Stereoisomers of 1,3,5,7-Tetrahydroxy-1,3,5,7-tetraisopropylcyclotetrasiloxane:Synthesis and Structures in the Crystal

摘要

The first synthesis of all four Stereoisomers of 1,3,5,7-tetrahydroxy-1,3,5,7-tetraisopropylcy-clotetrasiloxane,[i-PrSiO(OH)]_4 (all-trans-,cis-cis-trans-,cis-trans-cis-,and all-cis-1),is presented.The starting compounds,all-frans-,cis-cis-trans-,cis-trans-cis-,and all-cis-1,3,5,7-tetraaryl-1,3,5,7-tetraisopro-pylcyclotetrasiloxanes,were prepared by the hydrolysis of the corresponding arylisopropyldichlorosilanes,i-PrArSiCl_2 (Ar=Ph,p-tolyl),and subsequent separation of isomers.A combination of dephenylchlorination of tetraarylcyclotetrasiloxanes and the following hydrolysis proved to be an efficient method for the stereospecific transformation of aryl-substituted cyclotetrasiloxanes into (i-PrSiO(OH))_4.For example,treatment of cis-trans-cis-1,3,5,7-tetraphenyl-1,3,5,7-tetraisopropylcyclotetrasilane with HCl and AlCl_3,followed by hydrolysis in the presence of pyridine,resulted in the exclusive formation of cis-trans-cis-1 in 92% yield.The structures of cis-cis-trans-1,cis-trans-cis-1,and all-cis-1 were determined by X-ray crystallography.All isomers were found to construct unique packing structures by intermolecular hydrogen bonding;cis-trans-cis-1 composed an infinite antiladder structure,and cis-cis-trans-1 formed a sheetlike structure.