Thiins, dihydro

Thiin, cw-3,5-di-t-butyItetrahydro-conformation, 3, 888 Thiin, dihydro-derivatives synthesis, 3, 931, 933... 

Sulphines may react as dienophiles with 1,3-dienes with the formation of cyclic sulphoxides. Unstable 2,2-dichloro-5,6-dihydro-2ff-thiin-l-oxide 191 was formed in an exothermic reaction between 173aandcyclopentadieneat — 40 (equation 101). The simplest, parent sulphine, CH2 = S = O, prepared in situ by treatment of a-trimethylsilylmethanesulphinyl chloride with cesium fluoride, reacts with cyclopentadiene to give bicyclic, unsaturated sulphoxide 192 as a mixture of two diastereoisomers in a 9 1 ratio (equation 102). On the other hand, a,j8-unsaturated sulphine 193 (generated by thermolysis of 2-benzylidene-l-thiotetralone dimer S-oxide) in boiling toluene behaves as a 1,3-diene and was trapped by norborene forming sulphoxide 194 in 78% yield ° (equation 103). 

Table 1 shows the two dihydrothiopyrans, and the two corresponding benzo fused systems. The monocycles (5,6-dihydro-2//- thiin and 3,4-dihydro-2iT-thiin) are quite clearly from their chemistry an allylic sulfide and an enol sulfide respectively, and in many of the reactions they exhibit they are perfectly comparable with acyclic counterparts. Once again, as for the tetrahydrothiopyrans, in many cases the principal chemical interest is related to the effects of preferred conformations on the stereochemistry of particular conversions, but this will not be discussed in great length as it is entirely predictable from classical alicyclic work. Where differences exist they may be attributed to the interaction of the heteroatom with the neighbouring alkene, which is not too considerable, and more importantly the reactivity of the sulfur atom in its own right. The benzo fused compounds, of course, have their own particular chemistry which has received considerable attention over many years, some of which will be discussed. 

Half-chair 3,6-Dihydro-2//-pyran, 3,6-dihydro-2//-thiin,b 3,6-dihydro-l,2-dioxinc... 

By disproportionation. Dihydro compounds often disproportionate (Scheme 73), i.e., form a mole equivalent of aromatic and a mole equivalent of tetrahydro derivative for example, the dihydrocinnoline 498 on treatment with hydrochloric acid gives 4-phenylcinnoline and 4-phenyl-l,2,3,4-tetrahydrocinnoline 2H- (e.g., 499) and 4/7-thiins on treatment with acid form thiinium salts and the corresponding tetrahydrothiin. 

H-Thiin (S)-4-[2-(Methoxy-methyl)-pyrrolidino]-5,6-dihydro- E21c, 2910 (Oxo -> En-NR2)... 

H-Thiin 6-Chloro-3,4-dimethyl-6-[2-(methoxy-methyl)-pyrrolidino-sulfonyl]-5,6-dihydro- -1-oxid E21e, 5060 (1,3-Dien +... 

BRN 1432554 Carboxin sulfone Caswell No. 627A Dcmod, 2,3-Dihydro-5carboxanilido-6-methyl-1,4-oxa-thiin, 4,4-dioxide 2,3-Dihydro-6-methyl-5-phenylcarb-amoyl-1,4-oxathiin 4,4-dioxide 5,6-Dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carboxamide 4,4-dioxide ... 

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