1.2.3- Thiadiazines, monocyclic

Monocyclic 1,2,4-thiadiazines 29 have been claimed to result from the treatment of thiamine hydrochloride and related thiazolium compounds... 

The main successful applications of monocyclic 1,2,4-thiadiazines in earlier years have been the use of bis[4-(3,4,5,6-tetrahydro-l,l-dioxo-2//-l,2,4-thiadiazinyl)]methane (62, Taurolidine, Taurolin, Drainsept) as an antibacterial agent and 3,4,5,6-tetrahydro-2//-l,2,4-thiadiazine 1,1-dioxide (63, Taurultam) as both an antibacterial and antifungal agent (66FRP1458701). Claimed uses of 1,2,4-thiadiazines are listed in Table 11. 

Not much is known about the properties of 1,2,5-thiadiazines. However, there is one outstanding property the contraction of the 1,2,5-thiadiazine ring, which is shown both by monocyclic 1,2,5-thiadiazines and 2,1,4-benzothiadiazines. For instance, 1,2,5-thiadiazine 187, which is stable at low temperatures, tends to revert to 1,2,5-thiadiazolium cyanide 185 on standing at room temperature for several days (79TL1281). In this contraction, the ring sulfur atom is retained. Usually the sulfur atom is extruded to give imidazole derivatives, e.g., 1,2,5-thiadiazine 184 (R = i-Pr), when heated, yields thiazolidinethione 194 (49JOC946). In the 2,1,4-... 

R. E. Busby has written a chapter on thiadiazines containing adjacent sulfur and nitrogen ring atoms. This chapter complements one in Volume 44 which dealt with sulfamides of this type. H. Quiniou and O. Guilloton of Nantes have covered the chemistry of monocyclic 1,3-thiazines, a group that, surprisingly, has not been reviewed comprehensively for many years. Finally, E. V. Kuznetsov and I. V. Shcherbakova of Rostov collaborate with A. T. Balaban of Bucharest in a summary of the chemistry of benzo[c]pyrylium salts. This review complements the review by a group of authors under the leadership of Balaban who covered the chemistry of pyrylium salts in Supplement 2 of this series, which appeared in 1982. 

There are also ring transformations of monocyclic and benzisothiazolium salts by ring extension to 1,3-thiazines, quinolines, 1,4-benzothiazepines and 1,2,3-thiadiazine 1,1-dioxides. 

Pyrimidines fused to other six-membered rings, most frequently in the form of bicyclic structures, can be degraded to corresponding substituted monocyclic pyrimidines. Fused pyrimidine structures described are benzo- (quinazolines), pyrano[2,3-tf]-, pyrazino[2,3-i/j- (pteridines), pyrimido[l,2-u]-, pyrimido[4,5-i/]pyrimidines, and pyrimido[5,4-e]-a -triazines, pyrimido[5,4- f]-v-triazine, pyrim-ido[4,5-i/][l,3]oxazines, pyrimido[5,4-i/][l,3]oxazine, pyrimido[4,5- ][l,4]thiazines, pyrimido[5,4- ][l,4]thiazines, and pyrimido[4,5-e][l,2,4]thiadiazines. References to these reactions can be found in . 

Although there is some theoretical evidence for heteroaromaticity in the tetrafluoroborate salts of 4-alkoxy-2,l,3-benzothiadiazines (61 Section 6.16.4.1), none of the monocyclic systems covered in this chapter possesses aromatic character. Hence, the chemistry of these systems, along with that of 12, 2,6- and lA, 2,6-thiadiazines and their benzologues, is considered in the following Section. 

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