Rings containing One Heteroatom

CENTRAL RING CONTAINING ONE HETEROATOM Reaction of 2-bromobenzoic acid (1) with chloroSulfonic acid proceeds to afford the sulfonyl chloride 2 treatment with dimethylamine leads to the corresponding sulfonamide (3). Condensation of bromoacid 3 with the anion from thiophenol in the presence of copper powder results in displacement of halogen by sulfur... 

The three-membered rings containing one heteroatom, because of ring strain, are much more reactive than normal ethers, sulfides and amines. Under basic or neutral conditions ring fission takes place preferentially at the least substituted carbon and is accompanied by inversion, i.e. SN2 type under... 

As explained in Chapter 3.2, the reactivity of six-membered rings containing two heteroatoms bears the same relationship to six-membered rings containing one heteroatom as do the latter to benzene. Hence many of the methods listed for the preparation of pyridines by substituent introduction and modification in Table 1 of Section 4.2.4.1 are also applicable to the preparation of analogous azines. 

This chapter covers bicyclic ring systems containing two five-membered rings where each ring contains one heteroatom and neither heteroatom is situated at the position of the ring junction. These 5 5 fused heterocyclic systems are represented by the general structures 1-4, wherein X and Y may be the same or different heteroatoms and represent O, NH, S, Se, and Te. The fully conjugated title compounds have a central C-C bond and are isoelectronic with the 10-7i-electron pentalene dianion 5 (Fig. 1). 

Reactivity of Five-Membered Rings Containing One Heteroatom... 

Rings containing One Heteroatom.—Oxygen Heterocycles. Base-catalysed addition of 17j8-hydroxy-5a-androstan-3-one to glyoxylic acid, to afford either the hydroxy-keto-acid (197) when the reaction is performed at room temperature, or the rra 5-ayS-unsaturated acid (199) in high yield when done under reflux, provides an entry to both cis-lactone (198) and trans-lactone (201). 

Most of the compounds reported in this chapter are the naphthyridines fused with a five-membered ring containing one heteroatom, i.e. pyrrolo-, furo- and thienonaphthyridine compounds. Some other ring systems, which are the few known examples of the numerous possible structures, have only been studied sparsely and they will be presented briefly in Section 8.37.2.8. 

The TT-excessive heteroaromatics are tive-membered rings containing one heteroatom. 

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