General Synthetic Aspects

In principle two different synthetic approaches may lead to dihetero-tricyclodecanes of the types G 1-G 5 starting either from suitably functionalized 9-heterobicyclo- 

Syntheses 9-Heterobicyclo[3.3.1 Jnonanes or 9-Heterobicyclo[4.2.1]-nonanes Dihetero-tricyclodecanes 

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This catalytic system allows three independent transformations to occur in sequence the Heck reaction, N-oxidation and asymmetric dihydroxylation (AD). The mechanism of the Heck reaction is discussed in the previous section. Here we take a closer look at the last two steps. They are coupled processes, based on the Sharpless asymmetric dihydroxylation reaction [22, 23]. Several recent reviews on Sharpless asymmetric dihydroxylation cover the general synthetic aspects [24-27], together with methods for immobilization of the osmium catalysts [28]. 

A number of general reviews related to the topics covered in this chapter have appeared (Table 1) and others will be discussed in the section dealing with synthetic aspects (Section 4.04.3.1). The Sokolov review is particularly noteworthy since it is quite recent and complete, containing 304 references to pyrazoles and isoxazoles. 

As we shall not be concerned directly with purely synthetic aspects of the photo-cyclization we would like to refer the interested reader to the comprehensive general reviews of Stermitz Blackburn and Timmons and to the yearly reviews of Gil-bert ... 

This chapter will concentrate primarily on features of the chemistry of diboron compounds of particular interest from the organometallic point of view. While our limited scope does not permit a comprehensive review of all aspects of diboron chemistry, we will initially survey some general features of the subject, with emphasis on unique synthetic aspects and on properties particularly characteristic of compounds containing a simple electron-pair bond between boron atoms. Previously, we published several review articles provided some aspects on boron chemistry,8 16 and including natural boron-containing compounds.17,18... 

Several reviews have been published in relation to aromatic SRN1 reactions [6-9], and to the synthetic applications of the process [10,11]. In this chapter an introductory short survey of the general mechanistic aspects, the aromatic substrates and nucleophiles involved in the photoinduced SRN1 mechanism will be presented. The main emphasis being related to its synthetic capability, target applications and to the more recent advances in the field. 

The reactions of silenes with aldehydes and ketones is another area whose synthetic aspects have been particularly well-studied4,6 7 10 12. The favoured reaction pathways for reaction are generally ene-addition (in the case of enolizable ketones and aldehydes) to yield silyl enol ethers and [2 + 2]-cycloaddition to yield 1,2-siloxetanes (equation 44), but other products can also arise in special cases. For example, the reaction of aryldisilane-derived (l-sila)hexatrienes (e.g. 21a-c) with acetone yields mixtures of 1,2-siloxetanes (51a-c) and ene-adducts (52a-c) in which the carbonyl compound rather than the silene has played the role of the enophile (equation 45)47,50 52 98 99. Also, [4 + 2]-cycloadducts are frequently obtained from reaction of silenes with a,/i-unsaturated- or aryl ketones, where the silene acts as a dienophile in a formal Diels-Alder reaction6 29,100-102. 

Electrocatalytic processes are discussed from a mechanistic point of view in Section III.B.5. However, some synthetic aspects as pertain to alkyl monohalides are relevant here. Electrocatalytic processes involve the formation of organometallic species characterized by the consumption of significantly less than a stoichiometric quantity of current, and can be generally illustrated by the process shown in Scheme 3. 

In this sub chapter the most important synthetic aspect of the RCM of unsaturated organosilicon compounds will be discussed. For a general review on RCM see Refs. [59,122-124]. For a review on RCM of silyl dienes see Refs. [6,7]. A number of valuable synthetic applications have been proposed over the last few years. As follows from the data available, from the point of view of the application of RCM of vinyl and allylsilanes, the most important are silicon-tethered processes. For a general review on the silicon tethered processes see Refs. [125,126],... 

The most general method of cyclization through C-O bond formation is lactonization, and its synthetic aspects, including alcohol or acid moiety activation, enantio- and diastereoselectivity, were reviewed recently <2006CRV911>. 

Most reactions of Grignard reagents acting as a base involves enoiates. Several papers describe mechanistic and stereochemical aspects of magnesium enoiates. Others deal with purely synthetic transformations. This section will focus specifically on magnesium enoiates. Mechanistic studies are first reviewed, followed by general synthetic applications. 

While it is true that this chapter has left out many of the notable syntheses in the field, the omission was deliberate, so as to highlight certain aspects of generalized synthetic strategies, rather than to focus on singularly unique (albeit elegant) reactions. The following sections systematically document in full the synthetic achievements in the leukotriene field. 

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