Other Organic Transformations

First discovered by Otto Paul Hermann Diels and Kurt Alder in 1928, the Diels-Alder reaction involves the cycloaddition of a conjugated diene with substituted alkene (dienophile) to yield a substituted cyclohexene product. These products can be further used in the synthesis of natural products. A lesser-known reaction is the hetero-Diels-Alder (HDA) reaction. In 1974, Danishefsl et al. developed a diene that can easily produce dihydro-pyranones. ° Since then, much research has been performed with Danishefksy s diene in order to develop new Lewis-acid catalysts for Diels-Alder reactions. 

A few years later, Himanen et al. used a chiral Schiff-base chromium complex in a HDA reaction to synthesise trisaccharides. Typically, these molecules are synthesised by coupling monosaccharides however, the protection steps and stereochemical control make their synthesis tedious. Researchers have since discovered an easier means of coupling monosaccharides by a de novo synthesis. This process does not require stereochemical control or control of the position of the glycosidic linkage. As a 

---

This review of some aspects of the organometallic chemistry of iridium is certainly not exhanstive. There have been some types of complexes that have receive little notice such as those containing polyolefmic hgands and related compounds. Also, there are other organic transformations that may be catalyzed by iridium complexes. However, throughout this chapter the reader has been directed to a number of primary references as well as a number of review articles that will delve into some areas of iridium organometallic chemistry more deeply. 

Indium(III) chloride and indium(III) triflate have been introduced to organic syntheses as versahle Lewis acids. They are stable in water, and catalyze a variety of organic reachons, e.g. the Diels-Alder reaction, the aldol reaction, Michael addi-hon, the Friedel-Crafts reaction, and other organic transformations. 

The present F C reaction proceeded through the in situ generation of aliphatic imines that were delivered via the protonation of the enecarbamates by the phos phoric acid catalyst (Figure 3.4). Phosphoric acid functioned as an efficient catalyst for the dual transformation that involved the in situ generation of imine and the enantioselective carbon carbon bond formation with indole. This protocol offers the distinct advantage of generating in situ unstable aliphatic imines from storable and thus easily handled enecarbamates, and hence is applicable to other organic transformations. In fact, Terada et al. applied the present method to an enantiose lective direct Mannich reaction [51]. The method provides an efficient pathway to p alkyl P aminocarbonyl derivatives in optically active forms. 

Use of iron(iii) oxide has been reported for a number of other organic transformations, most notably a 3-component aldehyde, alkyne and amine coupling, and for the C(sp )-H borylation of arenes using bis(pinacolato)diboron. ... 

This section deals with oxidation reactions as an initiative step of the domino process in combination with many other organic transformations. In 2004, Snaith and coworkers [3] demonstrated a simple and efficient method to synthesize 3-substituted 4-piperidinones 4 using a domino oxidation/carbonyl-ene/oxidation reaction (Scheme 9.1). This domino reaction comprises oxidation of unsaturated alcohol 1 using PCC (pyridinium chlorochromate) to give the corresponding aldehyde 2, followed by a carbonyl-ene type reaction to yield the secondary cyclic alcohol 3, which was oxidized under the reaction conditions to give 3-substituted 4-piperidinones 4 in good yields. 

Previous reviews have dealt with metal-catalyzed [93] and stoichiometric [94] oxidation of amines in a broad sense. This section will be limited to the selective oxidation of tertiary amines to N-oxides. Amine N-oxides are synthetically useful compounds [95, 96] and are frequently used as stoichiometric oxidants in osmium-[97-99] manganese- [100] and ruthenium-catalyzed [101,102] oxidations, as well as in other organic transformations [103-105]. Aliphatic tert-amine N-oxides are usefid surfactants [96] and are essential components in hair conditioners, shampoos, toothpaste, cosmetics, and so on [106]. Chiral N-oxides have been used in asymmetric catalysis involving metal-free catalytic transformations [107] as well as metal-catalyzed reactions where the N-oxide serves as a ligand [107, 108]. Chiral tertiary amine N-oxides were recently used as reagents in asymmetric epoxidation of a,(3-unsaturated ketones [109]. 

It is important that this two-step route is achieved using components of the [2-I-2-I-2] cycloaddition in equivalent amounts. A variety of terminal alkynes may be used. The heterobiaryls can also be synthesized using 2-iodopyridine or 2-iodothiophene as the aryl iodide component in the coupling reaction [98]. Further development of this methodology expanded the use of arylboronates as multipurpose intermediates in other organic transformations. 

---