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

The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.

Cascade reactions in total synthesis.

I. Introduction 1485II. Scope of This Review 1485III. Transformations of Cyclobutane Derivatives inOrganic Syntheses1486A. Ring-Opening Reactions 1486B. Ring-Contraction Reactions 1493C. Ring-Expansion Reactions 14951. Five-Membered Rings 14952. Six-Membered Rings 15093. Seven-Membered Rings 15174. Eight-Membered Rings 15215. Nine-Membered Rings 1523IV. Transformations of Cyclobutane Derivatives inNatural Product Syntheses1524A. Ring-Opening Reactions 1524B. Ring-Expansion Reactions 15261. Five-Membered Rings 15262. Six-Membered Rings 15293. Seven-Membered Rings 15324. Eight-Membered Rings 1533V. Conclusion 1534VI. Acknowledgments 1534VII. References 1534

The application of cyclobutane derivatives in organic synthesis.

Life on earth is based on compounds that have carbon frames and backbones. Today, chemists have added to the world of biomolecules and biopolymers approximately 107 different synthetic molecules and polymers, the structures of which also depend on the formation of strong, stable carbon–carbon bonds. Although the stability of carbon–carbon bonds has been recognized for more than a century, the two natural modifications graphite and diamond were, until recently, the only allotropic forms of carbon on earth that were available in macroscopic quantities and were structurally well characterized. With the synthesis of macroscopic quantities of buckminsterfullerene (C60) and the higher fullerenes (C70, C76, C78, etc.) and the exploration of the fascinating properties of these all-carbon spheres, this situation has completely changed. In the coming decades, the design, preparation, and study of novel molecular and polymeric allotropic forms of carbon will be a central topic in chemistry. Research in this area will dramatically advance the fundamental knowledge on carbon-based matter and, as already illustrated by the ongoing work on C60, generate unprecedented technological perspectives. This review surveys synthetic organic-chemical approaches toward the preparation and study of all-carbon molecules and polymers that differ from the familiar networks of graphite and diamond as well as from the fullerenes. We will also discuss the ongoing research on fullerenes with a particular focus on the synthetic approaches to these all-carbon spheres and their transition metal complexes.

Synthetic approaches toward molecular and polymeric carbon allotropes

Die Entwicklung und Umsetzung von Kaskadenreaktionen hat zu beachtlichen neuartigen, eleganten und effizienten Synthesestrategien gefuhrt. Als besonders anspruchsvoll erwies sich die Anwendung von Kaskadenreaktionen in der Naturstoffsynthese, doch gerade hier winken verbluffende und zugleich aufschlussreiche Ergebnisse als Belohnung. In diesem Aufsatz werden ausgewahlte Kaskadenreaktionen in der Totalsynthese erlautert, wobei neuere Anwendungen besonders hervorgehoben werden. Die erorterten Beispiele sollen die Leistungsfahigkeit dieser Prozesse beim Aufbau von komplexen Molekulstrukturen veranschaulichen und ihr Potenzial fur zukunftige chemische Synthesen verdeutlichen.

Kaskadenreaktionen in der Totalsynthese

tert-Butoxyquinones were prepared from the thermal ring expansion of 4-alkynyl-, 4-alkenyl-, and 4-aryl-tert-butoxycyclobutenones and shown to be readily converted to hydroxyquinones upon treatment with trifluoroacetic acid at low temperature. The synthetic scope of this methodology as well as its specific utilization in the synthesis of a semisquaric acid, and the natural products, (±)-terreic acid, (±)-perezone, and (±)-isoperezone, are described

Synthesis of hydroxyquinones and related compounds: semisquaric acids, (.+-.)-terreic acid, (.+-.)-perezone and (.+-.)-isoperezone

A potentially general regiospecific synthesis of benzo- and naphthoquinones is described. This method starts with dimethyl squarate (1), which is converted to the cyclobutenone ketal 9 upon sequential treatment with an organolithium reagent and then BF 3 etherate or TFAA in THF/methanol. Treatment of these with a second lithium reagent followed by hydrolysis gives the cyclobutenones 5.Addition of an alkynyl-,alkenyl- or aryllithium agent to 5 followed by hydrolysis of the ketal linkage gives the corresponding 4-alkynyl-4-alkenyl- or 4-aryl-4-hydroxycyclobutenones 7-9 and these readly rearrange to the respective quinones or hydroquinones upon thermolysis in refluxing benzene.In a similar fashion,15 was employed as a reagent to prepare mono- and disubstituted hydroquinones and quinones

Harold W. Moore

Papers

Synthesis of hydroxyquinones and related compounds: semisquaric acids, (.+-.)-terreic acid, (.+-.)-perezone and (.+-.)-isoperezone

A potentially general regiospecific synthesis of substituted quinones from dimethyl squarate

Synthesis of p-chlorophenols (and-naphthols) from the thermal rearrangement of 4-chlorocyclobutenones

Synthesis of the bicyclo[3.2.0] ring systems from 4-allylcyclobutenones. Intramolecular ketene/alkene cycloadditions

Rearrangements of azidoquinones. XVI. Thermal and photolytic rearrangements of 2,5-diazido-1,4-quinones. Synthesis and chemistry of cyanoketenes