The AAAA·DDDD Hydrogen Bond Dimer. Synthesis of a Soluble Sulfurane as AAAA Domain and Generation of a DDDD Counterpart

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Contents Vol 62(11)

doi:10.1071/CH09113

The AAAA·DDDD Hydrogen Bond Dimer. Synthesis of a Soluble Sulfurane as AAAA Domain and Generation of a DDDD Counterpart^*^,^†

Jörg Taubitz ^A ^B, Ulrich Lüning ^A ^C

^A Otto-Diels-Institut für Organische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24098 Kiel, Germany.
^B Present address: School of Chemistry, University of Melbourne, 30 Flemington Road, Parkville, Vic. 3010, Australia.
^C Corresponding author. Email: luening@oc.uni-kiel.de





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Australian Journal of Chemistry 62(11) 1550–1555 http://dx.doi.org/10.1071/CH09113
Submitted: 25 February 2009 Accepted: 22 April 2009 Published online: 20 November 2009

Abstract

Sulfurane 5b with solubility enhancing substituents has been synthesized to be used as an AAAA recognition site in quadruple hydrogen bond heterodimers. A complementary DDDD partner [4b + H⁺] has been generated from a DDAD domain 4b by protonation. The association constant for the heterodimer complex formation has been determined by NMR titration in chloroform.

^* Dedicated to Professor Dr Christoph Rüchardt on the occasion of his 80th birthday.

^† Multiple Hydrogen Bonds 6. Part 5: Ref.[17]

^‡ In this work, only those multiple hydrogen bonding patterns are discussed in which the hydrogen bonds are in close proximity to each other and separated by not more than one atom. For our studies we consider a suitable DDDD counterpart a molecule that fulfills the following criteria: (a) It needs to be soluble in chloroform, so that we can perform a NMR titration and can compare our results to our previous work. (b) The molecule should not be too flexible. In particular, intramolecular hydrogen bonds should be avoided because these must be broken in order to form a complex using the binding motif. Therefore, ureas such as triuret or its derivatives are not suitable for our work.^[³^] (c) The DDDD domain must match the AAAA pattern in curvature and distance. Therefore, multiple urea units^[³^,⁴^] or pattern in which the NH units are separated by more than one atom^[⁵^] are not suitable although they contain four or more NH units.

^¶ 7a = keto form (60%), 7b = enol form (40%).

^§ As reported in ref. [13], sulfuranes are not stable when they are reacted with strong electrophiles. Therefore, it must be taken into account that protonation also could destroy the sulfurane. However, the methylation of a sulfurane is an irreversible reaction, the protonation a reversible one. Furthermore, decomposition by methylation primarily occurs with unsymmetrically substituted sulfuranes, and during the course of our titrations no decomposition was observed.