Preparation of the Target

Proudnikov et al. [17] presented a preparation method based on the introduction of aldehyde groups by partial depurination of DNA or oxidation of the 3 -terminal ribonucleoside in RNA by sodium periodate. We have routinely used this method to couple fluorescent dyes with attached hydrazine groups to the aldehyde groups. This bond is then stabilised by reduction. 

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A series of benzo[fc]benzo[2,3-cfjthiophen-6,9-diones 12 has been prepared in modest yields by palladium mediated cyclization of the precursors 13. However, the necessity to use stoichiometric amounts of the palladium source precludes cost effective preparation of the targets. The required substrates 13 may be constructed by palladium catalyzed reactions between the appropriate phenols with 2,3-dimethylbenzoquinone <06SC3319>. 

A series of 3-oxothiophene derivatives has been prepared by intramolecular thia-anti-Michael addition of a thiol anion to an enone functionality, resulting for instance in preparation of the target 20 by treatment of the precursor 21 with an amine <06JOC8006>. 

In the molecule of polyethylene or, for example, phenol, it is trivial to recognize the structural elements corresponding to available natural precursors and hence to elaborate a logistically simple scheme for the preparation of the target products. However, in the majority of cases the well-trained eye of the professional is required in order to identify the basic fragment(s) present in the complex target molecule which can be derived from a suitable precursor(s). This skill rests primarily in the ability to refer easily to the rich arsenal of synthetic... 

Once the appropriate imidates, amide hydrazones, or hydrazides are made successfully, the preparations of the target open-chain diazine (N-N) ligands is usually fairly straight-forward. 

The retrosynthetic analysis outlined in scheme 1 suggested that the reaction of the amine (2) with a readily available arylisocyanate (3) would be the key step in the preparation of the target molecules (1). 

Preparation of the target disaccharide III.7 is described as follows. Transformation of azide III.32 to the A-acetate in.35 was achieved in 81% yield by sodium... 

Dichloro-5-(l-o-carboranylmethyl)-6-methylpyrimidine (674) is said to be a potential synthon for the preparation of 5-(l-o-carboranylmethyl)-6-methylpyrimidines chemoselective nucleophilic substitution of the chlorine atoms can be effected, and the cage can be selectively degraded for the preparation of more water-soluble Wo-undecarborate derivatives. Preparation of the target molecule (674) is effected by the addition of decaborane to an appropriate alkyne (673) as shown in Equation (19) <9lJOC2391>. 

There are no literature references from the covered period that report preparations of the target compounds by transformations of other heterocyclic structures. 

The research groups of Chiacchio, Romeo and Merino have extended the 1,3-dipolar cycloaddition methodology for the enantioselective synthesis of J, 0-nucleosides by using of N-glycosyhiitrones, which can serve as versatile building blocks in the preparation of the target modified nucleosides [58]. The chiral aiudhary can be easily introduced before the cycloaddition pro-... 

Preprepared (ADC)Pd complexes H2 (Fig. 11.6) was employed [29] as catalyst for the Buchwald-Hartwig amination of aryl halides (for the recent surveys on the Buchwald-Hartwig cross-coupling, see References [62-65]). The obtained results (Scheme 11.13) were compared with those for the structurally related oxyamino- (H4), thioaminocarbene (H5), and the related NHC complex, H14. Catalysts H2, H4, and H5 were efficient in the amination of bromobenzene (yields range from 82% to 92%), demonstrating activities similar to those of the NHC complex H14 (yield 84%). With 2-chloropyridine as the substrate, H2, H4, and H14, allowed the preparation of the target product in a quantitative yield. Catalyst H5 demonstrated a moderate efficiency (yield 47%). 

Liebeskind s second-generation approach to the stereocontrolled synthesis of 2,3,6-trisubstituted piperidines was based on the use of a range of molybdenum-containing scaffolds that were not only general and efficient precursors for the regjo- and stereodivergent preparation of the targets, but could also be obtained in enantiomerically pure form. This impressive... 

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