Heterocyclic Compounds of Quadricovalent Sulphur

Much of the work reported in this area during the past two years involves the consolidation or extension of ideas previously reported in preliminary form. A short review of Cava s work on thieno[3,4-c]thiophens has been published.  

The thiapyrans (7) and (8) react with sodium amide in liquid ammonia or with t-butyl-lithium in THF to give the stable deep red anion (9). The high acidity of the thiapyran (7) (pK, ca. 20) compared with that of the oxygen analogue (10) (pK, ca. 35) discounts phenyl conjugation as a major source of 

The mass spectra of 3,5-dimethyl- (12 R=H) and 3,4,5-trimethyl- (12 R=Me) 1,2-dithiolium bromide show a strong peak arising from the loss of H from the cation. The dithiabenzene structures (13) are suggested as alternatives to (14) for the ions responsible for these peaks. 

The question of the importance of 3d-orbitals in supporting electron delocalization through sulphur was examined by studying inter alia 

Tamura, T. Miyamoto, H. Taniguchi, K. Sumoto, and M. Ikeda, Tetrahedron Letters, 1973, 1729. 

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Heterocyclic Compounds of Quadricovalent Sulphur , D. H. Reid, in Organic Compounds of Sulphur, Selenium and Tellurium , ed. D. H. Reid, Royal Society of Chemistry, London, 1970, vol. 1, pp. 309-320. 

In general, these Reports cover the period from April 1974 to March 1976 unless otherwise stated. Due to necessary limitations of space, the topics have, in parts, been treated more summarily than in previous Reports. A review of the chemistry of thiepins and dithiins, omitted from Volume 3, has been included in this volume, but accounts of the chemistry of thiazepines and of heterocyclic compounds of quadricovalent sulphur have been held over to Volume 5. 

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