Substituent ring assemblies

Even in cases where a parent heterocyclic skeleton is not numbered as a whole (e.g., spiro method 6a, ii and ring assembly nomenclature) it is important to realize that substituent prefixes (including hydro) should appear before the whole parent name, not before the individual component names (see example 184). 

Since thirteen of the possible fourteen ring systems, and three of the possible seven benzo fused systems are known, many in several oxidation states and with a wide range of substituents, it is only possible in this section to discuss the more general approaches to synthesis of the rings. Assembly of the rings will be described from non-cyclic fragments... 

Aromatic" compounds are those derived from benzene and similar ring systems. As with aliphatic nomenclature described above, the process is determining the root name of the parent ring determining priority, name, and position number of substituents and assembling the name in alphabetical order. Functional group priorities are the same in aliphatic and aromatic nomenclature. See p. 676 for the list of priorities. 

The preparation of substituted terpyridine frameworks is well documented. Typical substitution patterns focus on functionahzation at the 4 -positions [26, 27]. Here, we will focus on preparations of terpyridines specifically modified at the 6- and 6 -positions, because substituents at these positions are positionally disposed to interact with metal-bound substrates. For clarity, this section will be limited to discussions of two common strategies for the synthesis of appended terpyridine ligands, namely early and late-stage ring assembly approaches. 

Most parent structures consist essentially of an assembly of rings and/or chains, the degree of hydrogenation of which is defined (usually completely saturated or containing the maximum number of non-cumulative double bonds in cyclic portions), and having no attached functional substituents (the carbohydrates are a notable exception to this). The stereochemistry at all (or most) chiral centres is defined thus such parent structures are sometimes referred to as stereoparents . Some examples are shown (77)-(83). 

The problem of assembling three adjacent substituents on the benzene ring of (25) suggests using... 

Although 1,3,2-diazaphospholenium cations are usually prepared from neutral NHPs or 1,3,2-diazaphospholes via Lewis-acid induced substituent abstraction or A-alkylation, respectively (cf. Sect. 3.1.2), the group of Cowley was the first to describe a direct conversion of a-diimines into cationic heterocycles by means of a reaction that can be described as capture of a P(I) cation by diazabutadiene via [4+1] cycloaddition [31] (Scheme 4). The P(I) moiety is either generated by reduction of phosphorus trihalides with tin dichloride in the presence of the diimine [31] or, even more simply, by spontaneous disproportionation of phosphorus triiodide in the presence of the diimine [32], The reaction is of particular value as it provides a straightforward access to annulated heterocyclic ring systems. Thus, the tricyclic structure of 11 is readily assembled by addition of a P(I) moiety to an acenaphthene-diimine [31], and the pyrido-annulated cationic NHP 12 is generated by action of appropriate... 

This procedure illustrates a fundamentally new method for constructing substituted tetrahydrofurans.5-10 This practical method assembles the tetrahydrofuran ring from allylic diol and carbonyl components and in the process forms three ring bonds C(2)-C(3), C(4)-C(5) and 0-C(5). Both aldehydes (eq 1) and ketones (illustrated in the present procedure) can be employed as the carbonyl component. Although it is often convenient to isolate the acetal intermediate, conversion to the 3-acyltstrahydrofuran can also be accomplished in many cases by the direct reaction of the diol and carbonyl components.8 High ds stereoselectivity (at least 20 1) is observed in the preparation of tetrahydrofurans that contain single side chains at carbons 2 and 5 (eq 1). The kinetically controlled product also has the cis relationship of these side chains and the 3-acyl substituent. 

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