General synthetic approaches

Therefore the synthetic access to fluorinated phthalocyanines is mainly determined by availability of such synthons appropriately substituted with fluorine atoms or/and fluorinated groups. A limitation that should be taken into account is connected with a possibility of aromatic nucleophilic substitution of fluorine. This side-reaction can be usually avoided by choosing appropriate non-nucleophilic conditions for template cyclotetramerization. 

The approach (ii) is usually applied for modification of perfluorinated phthalocyanines by nucleophilic substitution of fluorine atoms or in the case of easy accessibility of non-fluorinated phthalocyanines containing active groups, which can be exchanged by fluorine or fluorinated substituents. 

Synthesis of metal alkoxides has been studied for more than a century by different researchers, who have proposed a large variety of synthetic techniques aimed at preparation of different distinct derivatives. In the 1950s in the course of the systematic studies Bradley suggested a few general techniques [196]. In the present review we would like to differentiate the methods that had technological applications and those that are mostly used in laboratory practice. 

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Estrone (54, Chart 6) contains a full retron for the o-quinonemethide-Diels-Alder transform which can be directly applied to give 55. This situation, in which the Diels-Alder transform is used early in the retrosynthetic analysis, contrasts with the case of ibogamine (above), or, for example, gibberellic acid (section 6.4), and a Diels-Alder pathway is relatively easy to find and to evaluate. As indicated in Chart 6, retrosynthetic conversion of estrone to 55 produces an intermediate which is subject to further rapid simplification. This general synthetic approach has successfully been applied to estrone and various analogs. ... 

Azepines are much less common than the 1H- and 3//-isomers, and one of the few general synthetic approaches to this system is by base-catalyzed ring expansion of 4-(chloromethyl)-l, 4-dihydropyridines. e. g. I.29 Curiously, the ring expansion is also effected by potassium cyanate in refluxing ethanol. 

Organometallic polymer precursors offer the potential to manufacture shaped forms of advanced ceramic materials using low temperature processing. Polysilazanes, compounds containing Si-N bonds in the polymer backbone, can be used as precursors to silicon nitride containing ceramic materials. This chapter provides an overview of the general synthetic approaches to polysilazanes with particular emphasis on the synthesis of preceramic polysilazanes. 

Phosphorus is the most common donor atom in Ni° chemistry. Likewise, As- and Sb-based ligands are well suited for stabilizing low-valent Ni°. Ni° phosphine chemistry is extensive, and the general synthetic approaches have been summarized previously. 

A. Yashiro, Y. Nishida, M. Ohno, S. Eguchi, and K. Kobayashi, Fullerene glycoconjugates A general synthetic approach via cycloaddition of per-O-acetyl glycosyl azides to [60]fullerene, Tetrahedron Lett., 39 (1998) 9031-9034. 

Many of the metal-organic catalysts that are utilized today in catalytic processes can be considered as metal ligand compounds. The general synthetic approach is to identify scaffolds, which lead to an easy access of a library of considerable diversity Figure 11.10 illustrates this approach. Usually ligands that contain heteroatoms (such as imines or phosphines) are the preferred compounds that give... 

As commented in the introduction of this chapter, the most general synthetic approach to allenylidene complexes employs propargylic alcohols HC=CCR R (OH) as source of the unsaturated C3 skeleton. In 1982, Selegue introduced for the first time this synthetic strategy for the high yield preparation of the cationic Ru(II)... 

The Michael addition followed by Intramolecular Ring Closure (MIRC) reactions have been recognized as a general synthetic approach to carbocyclic three-membered ring derivatives [1]. The enhanced Michael reactivity of methyl 2-chloro-2-cyclopropylideneacetate (1-Me) towards thiolates, alkoxides, lithiated amides and cyclohexadienolates (see below) allows one to perform highly efficient assemblies of spiropentane, tricyclo [3.2.1.0 ]octane, bicyclo [2.2.2] octane... 

Allenylsilanes serve as valuable three-carbon components in a general [3+2] annulation method for the synthesis of five-membered rings. A variety of general synthetic approaches to allenylsilanes have recently been developed and a number of specialized routes to various specific functionalized derivatives are available as well. The present procedure... 

A general synthetic approach to the thietes is provided by a Hoffmann elimination from aminothietanes 148 (Eq. 24). Other thiete derivatives... 

In principle then, these saturated imides and derivatives are beyond the scope of this chapter. However, the synthesis and reactions of some 3-unsubstituted derivatives of 179 are included in the interest of completeness. No attempt has been made to provide an exhaustive review of all examples of 2,4-oxazolidinediones. Rather, selected examples from the recent literature that illustrate general synthetic approaches or novel reactions are described. 

The considerations that (Z), as a vinylogous amide, may undergo hydrolysis to (Y) whereas (Y) and (Z), being derivatives of /3-ketocarboxylic acids, can be subjected to acid cleavage suggest starting with (Z) itself as a general synthetic approach (Scheme 2). 

Retrosynthetic Scheme 1 shows the general synthetic approach. Under certain conditions, the preparation of the /3-ketocarboxylic acids R4—CO—CH2—COOH or their esters might become the largest chal-... 

General Synthetic Approaches for High Performance Explosives (HNIW/CL-20 etc.)... 

Before presenting the various syntheses of L-ascorbic acid that have been developed since its structure was determined, it is appropriate to comment on the general, synthetic approaches that have been used. 

An outstanding input into the chemistry of metal alkoxides was made by the dissertation of V. E. Tishchenko, which was devoted to aluminium alkoxides. It was published in 1899 (unfortunately only in Russian) [1585] and—in contrast to his works on organic chemistry — is practically unknown by foreign chemists. A number of general synthetic approaches to metal alkoxides have been developed. The main regularities for the variation of the properties in the homologous sales and ramification of the radical were found to determine the main directions of the thermal decomposition. He made also the proposal to use the Al(OR)3 in ester condensation of aldehydes (Tishchenko reaction) (see also Chapter 12, Section 12.5). 

A novel route to the azepinone system in 93 and 94, based on an intramolecular nitrone-eneallene cycloaddition (in 91 and 92, which were accessed in turn from 88 via 89 and 90) and subsequent rearrangement via N-O bond homolysis and an electrocyclic recyclization step) has been described (Scheme 11) <2005EJ02715>. On heating 93 in toluene, equilibrium with the isomeric azepinone 95 was established, although comprising less than 3% of 95. The general synthetic approach was applied to the synthesis of an analogue of the alkaloid astrocasine. 

Sequential Chain Extension. The general synthetic approach adopted in our published work was to employ sequential chain extension reactions rather than block synthesis. Since two of... 

The general synthetic approaches for expanded porphycenes rely upon the insertion of alkylidene or alkylidyne moieties either as the meso-bridge or between the 2 and 2 positions of the bipyrrole subunits. Thus, the vinylogous dialdehyde 72 (Scheme 35) obtained from 4,4 -dipropyl-2,2 -bipyrrole with 3-(dimethyl-l-amino)acrolein has been converted to (1993PAC143) to 73 using a standard McMurry-type coupling. Expanded porphycene 73 with TFA precipitates as dication 74. 

Scheme 11.1 General synthetic approach to symmetric and asymmetric naphthalene diimides.

An environmentally greener process for the synthesis of HFCs can be envisioned through an intermediate inorganic metal fluoride that is capable of fluor-inating a C-H bond of a desirable hydrocarbon and could be regenerated to the appropriate oxidized metal fluoride with oxygen and HF. The general synthetic approach is shown in equations (6a) and (6b) and the net reaction is shown in equation (6c). 

A general synthetic approach consists of the reaction of 1,2-diaminopyrazines or A,A -dimethyl-ethane-1,2-diamines with glyoxal. This method has already been described in CHEC-I. Additionally, some new approaches have been developed. Nucleophilic exchange of the chlorine atoms of 5,6-dichloropyrazine-2,3-dicarbonitrile (118) by 1,2-diamino compounds affords the pyrazino[2,3-6]py-razines (119) and (120) (Scheme 20) <88LA1197>. Variation of the amines and treatment with hydrazine hydrate forms several polyaza derivatives <88LA1197>. 

Cycloaddition reaction of diazadienes (generated in situ from an -halogenated hydrazone) with alkenes yielding 2,3,4,5-tetrahydropyridazines followed by aromatization is a general synthetic approach to substituted pyridazines (e.g., 131) a representative example is shown in Scheme 67 <1995TL5703>. 

Reductive cyclization of nitrostyrene precursors has also proven to be a useful route to 5,6-dihydroxyindole and its derivatives, as illustrated by the efficient preparation of the system 32 (Scheme 18) <1999S793>. A general synthetic approach to indoles involves a palladium-catalyzed reductive cyclization of 2-nitrostyrenes <1997JOC5838>. This procedure was used in the synthesis of several natural products, e.g., 4-(methoxymethyl)-2-methylindole 33 (Scheme 19), a constituent of a tricholoma species <1999JOC9731, CHEC-III(3.03.2)282>. 

From other o-substituted benzenes. Standard reactions of aliphatic chemistry can be applied for example, chroman 102 can be prepared by ring closure of 101. 4-Quinolones result from the Camps reaction (103 104), and flavonone 106 is prepared by cyclization of 105. The nucleophile-induced cyclization of suitably substituted 0-alkynylanilines 107 provides a general synthetic approach to quinolines 108 (Scheme 66) . Similar cyclizations of o-alkynylphenols lead to the formation of coumarins . 

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