Six-membered heterocycles with more than one heteroatom

Space restrictions mean that the reactivity of multiheteroatom systems or fused systems where both rings are heterocyclic cannot be covered in this section - the reader is referred to the relevant CHEC volumes. Space again dictates that the chemistries of oxygen- and sulfur-containing six-membered heterocycles, and the chemistry of monocyclic six-membered heterocycles with more than one heteroatom, are only briefly indicated alongside the description of pyridine/quinoline/isoquinoline chemistry, but especially where these are not shown by the pyridine prototypes, but again the reader should study the CHEC volumes for a full discussion. The inclusion of an extra heteroatom in a six-membered system exaggerates the effect of the first and so often it is possible to predict properties by extrapolation however, the same is not true for the five-membered systems, so these heterocycles with more than one heteroatom are considered in detail and separately. 

Six-Membered Heterocycles with More than One Heteroatom... 

Section 3.1 is a brief overview Section 3.2 deals with six-membered heterocycles, including those with more than one heteroatom in the ring Section 3.3 deals with five-membered heterocycles with one heteroatom Section 3.4 deals with five-membered heterocycles with more than one heteroatom in the ring Section 3.5 covers small (three- and four-membered) and large (>six) ring heterocycles. 

An even longer chapter of six-membered phosphorus heterocycles with more than one heteroatom is represented by those with 2 (j -phosphorus. The first synthesis of a 2 -phosphinin, the 1,1-diphenyl compound (11) was described in 1963 <63AG(E)479>. Because of the ready availability of... 

For several reasons the development of the chemistry of 6n heteroaromatic arsenic systems, for example arsinine (3), was much less vigorous than that of the phosphinines. While t-butylphos-phaethyne (4) and several other phosphaethynes are important building blocks for the synthesis of six-membered aromatic phosphorus heterocycles with more than one heteroatom, only one compound with a C=As triple bond, the 2,4,6-tri- -butylphenyl derivative (5), has been described <86AG(E)264>, and this has not been thoroughly studied. The only six-membered As-heteroaromatic system with more than one heteroatom is the l,3A -azarsinine (6) <88TL535>. Since pentavalent... 

The heterocyclic six-membered ring halogen derivatives with more than one heteroatom in the ring have a higher degree of imidoyl halide... 

According to WHO fact sheet, CVD is the main cause of death globally more people die aimually from CVD than from any other cause. An estimated 17.3 million people died from CVD in 2008, representing 30% of all global deaths. Of these deaths, an estimated 7.3 million were due to coronary heart disease and 6.2 million were due to stroke. The number of people who die from CVD, mainly from heart disease and stroke, will increase to reach 23.3 million by 2030. CVDs are projected to remain the single leading cause of death [87]. On the other hand, 1,4-dihydropyridines (1,4-DHPs) are an important class of six-membered heterocycle with one heteroatom. This medicinally important... 

Scheme 11.13. A representation of a portion of the pathway of gluconeogenesis. The 6-phosphate of glucose is considered capable of hydrolysis to glucose with the appropriate hydroiyase (EC 3.1.3.9) catalyst. The anomer shown is a (because the hydroxyl on the ano-meric carbon is cis or syn to the hydroxyl at C5, Scheme 11.14). A caution concerning nomen-ciature is needed. In the acyclic form, it is clear which carbon is number six. Cyclization to the six-membered ring pyranose (oxane) (or furanose [oxolane] when the five-membered ring forms) leaves ns with a nomenclature problem since the carbon that was C-1 (the ano-meric carbon) is often referred to as C-1 in both structures that involve formation of bonds to that carbon as well as in reactions that may occur at that carbon. However, it will be recalled (Chapter 5) that the nomenclature of cyclic ethers (and other heterocycles) generally requires that the heteroatom (or a heteroatom if more than one is present) receive the lowest number. So, the lUPAC and the lUBMB numbering system is used for archiving purposes, while the trivial nomenclature is commonly used in the literature. Both systems will be found here as appropriate.

---