3- Membered rings three heteroatoms

Three-membered Rings, Two Heteroatoms including Other Elements... 

IV. Five-Membered Rings Three or More Heteroatoms... 

Keywords Five-membered rings Four-membered rings Heterocycles containing unusual heteroatoms Rings with more than six members Six-membered rings Three-membered rings... 

Sulfur containing heterocycles are also common Compounds m which sulfur is the heteroatom m three four five and six membered rings as well as larger rings are all well known Two interesting heterocyclic compounds that contain sulfur-sulfur bonds are hpoic acid and lenthiomne... 

Table 1 X-Ray Structures of Compounds with Five-membered Rings and Two, Three or Four Heteroatoms ...

Exocyclic unsaturation can stabilize small ring heterocycles. In three-membered rings it is difficult to separate the contributions from increased angle strain and from electronic interactions between the unsaturation and the heteroatom. In four-membered rings such separation has been done 74PMH(6)199, p. 235). The CRSEs change from oxetane... 

Onium ions of small and large heterocyclics are usually produced by electrophilic attack on a heteroatom. In three- and four-membered rings nucleophilic attack on an adjacent carbon follows immediately, in most cases, and ring opening stabilizes the molecule. In large rings the onium ion behaves as would its acyclic analog, except where aromaticity or transannular reactions come into play (each with its electronic and steric pre-conditions). A wide diversity of reactions is observed. 

Beyond the scope of this chapter, but similar in mode of formation and reactivity to the title compounds, are some three-membered rings with three heteroatoms. Oxadiaziridine... 

STRUCTURE OF THREE-MEMBERED RINGS WITH TWO HETEROATOMS... 

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