Hypervalent heterocycles

Oxidation of 4H-pyran-4-thiones with thallium(III) trifluoroacetate was used in the one pot synthesis of l,6-dioxa-6n-thiapentalenes, a hypervalent heterocyclic system [57] (equation 27)... 

The chemistry of 7r-hypervalent heterocyclic systems is one of the important fields in that of hypervalent compounds. A number of 7r-electron systems containing a 10—S—3 framework have been prepared, and their structures and reactivities have been investigated [79]. In general, all atoms bonded to central atom in 7r-sulfuranes such as trithiapentalene are in the same plane. The equatorial bond has the characterization of a double bonding system and the two apical bonds are a 3-center 4-electron bond. As the sp2 type carbon atom or heteroatom having a lone electron pair is located in the two five-membered ring systems, a 1271 conjugated system is constructed and plays an important part in the stability of 7r-sulfurane. 

Keywords Benziodoxoles Hypervalency Hypervalent Hypervalent boron Hypervalent bromine Hypervalent heterocycles Hypervalent iodine Hypervalent silicon Hypervalent sulfur Iodine heterocycles... 

Figure 6 Examples of hypervalent heterocycles of the lower group 14 elements.

Hypervalent heterocyclic structures are typical of arsenic, antimony, and bismuth. The chemistry of these compounds has been overviewed by K.-Y. Akiba (2011HC207) and several specific examples are illustrated by structures 36—44 (Figure 9). 

Isothiazolo[5,l-e]isothiazoles [6a-Thia-l,6-diazapentalenes].—Full details have now been provided of a synthesis of compounds of this novel class of hypervalent heterocyclic compounds, which are structurally analogous to 6a-thiathiophthens (see Vol. 2, p. 585), from 6-methyl-l,6a-dithia-6-azapentalenes (81) by successive alkylation and reaction with methylamine. ... 

---