Synthesis and conformation of 2-silylethynyl-substituted 2,4,4,6-tetramethyl-1,3-dioxanes

Abstract

The 1,3-dioxanium salts are not only active reagents, but also substances for the investigation of conformational transitions of the six-membered 1,3-dioxa ring under the influence of substituents at positions 2, 4, and 6, as well as the positive charge on the meso-carbon atom of the O=C + =O portion [1][2][3][4][5][6][7]. The 1,4-twist conformation of the six-membered ring of the acyloxonium ion --the 2,4,4,6-tetramethyl-l,3-dioxanium cation --was previously established [4]. The last is a precursor of the little-studied 2,2,4,4,6-substituted 1,3-dioxanes. In the case of 2-methyl-and 2-(4-bromophenyl)-2,4,4,6-tetramethyl-1,3-dioxanes, it was shown by the methods of IH and 13C NMR that the ring of the first compound can occur both in the 1,4-twist conformation [8] and the 2,5-twist conformation [9, 10], and the second has the form of a chair with the axial disposition of the 4-bromophenyl and methyl substituents at positions 2 and 6 [9, 10], whereby the conformation of its molecule is unchanged in the solid state according to the data of X-ray diffraction analysis [11].We showed [12, 13] that the reaction of 1,3-dioxanium salts with the silicon-containing Iotsich reagents affords 2-silylethynyl-substituted 1,3-dioxanes. In the continuation of these investigations, it seemed expedient to study the reactivity of 2,4,4,6-tetramethyl-l,3-dioxanium perchlorate (I) in the conditions of the organomagnesium synthesis with the aim of synthesizing new 2,2,4,4,6-substituted 1,3-dioxanes of interest in a stereochemical regard.Reaction of the salt (I) with mono-and diethynylmagnesium bromides gave, for the first time, the 2-silylethynyl-l,3-dioxanes (Ila-c).