Heterocyclic compounds synthesized from reviews

In addition to the examples of coumarin syntheses given in the reviews mentioned above and in the treatise on heterocyclic compounds (B-51MI22400), more recent studies have made use of the Perkin synthesis. These include the use of substituted phenoxyacetic acids to prepare 3-phenoxycoumarins (78CI(L)628> and the synthesis of chlorocoumarins from chlorosalicylaldehydes (81T2613). The use of DBU in place of sodium acetate was necessary to effect the ring closure of a number of o-hydroxyketones (78BCJ1907). 

The syntheses and biological activity of ring-A heterocyclic steroids have been reviewed. The JV-cyano-2-aza-A-norandrostane (333) was synthesized from the dibromo-seco-compound (331) via the JV-phenyl-2-aza-A-norandrostane (332) (Scheme 17). The mixture of iodoisothiocyanates (334) and (335) (see ref. 

ABSTRACT The syntheses, transformations and some of the biological features of 2-aminocyclopentanecarboxylic acid are reviewed. The (15,2/ ) enantiomer (cispentacin) was recently isolated from different natural sources. c/s-2-Aminocyclopentacecarboxylic acid is also a component of the antibiotic amipurimycin. The paper discusses the syntheses of the racemic compounds, resolutions of the racemates and enetioselective syntheses of the title compounds. The transformations to heterocyclic compounds, applications in peptide syntheses, and biological effects are reviewed. 

A variety of trisubstituted 1,2,4,6-thiatriazines with a tetravalent sulfur atom bearing a carbon-based substituent can be synthesized from the trichlorothiatriazine 32. Since the sulfur-bound chlorine atom is the most reactive, it can be displaced first to produce 169 (Scheme 25). The chlorine atoms at C-3 and C-5 of 169 can be displaced sequentially to produce trisubstituted compounds having three different substituents. This approach is the subject of two reviews by Stoller, the earlier of which gives also a historical overview of prior strategies employed in synthesizing such heterocycles <2000JHC583, 2003C725>. 

The syntheses of some C-labelled key intermediates from CO are illustrated In Scheme 1.1. These compounds are prepared on a relatively large-scale by manufacturers. Yields are high as the methods are frequently scaled-down versions of industrial processes or utilise specialised equipment, they are not always suitable for use in the majority of chemical laboratories. For example, [ Cjmethanol is prepared by catalytic reduction of with hydrogen under pressure [59]. The method can be automated and used for the continuous preparation of large batches. In the majority of cases, the user may well find that he is unable to prepare intermediates of this type as cheaply as they can be purchased. Scheme 2.2 illustrates the preparation of widely used N-labelled compounds. More detailed reviews of the basic synthetic processes have been published [15, 26,60—63] and many of the preparations have been described in individual publications. Some more specialised labelled compounds such as amino acids, fatty acids, organic heterocycles, and sugars are also available commercially. 

Thiadiazoles encompass five-membered aromatic compounds with two nitrogen atoms and a sulfur atom. The chemistry of these class of molecules has been extensively studied and reviewed. The 1,2,3-thiadiazoles are known to display a wide variety of biological activities, and can be accessed by the Hurd-Mori cyclization of hydrazones with thionyl chloride. Although 1,2,3-thiadiazole belongs to a well-studied class of heterocycles, most of the substituted 1,2,3-thiadiazoles are synthesized from then-acyclic counterparts instead of functionalization of the 1,2,3-thiadiazole. 

Preparation of thiadiazoles via the Hurd-Mori cyclization has led to the synthesis of a variety of biologically active and functionally useful compounds. Discussion of reactions prior to 1998 on the preparation of thiadiazoles have been compiled in a review by Stanetty et al Recent syntheses of thiadiazoles as intermediates for useful transformations to other heterocycles have appeared. For example, the thiadiazole intermediate 36 was prepared from the hydrazone 35 and converted to benzofuran upon treatment with base. Similarly, the thiadiazole acid chloride 38 was converted to the hydrazine 39 which, upon base treatment, provided the pyrazolone, which can be sequentially alkylated in situ to provide the product 40. ... 

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