5-d)pyrimidinones on Flash Vacuum Pyrolysis.

N-(3,5-dichloro-2-pyridyl) formamide

Reactivity of Carbenes and Ketenes in Low-Temperature Matrices. Carbene CO Trapping, Wolff Rearrangement, and Ketene-Pyridine Ylide ( Zwitterion) Observation.