Conformational flexibility of 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline and its monoheterocyclic analogs

• Published in: Russian journal of general chemistry 2014-07, Vol.84 (7), p.1325-1329
• Main Authors: Shainyan, B. A., Kleinpeter, E.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Chemistry/Food Science
• ISSN: 1070-3632; 1608-3350
• DOI: 10.1134/S1070363214070135

Conformational behavior of the first cyclic organosilicon vinylsulfide, 4,4-dimethyl-3,4-dihydro-2 H -1,4-thiasiline as well as its monoheterocyclic analogs, 3,4-dihydro-2 H -pyran, 3,4-dihydro-2 H -thiopyran, and 1,1-dimethyl-1,2,3,4-tetrahydrosiline is studied in comparison with the carbocyclic analog, cyclohexene, using the methods of low-temperature NMR spectroscopy and theoretical calculations at the DFT and MP2 levels of theory. The barrier to the ring inversion with respect to that in cycloxene is increased in 3,4-dihydro-2 H -pyran and 1,1-dimethyl-1,2,3,4-tetrahydrosiline, but, in contrast to the suggestions made in the literature, is decreased in 3,4-dihydro-2 H -thiopyran. In 4,4-dimethyl-3,4-dihydro-2 H -1,4-thiasiline the barrier is intermediate between those in the corresponding monoheterocycles, 1,1-dimethyl-1,2,3,4-tetrahydrosiline and 3,4-dihydro-2 H -thiopyran. The observed variations are rationalized from the viewpoint of the interaction of the π-electrons of the C=C double bond with the orbitals of heteroatoms in the ring. The structure of the transition state for the ring inversion is discussed.