Substituents Attached to Ring Sulfur Atoms

Reactions of substituents attached to ring sulfur atoms in 1,2,4-thiadiazoles are virtually unknown. 

Reactivity of Substituents Attached to Ring Sulfur Atoms 759... 

Only a few reactions of the substituents attached to ring carbon atoms of bicyclic systems 1-34 have been reported. Methylation of compound 100 occurs at sulfur to give 101 (Equation 6) <2005BMC1847>. Horner-Emmons reaction of phosphonate 102 with benzaldehyde leads to triazole 103 as a single /. -stereoisomer (Equation 7) <2004TL1877>. 

There are no examples of reactions of substituents attached to ring oxygen atoms compounds with substituents on sulfur atoms other than oxygen (sulfoxides and sulfones) have not been reported and computations have not appeared in the accessible literature. The syntheses and reactivities of sulfoxides and sulfones are covered by the sections concerned with 1,2-oxathianes, 1,2-dithianes, and their derivatives. 

Concerning the transformation of substituents, a special note should be made on a series of ring-closure reactions carried out on the side chain of some [l,2,4]triazolo[4,3-r]benzo[l,2,3]triazines published by Moustafa <2001SC97>. The results are summarized in Scheme 18. This scheme shows that by transformation of the R group attached to the sulfur atom of derivative 97 a fairly large set of cyclic products - involving thiazolidone 97a, [l,2,4]triazole 97b, coumarone and its imine 97c and 97d, respectively, benzoxazylpyrane, 97e, thiophene 97f, and cyclopenta- or cyclohexa-fused protected pyrone 97g substituents - have been obtained. 

In the reviewed period of 1995-2007, no synthetic work on the reactivity of substituents attached to ring heteroatoms was published. Oxidation at ring sulfur atoms is reviewed in Section 4.12.6.2.5. Cleavage reactions with formation of the intermediate sulfonium species (dedithioacetalization process) and reactions with organometallic reagents occurring at ring sulfur atoms of 1,3-dithiolanes are described in Section 4.12.6.2.1. 

It is interesting to note that the reaction of trans-henzal-acetophenone with ylide 162a affords (15, 25 )-phenylcyclopropane with 35.3% optical purity, whereas its enantiomer having the (li ,2/ )-configuration is formed when tranj-benzalacetophenone is reacted with ylide 162b. Studies on the relationship between the steric requirements of the substituents attached to the chiral ylide sulfur atom and the optical purity of the cyclopropane rings formed have shown that increases in the steric size of the iV,iV-dialkylamino... 

Very few publications are available on the reactivity of substituents attached to the ring nitrogen and sulfur atoms of thiadiazole. The N-benzyl group in (107) can be removed with AICI3 to give the cyanamide (108) and the antiviral compound (109) on further treatment with base <92MI 410-01 >. 

Substituents attached to a heterocyclic ring through a sulfur atom exist in wider variety than those through oxygen. Besides the simple thio analogues—the thiols (mercaptans), thioethers, thioesters and the like—they include compounds of various higher oxidation states of sulfur, including sulfoxides, sulfones, sulfinic and sulfonic acids and their derivatives. 

The nature of the aryl substituent attached to phosphorus has a subtle influence on the ring size of the organophosphorus-sulfur heterocycle obtained from the reactions of ArPCl2 (Ar = aryl) and a source of sulfide. The six-membered ring cyclo-(Mes PS)3 is formed from treatment of Mes PCl2 with lithium sulfide the P3S3 ring adopts a chair conformation with the sulfur atoms... 

In general, substituents attached to furan, thiophene and pyrrole ring carbon atoms (we consider separately substituents attached to pyrrole nitrogen or thiophene sulfur) react similarly to those on benzenoid nuclei, but there are some important differences ... 

Reactivity of the Substituent Attached to the Ring Sulfur Atom 409... 

In CHEC-II(1996), Pummerer reactions were considered as reactions of a substituent attached to a ring sulfur atom because they are initiated by electrophilic attack at the sulfoxide oxygen. In this chapter, the Pummerer reaction has been discussed in Section 2.07.6.3.2. 

REACTIVITY OF SUBSTITUENTS ATTACHED TO THE RING CARBON ATOMS AND TO THE RING NITROGEN AND SULFUR ATOMS... 

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