Direct synthesis of polymacrocyclic boron compounds. A convenient method for the synthesis of hemicarcerands Victor Barba * , Isabel Betanzos Centro de Investigaciones Quı ´micas, Universidad Auto ´ noma del Estado de Morelos, Av. Universidad 1001, C.P. 62209 Cuernavaca, Morelos, Mexico Received 23 April 2007; received in revised form 5 July 2007; accepted 5 July 2007 Available online 31 July 2007 Abstract Six new hemicarcerand-like compounds have been synthesized via condensation reaction of 3-aminophenylboronic acid with 5,5 0 -methylene-bis(2-hydroxybenzencarbonyl) derivatives. The one-pot reaction constitutes an interesting approach to design molecular containers by direct synthesis in moderate yields. The strategy involves a self-assembly process through the formation of N–B coordi- native bonds. The X-ray structural analysis for one derivative illustrates the inclusion of two benzene molecules within the cavity, show- ing in a first approximation the capability of the polymacrocyclic compounds to function as molecular receptors. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Boron; Polymacrocycles; Self-assembly; Hemicarcerands; Schiff bases 1. Introduction At the present, supramolecular chemistry is one of the most explored topics. One of the main goals is to improve the synthesis of molecular receptors, with the possibility to modulate the volume and periphery of the cavity in a pre- dictable fashion [1]. In this context, the simplicity of the method used for the synthesis of calixarenes has allowed to perform an extensive exploration of these macrocycles as molecular receptors and molecular building blocks [2]. In order to improve their efficiency as molecular contain- ers, several structural modifications have been realized in the calix base rims, e.g. the replacement of the phenol units by heteroaromatic rings [3] or the introduction of heteroa- toms connecting the aromatic moieties [4]. Furthermore, double cone structures can be obtained by connecting two calix-like structures to provide systems with interesting properties in the molecular recognition area [5]. The coupling can take place through one single linker, or as many linkers as phenol rings are involved in the calixarene structure [6]. Although several synthetic methods have been described, coupling process between two calixarene units follows three well defined steps: (i) calixarene synthesis, (ii) functionalization of the groups located at the rims in either the lower or the upper part and (iii) coupling reaction between the calixarene units. The double cone structures can be carcerands or hemicarcerands, the differ- ence being that carcerands permanently imprison guests during the cavitand shell closure, even at high tempera- tures. In the contrary, hemicarcerands contain portals that allow the entrance and egress of guest molecules [7]. Recently, we reported a method to prepare trimeric boron calix like compounds with a double cone conforma- tion from 3-aminophenylboronic acid and salicylaldehyde derivatives [8]. In these compounds, the formation of N!B coordination bonds is a determinant factor for the rim closure and several structural analyses have been car- ried out in order to investigate the stability of the N–B coordination bonds [9]. Recently, dendrimeric compounds having a macrocyclic core containing N–B dative bonds within their structure have been reported [10]. It was shown that these molecules can be useful in the molecular 0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2007.07.035 * Corresponding author. Tel./fax: +52 7773297997. E-mail address: vbarba@ciq.uaem.mx (V. Barba). www.elsevier.com/locate/jorganchem Journal of Organometallic Chemistry 692 (2007) 4903–4908