Borylation of calix[4]resorcinols under ultrasonic irradiation

Abstract

The use of ultrasonic irradiation in the reactions of trialkyl borates with octahydroxytetraoctyl[l 4 ] metacyclophane allowed us obtaining tetraalkoxyboratocavitands with higher yields and under milder conditions. We first obtained 1,3,2-dioxaborolane and 1,3,2-dioxaborinane derivatives of tetraoctyl[l 4 ]metacyclophane using ultrasonic irradiation. Boratocavitands were converted into the corresponding amine complexes with isobutylamine.Since recently, an increased attention is paid to structural, chemical, physicochemical aspects and application of the class of calixarene compounds. This is due to the existence of a hydrophobic cavity in the molecules of these compounds that is capable of complexing with the molecules of neutral organic compounds and ions [1][2][3][4]. Due to the presence of hydroxy groups, the calixarenes can be subjected to functionalization, which leads to a change in the size and geometry of the cavity and its ability of effective and selective bonding. The calixarenes whose molecules include a hetero-element may have practical value as a complexing agents and metals extractants, and can serve as the models of enzymatic and other biochemical processes. Among the calixarenes with the elements introduced through the HO groups the most attention attracted the cavitands O-and Cphosphorylated at the lower and upper rims [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. At the same time, other calixarenes of the O-element type (O-sulfonylated [20], O-and C-silylated [21-26] and O-borylated cavitands [27]) have been less studied.It is known that the reaction of calixresorcynols with triisobutyl borate in boiling toluene leads to the formation of tetraalkoxyborato-cavitands [28]. In order to increase the reactivity of borates in these reactions we exerted ourselves to search for initiators of these transformations. We have previously shown that the reaction of thiophosphorylation of trialkyl borates under ultrasonic irradiation occurs considerably faster,