Synthetic approaches recording

About a half-dozen cases are recorded on the formation of A3-triazolines the sodium borohydride reduction of triazolium compounds5 and the vinyl azide additions to triazolinediones6 appear most promising for extended application. Only three synthetic approaches exist for the A4-compounds, of which the route employed by Mohr and Hertel2-2a has greater general applicability. 

I. Ugi, Record of Chemical Progress, 30,289 (1969). A Novel Synthetic Approach to Peptides... 

Another synthetic method for the preparation of aziridinyl ketones involves the initial modification of unsaturated ketones, with formation of /3-methoxyamino derivatives, followed by treatment with either metal alcoholates [11, 28, 29, 30, 31], or hydroxylamine hydrochloride and then potassium hydroxide [32]. An obvious drawback of this approach is the possibility of obtaining an exclusively unsubstituted nitrogen atom for the aziridinyl ketones. Among the advantages are high yields for these reactions. For example, Jin et al. [31] recorded yields of aziridine 18 of 99%. In other publications the yields of target compounds were reported to be around 90%. 

There has been a significant level of activity in the synthetic arena directed toward the preparation of lycorine and related alkaloids, and a number of successes have been recorded. Although a variety of strategies for the elaboration of the tetracyclic skeleton of lycorine have evolved, the most common ones, and those that have ultimately led to the total syntheses of the target alkaloids, are of the general type A — C —> B - D and A— C D B. Of some importance is an approach which involves prior construction of the C and D rings followed by the elaboration of the A and B rings. At this juncture, it is appropriate to note... 

In the early days of this Advances series, authors were offered the opportunity to record experimental procedures as part of their contributions, but this has been rarely used in recent years. However, the practice is revived here in the article by El Nemr and El Ashry (Alexandria) on the synthesis of trehazolin, a natural nitrogen-containing pseudodisaccharide that is an inhibitor of the enzyme trehalase, together with various analogues. These synthetic targets can be approached in a wide variety of ways, and the authors present for each synthetic sequence sufficient detail to permit an experienced synthetic chemist to repeat the procedure. 

Encoding techniques provide an alternative to deconvolution. In this method, a unique tag molecule or set of tags is introduced at each synthetic step to define each synthon used during library construction. This approach accurately records in the tag bar code those synthetic steps and exact synthons that any... 

From the earliest recorded times, man has utilized natural polymers. Such materials as asphalt, amber, and gum mastic are referred to in the written records of very early civilizations and, later, of the ancient Greeks and Romans. The pattern of use followed the classic human approach, namely, putting something to work without understanding its fundamental nature. Unfortunately, this failure to study delayed the effective utilization of synthetic polymers until the twentieth century. 

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