Effect of gem 2,2 '-disubstitution and base in the formation of spiro- and ansa-1,3-propandioxy derivatives of cyclotriphosphazenes
Uslu, A. and Coles, Simon J. and Davies, David B. and Esen, M. and Hursthouse, Michael B. and Kiliç, A. (2010) Effect of gem 2,2 '-disubstitution and base in the formation of spiro- and ansa-1,3-propandioxy derivatives of cyclotriphosphazenes. Inorganica Chimica Acta 363 (13), pp. 3506-3515. ISSN 0020-1693.
The gem-dialkyl effect has been investigated in the reactions of cyclotriphosphazene, N3P3Cl6 1, with various 2,2'-derivatives of 1,3-propandiol, CXY(CH2OH)(2), in either THF or DCM to form spiro (6-membered) and ansa (8-membered ring) derivatives. The reactions were made with a number of symmetrically-substituted (X = Y, methyl, ethyl, n-butyl and a malonate ester) and unsymmetrically-substituted (X not equal Y, methyl/H, phenyl/H, methyl/n-propyl, ethyl/n-butyl and Br/NO2) 1,3-propandiols. The products were analysed by H-1 and P-31 NMR spectroscopy and some of the spiro and ansa derivatives were also characterized by X-ray crystallography. Reactions of 1 with unsymmetrically-substituted 1,3-propandiols results in the formation of two structural isomers of ansa-substituted compounds, both isomers (endo and exo) have been structurally-characterized by X-ray crystallography for the ethyl/n-butyl derivative. It is found that the regioselectivity of the reaction is changed when the base is changed. The relative proportions of spiro and ansa compounds formed under different reaction conditions were quantified by P-31 NMR measurements of the reaction mixtures. The results were rationalised mainly in terms of the electronic effect of the substituents, whereas the steric effect has a secondary role in the formation of both spiro and ansa compounds. (C) 2010 Elsevier B.V. All rights reserved.
|Keyword(s) / Subject(s):||Cyclotriphosphazene, gem-Dialkyl effect, regioselectivity, spiro, ansa|
|School:||Birkbeck Schools and Departments > School of Science > Biological Sciences|
|Date Deposited:||09 Jun 2011 14:25|
|Last Modified:||17 Apr 2013 12:20|
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