G. M. Drew, W. Kitching
Jul 7, 1981
Citations
0
Influential Citations
17
Citations
Journal
Journal of Organic Chemistry
Abstract
A number of 1,3-dithianes substituted with trimethylsilyl, stannyl, and plumbyl groups at the 2-position have been synthesized and their 1H and 13C NMR spectra obtained. Examination of chemical shifts, low-temperature spectra, and metal-13C coupling constants in certain 2,2-disubstituted 1,3-dithianes lead to the conclusion that these metalloidal groups have a much greater equatorial preference (at C-2) in 1,3-dithiane than in cyclohexane. For example, trimethylplumbyl, with an A value of 0.7 kcal/mol in cyclohexane, has an A value at C-2 in 1,3-dithiane in excess of 2 kcal/mol, whereas for simple alkyl groups, comparable A values are found for both systems. These results are related to the very large equatorial preference (>6 kcal/mol) of a 2-lithio group in 1,3-dithiane. Inter alia it is shown that electrophilic substitution by trimethyltin chloride on 5-tert-butyl-2-lithio-1,3-dithiane proceeds with overall retention of configuration.