Systems containing Four Heteroatoms

In CHEC-II(1996), Chapter 7.03 <1996CHEC-II(7)89> was devoted to 5-5 fused heterocyclic systems containing four heteroatoms arranged 1 3, with no heteroatoms at the bridgehead position, that is, heterocycles of general structure 1 and 2. 

Systems Containing Four Heteroatoms 1,3,4,6-Thiatriazepines were obtained from reaction of 1,4-dichloro-2,3-diazabutadienes with cyclic thioureas (Scheme 31). 

Reports concerning bridgehead nitrogen bicyclic systems containing four extra heteroatoms (3 1) are rare <1996CHEC-II(8)729>. Only four such ring systems, 1-4, have been reported previously. Related ring systems reported in the last decade are l,2-dihydropyrimido[l,2- ]-l,2,4,5-tetrazin-6-ones 5, 67/-[l,2,4,5]tetrazino[3,2- ] quinazolin-6-ones 6, thioxotetrazinoquinazoline 7, and pyrimido[l,2- ]-l,2,4,5-tetrazin-6-ones 8. 

Table 3) are described in the literature although the rarer 1,3,2- and 1,5,2-isomers are only known as the fully oxidized tetraoxides. Oxadiazines (Table 4) of all six types are reported, four of the isomers having an extensive and well established chemistry. The 1,2,3-and 1,2,6-isomers have been reported, but there is no spectroscopic evidence to support either structure. All the six isomeric thiadiazines (Table 5) are known with only the 1,5,2-isomer being poorly described. In line with the oxadiazines and thiadiazines being the most well known ring systems containing three heteroatoms, they are also the most well reviewed to date. 

The subject of heterocyclic chemistry is vast, so in this book the focus is on the more common four-, five- and six-membered systems contain-ing one heteroatom. Little attempt is made to extend the coverage to more complex heterocycles, so that students interested in extending their knowledge will need to consult more advanced works. Fortunately, there is a very wide choice excellent texts include Heterocyclic Chemistry by Gilchrist and Heterocyclic Chemistry by Joule and Mills. In addition, there are many authoritative compilations that deal with heterocyclic chemistry in much more depth. ... 

Abstract This chapter is devoted to recent progress in the chemistry of the 5 5 fused heterocyclic systems. There are four possible modes of 5 5 fusions of the simple five-membered heterocycles leading to four structures containing one heteroatom in each ring. The heteroatoms may be the same or different and may be O, NH, S, Se, Te, P, As, or Sb. The fully conjugated hetero analogs of pentalene dianion have a central C-C bond and are isoelectronic with the 10-7t-electron pentalene dianion. The scope of the chapter is outlined with a survey of various structural types and nomenclature of the parent compounds and their derivatives. New synthetic procedures and synthetic applications of title compounds are presented. This review has concentrated on the new developments achieved from 1997 to September 2007. 

Compounds containing Heteroatom Ring Systems. A four-membered diaza-phosphete (69) is the product from reaction between ammonium chloride... 

Only few examples were reported related to these ring systems. Moreover, only those fused with three-membered ring mainly containing one heteroatom oxygen were reported. No examples can be found with a four-membered ring containing two heteroatoms. 

Systems containing Sulphur as the only Heteroatom. - A variety of sulphur-containing cyclophanes were synthesized by the dilution principle, using an improved apparatus. The equipment will prove valuable in the preparation of many macrocyclic systems. The iron-catalysed reaction between bis-(2,4-dimethoxyphenyl) sulphide and S2CI2 gave four macrocyclic systems, including (47). The formation of (47) occurs by the unusual electrophilic cleavage of C-aryl-S bonds. 

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