Known synthetic pathways

These ring systems are extensively used in dyes and pigments and are easily fine mned by adding substituents following well-known synthetic pathways. Inevitably,... 

In the synthesis of phenothiazines, ring closure successfully rivals with other reactions involving functional group insertion, removal or modification, and the scope of this review is to summarize the cyclization reactions known to produce the phenothiazine ring based on a retrosynthetic analysis scheme. Although we tried to ensure the coverage of all known synthetic pathways, the literature references are, however, limited to the most significant examples (the same procedure, e.g. thionation, has been used without relevant modifications by a spate of authors). 

Overview of Known Synthetic Pathways for DALA Production... 

Many methods for chemical synthesis of a-amino acids have been estabUshed. Because excellent reviews have been pubUshed (25,38), weU-known reactions are introduced here only by their names and synthetic pathways. 

Recently, Meier et al. synthesized the most extended OP Vs (81) known to date [104]. Four different synthetic pathways were used for the generation of these OP Vs the final step involves the formation of one or two olefinic double bonds via a Wittig-Horner-type, a Siegrist-type or a McMurry-type condensation. 

Algal blooms in fresh water ponds occasionally poison livestock and waterfowl. Axenic cultures of Anabaena flos-aquae NRC 44-1 were shown to produce the toxic principle (5) which can be present in the algae and in the water of mature cultures (6). The discovery of the toxin was fortuitous in the sense that AChR agonists do not have a (known) constructive function in the algae evolution of the synthetic pathway was likely a by-product of metabolic pathways in the algae. The compound became evident only through its toxic effects on other organisms. 

In 1978 we described a synthetic methodology as a repeating-step principle , which led us to the first cascade molecules , today known as dendritic molecules [17]. We recognized then that a synthetic pathway, which allows consecutive repetition, implies the advantage of likewise reactants and reaction conditions and is suited for the building of more or less structure perfect highly branched molecules, particularly of polyamines (Fig. 4). 

In the last decade, numerous compounds of these types have been the subject of detailed CVD studies, demonstrating their potential for the deposition of the corresponding binary materials. Most of the work has concentrated on binary nitrides and phosphides, while the deposition of binary MSb films has been studied to a far lesser extent. The lack of potential precursors has been the major problem for the deposition of group 13-antimonide films for many years. Only a very few group 13-Sb compounds have been known until we and Wells established general synthetic pathways as was shown in Sections 2 and 3. Consequently, detailed investigations concerning their potential to serve for the deposition of the desired materials... 

Poly(amic acids) in which the ortho-carboxylic group has been chemically modified to either an ester- or amide moiety have been known for many years. However, their commercial significance was non-existent until very recent applications involving dielectric insulators [48] and photosensitive polyimide precursors [49, 50]. As with many synthetic pathways, there are generally several ways to arrive at the same goal. Similarly, the preparation of derivatized poly(amic acids) can be divided into two general categories ... 

The synthetic approach used in this work is shown in Scheme 9. Two known solution pathways were used to convert shikimic acid to an epoxide intermediate. In fact, both the (-)35 and the (+)36 enantiomers were formed. After minor synthetic transformations, these epoxides were linked to Ten-tagel S aminomethyl resin with an o-nitrophenyl-derived photocleavable linker 7437 via amide bond formation to give intermediate 75. The first point of variation was added via various iodo-benzyl nitrone carboxylic acids 76 via 1,3-dipolar addition/esterification reactions. Highly constrained resin-bound tetracyclic hydrooxazoles 77 were thereby produced. 

Only a few synthetic pathways to the pyridazino[l,2-a]pyridazine ring system are known. Most of these involve condensation of pyridazine derivatives which are unsubstituted at positions 1 and 2 with diacid chlorides (67JA4875), y-ketoacid chlorides (69JOC2720) and... 

The single known example of a deprotonation of an alkylamido ligand suggests that a potentially convenient synthetic pathway may not be generally useful owing to the low acidity of the aliphatic C—H bonds (equation 99). 

Some non-standard synthetic pathways to compounds of the naph-tho[bc]pyran series are known. One consists in generation of the complex heterocyclic dehydrobenzene derivative 291, which then undergoes an intramolecular [4 + 2] cycloaddition to afford the bridge system 292. The latter is transformed into naphtho[bc]pyran-3-one 293 on reduction, followed by treatment with acid (8ITL4877 86AJC635). An unusual course... 

The synthetic pathway for a drug or analogue must start with readily available materials and convert them by a series of inexpensive reactions into the target compound. There are no obvious routes as each compound will present a different challenge. The usual approach is to work back from the target structure in a series of steps until cheap commercially available materials are found. This approach is formalized by a method developed by S Warren, which is known as either the disconnection approach or retrosynthetic analysis. In all cases the final pathway should contain a minimum of stages, in order to keep costs to a minimum and overall yields to a maximum. 

Comparatively little is known about phosphetane coordination compounds, which first appeared in 1984 <1984NJC453>, and are now accessible through two distinct synthetic pathways. The first is direct coordination of phosphetanes to the desired metal center. The second is a built-up method from its components within a metal... 

The chemical transforms are the heart and soul (11) of LHASA which has a database of over 600 common chemical reactions. This feature, ironically, shows its limitations. The empirical information about known chemical reactions limits the generation of synthetic pathways. The value of LHASA, however, is in its ability to investigate all possible known synthetic routes, a task which a chemist would find exceedingly tedious. 

The advancement of supra-Cp- metal chemistry followed along the lines of convenience concerning the ligands employed. It is no accident that the perarylated Cp coordination chemistry was developed first and most extensively. The feasible synthetic pathways to the parent dienes had already been worked out by organic chemists, and the dienes were fairly easy to prepare from inexpensive, commercially available starting meterials. Tri-and tetraphenylcyclopentadiene have been known for over 90 years (31,32). A convenient synthesis for tetra- as well as for pentaphenylcyclo-pentadiene was described in 1925 (33). 

The use of organolithium intermediates in tandem synthetic sequences combines the versatility of the very well known organolithium reagents and their highly stereoselective chemistry, with the economic and environmentally friendly advantages of the one-pot and/or cascade strategy, when compared with the conventional stepwise synthetic pathways. 

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