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

This review focuses on classifying different types of long wavelength absorbing BODIPY dyes based on the wide range of structural modification methods that have been adopted, and on tabulating their spectral and photophysical properties. The structure–property relationships are analyzed in depth with reference to molecular modeling calculations, so that the effectiveness of the different structural modification strategies for shifting the main BODIPY spectral bands to longer wavelengths can be readily compared, along with their effects on the fluorescence quantum yield (ΦF) values. This should facilitate the future rational design of red/NIR region BODIPY dyes for a wide range of different applications.

Structural modification strategies for the rational design of red/NIR region BODIPYs

Perfluoroalkylation with Organosilicon Reagents

This review is essentially an update of one entitled “πBonding and The Lone Pair Effect in Multiple Bonds Between Heavier Main Group Elements” which was published more than 10 years ago in this journal.1 The coverage of that survey was focused on the synthesis, structure, and bonding of stable compounds2 of heavier main group elements that correspond to the skeletal drawings reproduced in Tables 1 and 2. A row of numbers is listed at the bottom of each column in these tables. This refers to the number of stable complexes from each class that are currently known. The numbers in parentheses refer to the number of stable species that were known at the time of the previous review. Clearly, many of the compound classes listed have undergone considerable expansion although some remain stubbornly rare. The most significant developments for each class will be discussed in detail under the respective sections. As will be seen, there are also a limited number of multiple bonded heavier main group species that do not fit neatly in the classifications in Tables 1 and 2. However, to keep the review to a manageable length, the limits and exclusions, which parallel those used earlier, are summarized as follows: (i) discussion is mainly confined to compounds where experimental data on stable, isolated species have been obtained, (ii) stable compounds having multiple bonding between heavier main group elements and transition metals are not generally discussed, (iii) compounds in which a multiple bonded heavier main group element is incorporated within a ring are generally not covered, and (iv) hypervalent main group compounds that may incorporate faux multiple bonding are generally excluded. Such compounds are distinguished from those in Tables 1 and 2 in that they apparently require the use of more than four valence bonding orbitals at one or more of the bonded atoms. The remainder of this review is organized in a similar manner to that of the previous one wherein the compounds to be discussed are classified according to those summarized in Tables 1 and 2. The key unifying feature of almost all molecules discussed in this review is that they are generally stabilized by the use of bulky substituents which block associative or various decomposition pathways.3 Since the previous review was published in 1999, several review articles that cover parts of the subject matter have appeared.4

π-Bonding and the Lone Pair Effect in Multiple Bonds Involving Heavier Main Group Elements: Developments in the New Millennium

Carbenes : Synthesis, properties, and organometallic chemistry

Acentric Extended Solids by Self Assembly of 4,4′-Bipyrazolyls

A reaction of phosphorus tribromide with a compound containing two 2,5-dimethyl-1-arylpyrrolyl-3 residues bound through a phosphorus atom gave rise to a new phosphorus-containing heterocyclic system, 1,4-diphosphinine. The new products thus obtained have been characterized and described. © 2002 John Wiley & Sons, Inc. Heteroatom Chem 13:46–52, 2002; DOI 10.1002/hc.1105

Heterocondensed 1,4-diphosphinines

Effets of pπpπ conjugation in phosphaalkenes have been considered by taking into account the results of X-ray structural studies and ab initio quantum-chemical calculations. The structural consequences of the conjugation depend to a certain extent on the character of the substituent and the place of its attachment to the double PC bond. Depending on the location of the substituent, bond polarization may strengthen or weaken (compensate for) the conjugation effects. A high contribution of the s-character of the lone electron pair of the P atom is an essential feature of the electron structure of a phosphaalkene.

Peculiarities of pπ ? pπ conjugation in aminosubstituted phosphaalkenes

The Knoevenagel condensation of aliphatic aldehydes with CH acids, malonodinitrile, cyanothioacetamide, cyclohexane-1,3-dione, dimedone, 4-hydroxycoumarin, 3-aminophenol, and N-(cyclohex-1-enyl)-morpholine leads to formation of 4-alkyl-substituted partially hydrogenated quinolines, fused 4H-pyrans, and 2-amino-4-ethyl-5-methylbenzene-1,3-dicarbonitrile. The structure of the latter was proved by the X-ray diffraction data.

Aliphatic aldehydes in multicomponent syntheses of 4-alkyl-substituted partially hydrogenated quinolines, fused 4H-pyrans, and 2-amino-4-ethyl-5-methylbenzene-1,3-dicarbonitrile

Alexander N. Chernega

Papers

Acentric Extended Solids by Self Assembly of 4,4′-Bipyrazolyls

Heterocondensed 1,4-diphosphinines

Peculiarities of pπ ? pπ conjugation in aminosubstituted phosphaalkenes

Aliphatic aldehydes in multicomponent syntheses of 4-alkyl-substituted partially hydrogenated quinolines, fused 4H-pyrans, and 2-amino-4-ethyl-5-methylbenzene-1,3-dicarbonitrile

The Aza Curtius Rearrangement