4,4-Dimethyl-3,4-dihydro-2H-1,4-thiasiline – the first cyclic organosilicon vinyl sulfide

Synthesis of 4,4-diphenyl-3,4-dihydro-2H-1,4-thiasiline

“…Compound 3 is more stable than its analogue 1 and can be stored without notable decomposition for several weeks, whereas compound 1 is completely decomposed within 2-3 days. The formation of siloxanes with the terminal vinyl group [CH 2 =CHSCH 2 CH 2 Si(R) 2 ] 2 O by the cleavage of the Si−C sp2 bond in the present (R=Ph) and previous study (R=Me) [1] seems nontrivial because the isomeric siloxanes [CH 3 CH 2 SCH=CHSi(R) 2 ] 2 O formed by the cleavage of the Si−C sp3 bond should be thermodynamically preferable due to conjugation. Indeed, theoretical calculations of the products of hydrolysis showed that of the two isomeric silanols (predecessors of siloxanes) Me 2 Si(OH)CH 2 CH 2 SCH=CH 2 and Me 2 Si(OH)CH=CHSCH 2 CH 3 , the latter isomer is 4.9 kcal/mol more stable.…”

“…Note that compound 1 under the same conditions was fully polymerized. [1] The best yield of product 3 (81%) was reached under the conditions optimized earlier for 1,[1] that is, with trifluoroacetic anhydride in the presence of pyridine in CH 2 Cl 2 at 0 • C. The difference between sulfoxide 13 and its Si-dimethylated analogue is that no bis[(2-vinylthio)ethyl]tetraphenyldisiloxane 14 similar to siloxane 2 is formed under these conditions. Compound 3 is more stable than its analogue 1 and can be stored without notable decomposition for several weeks, whereas compound 1 is completely decomposed within 2-3 days.…”

“…[1,5] As will be shown below, the synthesis of heterocycle 3 is not a simple replica of the synthesis of 1, but requires a search for conditions, which for some transformations are different from the earlier described for preparation of 1.…”

“…Analytically pure compound 11 was isolated in 58% yield by column chromatography, eluent pentane:ether from 50:0.5 to 1:1, R f = 0.24, as white crystals with m.p. 71-72 • C. 1 The assignment was made by the use of the j-modulated 13 C NMR spectrum.…”

“…The first representative, 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline, was synthesized by us by the Pummerer rearrangement of 4,4-dimethyl-1,4-thiasiline 1-oxide. [1] As distinct from linear analogues R 3 Si−CH=CH−SR, which were synthesized as stable compounds by free-radical addition of thiols to ethynyl silanes, [2,3] compound 1 is hydrolytically unstable, decomposing to bis[(2-vinylthio)ethyl]tetramethyldisiloxane 2.…”