title: Stereoisomerization of Cyclic Silanols.
abstract: Stereoisomerization of readily available all-cis-1,3,5,7-tetrahydroxy-1,3,5,7-tetraisobutylcyclotetrasiloxane (1 a) was carried out under acidic conditions to afford cis-trans-cis (1 b), all-trans (1 c), and cis-cis-trans (1 d) isomers. The compounds in the reaction mixture could be easily separated into 1 a and a mixture of 1 b, 1 c, and 1 d by the treatment with chloroform. Compounds 1 b, 1 c, and 1 d were further separated and isolated, and each structure was identified. The experimental results indicated that the most plausible mechanism is a substitution reaction at the silicon center via a pentacoordinate intermediate without a cyclic siloxane bond cleavage reaction. The obtained isomer 1 a or 1 b further reacted with dichlorodiphenylsilane in the presence of triethylamine to give syn-type laddersiloxane (2 a) or anti-type laddersiloxane (2 b), respectively.
authors.affiliation: Department of Chemistry and Chemical Biology, Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, 376-8515, Japan.
authors.forename: Hisayuki
authors.initials: H
authors.lastname: Endo
authors.affiliation: Department of Chemistry and Chemical Biology, Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, 376-8515, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Takeda
authors.affiliation: Department of Chemistry and Chemical Biology, Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, 376-8515, Japan.
authors.forename: Masafumi
authors.identifier: http://orcid.org/0000-0003-2158-1644
authors.initials: M
authors.lastname: Unno
keywords: isomerization; materials science; reaction mechanisms; silicon; structure elucidation