V. Kuznetsov, S. A. Bochkor
2001
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Journal
Journal of Structural Chemistry
Abstract
V. V. Kuznetsov and S. A. Bochkor UDC 541.313.3:541.631,3-Dioxa-2-silacyclohexanes are convenient models for investigating the effect of heteroatoms on the conformationalcharacteristics of cyclohexane heteroanalogs. The molecules either equilibrate between two invertomers or have chair andoccasionally 1,4- and 2,5-twist conformations depending on the number, nature, and position of substituents [1]. Accordingto empirical calculations for the 2,2,4- and 2,2,5-trimethyl as well as 2,2,4,5-tetramethyl derivatives, the fundamentalminimum on the potential energy surface represents the chair conformer [2, 3]. At the same time, cis-4,5-dimethyl-1,3-dioxane[4, 5] as well as stereoisomers from the series of 4,5-dimethyl-1,3-dioxa-2-heterocyclohexanes, for example, cyclic sulfites[6, 7] and 1,3,2-dioxaborinanes [8] are known to be conformationally nonhomogeneous. Therefore it was of interest toestimate the conformational composition of the cis- and trans-isomers of 2,2,4,5-tetramethyl-1,3-dioxa-2-silacyclohexane(I), which is the simplest representative of the poorly characterized six-membered cyclic silicon esters with two chiralcenters in the carbon moiety of the ring. These calculations were accomplished using the SCF MO LCAO method in PM3[9] and AM1 [10] parametrizations and