Synthesis of new oxa-, thia- and selenacalixarenes by nucleophilic aromatic substitution reactions

 

In previous work, we have been studying the synthesis and reactivity (e.g., in SNAr reactions) of 4,6-dichloropyrimidines as structural components of meso-pyrimidinyl-substituted porphyrinoids and pyrimidine dendrimers1. This work has now been extended to calixarene chemistry.

 

Novel oxacalix[m]arene[m]pyrimidines have been synthesized by SNAr reactions on halogenated pyrimidine building blocks2. Depending on the SNAr conditions, either a mixture of oxacalix[n]arenes, ranging from the oxacalix[4]- up to the oxacalix[12]arene, could be prepared or the oxacalix[4]arene could be synthesized selectively in a high yield (up to 80%)。

 

Some parameters controlling the ring size selectivity were clarified. A high reactivity of both reaction partners in the SNAr seems to be crucial to obtain the oxacalix[4]arene macrocycle with a high yield and selectivity. The pyrimidine and the nucleophilic component were both varied, allowing us to prepare some functionalised oxacalix[4]arenes. Moreover, the procedure also allows the preparation of analogous thiacalix[4]arenes. The ease of elaboration of the substitution pattern, the remarkably symmetrical cavity of the oxacalix[4]arene (as observed from the single-crystal X-ray structure), the tunable macrocycle size and their good solubility make the presented heteracalix[n]arenes versatile platforms for further exploration of selective recognition processes of various guest molecules (cations, anions and neutral species, depending on the substituents). Some recent progress will be reported concerning the functionalisation of the pyrimidine rings3 and the selective synthesis of calix[6]arene or calix[8]arene derivatives, respectively based on a [3+3]- or [5+3]-approach4.

 

References
[1] Smeets, S.; Asokan, C. V.; Motmans, F.; Dehaen, W. J. Org. Chem. 2000, 65, 5882; Maes, W.; Amabilino, D. B.; Dehaen, W. Tetrahedron 2003, 59, 3937; Maes, W.; Vanderhaeghen, J.; Smeets, S.; Asokan, C. V.; Van Renterghem, L. M.; Du Prez, F. E.; Smet, M.; Dehaen, W. J. Org. Chem. 2006, 71, 2987; for an overview see Maes, W. ; Dehaen, W. ; Pol. J. Chem., 2008, 82, 1145-1160.
[2] Maes, W.; Van Rossom, W.; Van Hecke, K.; Van Meervelt, L.; Dehaen, W. Org. Lett. 2006, 8, 4161.

[3] Van Rossom, W.; Maes, W.; Kishore, L.; Ovaere, M.; Van Meervelt, L. ; Dehaen, W. ; Org. Lett. 2008, 10, 585-8.
[4] Van Rossom, W. ; Ovaere, M. ; Van Meervelt, L. ; Dehaen, W. ; Maes W. ; Org. Lett. 2009, 11, 1681-1684.