Heterocycles containing one sulfur atom

HETEROCYCLES CONTAINING ONE SULFUR ATOM 6.4.2.1 Thiopyrans and analogues... 

Three-, five-, six- and seven-membered heterocycles containing one sulfur atom, except for those described above, can be obtained from various organic substances and sulfur monochloride. 

HETEROCYCLES CONTAINING ONE SULFUR ATOM 6A2.1 Thiopyrans and anali es... 

The present review is concerned with four-membered heterocycles that contain one sulfur atom either alone or associated with another heteroatom. The classes of compounds that will be discussed are the thietanes (1) and thietes (2), the 1,2-oxathietanes (3), the / -sultines and -sultones (4 and 5), the 1,2- and 1,3-thiazetidines (6 and 7) and thiazetes (8), the 1,2- and 1,3-thia-phosphetanes (9 and 10), and the 1,3-silathietanes and 1,3-selenathietanes (11 and 12). 

REDUCTION OF HETEROCYCLES CONTAINING ONE NITROGEN ATOM AND ONE SULFUR OR SELENIUM ATOM... 

The preparation of five-membered rings in solid-phase organic chemistry has been reported in several publications. Versatile syntheses of these heterocycles with different numbers and kinds of heteroatoms have been described. The synthesis of five-membered rings containing one nitrogen atom (Fig. 3.6) as pyrrolidines (231) [311-316] pyrroles (232) [317-320] pyrrolidinones (233) [321-323] pyr-rolinones (234) [324—326] 2,5-pyrrolidinediones (235) [327-329] 2,4-pyrrolidine-diones (236) [330-332] 2,5-pyrrolinediones (237) [333] or heterocycles with one oxygen or one sulfur atom like tetrahydrofurans (238) [334—336] 2,5-dihydrofurans (239) [337], furans (240) [338, 339], yS-lactones (241) [340-343], 2,5-dihydrofura-nones (242) [344] (Scheme 3.35) and thiophenes (243) [345, 346] can be accomplished on solid supports. 

The following four-membered ring heterocycles 1-5, which contain one oxygen and one sulfur atom, are known. Of these the 1,2-oxathietanes are quite common with numerous examples of their oxidised forms, namely the /3-sultines and the /3-sultones, reported over the decades. These systems will form the major part of this chapter. 1,2-Oxathietes, 1,3-oxathietanes, and their S-oxides are still quite rare but examples have been reported and will be highlighted within the chapter where appropriate. 

Figure 2 X-ray diffraction data for four-membered ring heterocycles containing one oxygen and one sulfur atom.

An especially interesting situation is found in the field of heterocycles containing more than one sulfur atom. Here two different relatively stable conformations (f.i. chair and twist-boat form) have often been detected in the NMR-spectra they are intercon-verted by two processes (version and pseudorotation) which differ significantly in the height of their energy barrier. In a few cases the mobile heterocycles crystallize in only one of these conformations. 

Furan 84 is a five-membered r-excessive aromatic heterocycle containing one hetero oxygen atom. It is unstable in acids, forming tars, so like pyrrole (Chapter 6, p 182) the substrate cannot be sulfonated by sulfuric or chlorosulfonic acid. However, again like pyrrole, treatment of furan 84 with sulfur trioxide in either dioxan or pyridine yields the 2-sulfonic acid 85 (Equation 23). 

Substances that contain one or more atoms other than carbon as part of a nng are called heterocyclic compounds Rings m which the heteroatom IS oxygen nitrogen or sulfur rank as both the most common and the most important... 

Part 2 (Volumes 2 and 3) deals with mono- and poly-cyclic compounds with one or more six-membered heterocyclic ring, with nitrogen, oxygen and sulfur as the heteroatoms. Volume 2 contains the six-membered rings with one nitrogen atom (Part 2A) and Volume... 

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